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The biological control of Centaurea diffusa lam. and C. maculosa lam. by Urophora affinis frauenfeld… Roze, Liga Dace 1981

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THE BIOLOGICAL  CONTROL OF  CENTAUREA DIFFUSA LAM. AND  C. MACULOSA  LAM.  BY UROPHORA AFFINIS FRAUENFELD AND U. OUADRIFASCIATA MEIGEN (DIPTERArTEPHRITIDAE)  by L i g a Dace Roze B.Sc.  A Thesis  ( P i n t . Sc.) U n i v e r s i t y of Western O n t a r i o ,  1974  Submitted i n P a r t i a l F u l f i l m e n t of the Requirments f o r the  Degree of Doctor o f P h i l o s o p h y i n the Department of P l a n t  We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d  THE UNIVERSITY  OF BRITISH COLUMBIA  May, ©  1981  L i g a Dace Roze, 1981  Science  standard  In p r e s e n t i n g t h i s  thesis  an advanced degree at  further  fulfilment  the U n i v e r s i t y of  the L i b r a r y s h a l l make it I  in p a r t i a l  freely  of  the  requirements  B r i t i s h Columbia, I agree  available  for  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f  of  representatives.  this thesis for  It  financial  this  thesis  gain s h a l l not be allowed without my  of  The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  Date  or  i s understood that copying or p u b l i c a t ion  written permission.  Department  that  reference and study.  f o r s c h o l a r l y purposes may be granted by the Head of my Department by h i s  for  ii ABSTRACT The  aim o f t h i s  study was t o determine the e f f e c t s o f the s e e d - r e d u c i n g  f l i e s , Urophora a f f i n i s F r a u e n f e l d Tephritidae)  and U. q u a d r i f a s c i a t a Meigen  Columbia, Canada.  the  The g a l l - f o r m i n g  knapweed, r e s p e c t i v e l y )  f l y larvae  feed  in British  i n immature knapweed  L a r v a l d e n s i t i e s p e r head peaked i n 1977, f i v e and s i x y e a r s a f t e r  f l i e s were i n t r o d u c e d  Average l a r v a l  against  d i f f u s e and s p o t t e d  knapweed, r e s p e c t i v e l y .  d e n s i t i e s above 0.5 and 1.0 p e r d i f f u s e and s p o t t e d  head, r e s p e c t i v e l y , caused d i s t a l head a b o r t i o n . not  (Diptera:  on the rangeland weeds, Centaurea d i f f u s a Lam. and C. maculosa  Lam. (Compositae; d i f f u s e and s p o t t e d  heads.  gall  Normally d i s t a l heads do  a b o r t , but p r o x i m a l heads may a b o r t a"t a n t h e s i s :  a f f i n i s caused d i s t a l head a b o r t i o n  knapweed  I t appeared t h a t U.  by s u p e r p a r a s i t i z a t i o n o f the heads.  P r o x i m a l heads t h a t would n o r m a l l y a b o r t developed i n knapweed t h a t had many superparasitized larvae  The  d i s t a l heads.  Density-dependent m o r t a l i t y  i n the p r e - g a l l stage p r o b a b l y r e s t r i c t s  two g a l l - f l y s p e c i e s  affinis  first-instar  increase  larval  i s suppressed.  U. q u a d r i f a s c i a t a , maturity required  attack  of f i r s t - i n s t a r  numbers o f JJ. a f f i n i s .  t h e same p a r t of the p l a n t ,  and when U_.  d e n s i t i e s exceed 0.5 p e r head, U. q u a d r i f a s c i a t a  U. a f f i n i s , which o v i p o s i t s i n younger heads than  saturate  oviposition sites  by U. q u a d r i f a s c i a t a .  b e f o r e they r e a c h the stage of  These s p e c i e s  a r e not e c o l o g i c a l  homologues and U. a f f i n i s w i l l n o t d i s p l a c e U. q u a d r i f a s c i a t a because U« quadrifasciata  emerges one week e a r l i e r  d e n s i t i e s a r e h i g h , U. q u a d r i f a s c i a t a during  the f i r s t  headed p l a n t s  than U_. a f f i n i s , and when U. a f f i n i s  can s u r v i v e  g e n e r a t i o n and c a p i t a l i z e  during  i n large-headed  plants  on the heads produced by s m a l l -  the second g e n e r a t i o n when U. a f f i n i s d e n s i t i e s a r e low.  iii Gall-fly  l a r v a e not o n l y reduce seed numbers i n a t t a c k e d heads, but g a l l  f o r m a t i o n p u l l s n u t r i e n t s from o t h e r p a r t s of the p l a n t , c a u s i n g a f u r t h e r decrease i n the number of seeds i n unattacked heads and an i n c r e a s e i n the percentage of heads t h a t remain undeveloped.  Viability  of d i f f u s e knapweed  seed decreased by 30% accompanied by a l o s s of the waxy seed coat and darkbrown p i g m e n t a t i o n .  There was some l o s s i n v i a b i l i t y of s p o t t e d knapweed  seeds, but the major e f f e c t on t h i s s p e c i e s was a 33% r e d u c t i o n i n average seed weight.  The combined e f f e c t s of U_. a f f i n i s and U. q u a d r i f a s c i a t a were  an 80% r e d u c t i o n i n seed numbers on both d i f f u s e and s p o t t e d knapweed. of  Most  t h i s was caused by U. a f f i n i s .  - Although the g a l l f l i e s reduce the number of seeds, they w i l l have a n e g l i g i b l e e f f e c t i n s l o w i n g the r a t e of spread of d i f f u s e and s p o t t e d knapweed because  of the e x t e n t of the i n f e s t a t i o n s and the ease of spread by seed.  Experiments  i n s e e d i n g showed t h a t h a b i t a t and weather c o n d i t i o n s determine  knapweed g e r m i n a t i o n and s e e d l i n g s u r v i v a l i n new l o c a t i o n s more than the d e n s i t y of seeds sown.  T h i n n i n g t r i a l s on s e e d l i n g s showed t h a t  density-  dependent c o m p e t i t i o n between s e e d l i n g s r e g u l a t e d knapweed p o p u l a t i o n d e n s i ties.  I f a l l seeds were d e s t r o y e d , e r a d i c a t i o n of d i f f u s e and s p o t t e d knap-  weed i n f e s t a t i o n s would take over t h r e e y e a r s because  both s p e c i e s can grow  v e g e t a t i v e l y f o r two o r more y e a r s as r o s e t t e s b e f o r e b o l t i n g . knapweed may b o l t and produce the r o s e t t e s t a g e .  Life  Spotted  seed heads f o r as many as t h r e e y e a r s a f t e r  t a b l e s t u d i e s i n d i c a t e t h a t the g a l l f l i e s a t t a c k  knapweed too l a t e i n the l i f e c y c l e to be e f f e c t i v e .  iv TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  vi  LIST OF FIGURES  viix  STATISTICAL INFERENCES  xi  ACKNOWLEDGMENT  x i i  I INTRODUCTION A. BIOLOGICAL CONTROL OF WEEDS  1  B. KNAPWEED IN BRITISH COLUMBIA  2  C. BIOLOGICAL CONTROL OF DIFFUSE AND SPOTTED KNAPWEED  6  D. THIS STUDY  9  I I KNAPWEED/GALL FLY SYSTEM A. LABORATORY AND GREENHOUSE STUDIES . i . D i f f u s e and s p o t t e d knapweed head p r o d u c t i o n i i . U r o p h o r a a f f i n i s and U.  10  quadrifasciata  a. Emergence and l a r v a l weights  19  b. S u p e r p a r a s i t i s m of d i f f u s e knapweed by U. a f f i n i s  24  c. G a l l - f l y  29  head-size  preferences  B. FIELD STUDIES i.Synchrony  o f g a l l - f l y a t t a c k w i t h knapweed phenology  i i . G a l l - f l y densities  37  on r e l e a s e s i t e s  i i i . T h e r o l e of h e t e r o g e n e i t y g a l l - f l y abundance  49  i n d i f f u s e knapweed head s i z e on ;  i v . P a r a s i t i s m of d i f f u s e knapweed by f i r s t and second genera t i o n s o f g a l l f l i e s i n 1977 v.Effect  of g a l l f l i e s on undeveloped heads  v i . E f f e c t of g a l l f l i e s on d i f f u s e and s p o t t e d knapweed weight, appearance and v i a b i l i t y  68  74 86  seed 96  V  Page v i i . S u r v e y of rangeland d i f f u s e and s p o t t e d knapweed y i e l d i n 1977 *.  seed 102  v i i i . V a r i a t i o n i n seed weight and numbers i n a s p o t t e d knapweed p o p u l a t i o n  I l l  i x . E f f e c t of g a l l f l i e s on knapweed seed number on the r e l e a s e s i t e s from 1975 to 1977  116  I I I KNAPWEED DEMOGRAPHY A. EFFECTS OF SEED REDUCTION ON KNAPWEED POPULATIONS  135  B. SURVIVAL AND FERTILITY SCHEDULES  151  C. KNAPWEED SEED SOWING TRIALS  170  IV CONCLUDING DISCUSSION A. INTRODUCTION  187  B. REASONS FOR FAILURE OF THE GALL FLIES TO CONTROL KNAPWEED i . R e s i l i e n c e - o f knapweed  190  i i . Phenology of U. af f i n i s and U. q u a d r i f a s c i a t a i i i . L o n g e v i t y and a g g r e s s i v e n e s s of v e g e t a t i v e stages i v . P l a s t i c r e a c t i o n s by knapweed to a decrease v.Knapweed e s t a b l i s h m e n t from seed C. FUTURE ASPECTS OF KNAPWEED CONTROL D. RECOMMENDATIONS FOR BIOLOGICAL CONTROL OF WEEDS V LITERATURE CITED  191 192  i n seed d e n s i t y . 194 195 195 •. . 198 202  vi LIST OF TABLES Table I  Page B i o l o g i c a l c o n t r o l agents r e l e a s e d i n B r i t i s h d i f f u s e and s p o t t e d knapweed  Columbia a g a i n s t 7  II  Comparison o f U. a f f i n i s and U. q u a d r i f a s c i a t a l a r v a l weights  III  E f f e c t of c a g i n g i n d i v i d u a l d i f f u s e knapweed heads w i t h U. a f f i n i s  21  27  IV  Gall-fly  V  Mean d a i l y temperature (°C) and t o t a l p r e c i p i t a t i o n the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s  VI  Average numbers of U. a f f i n i s per head on the d i f f u s e knapweed r e l e a s e s i t e from 1975 to 1978  54  Average numbers of U. a f f i n i s per head on the s p o t t e d knapweed r e l e a s e s i t e from 1975 to 1978  55  Average numbers of U. q u a d r i f a s c i a t a per head on the d i f f u s e knapweed r e l e a s e s i t e from 1975 to 1978  59  Average numbers o f U. q u a d r i f a s c i a t a p e r head on t h e s p o t t e d knapweed r e l e a s e s i t e from 1975 to 1978  59  Comparison of average numbers q f U. a f f i n i s and U. q u a d r i f a s c i a t a per head and average head numbers p e r s m a l l - and l a r g e headed d i f f u s e knapweed p l a n t s on the r e l e a s e s i t e i n 1977  70  Comparison of average head and g a l l p r o d u c t i o n d u r i n g f i r s t and second f l y g e n e r a t i o n s on the d i f f u s e knapweed r e l e a s e s i t e i n 1977  77  E s t i m a t e of f i r s t - and s e c o n d - g e n e r a t i o n on d i f f u s e knapweed i n 1977  79  VII  VIII  IX  X  XI  XII  XIII  head-size  preferences  32 (mm) f o r 46  g a l l - f l y fecundities  Comparison of g a l l - f l y a t t a c k of s m a l l - and large-headed knapweed d u r i n g f i r s t and second g e n e r a t i o n s  diffuse 81  XIV  1976 survey  f o r undeveloped heads i n d i f f u s e knapweed p o p u l a t i o n s  89  XV  1977 survey  f o r undeveloped heads i n d i f f u s e knapweed p o p u l a t i o n s  89  XVI  1976 survey  f o r undeveloped heads i n s p o t t e d knapweed p o p u l a t i o n s  90  XVII  1977 survey  f o r undeveloped heads i n s p o t t e d knapweed p o p u l a t i o n s  90  XVIII  C l i m a t e and a l t i t u d e f o r surveys p o p u l a t i o n s i n 1976 and 1977  of d i f f u s e and s p o t t e d knapweed 94  Table XIX  E f f e c t of g a l l f l i e s on d i f f u s e and s p o t t e d knapweed seed v i a b i l i t y and weight i n 1976  XX  Comparison of germinated, n o n - v i a b l e and dormant seeds from d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s  XXI  Survey of d i f f u s e knapweed seed weight and y i e l d  i n 1977  XXII  Survey of s p o t t e d knapweed seed weight and y i e l d  i n 1977  XXIII  Expected and a c t u a l seed y i e l d s per p l o t on d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s , and the estimated r e d u c t i o n i n y i e l d from 1975 to 1977  XXIV  Average numbers of d i f f u s e and s p o t t e d knapweed p l a n t s per p l o t f o r each t h i n n i n g r a t e i n 1977  XXV  Average number of d i f f u s e and s p o t t e d knapweed p l a n t s per p l o t f o r each s i z e c l a s s i n the s p r i n g of 1977, and t h e i r f a t e s by the f a l l of 1977. Average head p r o d u c t i o n f o r each s i z e c l a s s i n the f a l l of 1977  XXVI  S u r v i v o r s h i p and f e r t i l i t y  o f d i f f u s e knapweed  XXVII  S u r v i v o r s h i p and f e r t i l i t y  of s p o t t e d  XXVIII T o t a l d a i l y p r e c i p i t a t i o n (mm) XXIX * Mean d a i l y temperature  knapweed  f o r Kamloops and Westwold i n 1977  (°C) f o r Kamloops and Westwold i n 1977  XXX  Comparison  of Kamloops and Westwold seed sowing  sites  XXXI  P e r c e n t a g e dead d i f f u s e and s p o t t e d knapweed by the f a l l of 1977, of the number counted i n the s p r i n g of 1977, on the Kamloops, s p r i n g 1976 sowing t r i a l  XXXII  Comparison of d i f f u s e and s p o t t e d knapweed r o s e t t e e s t a b l i s h m e n t d u r i n g the 1977 growing season f o r the Kamloops, f a l l 1976 sowing t r i a l  XXXIII Average numbers of d i f f u s e and s p o t t e d knapweed p l a n t s produced by the f a l l of 1977 on the Westwold, f a l l 1976 sowing t r i a l , and the death r a t e s d u r i n g the 1977 growing season XXXIV  1976 and 1977 weather d a t a f o r Kamloops and Westwold  LIST OF FIGURES Figure 1  D i f f u s e knapweed  2. Spotted knapweed 3  D i f f u s e and s p o t t e d  knapweed seeds  4  U. a f f i n i s g a l l s i n a s p o t t e d  5  Average numbers of d i f f u s e and s p o t t e d a p p e a r i n g each four-day i n t e r v a l  6  P e r c e n t d i f f u s e knapweed heads i n developmental stages  7  Percent spotted  8  B r a n c h i n g p a t t e r n and sequence of head appearance f o r a t y p i c a l d i f f u s e knapweed p l a n t  9  Knapweed head s i z e s a v a i l a b l e and accepted f o r o v i p o s i t i o n by gall flies  knapweed head knapweed heads per p l a n t  knapweed heads i n developmental stages  10  Average numbers of heads i n young and o l d bud s t a g e s on d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s i n 1976  11  Average number o f male and female g a l l f l i e s per branch on the d i f f u s e knapweed r e l e a s e s i t e i n 1976  12  Average numbers o f U. a f f i n i s and U. q u a d r i f a s c i a t a p e r p l o t on the d i f f u s e knapweed r e l e a s e s i t e i n 1977  13  Average numbers o f heads i n young and o l d bud stages on the d i f f u s e knapweed r e l e a s e s i t e i n 1977  14  Average numbers of male and female g a l l f l i e s per s t a l k on the s p o t t e d knapweed r e l e a s e s i t e i n 1976  15  Mean r a t i o s of g a l l f l i e s : h e a d s on the d i f f u s e knapweed r e l e a s e , s i t e i n 1977  16  R e l a t i o n s h i p between the percentage dead f i r s t - i n s t a r l a r v a e which d i e d b e f o r e g a l l f o r m a t i o n and the average number o f f i r s t - i n s t a r l a r v a e per head f o r f i r s t g e n e r a t i o n s of U. a f f i n i s on d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s  17  R e l a t i o n s h i p between the average number of U. q u a d r i f a s c i a t a and U. a f f i n i s f i r s t - i n s t a r l a r v a e per head on s p o t t e d knapweed f o r f i r s t generations of f l i e s  18  C o r r e l a t i o n between the average number of U. q u a d r i f a s c i a t a and U. a f f i n i s f i r s t - i n s t a r l a r v a e per head on d i f f u s e knapweed f o r f i r s t g e n e r a t i o n s of f l i e s  ix Figure  Page  19  D i s t a l head s u p e r p a r a s i t i z a t i o n by U. a f f i n i s of d i f f u s e knapweed  71  20  D i s t a l head s u p e r p a r a s i t i z a t i o n by U. a f f i n i s o f s p o t t e d  71  21  R e l a t i o n s h i p between seed heads, undeveloped heads, s u p e r p a r a s i t i z e d heads, and average numbers o f f i r s t - i n s t a r U. a f f i n i s and U. q u a d r i f a s c i a t a p e r head a f t e r the end of the f i r s t a d u l t f l y generation  88  Appearance o f s p o t t e d knapweed seeds'from u n a t t a c k e d and a t t a c k e d heads by-U. a f f i n i s and f u s i f o r m U. a f f i n i s g a l l s  98  22  23  24  25  26  27  28  29  30  31  32  33  34  35  C o r r e l a t i o n between the number o f seeds p e r t e r m i n a l and s t a l k h e i g h t f o r s p o t t e d knapweed  knapweed  seed head 113  R e g r e s s i o n s o f the average number o f seeds p e r seed head and time on the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s  119  R e l a t i o n s h i p between the mean number o f U. a f f i n i s f i r s t - i n s t a r l a r v a e p e r head and the mean number o f d i f f u s e knapweed seeds p e r seed head  120  C o r r e l a t i o n between the mean number of U. a f f i n i s f i r s t - i n s t a r l a r v a e p e r head and the mean number o f s p o t t e d knapweed seeds p e r seed head  120  E f f e c t o f U. a f f i n i s on seed numbers p e r seed head on t h e d i f f u s e knapweed r e l e a s e s i t e i n 1975  123  E f f e c t o f U. a f f i n i s on seed numbers p e r seed head on the d i f f u s e knapweed r e l e a s e s i t e i n 1976  123  E f f e c t of U. a f f i n i s on seed numbers p e r seed head on the d i f f u s e knapweed r e l e a s e s i t e i n 1977  124  E f f e c t o f U. a f f i n i s on seed numbers per seed head on the s p o t t e d knapweed r e l e a s e s i t e i n 1975  125  E f f e c t o f U. a f f i n i s on seed numbers p e r seed head on t h e s p o t t e d knapweed r e l e a s e s i t e i n 1976  126  E f f e c t o f U. a f f i n i s on seed numbers p e r seed head on t h e s p o t t e d knapweed r e l e a s e s i t e i n 1977  127  E f f e c t o f U. q u a d r i f a s c i a t a on numbers of seeds p e r seed head on the d i f f u s e knapweed r e l e a s e s i t e i n 1977  129  E f f e c t o f U. q u a d r i f a s c i a t a on d i f f u s e knapweed seed numbers p e r seed head i n Vernon, 1977  129  E f f e c t o f U. q u a d r i f a s c i a t a on d i f f u s e knapweed seed numbers p e r seed head i n Vernon, 1979  130  X  Figure 36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  Page  Average d i f f u s e knapweed r o s e t t e diameter i n the s p r i n g and of 1977 f o r each t h i n n i n g r a t e  fall 144  The percentage o f d i f f u s e knapweed r o s e t t e s i n each f a t e c l a s s r e l a t e d to s p r i n g s i z e c l a s s e s  145  The percentage o f s p o t t e d knapweed r o s e t t e s i n each f a t e c l a s s r e l a t e d to s p r i n g s i z e c l a s s e s  145  The percentage o f s p o t t e d knapweed r o s e t t e s which b o l t e d s u c c e s s f u l l y , u n s u c c e s s f u l l y , o r were a r r e s t e d o f the t o t a l number i n each s i z e c l a s s which attempted to b o l t .  146  R e g r e s s i o n s of average s t a l k h e i g h t and average numbers o f seed heads per s t a l k on d i f f u s e knapweed r o s e t t e s i z e s  146  Average numbers o f d i f f u s e and s p o t t e d per p l o t i n 1977  knapweed s m a l l  159  Average numbers o f d i f f u s e and s p o t t e d per p l o t i n 1977  knapweed l a r g e  Cumulative numbers of d i f f u s e and s p o t t e d per p l o t i n 1977  seedlings  seedlings 159  knapweed s m a l l  rosettes 161  D i f f u s e and s p o t t e d knapweed r e g r e s s i o n s o f the c u m u l a t i v e number of s m a l l r o s e t t e s produced per p l o t i n 1977 (Y) , where X = ' log^g(time)  162  Average numbers o f d i f f u s e and s p o t t e d knapweed r o s e t t e s per p l o t i n the s p r i n g o f 1977 f o r the Kamloops, 1976 sowing t r i a l  174  T o t a l number of d i f f u s e and s p o t t e d knapweed seeds produced per p l o t by the f a l l o f 1977 f o r the Kamloops, s p r i n g 1976 sowing t r i a l  176  Average numbers o f d i f f u s e and s p o t t e d knapweed l a r g e s e e d l i n g s per p l o t i n the s p r i n g o f 1977 f o r the Kamloops, f a l l 1976 sowing t r i a l  177  Average numbers of d i f f u s e and s p o t t e d knapweed l a r g e s e e d l i n g s per p l o t i n t h e s p r i n g o f 1977 f o r the Westwold, f a l l 1976 sowing t r i a l  179  Percentage d i f f u s e knapweed appeared o f the number o f seeds sown on the Westwold, f a l l 1976 sowing t r i a l  181  Percentage s p o t t e d knanweed appeared o f the number of seeds sown on the Westwold, f a l l 1976 sowing t r i a l  181  xi STATISTICAL Throughout  INFERENCES  t h i s study numbers f o l l o w i n g - a r e s t a n d a r d e r r o r s o f the means.  V e r t i c a l l i n e s on graphs i n d i c a t e - one standard e r r o r . t e s t s were conducted a t p ^ . 0 5 , u n l e s s comparisons a r e t w o - t a i l e d  A l l statistical  otherwise stated.  A l l two-way  t - t e s t s , and a l l comparisons among t h r e e o r  more means were by a n a l y s i s o f v a r i a n c e  as i n E l l i o t t ,  1971 .  are used, N = sample s i z e ; r = c o r r e l a t i o n c o e f f i c i e n t ; R  1  q  =  Where  symbols  reproductive  e f f o r t ; x = mean and D.F. = degrees o f freedom.  1  E l l i o t t , J.M. 1971. Some Methods f o r t h e S t a t i s t i c a l A n a l y s i s o f samples of B e i i t h i c I n v e r t e b r a t e s . Freshwater B i o l o g i c a l A s s o c i a t i o n , S c i e n t i f i c P u b l i c a t i o n No. 25.  xii ACKNOWLEDGMENT My g r e a t e s t thanks go t o Dr. Bryan F r a z e r , my s u p e r v i s o r , f o r h i s h e l p and  direction.  I am i n d e b t e d  to Marina Devick and Laura Roze f o r t h e i r p a i n s t a k i n g work.  I am g r a t e f u l f o r the h e l p and i n t e r e s t o f t h e s t a f f a t t h e A g r i g u l t u r e Canada Research S t a t i o n , i n Kamloops, and use o f the f a c i l i t i e s Station.  a t the  P a r t i c u l a r l y I thank Dr. D. E. Waldern, Dr. A. McLean, Dr. W.  Majak, B i l l Hubbard and Imants B e r g i s . I a l s o thank the members o f the B r i t i s h Columbia M i n i s t r y o f A g r i c u l t u r e , Roy  S. C r a n s t o n and A l f H. Bawtree f o r t h e i r ready a s s i s t a n c e ,  I thank Tom W a l l a c e and o t h e r p e r s o n n e l  a t t h e B r i t i s h Columbia F o r e s t  S e r v i c e i n Kamloops, and i n M e r r i t , and Mr. Ed Smith i n V i c t o r i a , f o r their  support.  I am indebted and  to r a n c h e r s ,  L a r r y Buff  field  W i l l i a m Bostock, Hugh Robertson, L a r r y  for granting protected  s e c t i o n s o f t h e i r rangeland  Campbell for  studies.  S p e c i a l thanks t o Dr. P. H a r r i s f o r a d v i c e d u r i n g  the e a r l y part of t h i s  research. I thank Dr. J . D. Shorthouse, Dr. H. ZwHlfer, Dr. A. K. Watson and Dr. D. Berube f o r t h e i r a d v i c e I appreciate  and i n f o r m a t i o n .  the a s s i s t a n c e o f t h e remaining members o f my committee, Dr.  A. J . Renney, Dr. V. C. Runeckles, Dr. J . Myers, and e s p e c i a l l y Dr. W. G. Wellington. T h i s work was supported by t h e Bostock.Grant, t h e L. K l i n k F e l l o w s h i p , t h e B r i t i s h Columbia F o r e s t S e r v i c e , and i n p a r t by a N a t i o n a l Research C o u n c i l of Canada Grant t o Dr. J . Myers.  1 I INTRODUCTION A. BIOLOGICAL CONTROL OF WEEDS B i o l o g i c a l c o n t r o l of pests  i s n o t a new concept.  The a n c i e n t  Chinese used  the ant, O e c o p h y l l a smaragdina, t o c o n t r o l c a t e r p i l l a r s and b e e t l e s i n t h e i r c i t r u s groves (DeBach, 1974).  The f i r s t known d e l i b e r a t e i n t r o d u c t i o n  b i o l o g i c a l c o n t r o l agent by man o c c u r r e d c o l l e c t e d predatory oases.  of a  i n m e d i e v a l A r a b i a , when date growers  a n t s i n the nearby mountains and t r a n s p o r t e d  them t o  These were r e l e a s e d a g a i n s t phytophagous a n t s , which a t t a c k e d  the date  palm (van den Bosch and Messenger, 1973).  B i o l o g i c a l c o n t r o l i s recognized 1974;  t o be p a r t o f " n a t u r a l c o n t r o l " (DeBach,  v a n den Bosch and Messenger, 1973; H u f f a k e r e t al'. , 1971).  control i s described  Natural  by H u f f a k e r e^t a l . (1971) as " a l l f a c t o r s o f the e n v i -  ronment d i r e c t l y o r i n d i r e c t l y i n f l u e n c i n g n a t a l i t y and m o r t a l i t y o r movements i n t o and o u t o f the p o p u l a t i o n " .  However, one component o f t h e e n v i -  ronment o f an organism, such as i t s n a t u r a l enemies, may be a b l e i t s numbers.  In c o n t r a s t  to regulate  T h i s i s termed " n a t u r a l l y o c c u r r i n g b i o l o g i c a l c o n t r o l " .  t o n a t u r a l l y o c c u r r i n g b i o l o g i c a l c o n t r o l , where n a t u r a l enemies  are i n d i g e n o u s , " c l a s s i c a l b i o l o g i c a l c o n t r o l " i s the p r o c e s s whereby n a t u r a l enemies o f t a r g e t p e s t s (DeBach, 1974).  are discovered  and imported t o c o n t r o l the pest  The u s u a l procedure i s t o s e a r c h  country of the o r i g i n of the pest. r a l enemies a f t e r s c r e e n i n g  f o r s u i t a b l e agents i n the  Agents a r e i n t r o d u c e d  without t h e i r natu-  t e s t s have been conducted to ensure t h a t they w i l l  not be h a r m f u l t o b e n e f i c i a l organisms. r a l l y o c c u r r i n g b i o l o g i c a l c o n t r o l should  I n the f u t u r e , r e c o g n i t i o n o f n a t u equal,  o r even s u r p a s s ,  c l a s s i c a l b i o l o g i c a l c o n t r o l (van den Bosch, 1971).  efforts i n  2 B i o l o g i c a l c o n t r o l of p e s t s has been shown to be f a r cheaper than control  ( H a r r i s , 1971;  (1974) e s t i m a t e d  van  den Bosch and Messenger, 1973).  t h a t o n l y 54%  successes  have been  A w i d e l y p u b l i c i z e d case of weed c o n t r o l i n v o l v e d two  i n e r m i s and The  A l t h o u g h DeBach  of a l l t a r g e t p e s t s were s u c c e s s f u l l y con-  t r o l l e d w i t h b i o l o g i c a l c o n t r o l agents, these cular.  (). s t r i c t a , which occupied  c o n t r o l of Hypericum perforatum  over 24.3  specta-  cacti,  Opuntia  m i l l i o n ha i n A u s t r a l i a .  (Klamath weed, or S t . John's wort) by  the b e e t l e s C h r y s o l i n a quadrigemina and m i l l i o n ha i n C a l i f o r n i a  chemical  C_. h y p e r i c i , was  s p e c t a c u l a r on  (van den Bosch and Messenger, 1973)  have been l e s s s u c c e s s f u l i n B r i t i s h Columbia  ( H a r r i s et_ a l . ,  but  0.81  the b e e t l e s  1969).  The  c o n t r o l of the a q u a t i c a l l i g a t o r weed ( A l t e r n a n t h e r a p h y l l o x e r o i d e s ) i n some p a r t s of the U n i t e d and  Goeden, 1971)  S t a t e s by the f l e a b e e t l e , A g a s i c l e s spp.  shows t h a t t h i s method i s not r e s t r i c t e d  to  (Andres  terrestrial  weeds.  B. KNAPWEED IN BRITISH COLUMBIA B i o l o g i c a l c o n t r o l of the Composite weeds, Centaurea d i f f u s a Lam, C^. maculosa Lam.  ( d i f f u s e and  s p o t t e d knapweed, r e s p e c t i v e l y ) was  i n B r i t i s h Columbia because these weeds were t h r e a t e n i n g the 1.1 of rangeland Saskatchewan.  i n the p r o v i n c e , and were s p r e a d i n g The  begun  million  ha  i n t o p a r t s of A l b e r t a  and  annual l o s s to the B r i t i s h Columbia C a t t l e I n d u s t r y  due  to a r e d u c t i o n i n f o r a g e q u a l i t y by knapweed was per annum i n 1972.  and  Further estimates  estimated  to be  $350,000  suggested t h a t a l l o w i n g the weeds to  spread unchecked to t h e i r geographic l i m i t s would u l t i m a t e l y i n c r e a s e s p r a y i n g c o s t s to $33 m i l l i o n . 0.42  to 0.56  Picloram  (Tordon 22-K)  kg per ha i s the recommended treatment.  the c h e m i c a l was  o n l y $2.84 per ha i n 1976,  a p p l i e d at a r a t e of A l t h o u g h the c o s t of  the expense of p r o v i d i n g  spraying  3 equipment and manpower r a i s e d t h e c o s t t o an average of $20.75 p e r h a . Where spot s p r a y i n g was n e c e s s a r y  t o check s m a l l i n f e s t a t i o n s , t h e c o s t was as h i g h  as $398 p e r ha ( H a r r i s and Cranston,  1979).  D i f f u s e and s p o t t e d knapweed a r e n a t i v e s o f E u r a s i a , and a r e thought t o have entered first  the p r o v i n c e as contaminants o f a l f a l f a seed. Spotted knapweed was  r e p o r t e d i n V i c t o r i a i n 1893,  Washington i n 1907. of  and d i f f u s e knapweed was f i r s t - seen i n  These weeds w i l l r e a d i l y invade any s o i l i n t h e I n t e r i o r  B r i t i s h Columbia w i t h a d i s t u r b e d "A" h o r i z o n .  ( W a t s o n 1 9 7 2 ) .. The • ••  " I n t e r i o r " , " r e f e r s t o a n - u p l i f t e d p l a t e a u s t r e t c h i n g from l a t i t u d e 54°N, j u s t n o r t h o f P r i n c e George, south t o t h e i n t e r n a t i o n a l border between t h e C o a s t a l Range and t h e Columbian Mountain System.  On t h e average t h i s a r e a i s 200  m i l e s wide, and i s d r a i n e d by t h e N i c o l a , Okanagan, Thompson, C h i l c o t i n and F r a s e r watersheds. and  the r e s t i s timber  p e r s . comnw) 1972  About 10% i s open g r a s s l a n d , i . e . , about 1,417,500 ha, range, s u b - a l p i n e meadow and a l p i n e t u n d r a .  (Brink,  I t i s t h e open g r a s s l a n d t h a t knapweed r e a d i l y i n v a d e s .  d i f f u s e knapweed was found  as f a r n o r t h as t h e 51°N.  s p r e a d i n g northward t o i t s approximate g e o g r a p h i c a l l i m i t ,  In  L a t . , and was 53°N. L a t .  Spotted knapweed, which grows more r e a d i l y i n c o o l e r , m o i s t o r h a b i t a t s , was  p r e d i c t e d t o spread  knapweed may be found  even f u r t h e r n o r t h .  (Watson, 1972).  Spotted  a t a l t i t u d e s as h i g h as 1,200 m, but d i f f u s e knapweed  g e n e r a l l y grows o n l y as h i g h as 900 m (Watson and Renney, 1974). knapweed i n f e s t s about 7.5 times ( H a r r i s and Cranston,  These weeds spread  the area occupied  Diffuse  by s p o t t e d knapweed  1979).  by seed d i s p e r s a l .  Increase  i nvehicle traffic  the 1950's was l a r g e l y r e s p o n s i b l e f o r t h e spread  during  o f d i f f u s e and s p o t t e d  4 knapweed from o n l y a few h e c t a r e s t o t h e e s t i m a t e d 25,953 ha i n f e s t e d by d i f f u s e and 3,410 ha i n f e s t e d by s p o t t e d knapweed i n 1972 ( B r i n k , p e r s . comm.; Watson and Renney, 1974).  A p o s s i b l e cause f o r t h e r a p i d  deve-  lopment o f knapweed monocultures i s t h e i r s e c r e t i o n o f a l l e l o p a t h i c compounds.  F l e t c h e r and Renney (1963) demonstrated t h e i n h i b i t i o n o f germin-  a t i o n o f b a r l e y and l e t t u c e by knapweed exudates i n t h e l a b o r a t o r y . ( p e r s . comm.) found t h a t knapweed l e a f l i t t e r had a g r e a t e r  Majak  inhibiting  e f f e c t on b a r l e y seed g e r m i n a t i o n than d i d f r e s h knapweed l e a f m a t e r i a l , and t h a t g e r m i n a t i o n o f a l f a l f a , b a r l e y and r y e were i n h i b i t e d by l e a c h a t e s of s o i l i n which knapweed had been growing.  D i f f u s e and s p o t t e d knapweed germinate e i t h e r i n t h e s p r i n g o r i n the f a l l , and produce a many-leaved  r o s e t t e during the f i r s t  " r o s e t t e " i s a c i r c u l a r c l u s t e r of leaves r o s e t t e s crown tap r o o t s .  season o f growth.  (Benson, 1959), and knapweed  I n t h e Kamloops a r e a r o s e t t e s b o l t i n May, p r o -  d u c i n g s i n g l e s t a l k s which bear composite heads, o r " c a p i t u l a e " Jones and T u r r i l l ,  1954).  A  (Marsden-  Unopened heads w i l l be r e f e r r e d t o as heads i n  the bud stage i n t h i s study.  Some heads i n t h e bud stage a b o r t a t e a r l y  stages o f development - u s u a l l y when t h e head i s l e s s than 4 mm i n l e n g t h . In B r i t a i n almost a l l heads i n t h e bud stage can a b o r t on some knapweed plants  (Marsden-Jones and T u r r i l l ,  1954).  Heads which have opened to expose t h e f l o r e t s w i l l be r e f e r r e d t o as heads i n the flower stage.  The s p i n y ^ d i f f u s e knapweed heads  ( F i g . 1) produce  white o r p i n k f l o r e t s , b u t some o f the p l a n t s have p u r p l e f l o r e t s .  Spotted  knapweed heads.".usually have mauve f l o r e t s , and s p o t t e d knapweed d e r i v e s  5  F i g u r e 1.  D i f f u s e knapweed  1  F i g u r e 2.  f c.  t d  i  i  f f  l  f  l  us a  I I I !  » c.  F i g u r e 3.  mac  ul  os  t  a  D i f f u s e and s p o t t e d knapweed seeds (magnified 2X)  S p o t t e d knapweed  6 i t s name from the b l a c k - t i p p e d b r a c t s , which subtend the r e c e p t a c l e , the heads a s p o t t e d appearance  (Fig.  giving  2).  Opened-heads, w i t h w i t h e r e d f l o r e t s and f e r t i l i z e d o v a r i e s wiH""be> termed seed heads.  S p o t t e d knapweed produces about t w i c e as many seeds (termed'  " c y p c e l a s " by Marsd'en-Jones d i f f u s e knapweed (12.5).  and " T , u r r i l l , : l 9 5 4 ) ' per -head (26.6) as does  On the average d i f f u s e and s p o t t e d knapweed produce  832 and 372 seeds p e r p l a n t , r e s p e c t i v e l y , on r a n g e l a n d (Watson,  1972).  Seeds o f some Centaurea spp. have b r i s t l e s which spread on d r y i n g , thus f o r c i n g the seeds out o f the heads  (Harper, L o v e l l and Moore, 19^70).  Spotted  knapweed has many such b r i s t l e s , and s e e d s - o f - t h i s s p e c i e s a r e shed soon a f t e r m a t u r a t i o n , i n August.  D i f f u s e knapweed has v e r y s m a l l b r i s t l e s , o r  they may be absent, and because the l o n g , narrow heads o f t e n do not d e h i s c e u n t i l the w i n t e r , seeds i n d i f f u s e knapweed heads may be r e t a i n e d u n t i l t h e following spring.  D i f f u s e knapweed seeds a r e s m a l l e r  (1.099 mg) than s p o t t e d  knapweed seeds (1.778 mg; F i g . 3 ) . The h i g h e s t g e r m i n a t i o n % of both s p e c i e s i s on the s o i l s u r f a c e .  f o r seeds  (Watson, 1972)  D i f f u s e knapweed u s u a l l y d i e s a f t e r m a t u r a t i o n , but s p o t t e d knapweed produces numerous r o s e t t e s a t the bases o f mature following years.  s t a l k s , each o f which can b o l t i n  These r o s e t t e s , however, do n o t break o f f from the main  r o o t and grow as s e p a r a t e p l a n t s .  The p r o d u c t i o n of r o s e t t e s a t bases o f  mature s t a l k s , and t h e i r subsequent b o l t i n g w i l l be termed p e r e n n a t i o n . A more d e t a i l e d account o f knapweed b i o l o g y can be found i n Watson and Renney (1974).  C. BIOLOGICAL CONTROL OF DIFFUSE AND SPOTTED KNAPWEED  Two  seed-reducing  g a l l f l i e s , Urophora a f f i n i s F r a u e n f e l d and U.  f a s c i a t a Meigen ( D i p t e r a : T e p h r i t i d a e ) were i n t r o d u c e d  into several locations  i n B r i t i s h Columbia i n an attempt to stop the spread knapweed, and  u n l e s s otherwise  Table  I.  knapweed species i n B.C.  diffuse knapweed  The  Both s p e c i e s  f o l l o w i n g i s summarized from ZwBlfer  (1970)  B i o l o g i c a l c o n t r o l agents r e l e a s e d i n B r i t i s h Columbia a g a i n s t d i f f u s e and spottzed .knapweed,, (Data..from.Harris, 1980a) country agent  1  ... origin  . ,. indigenous host  location of T release  C. maculosa  Pritchard "A"  1970 1971  284 209  yes yes  Pritchard n n  , ,„ 1972  797  yes  U.a.  date , > estabnumbers . , . ,of .. , lishment released , release (status) N  *•••  B  Russia  C.  sterilis  **  Grand Forks U.q.  Russia  C.  sterilis  U.a.  France  C. maculosa  P r i t c h a r d "A"  and  U.q. "B"  U.  heads i n the bud  ^  u  Q Q J  25  yes  Chase  1971  97  yes  1970 1971  297 280  , Walachm  3  yes yes  = U_. q u a d r i f a s c i a t a  s i t e s a r e 265 m a p a r t , on the Bostock  a c c i d e n t a l l y burned i n 1976;  IJ. a f f i n i s and  g  1972  TT  ''"U.a. = U. af f i n i s ;  ±  Pritchard „ „ B  A**  a c c i d e n t a l l y sprayed  in  ranch  1975  q u a d r i f a s c i a t a females l a y eggs amongst b r a c t s of knapweed stage.  C o p u l a t i o n may  occur w i t h i n a few hours a f t e r emer-  gence, but o v i p o s i t i o n does not occur u n t i l the second or t h i r d day emergence.  spotted  noted.  France  spotted knapweed  of d i f f u s e and  to reduce e x i s t i n g i n f e s t a t i o n s (Table I ) .  r a p i d l y became e s t a b l i s h e d .  quadri-  after  stage which a r e o f f e r e d a r e probed by f e - r  A l l heads i n the bud  males i n the l a b o r a t o r y , however, o n l y heads a t p a r t i c u l a r stages 1  of deve-  8 lopment a r e a c c e p t e d f o r o v i p o s i t i o n .  U. a f f i n i s o v i p o s i t i n heads a t  younger stages of development than U. q u a d r i f a s c i a t a .  U. a f f i n i s f e -  males l a y about 120 eggs d u r i n g t h e i r l i f e t i m e s under o p t i m a l  conditions.  I f few heads a r e a v a i l a b l e f o r o v i p o s i t i o n , the eggs l a i d p e r head a r e n o t r e s t r i c t e d by the same, or o t h e r females. f l o r e t s o r the immature  ovaries.  First-instar  l a r v a e chew i n t o  G a l l s a r e formed around the l a r v a e .  a f f i n i s g a l l s a r e t y p i c a l l y hard and woody ( F i g . 4 ) , whereas JJ. q u a d r i f a s c i a t a g a l l s a r e t h i n and papery. t i v e t i s s u e produced i n s i d e t h e g a l l s three  U_.  the s m a l l e r  Both s p e c i e s f e e d on n u t r i -  (Shorthouse, p e r s . comm.) and have  instars.  F i g u r e 4. U. a f f i n i s g a l l s i n a s p o t t e d knapweed head  P r e l i m i n a r y f i e l d work i n B r i t i s h Columbia i n d i c a t e d t h a t most pupate i n May  larvae  a f t e r d i a p a u s i n g i n s i d e the g a l l s d u r i n g the w i n t e r .  emerge i n June and a t t a c k knapweed heads.  The progeny of the f i r s t  Adults adult  g e n e r a t i o n develop t o the t h i r d l a r v a l i n s t a r by e a r l y August, when a p r o p o r t i o n of the l a r v a e pupate and emerge as the second a d u l t ZwBlfer  (1970) found t h a t i n Europe some f i r s t - g e n e r a t i o n IJ. a f f i n i s  progeny a l s o pupate i n mid-summer. August.  generation.  Second a d u l t g e n e r a t i o n s emerge i n l a t e  9 D. THIS STUDY Gall flies  and knapweed were s t u d i e d m a i n l y a t P r i t c h a r d and Chase, where  the f l i e s had been r e l e a s e d d u r i n g release s i t e were r e l e a s e d  the e a r l y 1970's.  On t h e d i f f u s e knapweed  ( P r i t c h a r d "B"; T a b l e I ) U_. a f f i n i s and U_. q u a d r i f a s c i a t a together  i n 1972, and on t h e s p o t t e d  (Chase) TJ. a f f i n i s was r e l e a s e d a l o n e i n 1971.  knapweed r e l e a s e  Both s i t e s  South Thompson R i v e r V a l l e y , a p p r o x i m a t e l y 20 km a p a r t . knapweed r e l e a s e s i t e i s n e a r e s t than the s p o t t e d  knapweed r e l e a s e s i t e  (671 m).  when i t was s e v e r e l y  The d i f f u s e  The d i f f u s e knapweed r e -  site.  d i f f u s e knapweed r e l e a s e s i t e i s a r e l a t i v e l y  400 m, and was p r o t e c t e d  a r e i n the  Kamloops, a t a lower e l e v a t i o n (366 m)  l e a s e s i t e i s h o t t e r and d r i e r than t h e other  The  site  flat  area o f about 300 X  from l i v e s t o c k u n t i l the w i n t e r o f 1977/1978,  trampled by h o r s e s .  I n 1976 and 1977 the knapweed  s u r r o u n d i n g the s i t e was sprayed from the a i r , c r e a t i n g an i s l a n d o f knawpeed i n the m i d d l e o f p a s t u r e .  Gall flies  on the s p o t t e d  knapweed r e l e a s e s i t e were r e l e a s e d  half-way  up the c r e s t of a r i d g e t h a t was about 0.5 km l o n g and 50 t o 100 m h i g h . The  south-facing  north-facing  s l o p e was a s o l i d  s l o p e was f o r e s t e d .  infested ridge.  i n f e s t a t i o n of spotted The g a l l f l i e s  knapweed, but the  spread over the e n t i r e  I n 1977 the area below the r i d g e was sprayed f o r knapweed  c o n t r o l , and grazed, but there was no t r a m p l i n g  by l i v e s t o c k w i t h i n a 40 m  r a d i u s around the r e l e a s e p o i n t o f the f l i e s .  On both r e l e a s e s i t e s and  i n 1977 p o p u l a t i o n  the f l i e s  increased  exponentially  e s t i m a t e s reached 1 m i l l i o n  i n population  ( H a r r i s , 1980a).  size By  1975 U. q u a d r i f a s c i a t a spread from the d i f f u s e knapweed r e l e a s e s i t e t o the  10 s p o t t e d knapweed r e l e a s e s i t e ,  so t h a t when t h i s study began i n 1977,  s p e c i e s were monitored on both r e l e a s e s i t e s .  The  determine what e f f e c t s the g a l l f l i e s have had  on d i f f u s e and  weed r e l e a s e - s i t e p o p u l a t i o n s from 1975 ness of the f l i e s as seed-reducing  A. LABORATORY AND 1. D i f f u s e and  aim of t h i s t h e s i s i s to  and  s p o t t e d knap-  to p r e d i c t the u s e f u l -  b i o l o g i c a l c o n t r o l agents i n the  of B r i t i s h Columbia a g a i n s t d i f f u s e and  I I KNAPWEED/GALL FLY  to 1978,  both  Interior  s p o t t e d knapweed.  SYSTEM  GREENHOUSE STUDIES  s p o t t e d knapweed head p r o d u c t i o n :  1.Introduction: Phytophagous i n s e c t s may found  For example, Cameron (1935)  t h a t damage to ragwort by T y r i a jacobaeae c o u l d cause shoot  a t i o n and was  a f f e c t p l a n t phenology.  f l o w e r p r o d u c t i o n l a t e i n the growing season.  The  regener-  present  study  undertaken to d e f i n e the growth p a t t e r n of knapweed when a t t a c k e d by  head-feeding  gall flies.  the appearance of new  In t h i s study  the  the term "head i n i t i a t i o n " r e f e r s to  heads on knapweed s t a l k s , and  r o s e t t e p r o d u c t i o n at the bases of maturing  "perennation"  refers  to  stalks.  2. Method: D i f f u s e and  s p o t t e d knapweed r o s e t t e s were dug  the b e g i n n i n g diameter and  of November, 1976,  from the Kamloops a r e a at  were t r a n s p l a n t e d i n t o p o t s , 15.2  p l a c e d under a 16-hour p h o t o p e r i o d  i n a greenhouse.  cm i n When most  of the r o s e t t e s had b o l t e d ( a f t e r about one month), t h r e e d i f f u s e and s p o t t e d knapweed p l a n t s , which had day,  were a r b i t r a r i l y chos en.  produced t h e i r f i r s t heads on the same  T h e r e a f t e r the s i x p l a n t s were observed  2 days - 3 hours f o r the appearance of hew duced were c l a s s i f i e d  i n t o one  three  every  heads, when heads p r e v i o u s l y p r o -  of the f o l l o w i n g s t a g e s :  1) bud  (unopened  11 heads, g r e a t e r than 0.5 mm i n l e n g t h ) ; 2 ) f l o w e r head f l o r e t s which had n o t w i l t e d ) ; 3)seed head  (opened heads, exposing  (opened heads, but w i t h w i l t e d  f l o r e t s and f e r t i l i z e d o v a r i e s ) ; o r 4 ) a b o r t e d head  (heads which grow 3 to  5 mm i n l e n g t h w h i l e i n t h e bud s t a g e , then t u r n y e l l o w and d r y i n s t e a d o f completing development).  Lengths and widths o f .heads i n t h e bud s t a g e were  measured to t h e n e a r e s t 0.1 mm w i t h c a l i p e r s .  Heads a t d i s t a l ends of primary branches were denoted by I , I I , I I I . . . ; of secondary branches by i ,  ii,  iii...;  o f t e r t i a r y branches by a, b, c . . . ;  of q u a t e r n a r y branches by x', x", x'" ...; and o f branches d i v i d e d t o t h e f i f t h degree by x^, x^, x^....  F o r example,  a head a p p e a r i n g on the f i f t h  p r i m a r y branch, t h i r d secondary b r a n c h , f o u r t h t e r t i a r y b r a n c h , second q u a t e r n a r y b r a n c h , and t h i r d branch d i v i d e d t o t h e f i f t h degree would be coded V i i i  d^.  O b s e r v a t i o n s o f d i f f u s e and s p o t t e d knapweed head  appearance  c o n t i n u e d f o r 76 and 70 days, r e s p e c t i v e l y , when t h e p l a n t s s t a r t e d to p e r ennate.  Some o f t h e s p o t t e d knapweed r o s e t t e s , which were produced a t t h e  bases o f s t a l k s , s t a r t e d t o b o l t .  B o l t i n g from p e r e n n i a l r o s e t t e s does not  occur u n t i l t h e f o l l o w i n g s p r i n g i n t h e f i e l d , also indicated  and p r e l i m i n a r y f i e l d work  t h a t few heads a r e i n i t i a t e d a f t e r t h e s t a r t o f p e r e n n a t i o n .  T h e r e f o r e i t was assumed t h a t d i f f u s e and s p o t t e d knapweed i n t h i s study had produced maximum numbers o f heads b e g i n n i n g o f head  76 and 70 days, r e s p e c t i v e l y , a f t e r t h e  initiation.  3.Results: The average number o f new heads, which appeared a t one sampling time, was g r e a t e s t on day 28 f o r both d i f f u s e and s p o t t e d knapweed, w i t h s m a l l e r  peaks  o c c u r r i n g on day 8 and 12 f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y  12 (fig.  5).  D i f f u s e knapweed began t o f l o w e r and s e t seed on day 32 and 36,  respectively  ( F i g . 6 ) , and s p o t t e d knapweed began t o f l o w e r and s e t seed on  day 28 and 34 ( F i g . 7 ) .  T h e t r a t e o f head i n i t i a t i o n o f d i f f u s e knapweed was  g r e a t e r b e f o r e the f i r s t  seed head appeared:  from day 0 t o day 36, heads  appeared a t a rate o f 2.3% per day o f t h e t o t a l number o f heads produced, but from day 36 to day 76, o n l y 0.5% of the t o t a l number o f heads produced appeared per day.  S i m i l a r i l y , the r a t e of s p o t t e d knapweed head  initiation  from day 0 t o day 34 was 2.6% p e r day of the t o t a l number o f heads in  70 days, but a f t e r day 34, the r a t e dropped t o 0.3% per day.  produced  By day 34,  87% of t h e t o t a l number o f s p o t t e d knapweed heads had appeared.  Head a b o r t i o n u s u a l l y o c c u r r e d when the f i r s t sample, on d i f f u s e knapweed "A" p l a n t  seed head appeared.  ( F i g . 8 ) , the f i r s t  F o r ex-  seed head was ob-  served on day 36, and seven out o f the e i g h t heads which a b o r t e d appeared on day 38.  The r e m a i n i n g a b o r t e d head on t h i s p l a n t , i n p o s i t i o n X I I i i i ,  peared on day 56.  ap-  By the t e r m i n a t i o n o f the study, 10% and 20% o f the t o t a l  number o f d i f f u s e and s p o t t e d knapweed heads produced, r e s p e c t i v e l y , had aborted.  The f i r s t  Aborted heads were u s u a l l y i n p r o x i m a l p o s i t i o n s on branches.  head t o appear was a t the apex o f the s t a l k on the f i r s t p r i m a r y  branch, thus p r e v e n t i n g f u r t h e r s t a l k e l o n g a t i o n .  S i m i l a r i l y , lengths of  primary, secondary, t e r t i a r y , e t c . branches were l i m i t e d when the a p i c a l head appeared. the  F u r t h e r head p r o d u c t i o n on each branch always o c c u r r e d  d i s t a l t o the p r o x i m a l end.  F o r example,  from  on p l a n t "A" the o r d e r o f  head appearance on p r i m a r y branches I , I I , I I I . . . X I on the main a x i s was 2, 2, 4, 4, 6, 6, 8, 8, 8, 12, 20 and 34, r e s p e c t i v e l y ; on secondary branches i,  i i , iii...ix  on branch IV was 4, 6, 8, 8, 10, 18, 22, 22, and 24, r e s -  p e c t i v e l y ; on t e r t i a r y branches a, b, c, and d on branch IV i i i was 8, 12,  30  i  0  10  20  30  40  50  60  70  80  DAYS AFTER THE BEGINNING OF HEAD PRODUCTION Figure 5. Average numbers of d i f f u s e and spotted knapweed heads per plant appearing each four-day., i n t e r v a l , d i f f u s e knapweed 0 0; spotted knapweed XX  80  DAYS AFTER THE BEGINNING OF HEAD PRODUCTION F i g u r e 6.  P e r c e n t d i f f u s e knapweed heads i n d e v e l o p m e n t a l stages bud • •; flower H +; seed 0 -0: a b o r t e d * p e r c e n t heads appeared of t o t a l produced x  x  *• '  i—*  -  -P* '  DAYS  F i g u r e 7.  AFTER  THE  BEGINNING  OF  HEAD  PRODUCTION  Percent s p o t t e d knapweed heads i n developmental stages bud • — — — • ; flower H : + ; seed 0"--"0; aborted * — percent heads appeared o f t o t a l produced x —x  9  F i g u r e 8.  B r a n c h i n g p a t t e r n and sequence of head appearance f o r a t y p i c a l d i f f u s e knapweed p l a n t . Numbers g i v e the day o f head appearance. C i r c l e d heads a b o r t e d . For branch code, see method.  17 12 and 22, r e s p e c t i v e l y ; on the q u a t e r n a r y branches c', c" and c "  on  1  branch IV i i i c was  12, 22 and 30, r e s p e c t i v e l y ; and on b r a n c h I I i i b" the  o r d e r of head appearance on the two branches d i v i d e d to the f i f t h 18 and 20, r e s p e c t i v e l y . There was  The l a t t e r head was  degree  was  t h e r e f o r e coded I I i i b^.  a s h o r t e r time, on the average, between c o n s e c u t i v e head  appear-  ance on branches of a h i g h e r o r d e r ( i . e . , the l a r g e r p r i m a r y and secondary branches) than on branches of lower o r d e r ( i . e . , quaternary branches). in  the s m a l l e r t e r t i a r y  and  Heads i n d i s t a l p o s i t i o n s r e a c h e d the f l o w e r i n g stage  s i g n i f i c a n t l y l e s s time (32.9 - 0.5  and 30.3  - 0.7  days f o r d i f f u s e  and  s p o t t e d knapweed, r e s p e c t i v e l y ) than d i d heads i n more p r o x i m a l p o s i t i o n s (45.6 - 0.6  and 5 0 - 2  days f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y ) .  There was no s i g n i f i c a n t d i f f e r e n c e i n development to  the end of the bud stage between d i f f u s e  time from head  (39.6 - 0.8  (40 - 2 days) knapweed, when a l l the heads a r e averaged. stage can e l o n g a t e up to 0.5 mm day.  There was  days) and  initiation spotted  Heads i n the bud  per day, but the average r a t e i s 0.25 mm  per  no s i g n i f i c a n t d i f f e r e n c e between d i f f u s e and s p o t t e d knap-  weed i n the average time spent i n the f l o w e r s t a g e (5.23 - 0.08 days, r e s p e c t i v e l y ) .  and 5.4  -  0.2  On the average l e s s than 10% o f the t o t a l number of  heads f o r e i t h e r s p e c i e s were i n the f l o w e r stage a t any one time.  4.Discussion: There a r e d e f i n i t e phases i n d i f f u s e and s p o t t e d knapweed head During the f i r s t phase  t e r m i n a l heads on p r i m a r y branches appear,  p l a n t h e i g h t and b r e a d t h . proximal p o s i t i o n s .  production.  A f t e r a s h o r t pause  limiting  the p l a n t s produce heads i n  By the time the t h i r d , or " f l o w e r i n g " phase i s r e a c h e d ,  75% of the t o t a l number of heads have appeared.  In the t h i r d phase,  most heads f l o w e r i n the same o r d e r t h a t they appeared.  Only a few  distalheads  18 f l o w e r a t a time, and  on s m a l l p l a n t s , heads f l o w e r one  by one.  This prob-  a b l y ensures t h a t i n the advent of poor growing c o n d i t i o n s , such as a p e r i o d of drought i n August, at l e a s t some heads w i l l have completed maturation. and  Few  a d d i t i o n a l heads a r e i n i t i a t e d  some heads i n the bud  At t h i s p o i n t over 80% heads i n p r o x i m a l for  i n the f o u r t h phase, the seed  stage i n p r o x i m a l  p o s i t i o n s u s u a l l y abort.  of the t o t a l heads have appeared.  p o s i t i o n s i s v e r y slow, and  Development of  some heads may  weeks, u n t i l t h e i r t u r n comes f o r development.  not  Regardless  elongate  of the f a t e  of heads, or the number of a d d i t i o n a l heads produced, the sequence of i n i t i a t i o n of d i f f u s e and  T h i s e l i m i n a t e s the need f o r m e c h a n i c a l  of heads when heads must be marked f o r s t u d i e s w i t h g a l l  Head development p a t t e r n s  f o r d i f f u s e and  s p o t t e d knapweed a r e  the same, except t h a t fewer heads are produced by shorter maturation veloped  head  s p o t t e d knapweed i s so r e g u l a r t h a t head p o s i t i o n s  can be coded f o r f u t u r e r e f e r e n c e . tagging  time of the s t a l k .  flies.  essentially  s p o t t e d knapweed, w i t h  Branches of d i f f u s e knapweed a r e  a de-  i n the same manner as s t a l k s of s p o t t e d knapweed.  Watson (1972) found t h a t s p o t t e d knapweed r o s e t t e s c o u l d b o l t house without vernalization.  T h i s study  showed t h a t not  i n the  green-  o n l y s p o t t e d , but  d i f f u s e knapweed, c o u l d perennate without v e r n a l i z a t i o n .  5.Conclusions: 1. D i s t a l heads of d i f f u s e and e a r l i e r and  s p o t t e d knapweed appear f i r s t  f a s t e r than p r o x i m a l  2. Normally o n l y p r o x i m a l 3. Head a b o r t i o n b e g i n s stage.  stage,  and  develop  heads.  heads a b o r t .  approximately  when the f i r s t heads e n t e r the seed  also  19 4. U s u a l l y 75% of a l l heads appear b e f o r e any heads e n t e r the f l o w e r s t a g e . 5. The percentage of heads  i n the f l o w e r stage i s 10% or l e s s f o r d i f f u s e  and s p o t t e d knapweed under greenhouse  conditions.  6. A l t h o u g h s p o t t e d knapweed produces l a r g e r heads than d i f f u s e knapweed, the d u r a t i o n s of the bud s t a g e s are s i m i l a r . 7. Heads coded a c c o r d i n g t o branch p o s i t i o n s can be found a t l a t e r s t a g e s of p l a n t development,  ii.  r e g a r d l e s s of the a d d i t i o n a l number o f heads  Urophora a f f i n i s and U.  a)Emergence  produced.  quadrifasciata:  and l a r v a l w e i g h t s :  1.Introduction: Varley  (1947) found t h a t U. jaceana r e s i s t e d d e s i c c a t i o n when i s o l a t e d  t h e i r g a l l s and completed development stage i n g e l a t i n e c a p s u l e s .  from the t h i r d  weight w i t h emergence time.  i n s t a r t o the a d u l t  P r e l i m i n a r y work showed t h a t U_. a f f i n i s  do the same, and t h i s method of l a r v a l i s o l a t i o n was  from  used to r e l a t e d  T h i s study a l s o compares TJ. a f f i n i s and  could larval U.  q u a d r i f a s c i a t a l a r v a l weights and emergence t i m e s .  2.Method: P r e l i m i n a r y work showed t h a t d i a p a u s i n g U. a f f i n i s l a r v a e would not pupate u n t i l the s p r i n g u n l e s s they were c o l l e c t e d i n the f i e l d To ensure s u f f i c i e n t  a f t e r December 1 s t .  c o l d - s h o c k i n g , s p o t t e d knapweed seed heads  l e a s e s i t e were c o l l e c t e d i n January, 1976.  from the r e -  These seed heads w i l l be  called  s p o t t e d knapweed "1975" seed heads because they were produced d u r i n g the growing season.  1975  The seed heads were s t o r e d i n a r e f r i g e r a t o r a t 5°C.  Batches of heads were removed, opened, and t h i r d - i n s t a r U. a f f i n i s were d i s s e c t e d from t h e i r g a l l s , weighed i n gelatine capsules.  to the n e a r e s t 0.001  mg  The l a r v a e were i n c u b a t e d a t 27°C under a  larvae  and p l a c e d 16-hour  20 p h o t o p e r i o d , and the c a p s u l e s were checked d a i l y f o r emerged a d u l t s . first  l a r v a l b a t c h was  left  The  f o r 50 days, but l a t e r b a t c h e s were l e f t f o r  fewer days, due to a shortage of time. sex, were c o r r e l a t e d w i t h development  The weight o f each l a r v a e , and i t s time to the a d u l t s t a g e .  Seed heads were a r b i t r a r i l y c o l l e c t e d from the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s i n J a n u a r y , 1977. all,  These w i l l be c a l l e d "1976" seed heads.  In  5520 d i f f u s e and 3350 s p o t t e d knapweed seed heads were i n c u b a t e d i n  mesh cages  a t 29'C  under a 16-hour p h o t o p e r i o d .  Seed heads and s i d e s of  cages were m i s t e d d a i l y w i t h water, and a d u l t U_. a f f i n i s and U_. q u a d r i f a s c i a t a were c o l l e c t e d d a i l y from the cages.  Other seed heads,  arbitrarily  c o l l e c t e d from the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s i n O c t o b e r , 1976, were opened,  and U. a f f i n i s and U_. q u a d r i f a s c i a t a l a r v a e were d i s s e c t e d  from t h e i r g a l l s , and weighed  t o the n e a r e s t 0.01 mg.  Because  few U_. q u a d r i -  f a s c i a t a l a r v a e were found, d i f f u s e knapweed seed heads were randomly l e c t e d i n Vernon, where t h i s s p e c i e s had spread t o , i n September, these seed heads 60 U. q u a d r i f a s c i a t a l a r v a e were i s o l a t e d and weighed  t o the n e a r e s t 0.01  col-  1977.  from t h e i r  From  galls,  mg.  3.Results: The death r a t e o f IJ. a f f i n i s i n l a r v a l , p u p a l and a d u l t stages.  i n g e l a t i n e c a p s u l e s was  (before emerging e n t i r e l y  Some emerging a d u l t s had v e s t i g i a l wings.  50%.  The f l i e s  from the p u p a l case) The f o l l o w i n g d a t a was  c a l c u l a t e d u s i n g o n l y l a r v a e which developed i n t o normal a d u l t s . a f f i n i s l a r v a e from s p o t t e d knapweed "1975" seed heads were lighter  + (3.54 - 0.08  significant  mg)  than female l a r v a e  died  + (4.7 - 0.1 mg).  Male U_.  significantly There was  no  c o r r e l a t i o n between male U. a f f i n i s l a r v a l weight and days f o r  emergence ( r = 0.0851), nor between female U. a f f i n i s l a r v a l weight and days  21 f o r emergence ( r = -0.0696).  Males emerged s i g n i f i c a n t l y  earlier  females (34.1 - 0.6 and 36.1 - 0.6 days, r e s p e c t i v e l y ) . sex r a t i o  of normal U. a f f i n i s a d u l t s was 1.07  The male:female  (N = 119).  The average l a r v a l weight of U. a f f i n i s from "1975" s p o t t e d heads was s i g n i f i c a n t l y knapweed r e l e a s e s i t e s  heavier  than U_. af f i n i s  of U. q u a d r i f a s c i a t a from d i f f u s e  and s p o t t e d  less  (1.74 - 0.08 mg)  spotted  i n Vernon, was  than t h a t of U. a f f i n i s from the i n 1976.  sig-  diffuse  There was a t h r e e - to f o u r -  i n l a r v a l weight f o r both g a l l - f l y s p e c i e s .  T a b l e I I . Comparison  gall-fly species  and  The average l a r v a l weight  knapweed, c o l l e c t e d  knapweed r e l e a s e s i t e s  fold variation  from d i f f u s e  knapweed r e l e a s e s i t e i n 1976,  average weight was o n l y 0.8 - 0.3 mg.  nificantly  knapweed seed  i n 1976 (Table I I ) . Only f i v e IJ. q u a d r i f a s c i a t a  l a r v a e were found i n heads from the s p o t t e d and t h e i r  than  of U. a f f i n i s and U. q u a d r i f a s c i a t a l a r v a l weights  h o s t knapweed s p e c i e s and l o c a t i o n  year  mean weight (mg)  U. a f f i n i s  spotted release  knapweed, site  1975  4.15  U. a f f i n i s  spotted release  knapweed, site  1976  2.40  U. a f f i n i s  diffuse release  knapweed, site  1976  3.1  U. q u a d r i fasciata  spotted release  knapweed, site  1976  .8  U. q u a d r i fasciata  diffuse Vernon  knapweed,  1977  1.74  "weights f o l l o w e d  by a d i f f e r e n t  + + + + +  sample size  .09 a  119  0.5 b  472  .2  c  .3  5  .08 d  l e t t e r vary s i g n i f i c a n t l y  67  60  from one another  22 U_. q u a d r i f a s c i a t a s t a r t e d emerging  a f t e r 18 days o f i n c u b a t i o n a t 29°C from  d i f f u s e and s p o t t e d knapweed "1976" seed heads. c u r r e d a f t e r 45 days. d i f f u s e and s p o t t e d  IJ. a f f i n i s  No  f u r t h e r emergence o c -  s t a r t e d emerging  on days 21 and 23  knapweed, r e s p e c t i v e l y , but a few f l i e s were  a p p e a r i n g a f t e r 70 days of i n c u b a t i o n , when the study was  and 1.33,  s p o t t e d knapweed was  1.32  The  diffuse  r e s p e c t i v e l y , and t h a t of U. a f f i n i s  (N = 88, 645 and 3361,  still  terminated.  male: female sex r a t i o s of TJ. q u a d r i f a s c i a t a and U_. a f f i n i s from knapweed were 1.32  from  from  respectively).  4.Discussion: A l t h o u g h few IJ. q u a d r i f a s c i a t a were found i n the l a r v a l s t a g e i n r e l e a s e s i t e seed heads, t h e r e i s a s t r o n g i n d i c a t i o n t h a t U_. q u a d r i f a s c i a t a weighs about one h a l f of IJ. a f f i n i s body weight. The l i g h t weight  o f U. q u a d r i -  f a s c i a t a from Vernon, where no U. a f f i n i s were found, s u p p o r t s t h i s c o n c l u sion.  IJ. q u a d r i f a s c i a t a p r o b a b l y r e q u i r e s l e s s energy  ment than does U. a f f i n i s .  to complete  T h i s i s a l s o i n d i c a t e d by the t h i n n e r n u t r i t i v e  l a y e r i n s i d e U. q u a d r i f a s c i a t a g a l l s , on which the l a r v a e f e e d p e r s . comm.).  develop-  (Shorthouse,  P r o b a b l y each U_. q u a d r i f a s c i a t a g a l l reduces the p o t e n t i a l  seed y i e l d of d i f f u s e and s p o t t e d knapweed by h a l f  the amount of IJ. a f f i n i s .  U_. q u a d r i f a s c i a t a has an e a r l i e r and more c o n c e n t r a t e d p e r i o d o f emergence than IJ. a f f i n i s  i n the l a b o r a t o r y .  In the f i e l d IJ. q u a d r i f a s c i a t a  may  emerge e a r l i e r than U. a f f i n i s to a v o i d i n t e r s p e c i f i c c o m p e t i t i o n because both s p e c i e s a t t a c k knapweed heads i n the bud female emergence was  stage.  E a r l i e r male than  a l s o found by S t o r e y (1976) f o r U. a f f i n i s and  Wadsworth (1914) f o r U. j a c e a n a .  T h i s phenomenon may  ensure t h a t  by  females  are bred b e f o r e they b e g i n to o v i p o s i t when f l y d e n s i t i e s a r e s p a r s e .  23 L i k e U.  j a c e a n a , U_. a f f i n i s can complete development  i n s t a r to the a d u l t stage i n s i d e g e l a t i n e c a p s u l e s .  from the t h i r d  larval  The h i g h death r a t e i n  t h i s study i s a t t r i b u t e d to mechanical i n j u r y , or c o n t a m i n a t i o n by m i c r o organisms  d u r i n g d i s s e c t i o n of the g a l l s , r a t h e r than t o d e s i c c a t i o n .  Pre-  l i m i n a r y work showed t h a t p a r a s i t i z e d seed heads can be s t o r e d a t room tempe r a t u r e from October u n t i l February i n a dry p l a c e , w i t h no l a r v a l Because s m a l l e r l a r v a e were more d i f f i c u l t average l a r v a l weight  to i s o l a t e than l a r g e r  The male:female  sex r a t i o was  p r o b a b l y under-  estimated because males have a s m a l l e r body s i z e than f e m a l e s . study d i d show t h a t JJ. a f f i n i s l a r v a l weight was  affinis  But  this  not r e l a t e d to developmental  Thus s m a l l females p r o b a b l y do not emerge e a r l i e r  l a r g e females i n the f i e l d . (southwood, 1971;  ones,  f o r U_. a f f i n i s from "1975" s p o t t e d knapweed seed heads  i s probably overestimated.  time f o r each sex.  mortality.  than  F e c u n d i t y i n i n s e c t s i s r e l a t e d to female  Krebs, 1972).  size  T h e r e f o r e the p o t e n t i a l f e c u n d i t y of U_.  i s p r o b a b l y c o n s t a n t throughout the emergence phase of the f i r s t  gen-  e r a t i o n , g i v e n an abundance of o v i p o s i t i o n s i t e s and the same weather.  Some reasons f o r h e a v i e r Tj. a f f i n i s l a r v a e from d i f f u s e than from s n o t t e d knapweed i n 1976  are:  the o r i g i n a l s t r a i n s r e l e a s e d were d i f f e r e n t on the  two r e l e a s e s i t e s , the i n d i g e n o u s host p l a n t s were d i f f e r e n t  (Table I ) , o n l y  the s t r o n g e r l a r v a e s u r v i v e i n d i f f u s e knapweed due t o g r e a t e r c o m p e t i t i o n f o r food i n the s m a l l e r heads,  or s m a l l e r l a r v a e i n d i f f u s e knapweed seed  heads are more e a s i l y i n j u r e d because g a l l s tend to f u s e t o g e t h e r a t lower d e n s i t i e s i n d i f f u s e than i n s p o t t e d knapweed.  The male:female  sex r a t i o s i n t h i s study were a l l g r e a t e r than 1.0,  none were as h i g h as 3.15,  found by S t o r e y (1976) f o r U. a f f i n i s  but  i n spotted  24 knapweed.  High male:female  sex r a t i o s may,  a g a i n , ensure mating b e f o r e  oviposition.  5.Conclusions 1. U_.  q u a d r i f a s c i a t a has a p p r o x i m a t e l y h a l f the body weight o f U.  affinis.  2. Male U. a f f i n i s weigh l e s s than females. 3. Male U_. a f f i n i s  emerge e a r l i e r  than females.  4. U. q u a d r i f a s c i a t a emerge e a r l i e r 5. Developmental  than U.  affinis.  time f o r each sex of U. a f f i n i s  i s not c o r r e l a t e d w i t h body  weight. 6. Male:female i n 1976  on  sex r a t i o s of U. a f f i n i s release  and U. q u a d r i f a s c i a t a were about  1.3  sites.  b ) S u p e r p a r a s i t J s m of d i f f u s e knapweed by U.  affinis:  1.Introduction: Varley  (1947) found t h a t as U. j a c e a n a egg d e n s i t i e s i n c r e a s e d i n f i e l d  Centaurea n e m o r a l i s heads,  larval  m o r t a l i t y i n the p r e - g a l l s t a g e i n c r e a s e d .  V a r l e y c o n s i d e r d t h a t t h i s m o r t a l i t y was l a r v a e f o r food and space. woody g a l l s ,  due  to c o m p e t i t i o n among young  Both IJ. j aceana and IJ. a f f i n i s  produce  l a r v a e undergo t h r e e i n s t a r s b e f o r e p u p a t i o n , females  i n knapweed heads which a r e 3 to 4 mm  i n diameter, and females  hard, oviposit  oviposit  l a r g e numbers of eggs i n s i n g l e heads when no o t h e r heads a r e a v a i l a b l e . IJ. a f f i n i s 1970)  can l a y as many as 59 eggs per s p o t t e d knapweed head  and U. j a c e a n a was  found by V a r l e y  per s i n g l e C_. n e m o r a l i s head. average U. a f f i n i s  (ZwBlfer,  (1947) to l a y as many as 277  eggs  Roze and F r a z e r (19 79) p r e d i c t e d t h a t above  g a l l d e n s i t i e s of two and f o u r per d i f f u s e and s p o t t e d  knapweed head, r e s p e c t i v e l y , i n f i e l d p o p u l a t i o n s , some heads would  contain  25 a surplus ment.  of l a r v a e and these heads would a b o r t a t e a r l y  T h i s study determines  s t a g e s of d e v e l o p -  the e f f e c t on d i f f u s e knapweed heads of  exposure  to IJ. a f f i n i s .  2.Method: When t h i s study was begun a l l the d i f f u s e knapweed growing had  started  to f l o w e r .  i n the greenhouse  To o b t a i n p l a n t s i n the bud s t a g e , b o l t e d s t a l k s of  twelve f l o w e r i n g d i f f u s e knapweed p l a n t s were removed a t t h e i r bases, and the p l a n t s were a l l o w e d to perennate.  A l l but two of the s t r o n g e s t p e r e n -  n a t i n g s t a l k s were removed, and these were a l l o w e d t o r e a c h the bud s t a g e . The p l a n t s were a r b i t r a r i l y a s s i g n e d a number, and t h r e e p l a n t s , f o r each of f o u r treatments, were chosen  a t random.  The treatments were low a t t a c k ,  medium a t t a c k , h i g h a t t a c k and c o n t r o l .  Both s t a l k s on the p l a n t s were  t r e a t e d the same, but were c o n s i d e r e d as s e p a r a t e sampling u n i t s . t h e r e were s i x r e p l i c a t e s per treatment  Therefore,  ( t h r e e p l a n t s X two s t a l k s per p l a n t ) .  The p l a n t s were a t t a c k e d by m i t e s , which were c o n t r o l l e d by p e r i o d i c a l l y washing the f o l i a g e w i t h water. primary branches,  o n l y , reached  o v i p o s i t i o n by Tj. a f f i n i s of  As soon as the heads on t h e f i r s t 3 to 4 mm  three  i n l e n g t h , the o p t i m a l s i z e f o r  (ZwHlfer, 1970), they were caged w i t h a s i n g l e  pair  flies.  H* a f f i n i s a d u l t s were o b t a i n e d by c o l l e c t i n g p a r a s i t i z e d  d i f f u s e knapweed  seed heads on the d i f f u s e knapweed r e l e a s e s i t e i n January,  1977.  were i n c u b a t e d a t 29°C under a 16-hour p h o t o p e r i o d , and were m i s t e d w i t h water.  The heads daily  A d u l t s were c o l l e c t e d d a i l y , and s t o r e d f o r t h r e e days b e f o r e  use because o v i p o s i t i o n (ZwBlfer, 1970).  occurs on the t h i r d o r f o u r t h day a f t e r emergence  26 The  t u b u l a r cages, c l o s e d a t one end, were 5 cm l o n g and 3 cm i n diameter,  and were c o n s t r u c t e d of gauze.  A p i e c e of c o t t o n was wrapped around each  stem, one cm below the head, a p a i r of f l i e s open end of the cage was s l i p p e d over cotton with a drawstring.  i n t r o d u c e d i n t o a cage, and the  the head an t i g h t e n e d around the  P r e v i o u s work showed t h a t p l a n t s were not damaged  by c a g i n g , t h r e r e f o r e no heads on c o n t r o l p l a n t s were caged.  The f l i e s were  a b l e to move f r e e l y around the heads, i n s i d e the cages, and mating, as w e l l as head-probing were observed.  P a i r s of f l i e s were l e f t  f o r one, t h r e e and  f i v e days f o r low-, medium-, and h i g h - a t t a c k r a t e s , r e s p e c t i v e l y , on the s i n g l e heads. appeared.  Heads were coded, as p r e v i o u s l y ( s e c t i o n I I A i ) , when they  Caging c o n t i n u e d  grow f o r another found All  f o r t h r e e weeks, when the p l a n t s were l e f t to  t h r e e weeks.  The p l a n t s were h a r v e s t e d ,  from the code, and c l a s s i f i e d  i n t o bud, f l o w e r / s e e d ,  seed heads were opened and searched  and each head was or aborted  stages.  for galls.  3.Results: No g a l l s were found reached  i n heads on c o n t r o l p l a n t s .  Heads on c o n t r o l p l a n t s  o n l y about 3/4 of the s i z e of heads on p l a n t s which b o l t e d f o r  the f i r s t time.  The p e r c e n t a g e of a b o r t e d heads of t h e t o t a l number of  caged heads d i f f e r e d  s i g n i f i c a n t l y w i t h a t t a c k r a t e (Table I I I ) .  a s i g n i f i c a n t d i f f e r e n c e i n the percentage of a b o r t e d plants  (18 - 5%) and h i g h - a t t a c k - r a t e p l a n t s  the f i r s t t h r e e primary  There was  heads between c o n t r o l  (49 - 5 % ) , when a l l heads on  branches (caged + uncaged) a r e c o n s i d e r e d .  Average  g a l l d e n s i t i e s per seed head were low (Table I I I ) , and d i d n o t d i f f e r n i f i c a n t l y between a t t a c k r a t e s . which matured t o the seed  sig-  Only 12%, 5% and 26% of the caged heads,  stage, c o n t a i n e d g a l l s f o r low-, medium-, and h i g h -  attack rates, r e s p e c t i v e l y .  27 Table I I I .  E f f e c t o f caging i n d i v i d u a l d i f f u s e knapweed heads w i t h IJ. a f f i n i s _  . attactc r a t e  „  % aborted heads , . of number caged  x number o f g a l l s , _ .. p e r seed head  .2 - .2  medium  21-6% + 49-10  high  52-3  low  _  _  + .05 - .05 .5 - .3  s i g n i f i c a n t d i f f e r e n c e between a t t a c k r a t e s  No d i s t a l heads on primary of  branches o f c o n t r o l p l a n t s a b o r t e d , b u t 48%  the heads i n d i s t a l p o s i t i o n s on h i g h - a t t a c k - r a t e p l a n t s a b o r t e d .  a t t a c k e d p l a n t s aborted heads were of two t y p e s :  95% resembled h e a l t h y heads  i n t h e bud stage, but they were y e l l o w and d r i e d ; and 5% appeared were dark brown o r grey, and had hard o u t e r s h e l l s . detritus.  The f i r s t  On  swollen,  Some were f i l l e d  with  type o f head was n o t u s u a l l y l o n g e r than 3.5 cm, but  the second type was as l o n g as 5 cm and one was found  6 cm i n l e n g t h .  4.Discussion: Exposure o f d i f f u s e knapweed heads t o IJ. a f f i n i s I t i s probable  that high f l y d e n s i t i e s achieve  heads as prolonged  numerary eggs o r f i r s t - i n s t a r  i n head a b o r t i o n .  the same e f f e c t on knapweed  exposure by one p a i r o f f l i e s .  counted, t h e r e a r e two p o s s i b l e e x p l a n a t i o n s .  can r e s u l t  Because eggs were not  The f i r s t  i s that  l a r v a e caused head a b o r t i o n .  super-  N o r m a l l y , heads  w i t h U_. a f f i n i s a c t l i k e s i n k s , a t t r a c t i n g p l a n t energy which would have been used f o r v e g e t a t i v e growth and s e x u a l r e p r o d u c t i o n , but too many eggs or l a r v a e c o u l d s t i m u l a t e heads t o a degree where they abort p e r s . comm.).  These heads would be " s u p e r p a r a s i t i z e d " .  (Shorthouse,  Superparasitism .  has been d e f i n e d as "The phenomenon i n which more i n d i v i d u a l s o f a g i v e n  28 s p e c i e s o c c u r i n a h o s t i n d i v i d u a l than can develop  to maturity i n that  host...Where t h i s o c c u r s w i t h s o l i t a r y e n d o p a r a s i t e s , i n t e r n e c i n e b a t t l e or p h y s i o l o g i c a l s u p p r e s s i o n o f t h e supernumerary l a r v a e o r eggs r e s u l t s i n the s u r v i v a l o f a dominant i n d i v i d u a l . s e l f succumbs p r e m a t u r e l y and a l l p e r i s h . "  b e f o r e the supernumerary p a r a s i t e s a r e e l i m i n a t e d ,  (van den Bosch and Messenger, 1973)  not i s o l a t e d h o s t s l i k e i n s e c t s a r e . and  I n some c a s e s , however, the host i t -  the p l a n t s u r v i v e s .  JJ. a f f i n i s ,  But knapweed heads a r e  Only the s u p e r p a r a s i t i z e d heads a b o r t , i n contrast, suffers high m o r t a l i t y  i n s u p e r p a r a s i t i z e d heads.  The  second  e x p l a n a t i o n f o r d i s t a l head a b o r t i o n a f t e r exposure t o f l i e s i s  damage by females  testing  the heads f o r s u i t a b i l i t y , ( S h o r t h o u s e , p e r s . comm.).  The heads o f f e r e d  i n t h i s study were s m a l l e r than average,  they were produced  on p e r e n n a t i n g s t a l k s , and c o u l d have been e s p e c i a l l y  s u s c e p t i b l e to i n j u r y .  I t would be t o the advantage o f the p l a n t i f i t  c o u l d d e t e c t p r o b i n g b e f o r e egg d e p o s i t i o n and subsequently head.  I f heads a r e a b o r t e d e a r l y i n the growing season,  not be a f f e c t e d  p r o b a b l y because  a b o r t the probed  seed y i e l d may  ( T a n s k i y , 1969), and knapweed may have a b e t t e r chance a t  p r o d u c i n g seed l a t e r i n t h e growing season a f t e r peak f l y d e n s i t i e s . But Shorthouse  ( p e r s . comm.) found U_. a f f i n i s eggs i n aborted heads, and i t  seems a.jpoor s u r v i v a l t a c t i c by t h i s s p e c i e s t o d e s t r o y f u t u r e o v i p o s i t i o n s i t e s simply by t e s t i n g t h e i r s u i t a b i l i t y - f o r egg d e p o s i t i o n . in field  Therefore  s t u d i e s , any head i n a d i s t a l p o s i t i o n which a b o r t s w i l l be assumed  s u p e r p a r a s i t i z e d , w h i l e heads i n p r o x i m a l p o s i t i o n s which a b o r t w i l l be c l a s s e d as undeveloped.  Some heads can d e f i n i t e l y be i d e n t i f i e d as s u p e r p a r a s i t i z e d on the b a s i s o f  t h e i r s w o l l e n appearance, dark c o l o u r and hard o u t e r s h e l l . i n some of these heads i n d i c a t e s l a r v a l  The  detritus  f e e d i n g and the i n a b i l i t y  of  first-  i n s t a r s t o induce g a l l f o r m a t i o n , p r o b a b l y because of t h e i r s u r p l u s number. I n t r a s p e c i f i c c o m p e t i t i o n i s f u r t h e r shown from p r e l i m i n a r y f i e l d work, where some s u p e r p a r a s i t i z e d heads c o n t a i n e d s i n g l e , w e l l - d e v e l o p e d i n s t a r Uv a f f i n i s l a r v a e , but without  JJ. a f f i n i s p r o b a b l y  third-  their fusiform galls.  can cause head s u p e r p a r a s i t i z a t i o n of s p o t t e d knapweed,  but because s p o t t e d knapweed heads c o n t a i n l a r g e r and more numerous o v a r i o l e s than d i f f u s e knapweed, g r e a t e r .numbers.of  eggs must be l a i d per s p o t t e d  knap-,  weed head to cause head s u p e r p a r a s i t i z a t i o n .  5.Conclusions: • l.U_. a f f i n i s can cause d i f f u s e knapweed heads to a b o r t a t young stages o f development, p r o b a b l y because more l a r v a e h a t c h i n the*heads than i s room and food f o r g a l l  there  development.  2. About 5% of the s u p e r p a r a s i t i z e d heads can be p o s i t i v e l y i d e n t i f i e d the b a s i s of t h e i r s w o l l e n shape, -dark-colour and hard o u t e r 3. Aborted  on  shell.  heads i n d i s t a l p o s i t i o n s w i l l be c l a s s e d as s u p e r p a r s i t i z e d by  IJ. a f f i n i s and aborted heads i n p r o x i m a l p o s i t i o n s  on branches w i l l be  c l a s s e d as undeveloped.  c)Gall-fly  head-size  preferences:  1.Introduction: T h i s study makes two comparisons of head s i z e s s e l e c t e d by g a l l f l i e s f o r oviposition:  IJ. a f f i n i s on d i f f u s e and s p o t t e d knapweed, and U.  and U. q u a d r i f a s c i a t a on d i f f u s e knapweed.  affinis  30 2.Method: Seed heads were c o l l e c t e d a r b i t r a r i l y  from d i f f u s e and s p o t t e d knapweed r e -  l e a s e s i t e s i n January, 1976, and i n c u b a t e d a t 29*C under a 16-hour photop e r i o d , as i n s e c t i o n I I i i a.  D i f f u s e and s p o t t e d knapweed r o s e t t e s were-' -  dug i n October, 1975, from the Kamloops a r e a , and p l a n t e d i n t o pots.^••15.2 cm i n diameter.  The p l a n t s were s t o r e d i n an unheated s h e l t e r i n Vancouver  u n t i l December, when they were t r a n s f e r r e d to a greenhouse, and a l l o w e d to b o l t under a 16-hour p h o t o p e r i o d .  A f t e r emergence, f l i e s were s t o r e d f o r t h r e e days i n s e p a r a t e cages.  Then  the f l i e s were p l a c e d i n communal cages t h a t c o n t a i n e d young f l i e s , as w e l l as those which had been used i n the p r e v i o u s t r i a l s .  U. a f f i n i s ,  emerging  from d i f f u s e knapweed, were kept s e p a r a t e from those t h a t emerged from s p o t t e d knapweed, and U_. q u a d r i f a s c i a t a were s e p a r a t e d from U. a f f i n i s . F l i e s were a r b i t r a r i l y chosen from communal cages f o r each new t r i a l .  All  caged f l i e s were p r o v i d e d w i t h a yeast-honey s o l u t i o n from a c o t t o n p l u g , and the s i d e s of the cages were m i s t e d d a i l y w i t h water.  U. q u a d r i f a s c i a t a emerged o n l y from d i f f u s e knapweed i n s u f f i c i e n t  quantity  for t r i a l s .  trials  So few JJ. q u a d r i f a s c i a t a were o b t a i n e d t h a t o n l y f o u r  on d i f f u s e knapweed were made, compared w i t h seven and t h i r t y - o n e of IJ. a f f i n i s on d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y .  Experimental  u n i t s were d i f f u s e knapweed branches and s p o t t e d knapweed s t a l k s . t h r e e heads i n the o p t i m a l s i z e range, f o r U. a f f i n i s were a v a i l a b l e per t r i a l . d i f f u s e and 2 3 - 3 w i t h TJ. a f f i n i s .  >3 <8 mm  i n length  trials  At l e a s t  ( Z w B l f e r , 1970)  There were averages o f 16 - 1  s p o t t e d knapweed heads i n the o p t i m a l s i z e range per t r i a l The same o p t i m a l s i z e range as f o r U. a f f i n i s was assumed  f o r U. q u a d r i f a s c i a t a , and t h e r e were 5 7 - 5  d i f f u s e knapweed heads i n t h i s  31 range per t r i a l w i t h U_. q uad r i f as c i a t a In some t r i a l s i n other t r i a l s  M a t u r i t y of the p l a n t s v a r i e d .  o n l y p r o x i m a l heads were i n the o p t i m a l s i z e range, whereas d i s t a l heads were a v a i l a b l e .  s i z e range were l e f t  undisturbed  Heads not i n the o p t i m a l  on the s t a l k s .  Lengths and widths of a l l  the heads i n the bud stage were measured w i t h c a l i p e r s to the nearest 0.1  mm  ( e x c l u d i n g b r a c t s and s p i n e s ) , and head p o s i t i o n s were coded as i n s e c t i o n II A i .  Numbers o f f l i e s  per  t r i a l depended somewhat on t h e i r  but on the average t h e r e were 7 - 1  and 8 - 1  availability,  p a i r s of U. a f f i n i s per t r i a l  f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y , and 7 - 1  p a i r s of U. q u a d r i -  f a s c i a t a f o r d i f f u s e knapweed.  Cages were c o n s t r u c t e d of gauze, s t r e t c h e d over c y l i n d r i c a l w i r e 30 cm i n l e n g t h and 15 cm i n diameter. without  frames,  Cages were p o s i t i o n e d on the p l a n t s  damaging branches o r heads, and the f l i e s were caged f o r t h r e e daysy  a f t e r which the f l i e s  and cages were removed.  i n the greenhouse under n a t u r a l l i g h t Then the p l a n t s were h a r v e s t e d developed  The p l a n t s were l e f t  c o n d i t i o n s f o r the month of A p r i l .  and the heads were c l a s s i f i e d  or s u p e r p a r a s i t i z e d stages.  to mature  i n t o seed, un-  Heads were c o n s i d e r e d s u p e r p a r a s i t i z e d  if  they a b o r t e d a f t e r b e i n g exposed to the f l i e s , and were  at  the time of exposure.  >3 mm  i n length  A l l o t h e r heads which aborted were assumed to be  undeveloped.  3.Results: Head s u p e r p a r a s i t i z a t i o n o c c u r r e d o n l y by U. a f f i n i s on s p o t t e d knapweed. The  t e s t s p o t t e d knapweed p l a n t s had, i n some c a s e s , u n u s u a l l y l a r g e heads,.  and  g a l l counts g r e a t e r than 8 per head were not uncommon.  The h i g h e s t  count  was 17 U. a f f i n i s g a l l s per head. I t was assumed t h a t s u p e r p a r a s i t i z e d r.  32 s p o t t e d knapweed heads c o n t a i n e d above?.this-density  9 U. a f f i n i s l a r v a e i n t h i s  study.because  crowding seemed t o decrease g a l l s i z e , and i n c r e a s e t h e  m o r t a l i t y of the f l i e s .  Some s u p e r p a r a s i t i z e d heads were 5 t o 6 mm  a t t h e time o f c a g i n g , but most were 3 to 4 mm  long  long.  D i s t r i b u t i o n s o f t h e percentage a v a i l a b l e heads f o r o v i p o s i t i o n d i f f e r e d s i g n i f i c a n t l y w i t h t h e percentages o f p a r a s i t i z e d heads f o r a l l cases IV) a c c o r d i n g  to X  2  tests.  T a b l e IV. " G a l l - f l y h e a d - s i z e fly  U.  species  knapweed  preferences  l e n g t h / w i d t h head p r e f e r e n c e (mm)  *  degrees o f freedom  diffuse  ^•5 < 6, l e n g t h ^3 < 4, w i d t h  81.16 110.15  4 2  spotted  £ 4 < 5, l e n g t h $3 <4, w i d t h  332.50 290.30  4 4  diffuse  £ 5 < 6, l e n g t h ^3 < 6, w i d t h  47.76 21.13  1 1  affinis  U. q u a d r i f a s c i a t a  (Table  s i g n i f i c a n t d i f f e r e n c e between % a v a i l a b l e and % p a r a s i t i z e d heads f o r a l l cases  A l t h o u g h most o f t h e p a r a s i t i z e d heads were about 5 mm l o n g and 3.5 mm wide, frequency  d i s t r i b u t i o n s o f t h e p e r c e n t a g e o f heads p a r a s i t i z e d v a r i e d .  a f f i n i s p r e f e r r e d wider s p o t t e d than d i f f u s e knapweed heads and U. q u a d r i f a s c i a t a o v i p o s i t e d i n s i g n i f i c a n t l y l o n g e r  U.  2 ( %•201.24), 2  ( iC  30*32) and  2 wider  (^(-JJ  =  13.51) d i f f u s e knapweed heads than d i d U. a f f i n i s .  In t r i a l s  w i t h JJ. q u a d r i f a s c i a t a the p l a n t s had a l r e a d y reached t h e seed s t a g e , and o n l y p r o x i m a l heads were i n t h e bud stage. These heads were s i g n i f i c a n t l y 2 2 shorter ( 32.99) and narrower ( X = 24.85) than t h e d i f f u s e knapweed (.o) (z) heads used i n t r i a l s w i t h U. a f f i n i s . / O N  %5(H 40  30-  20-  10  %30 A  l l l l  1  1  i n ,  20  10  <2  £ 2 . ^ 3 *3<f  HEAD  *1<5  i,  ?s<6  LENGTH  I I  > 6 < 7 > 7 < 8 38<?  CLASS  (MM)  II  >3<10 » | 0  <2  22<3  £3<4  HEAD  ?4<5 ?S<6 >6<7 »7<8  WIDTH  CLASS  sg<9  ^<jo  (MM)  F i g u r e 9. Knapweed head s i z e s a v a i l a b l e and accepted f o r o v i p o s i t i o n by g a l l f l i e s i and i i : U. a f f i n i s on d i f f u s e knapweed; i i i and i v : U. a f f i n i s on s p o t t e d knapweed; v and v i ; U. q u a d r i f a s c i a t a on d i f f u s e knapweed. Heads a v a i l a b l e • • • ; heads accepted CZZ3  u>  34 ( F i g u r e 9 continued)  %50  1  40 H  30 H  20 H  II  10 J  <2.  * 2 0  HEAD  >3«f  »f<5  LENGTH  The range o f h e a d - s i z e s  >S<6  CLASS  and  heads  9 i i ) , arid"in s p o t t e d knapweed <7 mm wide ( F i g . 9 i v ) .  heads which were  i l  Z7<S  <2  »S<9  HEAD  (MM)  iZ<3 WIDTH  >f<5  CLASS  p a r a s i t i z e d by t h e f l i e s v a r i e d greatly:  o v i p o s i t e d i n d i f f u s e knapweed (Fig.  *<4<7  <7 mm l o n g  U. a f f i n i s  ( F i g . 9 i ) and < 5 mm wide  heads which were < 8 mm l o n g  IJ. q u a d r i f a s c i a t a accepted  > 4 <7 mm l o n g  (MM)  (Fig. 9iii)  d i f f u s e knapweed "..  ( F i g . 9v) and >2 <5 mm wide ( F i g . 9 v i ) .  4.Discussion: ZwBlfer  (1970) found t h a t U_. a f f i n i s  knapweed  from s p o t t e d knapweed  heads which were 3 t o 7 mm i n l e n g t h , and S t o r e y  U. a f f i n i s  from s p o t t e d knapweed  i n width.  Most o f the p r e s e n t  lar  r e s u l t s were s i m i l a r .  (1970) r e c o r d e d .  heads 4.1 - .5 mm  However, IJ. a f f i n i s i n -  heads than t h e 2.3 t o 3 mm  The p r e s e n t  t o Berube's (1980), where U. a f f i n i s  preference  (1976) found t h a t  p r e f e r r e d s p o t t e d knapweed  t h i s study p r e f e r r e d l o n g e r d i f f u s e knapweed range t h a t ZwBlfer  p r e f e r r e d spotted  r e s u l t s , however, a r e s i m i ^  on d i f f u s e knapweed  showed a  f o r heads 3.5 to 5.5 mm i n l e n g t h , but c o u l d o v i p o s i t i n heads  35 1.5 t o 9.5 mm l o n g .  Berube (1980) l e f t  the caged f l i e s w i t h  the p l a n t s f o r  one week and measured the heads o n l y a f t e r removing the cages. the heads were measured b e f o r e left  In t h i s  study  the f l i e s were r e l e a s e d , and the f l i e s were  on the p l a n t s f o r t h r e e days.  Knapweed heads i n the bud stage  elongate  an average o f 0.25 mm p e r day ( s e c t i o n I I A i ) , t h e r e f o r e the a c t u a l l e n g t h preference methods.  of TJ. a f f i n i s may be l a r g e r or s m a l l e r than suggested by the above T h i s may e x p l a i n , i n p a r t ,  the wide acceptance ranges o f heads  s u i t a b l e f o r o v i p o s i t i o n by g a l l f l i e s , but even when head e l o n g a t i o n the a t t a c k phase i s i g n o r e d , g a l l f l i e s i n the l a b o r a t o r y . more important  Head m a t u r i t y ,  accept  p o s i t i n g eggs.  a v e r y wide rage o f head s i z e s  r a t h e r than e x t e r n a l s i z e , i s p r o b a b l y  c r i t e r i o n f o r egg d e p o s i t i o n .  served JJ. a f f i n i s p r o b i n g  ZwBlfer  a  (1970) sometimes ob-  s p o t t e d knapweed heads f o r one hour without  JJ. a f f i n i s o v i p o s i t o r s have s m a l l sensory  ovi-  p o r e s , which may  be used t o d e t e c t the s i z e and developmental stage of the o v a r i o l e s 1970).  during  (ZwHlfer,  Knapweed used i n t h i s study had a great v a r i a t i o n i n head s i z e among  p l a n t s , where head s i z e i s a measure o f l e n g t h and w i d t h j u s t b e f o r e opens t o f l o w e r .  t h e head  The d i f f u s e knapweed a v a i l a b l e t o ZwBlfer may have had  s m a l l heads, and t h i s may e x p l a i n why ZwBlfer's  (1970) JJ. a f f i n i s p r e f e r r e d  such v e r y s h o r t d i f f u s e knapweed heads compared w i t h JJ. a f f i n i s i n t h i s study.  S i m i l a r i l y , the heads o f f e r e d i n t h i s study  were s m a l l e r than the ones o f f e r e d t o IJ. a f f i n i s .  to JJ. q u a d r i f a s c i a t a P o s s i b l y proximal  heads  a r e s m a l l e r than d i s t a l heads w i t h i n s i n g l e p l a n t s , and because JJ. q u a d r i f a s c i a t a was exposed o n l y t o p r o x i m a l l a r g e r than i n t h i s study.  heads, a c t u a l head p r e f e r e n c e s  c o u l d be  T h i s may e x p l a i n why Berube (1980) found JJ. qua-"  d r i f a s c i a t a t o p r e f e r such l a r g e d i f f u s e knapweed heads (7.5 t o 9.5 mm  long).  Head l e n g t h i s a b e t t e r measure than head w i d t h f o r e s t i m a t i n g the head s i z e p r e f e r r e d by g a l l f l i e s because JJ. a f f i n i s on d i f f u s e and s p o t t e d  knap-  weed, U_. q u a d r i f a s c i a t a on d i f f u s e knapweed, and U. j aceana on b l a c k  knap-  weed ( S t o r e y , 1976;  wide.  Probably  and V a r l e y , 1947) a l l p r e f e r r e d heads 3 to 4 mm  a b e t t e r method of e s t i m a t i n g head s i z e p r e f e r e n c e s would be to  base head s i z e on the f r a c t i o n which the head has e l o n g a t e d , maximum e l o n g a t i o n o c c u r s j u s t b e f o r e a n t h e s i s . heads 1/3  to 1/2 e l o n g a t e d ,  assuming t h a t  Thus U. a f f i n i s  prefers  and IJ. q u a d r i f a s c i a t a p r e f e r s heads 1/2  to f u l l  elongation.  " . . . s p e c i e s having  i d e n t i c a l e c o l o g i c a l niches  ( i . e . e c o l o g i c a l homologs)  cannot c o e x i s t f o r l o n g i n the same h a b i t a t " (DeBach, 1974).  U.  affinis  and U_. q u a d r i f a s c i a t a a r e not t r u e e c o l o g i c a l homologs because the s p e c i e s p r e f e r s knapweed heads a t more mature stages  latter  of development than  does the former, even though t h e r e i s c o n s i d e r a b l e o v e r l a p i n these p r e f e r ences.  Both s p e c i e s may  c o e x i s t a t low d e n s i t i e s .  can u t i l i z e heads a t younger stages a l l o v i p o s i t i o n s i t e s before quadrif asciata. fly  of development, t h i s s p e c i e s may  saturate-  they have reached the stage p r e f e r r e d by U_.  Thus JJ. a f f i n i s may  densities..  But because U_. a f f i n i s  suppress U_. q u a d r i f a s c i a t a a t h i g h  -  5.Conclusions: 1. U. a f f i n i s u s u a l l y o v i p o s i t s i n s m a l l e r heads than does U. q u a d r i f a s c i a t a , but  there i s considerable overlap  i n head s i z e p r e f e r e n c e s  by the two  species. 2. A b e t t e r measurement f o r g a l l - f l y p r e f e r e n c e o v i p o s i t i o n may a t e d , where f u l l flower.  of knapweed head s i z e s f o r  be the f r a c t i o n which the head i n the bud stage has e l o n g a t i o n i s the p o i n t j u s t b e f o r e  elong-  the head opens to  37 B. FIELD STUDIES 1. Synchrony  of g a l l - f l y a t t a c k w i t h knapweed  phenology:  1.Introduction: For maximum seed d e s t r u c t i o n g a l l - f l y the appearance oviposition.  emergence s h o u l d be s y n c h r o n i z e d w i t h  of knapweed heads a t the r i g h t s t a g e of development f o r There should be enough f l i e s  of the weeds to h e a v i l y a t t a c k a l l heads.  throughout the budding  period  T h i s i s a study of the abundance  of JJ. a f f i n i s and JJ. q u a d r i f a s c i a t a i n r e l a t i o n to the number o f knapweed heads a t the r i g h t release s i t e s .  s t a g e of o v i p o s i t i o n on the d i f f u s e and s p o t t e d knapweed  D i f f u s e knapweed p h e n o l o g i e s i n 1976 and 1977 were compared,  and d i f f u s e and s p o t t e d knapweed p h e n o l o g i e s were compared i n 1976.  2. Method: P r e l i m i n a r y work showed t h a t a d u l t g a l l f l i e s c o u l d be counted, sexed and identified  to s p e c i e s on. knapweed,- where they spend most of t h e i r time.  In  1976, a rope, marked i n meters, was a r b i t r a r i l y s t r e t c h e d a c r o s s the r e l e a s e s i t e on June 4 t h , one week b e f o r e sampling took p l a c e . weed p l a n t s and t h i r t y s p o t t e d knapweed s t a l k s  T h i r t y d i f f u s e knap-  ( i . e . single stalks  p e r e n n i a l p l a n t s ) , c l o s e s t t o each meter mark, were tagged a t t h e i r with blue p l a s t i c ribbons.  from bases  The f o l l o w i n g week, JJ. a f f i n i s and JJ. q u a d r i -  f a s c i a t a were counted and sexed b e f o r e s u n r i s e , when they were e s p e c i a l l y r e l u c t a n t to f l y .  A primary branch from each tagged d i f f u s e knapweed p l a n t  was taken by c h o o s i n g a random number, and removing The e n t i r e spotted' knapweed s t a l k was removed.  the c o r r e s p o n d i n g branch.  The rope was moved to a new  l o c a t i o n , and the p l a n t s tagged f o r the f o l l o w i n g week's sampling.  Weekly  sampling c o n t i n u e d u n t i l no f l i e s were found a t the end of the growing season.  Heads i n the bud stage on the samples were c l a s s i f i e d as young, i f  38 they were  $ 7 mm i n l e n g t h o f o l d i f they were  >7 mm i n l e n g t h .  s i z e appeared u n u s u a l l y l a r g e o r s m a l l , heads were c l a s s i f i e d they were  £ 2 / 3 e l o n g a t e d and o l d i f they were  I f head  as young i f  >2/3 e l o n g a t e d , where f u l l  e l o n g a t i o n was d e f i n e d as head l e n g t h j u s t b e f o r e the head opened t o f l o w e r . I t was assumed t h a t young heads were p r i m a r i l y a v a i l a b l e t o U. a f f i n i s w h i l e old  In  heads were a v a i l a b l e t o U. q u a d r i f a s c i a t a .  1977 o n l y the d i f f u s e knapweed r e l e a s e s i t e was monitored, and sampling  was not begun u n t i l June 27th because 1976 r e s u l t s did  not emerge u n t i l  the m i d d l e o f June.  showed t h a t the f l i e s  S i x 50 X 50 cm square p l o t s were  marked out i n t h e s p r i n g o f 1977 by throwing a square and d e l i n e a t i n g the p l o t w i t h b a l i n g twine where the square l a n d e d .  B e f o r e s u n r i s e , once a week,  a d u l t f l i e s on knapweed and on o t h e r v e g e t a t i o n w i t h i n t h e p l o t s were counted, and i d e n t i f i e d  to s p e c i e s and sexed.  Heads i n t h e bud stage were  classified  as young o r o l d as above.  3.Results: In  1976 peak numbers of d i f f u s e knapweed heads i n the young bud stage ( F i g .  lOi) (Fig.  and f i r s t g e n e r a t i o n s of U. a f f i n i s llii)  ( F i g . H i ) and U. q u a d r i f a s c i a t a  o c c u r r e d i n the m i d d l e o f J u l y .  generations of g a l l f l i e s  I n 1977 h i g h e s t counts o f f i r s t  ( F i g . 12) and d i f f u s e knapweed heads i n the young  bud s t a g e ( F i g . 13) o c c u r r e d on t h e f i r s t sampling date (June 2 7 t h ) .  Thus,  u n f o r t u n a t e l y , the e a r l y p e r i o d o f g a l l - f l y emergence and knapweed head appearance was missed. earlier  In  Male g a l l f l i e s on b o t h r e l e a s e s i t e s  appeared one week  than females i n 1976.  1976, a l t h o u g h peak numbers o f heads i n the young bud s t a g e appeared i n  H-  CW  c  CD  i  o  H  fD  >  1—' fD c fD 1-1 3 pu TOfo cn 09 c r ro fD c Cu cn 3 H- c  CO rtg fD c r rt fu cn fD  i-i ro H- 0) 3  CN  c  I-  1  o  Hi  3-  ON fD  •  fu Cu cn  •  H> 3  c  V •  0  M  Cu Cu  Hc r Hi O Hi c CU d 3-' cn  cn fD  6e  AVERAGE NUMBER OF SPOTTED  AVERAGE NUMBER OF D I F F U S E  KNAPWEED HEADS PER STALK  KNAPWEED HEADS PER BRANCH  F i g u r e 11.  Average number of male and female g a l l f l i e s per branch the d i f f u s e knapweed r e l e a s e s i t e i n 1976 i . U. a f f i n i s ; i i . U. q u a d r i f a s c i a t a . females 0 " • 0; males X X 1  41  o _j  D_ QL LU 0.  15  IS)  LU  10 < O LU 00  e LU  F i g u r e 12.  Average numbers of U. a f f i n i s and U. q u a d r i f a s c i a t a per p l o t on the d i f f u s e knapweed r e l e a s e s i t e i n 1977. U. a f f i n i s O; IJ. q u a d r i f a s c i a t a X — —  150 LU LO =3 LL I— LU O l-H  _ J  Q  0.  Ll_ IY.  O LU D_ QC LU IS) 00 O LU a O LU  100  0  a 0  50 J  LU Q. < 2  '1'  JUNE F i g u r e 13.  JULY  SEPTEMBER  Average numbers of heads i n young and o l d bud stages on the d i f f u s e knapweed r e l e a s e s i t e i n 1977. young bud stage 0 — 0 ; o l d bud stage XX  F i g u r e 14.  Average numbers o f male and female g a l l f l i e s p e r s t a l k on the s p o t t e d knapweed r e l e a s e s i t e i n 1976. P_- a f f i n i s ; i i . JJ. q u a d r i f a s c i a t a females 0 0; males X X  e a r l y J u l y on both d i f f u s e and s p o t t e d  knapweed r e l e a s e s i t e s , heads i n the  young bud stage were a v a i l a b l e f o r a s h o r t e r p e r i o d on :the s p o t t e d ( F i g . l O i i ) than on the d i f f u s e ' ( F i g . i l Q i )  knapweed r e l e a s e s i t e  (  Very few new heads were i n i t i a t e d a f t e r August 1 s t on t h e s p o t t e d r e l e a s e s i t e , but heads were produced  continuously  knapweed u n t i l t h e middle o f September. earlier  on t h e s p o t t e d  7i36.4). knapweed  i n low numbers on d i f f u s e  JJ. a f f i n i s was d e t e c t e d  one week  ( F i g . 1 4 i ) than on the d i f f u s e ( F i g . H i ) knapweed  r e l e a s e s i t e i n 1976.  On both r e l e a s e s i t e s  ( F i g s . 101 and l O i i ) i n 1976 no heads i n the o l d bud  stage were seen u n t i l the m i d d l e o f J u l y , w e l l a f t e r the time when JJ. q u a d r i f a s c i a t a had emerged ( F i g s . l l i i  and 1 4 i i ) , and numbers o f o l d buds were  43  to  Q < LU X  oo  LU  ZD Q <  LL O o  t-  < LU (J < LU > <  Figure  .H  15.  Mean r a t i o s of g a l l f l i e s : h e a d s on the d i f f u s e knapweed r e l e a s e s i t e i n 1977. U_. a f f i n i s : h e a d s i n the young bud stage O •—0 U- q u a d r i f a s c i a t a : h e a d s i n the o l d bud stage X X  44 never as p l e n t i f u l as young ones.  Second g a l l - f l y g e n e r a t i o n s  on the d i f f u s e knapweed r e l e a s e s i t e peaked  3 to 4 weeks l a t e r i n 1976  ( e a r l y September) than i n 1977  an i n t e r v a l s i m i l a r to t h a t between f i r s t g e n e r a t i o n s . were found  In 1976  August), gall  flies  on the d i f f u s e knapweed r e l e a s e s i t e as l a t e as the second week  i n October, but On  (early  i n 1977  no  f l i e s were found  a f t e r the m i d d l e of September.  s p o t t e d knapweed g a l l f l i e s d i d not appear i n samples u n t i l l a t e August  1976,  when v e r y few new  heads were b e i n g  were seen d u r i n g the s e c o n d - g e n e r a t i o n total flies  seen i n 1976  on d i f f u s e and  initiated.  emergence p e r i o d  and  69% and  affinis  (37% and  The  r e v e r s e was  the  58% of the t o t a l f l i e s seen i n 1976  t r u e f o r IJ. on the  s p o t t e d knapweed r e l e a s e s i t e s , r e s p e c t i v e l y , appeared as  ation  8% of  s p o t t e d knapweed r e l e a s e s i t e s , r e s -  p e c t i v e l y ) than d u r i n g the f i r s t g e n e r a t i o n . q u a d r i f as d a t a :  Fewer U.  diffuse  second-gener-  flies.  The r a t i o of g a l l f l i e s to d i f f u s e knapweed heads dropped to low  values.  between f i r s t - and  there  one U. a f f i n i s c i a t a to every  second-generation  to every  peaks.  seven heads i n the young bud  t h i r t y - f i v e heads i n the o l d bud  (JJ. a f f i n i s + JJ. q u a d r i f a s c i a t a ) to every (Fig.  15).  t h e r e was  one U. a f f i n i s  to every  277  heads i n the o l d bud  5.Discussion:  was  s t a g e , one-U. q u a d r i f a s -  s t a g e , and  one  gall f l y  s i x heads i n the young bud  On August 1 s t , between f i r s t and  IJ. q u a d r i f a s c i a t a were found of  On June 27th, 1977,  second g a l l - f l y  618 heads i n the young bud  stage  generations, s t a g e , and. no  i n samples, even though t h e r e were an average stage.  -  45 The mean d a i l y June temperature and t o t a l p r e c i p i t a t i o n i n 1976 was and 33.02 mm,  whereas i n 1977  the temperature i n June was  (19.3°C) and about h a l f as much r a i n f e l l  (16.5 mm;  16.1°C  about 3 C°warmer  Table V).  Because o f  the w e t t e r , c o o l e r s p r i n g of 1976, b o t h knapweed heads and f i r s t - f l y a t i o n s appeared l a t e r i n 1976  than i n 1977.  gener-  The warmer s p r i n g of 1977  t y p i c a l o f the t h i r t y - y e a r average f o r the Kamloops a r e a ,  therefore  early  June i s p r o b a b l y the normal time f o r head and a d u l t *f-ly< appearance. (1976) found t h a t weather  I n B r i t i s h Columbia  t h e r e was  conditions.  about 3 C° c o o l e r  an u n u s u a l amount o f r a i n f a l l  (34.0 mm),  than i n the warmer one of  the t i m i n g and d u r a t i o n of s e c o n d . g a l l - f l y gener-  a t i o n s a r e a l s o a f f e c t e d by weather f o r August, 1976 was  Storey  s i m i l a r i l y i n f l u e n c e d the emergence of U_. a f f i n i s ,  which appeared l a t e r i n the c o o l s p r i n g of 1975 1974.  was  The mean d a i l y  (17.78°C) than i n 1977 (122.17 mm)  temperature  (21.90°C), and  i n 1976 compared to  and compared a l s o the t h i r t y - y e a r average of 26.92 mm  1977  (Annonymous,  1976).  A l t h o u g h the June temperature on the s p o t t e d was  cooler  knapweed r e l e a s e s i t e i n 1976  (13.9°C) than on the d i f f u s e knapweed r e l e a s e s i t e  g a l l f l i e s emerged e a r l i e r on the s p o t t e d lease s i t e .  The s p o t t e d  facing slope.  (16.11°C),  than on the d i f f u s e knapweed r e -  knapweed r e l e a s e s i t e i s l o c a t e d on a s t e e p , s o u t h -  I t t h e r e f o r e r e c e i v e s more i n s o l a t i o n than the f l a t  bank,  which s l o p e s northward i n p l a c e s , on which the d i f f u s e knapweed r e l e a s e i s found. g a l l s was  Varley  site  (1947) found t h a t the average temperature i n s i d e U. j a c e a n a  5 C° warmer than a i r temperature.  Usually  the temperature i n p l a n t  t i s s u e s , such as buds or l e a v e s ,  i s much warmer i n d i r e c t s u n l i g h t than a i r  temperature ( W e l l i n g t o n ,  Gall-fly  1950).  warmer temperatures on the s p o t t e d  larvae probably experience  than on the d i f f u s e knapweed r e l e a s e  due to the t e r r a i n , r e s u l t i n g i n e a r l i e r head and f l y appearance on the  'i.  site  T a b l e V.  Mean d a i l y temperature (°C) and t o t a l p r e c i p i t a t i o n (mm) s p o t t e d knapweed r e l e a s e s i t e s  x d a i l y temp. (°C) on r e l e a s e month -  d i f f u s e knapweed  sites  s p o t t e d knapweed  f o r the d i f f u s e a n d 1  t o t a l precipitat*ion< (mm) on r e l e a s e s i t e d i f f u s e knapweed  1975  1976  1977  1975  1976  1977  1975  " 1976  January  -6.67  -2.78  -.41  -5.00  -2.78  -3.60  52.83  19.56  February  -8.33  .56  2.50  -7.22  1.11  .40  38.86  10.16  March  1.67  2.22  4.70  .56  0.00  2.70  15.24  April  7.78  9.45  10.50  5.56  7.22  8.30  May  13.33  13.89  13.50  11.67  June  16.67  16.11  19.30  July  22.78  19.45  August  18.33  September  1977  spotted  knapweed  1975  1976  1977  20.00 108.20  79.25  33.50  5.40  89.92  41.15  52.10  18.80  11.70  35.56  26.16  20.30  10.41  3.81  14.50  19.05  21.34  11.40  12.78* 11.60  18.80  21.08  22.60  29.72  55.88  44.70  15.00  13.89  16.90  29.21  33.02  16.50  34.80  51.05  37.60  19.90  20.56  17.22  17.70  13.97  32.26  24.60  31.75  32.77  44.20  17.78  21.90  16.11  16.11  20.20  23.88  122.17  34.00  42.16  139.45  23.40  15.56  15.56  13.50  13.89  13.89  12.00  8.13  8.89  26.50  7.62  11.43  46.10  October  7.78  8.33  8.30  7.22  6.67  7.00  9.65  20.07  8.30  61.26  23.88  20.80  November  2.78  2.78  .30  1.67  2.22  0.00  33.53'  14.22  50.10  66.29  14.22  84.50  December  -1.67  0.56  -6.60  2.22  0.00  -5.60  32.77  38.10  63.30  83.82  42.16  79.50  Weather d a t a f o r the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s a r e from Kamloops A i r p o r t and S o r r e n t o E a s t , r e s p e c t i v e l y , found i n C l i m a t e o f B.C., pub. by the B r i t i s h Columbia M i n i s t r y o f A g r i 'culture. . * d a t a from Sicamous  47 s p o t t e d than on t h e d i f f u s e knapweed r e l e a s e s i t e .  -  . E a r l i e r appearance o f  U_. a f f i n i s on s p o t t e d knapweed may by b e n e f i c i a l f o r t h i s f l y . s p e c i e s because s p o t t e d knapweed has a s h o r t , c o n c e n t r a t e d  budding phase on t h i s  site.  On d i f f u s e knapweed U. a f f i n i s does not g a i n much by emerging " e a r l i e r because heads a r e p l e n t i f u l u n t i l August.  Even i n t h e e x c e p t i o n a l l y c o o l , wet August o f 1976, s p o t t e d knapweed  ceased  to i n i t i a t e new neads a f t e r t h e m i d d l e o f August, when energy was d i v e r t e d to t h e development o f r o s e t t e s a t bases o f s t a l k s o f p e r e n n a t i n g most y e a r s few heads i n the bud stage can be found r e l e a s e s i t e a f t e r August 1 s t .  plants.  In  on t h e s p o t t e d knapweed  Thus s e c o n d - f l y g e n e r a t i o n s  here a r e a  waste o f energy on t h e p a r t o f the f l i e s u n l e s s they a r e a b l e t o d i s p e r s e to l o c a t i o n s where s p o t t e d knapweed matures l a t e . f e s t a t i o n s grew nearby, b u t have s i n c e been  P r i o r t o 1977 such i n -  sprayed*  In c o n t r a s t d i f f u s e knapweed does n o t e n t i r e l y cease head p r o d u c t i o n i n August because i t does not u s u a l l y perennate. r e s e r v e s and the weather i s not e x c e e d i n g l y knapweed p l a n t s c o n t i n u e  As l o n g as t h e r e a r e energy  hot and d r y , most d i f f u s e  to i n i t i a t e new heads u n t i l t h e s t a l k s a r e k i l l e d  by c o l d temperatures i n October.  (The r o o t s a r e s t i l l  a r e i n j u r e d t h e p l a n t perennates r e a d i l y . )  a l i v e , and i f they  Second f l y g e n e r a t i o n s  are able  to f i n d l a t e - a p p e a r i n g heads on t h i s s i t e , and i n f a c t , on some p l a n t s , the r a t i o o f f l i e s : h e a d s was l a r g e r than d u r i n g the f i r s t  generation.  Thus the  second g e n e r a t i o n i s e s s e n t i a l f o r seed r e d u c t i o n on d i f f u s e knapweed, but has  little  importance i n terms o f o v e r a l l e f f e c t on s p o t t e d knapweed.  The  l a r g e second g e n e r a t i o n produced by U. q u a d r i f a s c i a t a may be a s u r v i v a l  48 t a c t i c by t h i s s p e c i e s here and i n c o u n t r i e s o f o r i g i n . a f f i n i s a r e fewer f o r the second than f o r the f i r s t  Numbers o f TJ.  g e n e r a t i o n , and t h e r e  a r e as many heads i n o l d as i n young stages o f bud development i n August and  September.  Few heads reached  t h e o l d bud stage d u r i n g the f i r s t f l y  g e n e r a t i o n s because many heads were s u p e r p a r a s i t i z e d by U. a f f i n i s o r r e mained undeveloped.  The  assumption t h a t heads  U. a f f i n i s whereas heads proved  t o be v a l i d .  ^7 mm i n l e n g t h were p r i m a r i l y a v a i l a b l e t o >7 mm i n l e n g t h were l e f t  Berube (1980) found  f o r TJ. q u a d r i f a s c i a t a  that i n the f i e l d  U. a f f i n i s  probed heads 7 mm o r l e s s i n l e n g t h w h i l e i n no i n s t a n c e d i d TJ. q u a d r i \  f a s c i a t a attempt t o probe heads l e s s than 6 mm  long.  On the d i f f u s e knapweed r e l e a s e s i t e the r a t i o o f g a l l f l i e s  t o knapweed  heads i s v e r y low d u r i n g a p e r i o d o f about seven days between f i r s t - and second-fly generations  f o r two r e a s o n s :  generations are non-overlapping,  and JJ. a f f i n i s and U. q u a d r i f a s c i a t a f i r s t - and s e c o n d - g e n e r a t i o n peaks a r e s y n c h r o n i z e d .  emergence  Large numbers o f heads escape a t t a c k between f l y  g e n e r a t i o n s , o r may be a t t a c k e d o n l y v e r y l i g h t l y , thus a l l o w i n g f o r h i g h seed y i e l d by heads appearing d u r i n g t h i s i n t e r v a l .  T h i s i s one o f the major  weaknesses o f the two Urophora s p e c i e s as b i o l o g i c a l c o n t r o l  agents.  49 T h i s study showed t h a t male g a l l f l i e s found  emerge e a r l i e r than females, as  e a r l i e r i n the l a b o r a t o r y ( s e c t i o n I I A i i ) and a l s o by S t o r e y  5. C o n c l u s i o n s :  (1976).  •• •' •» • - •<- -  1. G a l l f l i e s u s u a l l y appear i n e a r l y June i n good synchrony w i t h knapweed head appearance.  Weather c o n d i t i o n s can d e l a y o r hasten  this  event.  2. F i r s t - and s e c o n d - f l y g e n e r a t i o n s do not o v e r l a p , and U. a f f i n i s  appear-  ance i s s y n c h r o n i z e d w i t h t h a t o f U. q u a d r i f a s c i a t a , a l l o w i n g t h e heads t h a t a r e produced between g e n e r a t i o n s , i n e a r l y August, t o escape heavy attack. 3.Second g a l l - f l y g e n e r a t i o n s on the d i f f u s e knapweed r e l e a s e s i t e a r e essential for efficient  seed r e d u c t i o n , but s e c o n d - f l y g e n e r a t i o n s on the  s p o t t e d knapweed r e l e a s e s i t e p r o b a b l y have l i t t l e 4.Spotted  e f f e c t on seed  yield.  knapweed has a s h o r t , c o n c e n t r a t e d p e r i o d o f head p r o d u c t i o n , but  d i f f u s e knapweed i n i t i a t e s new heads u n t i l f r o s t k i l l s  the s t a l k s i n the  fall. 5.Males emerge e a r l i e r than  ii.  females.  G a l l - f l y d e n s i t i e s on r e l e a s e s i t e s :  1.Introduction: Varley  (1947) found  t h a t l a r v a l m o r t a l i t y o f U. j a c e a n a i n C_. n e m o r a l i s  heads was " h i g h e r i n those f l o w e r heads c o n t a i n i n g many l a r v a e than i n those c o n t a i n i n g o n l y one or two. dependent, and overcrowding  Thus e a r l y l a r v a l m o r t a l i t y i s d e n s i t y  a t t h i s stage i s p o t e n t i a l l y a b l e t o l i m i t  the p o p u l a t i o n d e n s i t y . . . C l e a r l y some o t h e r f a c t o r s prevent  the p o p u l a t i o n  d e n s i t y r i s i n g t o such a l e v e l t h a t c o m p e t i t i o n between l a r v a e i s e f f e c t i v e as a c o n t r o l l i n g f a c t o r . "  V a r l e y subsequently  showed t h a t t h e c o n t r o l l i n g  50 f a c t o r was  the  c h a l c i d p a r a s i t e , Eurytoma c u r t a , and  could p o t e n t i a l l y contribute  Enemies i n c o u n t r i e s Eurytoma"tibialis, These p a r a s i t e s  the  a r e of the  the  Habrocytus spp.  chalcid  same genera as found by V a r l e y  of o r i g i n , Torymus spp.  comm.) have a l s o been r e p o r t e d TJ. a f f i n i s and g a l l and  TJ. j aceana may  larval  II A i i b ) .  The  (1947) to  egg  1947).  and  the  This  one  major d i f f e r e n c e  regulate  U.  affinis  f i r s t U.  affinis  and  (section  a f f i n i s instar,;  j a c e a n a i n s t a r develops  inside  (ZwBlfer, 1970;  Varley,  s u r v i v a l i n knapweed heads to  de-  competition  U.  populations.  q u a d r i f a s c i a t a have c o e x i s t e d  spotted  knapweed r e l e a s e  been r e l e a s e d  on s p o t t e d  q u a d r i f a s c i a t a on  of U.  f i r s t U.  the  ..  jaceana.  (1947) p r e d i c t i o n of density-dependent l a r v a l  i n the  sites,  s i n c e 1972  and  1975  on  respectively.  The  two  species  same year on d i f f u s e knapweed, but TJ. a f f i n i s  this site.  Varley  ('1947) and  populations.  of TJ.  Wadsworth (1914) i n d i c a t e d  a f f e c t e d by TJ. q u a d r i f a s c i a t a .  q u a d r i f a s c i a t a were monitored to f i n d  quadrifasciata  the  had  knapweed f o u r -years p r i o r to the d e t e c t i o n  j a c e a n a numbers were not  s i t i e s of U.  U.  quadrifasciata,  second i n s t a r hatches from the egg  were r e l e a s e d  t h a t U.  the  i s that  affinis  space as a p o t e n t i a l c o n t r o l l i n g f a c t o r of TJ. j a c e a n a w i l l  TJ. a f f i n i s and d i f f u s e and  but  study m o n i t o r s U.  food and  (1947) a t t a c k i n g  share heads w i t h U.  be  (ZwBlfer, p e r s .  t  termine i f V a r l e y ' s for  by V a r l e y  M e t z n e r i a spp.  U.  development i s s i m i l a r "as?*d iscussed p r e v i o u s l y  hatches from the egg, the  and  parasites  (ZwAlfer, p e r s . comm.).  c o n t r o l l i n g TJ. j a c e a n a . Furthermore, o t h e r enemies a t t a c k i n g in countries  trypetae  r e g u l a t i o n of TJ. j a c e a n a .  of o r i g i n of U_. a f f i n i s are  E_. r o b u s t a and  t h a t Habrocytus  any  regulating  G a l l denfactors  51 In  t h i s study the term " f i r s t - g e n e r a t i o n progeny" r e f e r s to the t o t a l number  of  first-instar  l a r v a e produced by the f i r s t  adult generation,  and the term -  " s e c o n d - g e n e r a t i o n progeny" r e f e r s t o t h e t o t a l number o f f i r s t - i n s t a r produced by the second a d u l t g e n e r a t i o n . progeny  F i r s t - and s e c o n d - g e n e r a t i o n • •::'  can not be t o l d a p a r t i n knapweed heads a t the end of the growing  season, and t h e i r d e n s i t i e s may for  larvae  d i f f e r greatly.  each f l y developmental stage was  T h e r e f o r e the m o r t a l i t y  found o n l y f o r f i r s t - g e n e r a t i o n  progeny  by c o l l e c t i n g heads between f i r s t - and second- a d u l t - g e n e r a t i o n emergence periods.  2.Method: On d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s U. a f f i n i s emergence i s s y n c h r o n i z e d w i t h t h a t of TJ. q u a d r i f a s c i a t a sample was  (section I I Bi) , therefore only  one  taken between f i r s t - and s e c o n d - g e n e r a t i o n peaks. .The time of t h i s  sample v a r i e d from y e a r to year depending on the date on which the l a s t , f i r s t - g e n e r a t i o n a d u l t s were seen, but most samples were taken i n the second week of August.  T h i s was  one week a f t e r t h e l a s t few f i r s t - g e n e r a t i o n  adults  were seen t o ensure t h a t a l l f i r s t - g e n e r a t i o n progeny developed g a l l s .  The  samples were s t o r e d a t room temperature f o r an a d d i t i o n a l week so a l l l a r v a e , which were d e s t i n e d to pupate, had done so. the  The second sample was  taken a t  end of the growing season when s e c o n d - g e n e r a t i o n a d u l t s had d i e d o f f ,  u s u a l l y by the end of September.  Sampling was  done by v a r i o u s methods.  I n 1975  on the r e l e a s e s i t e s were e s t a b l i s h e d i n May l i n e a t i n g a p l o t where i t landed. h a r v e s t e d f o r the f i r s t  sample,  f o u r 50 X 50 cm square p l o t s  by throwing a square and  de-  H a l f o f the heads were s y s t e m a t i c a l l y  and the remainder comprised the second  52 sample.  I n 1976, 1977 and 1978, samples were e n t i r e primary branches of  d i f f u s e knapweed and e n t i r e s t a l k s of s p o t t e d knapweed because both p r o duce a p p r o x i m a t e l y  s i m i l a r numbers of heads.  In 1976 heads were o b t a i n e d  from samples c o l l e c t e d f o r the p r e v i o u s study on g a l l - f l y knapweed phenology, t h i s study  synchrony  with  but i n 1977 and 1978 s e p a r a t e samples were c o l l e c t e d f o r  (N = 50 t o 60 branches,  and s t a l k s , f o r d i f f u s e and s p o t t e d •  knapweed, r e s p e c t i v e l y ) .  Heads were c l a s s i f i e d  i n bud, seed  s u p e r p a r a s i t i z e d o r undeveloped and g a l l s and seeds counted. quadrifasciata. classes:  ( i n c l u d i n g those heads i n f l o w e r ) ,  stages.  Heads i n the seed stage were opened  G a l l s were i d e n t i f i e d as U_. a f f i n i s or U_.  G a l l c o n t e n t s were c a t a g o r i z e d i n t o one of the f o l l o w i n g  dead f i r s t - i n s t a r l a r v a a f t e r g a l l f o r m a t i o n i f the g a l l was empty  (found f o r TJ. j aceana by V a r l e y , 1947, and assumed*'to occur here f o r U. a f f i n i s ) ;• dead second- o r t h i r d - i n s t a r l a r v a e i f any dead l a r v a l were found  remains  (found a l s o by V a r l e y f o r IJ. j aceana); dead a d u l t i f the a d u l t  had d i e d b e f o r e emergence from the g a l l or from the head; diapause  (third-  i n s t a r l a r v a ) i f the l a r v a had e i t h e r reached the t h i r d - i n s t a r stage o r appeared  h e a l t h y a t a younger stage and would p r o b a b l y r e a c h the t h i r d -  i n s t a r ; pupa i f the l a r v a e had pupated  o r was i n the p r o c e s s of d o i n g so; o r  empty p u p a l case i f a s e c o n d - g e n e r a t i o n a d u l t had a l r e a d y emerged. The sum of pupae + empty p u p a l cases i n the f i r s t  sample gave the number o f f i r s t -  g e n e r a t i o n progeny completing development to the a d u l t stage i n one season. in  S u p e r p a r a s i t i z e d heads were d i s t i n g u i s h e d from undeveloped  s e c t i o n I I A i i b, and i t was assumed t h a t o n l y U_. a f f i n i s caused  superparasitization.  The number of dead U. a f f i n i s  growing heads as head  f i r s t - i n s t a r larvae i n  the p r e - g a l l stage were assumed to be f o u r and e i g h t i n d i f f u s e and s p o t t e d  53 knapweed s u p e r p a r a s i t i z e d heads, r e s p e c t i v e l y .  These e s t i m a t e s a r e based  on g a l l and seed counts a t p o p u l a t i o n peaks when t h e r e were sharp d e c l i n e s i n seed counts per head.  Mean numbers of f i r s t - i n s t a r  l a r v a e per head were found f o r both TJ. a f f i n i s  and TJ. q u a d r i f a s c i a t a on d i f f u s e and s p o t t e d knapweed as the e s t i m a t e of f l y d e n s i t i e s i n heads.  I n c l u d e d i n the term "head" were counts of seed  and s u p e r p a r a s i t i z e d heads.  A v a l u e of n i l was g i v e n f o r JJ. q u a d r i f a s c i a t a  when s u p e r p a r a s i t i z e d heads were encountered.  Angular t r a n s f o r m a t i o n s  were made of the percentages of f l i e s i n each stage b e f o r e a n a l y s i s o f variance.  3.Results: a ) f i r s t - g e n e r a t i o n TJ. a f f i n i s : The mean number of f i r s t - i n s t a r 1975 to 1977 on both d i f f u s e lease s i t e s .  larvae per head-increased s i g n i f i c a n t l y  (Table VI) and s p o t t e d (Table V I I ) knapweed  From 1977 to 1978 t h e r e was a s i g n i f i c a n t  number of f i r s t - i n s t a r t h e r e was no s i g n i f i c a n t knapweed r e l e a s e s i t e .  =  re'—--  d e c r e a s e i n the mean  l a r v a e p e r head on the s p o t t e d knapweed s i t e , but d i f f e r e n c e between 1977 and 1978 on the d i f f u s e On the average, s i g n i f i c a n t l y  i n s t a r l a r v a e were produced p e r head 2 heads ( ^(]_.).  from  fewer numbers of f i r s t -  i n d i f f u s e compared t o s p o t t e d knapweed  4.67).  The percentage of f i r s t - i n s t a r  l a r v a e which d i e d b e f o r e g a l l f o r m a t i o n i n  s u p e r p a r a s i t i z e d heads i n c r e a s e d s i g n i f i c a n t l y d i f f u s e and s p o t t e d knapweed.  Similarily  from 1975 to 1977 on both  to the number of f i r s t - i n s t a r  l a r v a e per head, the percentage of f i r s t - i n s t a r  l a r v a e which d i e d b e f o r e g a l l  54 Table VI.  Average numbers of U. a f f i n i s per head on the d i f f u s e knapweed r e l e a s e s i t e from 1975 to 1978 SIG. a b 1  1975  enerat:  o  of fdLrsthead  x no. of f i r s t - i n s t a r l a r v a e per head  4-1  14-1  m  >  cd  O rH  % in stage instar  0) «_, H  •rl  +  dead f i f s f r r i n s t a r l a r v a e b e f o r e ...... g a l l formation  dead f i r s t - i n s t a r • u larvae after D 0) 3 P- g a l l f o r m a t i o n  60  4—1  .. 6  dead second- and third-instar larvae  2  third-instar larvae  87  pupae + empty p u p a l cases  11  o x no. of f i r s t - i n s t a r l a r v a e p e r head  .73  x no. of t h i r d - i n s t a r l a r v a e per head  .71  second 1 genet  •H •U  1976 .04  2.0  0%  19  0%  10  + + + +  1%  2  2%  49  2%  20  .03  1.77  .03  .82  + +  +  + + +  1977 .1  2.6  3%  22  2%  6  1%  1  3%  47  3%  24  +  .09  2.3  .06  .9  + +  +  + + + +  1978 .2  2.4  4%  31  2%  1.5  1%  1.5  4%  55  3%  11  .1  1.83  .1  .46  + +  +  .1  3%  *  .5%  *  4T  + + +  .5%  3%  *  2%  *  *  .09  *  *  .04  *  *  cd  X  +  +  +  +  s i g n i f i c a n t d i f f e r e n c e among means from 1975 to 1978 (a) and between 1977 and 1978 (b) denoted by *  f o r m a t i o n decreased s i g n i f i c a n t l y d i f f u s e knapweed.  from 1977 t o 1978 on s p o t t e d , but not on  The percentage o f f i r s t - i n s t a r  g a l l f o r m a t i o n on d i f f u s e knapweed d i f f e r e d  l a r v a e which d i e d  significantly  after  w i t h time, w i t h the  h i g h e s t p e r c e n t a g e o c c u r r i n g i n 1976 and a subsequent d e c l i n e . u n t i l - 1978. s p o t t e d knapweed the percentage of f i r s t - i n s t a r f o r m a t i o n was not s i g n i f i c a n t l y nificant  l a r v a e which d i e d a f t e r  d i f f e r e n t between y e a r s .  There was no  d i f f e r e n c e between y e a r s i n the p e r c e n t a g e of second- and  gall sig-  third-  i n s t a r l a r v a e which d i e d , nor i n the p e r c e n t a g e of dead a d u l t s , i n e i t h e r d i f f u s e or s p o t t e d  knapweed.  On  55 T a b l e V I I . Average numbers o f TJ. a f f i n i s p e r head on the s p o t t e d r e l e a s e s i t e from 1975 t o 1978  knapweed  i SIG. 1975 no. o f f i r s t - i n s t a r l a r v a e p e r head  X  i  4-1  c  cn  t-  o  •H  4-1 cfl  u  1•r* 4cd  o  QJ4  rt—<  cu 60  QJ  4-1  M  0)  •C  cu cu ni  4-1  O  iH  CU  M  stag insta  firs  4-> >  c  second  •H  C  O H  4-1 tfl cu  c  QJ 60  .9 ±  .1976 .1  3.8  dead f i r s t - i n s t a r larvae before g a l l formation  2 - 2%  4  dead f i r s t - i n s t a r larvae after g a l l formation  0%  3  dead second- and third-instar larvae  0%  2  dead a d u l t s emergence  0%  before  77  pupae + empty p u p a l cases  21 ± 5%  x no. o f f i r s t - i n s t a r l a r v a e p e r head  ±5%  1.5 ±  +  +  +  .2  6.0  2%  23  1%  2.0  1%  1  76 15  3.9  .1  1.33 ± .09  3.0  + + + +  +  1978 .2  2.8  3%  6  I  ~r  t  -r  .7%  2.9  1%  2.2  i  0%  third-instar larvae  x no. o f f i r s t - i n s t a r l a r v a e p e r head  +  1977  -h  0% 3%  69  2%  5  .2  4.9  .1  2.8  + + + +  .9 3%  74  1%  14  .2  2.6  .2  1.19  + +  +  + + + + + +  a  b  .1  *  *  2%  *  *  2%  *  A  .1  *  *  .08  *  *  .9%  .8%  .9% 2%  """significant d i f f e r e n c e among means from 1975 to 1978 (a) and between 1977 and 1978 (b) denoted by *  The  c o r r e l a t i o n between t h e d e n s i t y o f f i r s t - i n s t a r  l a r v a e p e r head w i t h the  p e r c e n t a g e o f l a r v a e which d i e d .in t h e pre-^gall stage was n o t s i g n i f i c a n t i n : e i t h e r d i f f u s e ,(r = 0.93, 'at 2 D.F.) o r s p o t t e d knapweed -D.F.). .However, on s p o t t e d increased  ( r = 0.97, a t 2  knapweed, as d e n s i t i e s o f f i r s t - i n s t a r  from 1975 to 1977, the percentage o f f i r s t - i n s t a r  l a r v a e which d i e d  before  g a l l formation  larval  d e n s i t y decreased, so d i d the p e r c e n t a g e of l a r v a e which d i e d  g a l l formation  also increased,  larvae  ( F i g . 16ii")'.i  and i n 1978, when t h e f i r s t - i n s t a r  Similarily,  before  as t h e d e n s i t y o f f i r s t - i n s t a r  '•  56 %**0 -i  1978 X  30H  o  1977 X 20  1976 X  H  10 4  LU O  LL. LU 00  LU  r—  -TT^  —l 1.5  l.o  P .5  1  2.0  f 3.0  1  2.5  a: %30 xi.  to  CO  CL  iyz  20H  i—i  u_ O  ft Q icH 1978 X 1975 X 1  2  AVERAGE NUMBER  F i g u r e 16.  1976 X  ~r  3 3  T-  .if  5  OF F I R S T - I N S T A R U. A F F I N I S .LARVAE  -  6  PER HEAD  R e l a t i o n s h i p between t h e p e r c e n t a g e dead f i r s t - i n s t a r l a r v a e which d i e d b e f o r e g a l l f o r m a t i o n and t h e average number o f f i r s t - i n s t a r l a r v a e p e r head f o r f i r s t g e n e r a t i o n s o f U. a f f i n i s on d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s . i.  d i f f u s e knapweed;  i i . spotted  knapweed  57 l a r v a e i n d i f f u s e knapweed heads i n c r e a s e d from 1975 at the f i r s t - i n s t a r  t o 1977,  stage b e f o r e g a l l f o r m a t i o n i n c r e a s e d  d i f f u s e knapweed, between 1977  and 1978,  t h e r e was  the m o r t a l i t y  (Fig. 16i).  no s i g n i f i c a n t  between f i r s t - i n s t a r d e n s i t i e s per head, nor i n the percentage of  On  difference first-  i n s t a r l a r v a e which d i e d b e f o r e g a l l f o r m a t i o n .  The p e r c e n t a g e of t h i r d - i n s t a r l a r v a e , or those l a r v a e which  tered  pause i n mid-summer, decreased s i g n i f i c a n t l y from 87 - 2% i n 1975 3% i n 1976  dia-  to 49 -  on d i f f u s e knapweed, and i n subsequent y e a r s d i d not d i f f e r  n i f i c a n t l y w i t h the percentage i n 1976.  On s p o t t e d knapweed t h e r e was  signo  s i g n i f i c a n t d i f f e r e n c e i n the percentage of t h i r d - i n s t a r l a r v a e produced between y e a r s .  The percentage of pupae p l u s empty p u p a l cases f o l l o w e d o p p o s i t e t r e n d s on d i f f u s e compared to s p o t t e d knapweed.  From 1975  to 1977  i n c r e a s e d s i g n i f i c a n t l y on diffuse knapweed and from 1977 creased s i g n i f i c a n t l y .  from 1977  to 1978  i t de-  On s p o t t e d knapweed the percentage o f pupae p l u s  empty p u p a l cases decreased s i g n i f i c a n t l y significantly  t h i s percentage  to 1978.  progeny c o m p l e t i n g development  from 1975  to 1977,  and  increased  U s u a l l y the percentage o f f i r s t - g e n e r a t i o n  to the a d u l t stage d i d not exceed 20%  on  e i t h e r d i f f u s e or s p o t t e d knapweed.  b ) f i r s t p l u s second U. a f f i n i s g e n e r a t i o n s : The mean number of f i r s t - i n s t a r l a r v a e per head i n c r e a s e d s i g n i f i c a n t l y 1975  to 1977  and decreased s i g n i f i c a n t l y from 1977  and s p o t t e d knapweed r e l e a s e s i t e s . the mean number of f i r s t - i n s t a r s p o t t e d knapweed  2 , ,= 2.14).  There was  t o 1978  from  on both d i f f u s e  no s i g n i f i c a n t d i f f e r e n c e i n  l a r v a e produced per head between d i f f u s e and However, i n most y e a r s t h e r e were about  58 twice as many f i r s t - i n s t a r  larvae per spotted  as p e r d i f f u s e knapweed head.  The mean number of t h i r d - i n s t a r (diapause) l a r v a e p e r head on d i f f u s e knapweed i n c r e a s e d  significantly  from 1977 to 1978.  from 1975 t o 1977 and decreased  No t r e n d on s p o t t e d  significantly  knapweed was observed, but t h e r e was  a s i g n i f i c a n t d i f f e r e n c e i n numbers o f t h i r d - i n s t a r l a r v a e p e r head among y e a r s w i t h the h i g h e s t  density  i n 1977.  c ) f i r s t - g e n e r a t i o n U. q u a d r i f a s c i a t a : The mean number o f f i r s t - i n s t a r 1975 t o 1978 on d i f f u s e knapweed release s i t e increased  l a r v a e p e r head decreased s i g n i f i c a n t l y (Table V I I I ) , but on t h e s p o t t e d  from  knapweed  (Table I X ) , numbers remained low from 1975 t o 1977, and then  suddenly  i n 1978 when U. a f f i n i s d e c l i n e d  ( F i g . 1 7 ) . On t h e  d i f f u s e knapweed r e l e a s e s i t e there was a s i g n i f i c a n t n e g a t i v e  correlation  between numbers o f f i r s t - i n s t a r U_. q u a d r i f a s c i a t a and f i r s t - i n s t a r U. a f f i n i s l a r v a e p e r head f o r f i r s t  generations  ( F i g . 1 8 ) . No empty U_. q u a d r i f a s c i a t a  g a l l s were found in- e i t h e r d i f f u s e o r s p o t t e d  knapweed heads, and dead  t h i r d - i n s t a r l a r v a e and dead a d u l t s were found i n d i f f u s e knapweed o n l y i n 1978 and 1976, r e s p e c t i v e l y . knapweed heads.  Therefore  No dead U. q u a d r i f a s c i a t a were found i n s p o t t e d  on both d i f f u s e and s p o t t e d  tage o f t h i r d - i n s t a r l a r v a e f o l l o w e d empty p u p a l c a s e s .  opposite  trends  knapweed the p e r c e n -  to the percentage o f  On - d i f f u s e knapweed the percentage o f p u p a t i n g f l i e s r e -  mained above 80% from 1975 t o 1977, but f e l l  t o 45% i n 1978.  On  knapweed 92% o f the l a r v a e pupated i n 1978 when U_. q u a d r i f a s c i a t a dense, but i n p r e v i o u s  was most  y e a r s when U. q u a d r i f a s c i a t a was r a r e , the percentage  of pupae v a r i e d from 67% t o 100%. which pupated was g r e a t e r sites.  spotted  On the average the percentage o f l a r v a e  f o r U. q u a d r i f a s c i a t a than f o r TJ_. a f f i n i s on both  59 Table V I I I .  Average numbers o f U. q u a d r i f a s c i a t a p e r head on the d i f f u s e knapweed r e l e a s e s i t e from 1975 to 1978  1975 x no. o f f i r s t - i n s t a r .54 l a r v a e p e r head  teratic  a u a  dead  third-instar  first  cu j-i .c cn larvae 4-1 C TJ •H CO CO 14-1 1 CUdead a d u l t s X 60 O 4J emergence CD QJ U U 60 -H CU  N  c  14-1  bC  .24  12 88  + +  first-instar .29 p e r head  +  third-instar p e r head .10  +  1977  +  .05  .15  0% 4  0%  C H  o x no. o f larvae C 4-1 o cn d x no. o f C O Cc O cn larvae cu  .04  0%  before  third-instar l arvae CO <4-4 0) o aj c > pupae + empty •H • U o cd p u p a l cases nj  4J  +  1976  3%  11  3%  85  .02  .33  .01  .04  + + +  1978  +  .05  0% 2% 19  6%  81  + +  .10  .06  .41  .01  .32  + +  +  9  0%  6%  i SIG. a b  *  A  14%  *  A  14%  A  A  .02  *  A  .01  A  A  .03 1  0% 11%  46  11%  45  .07  .06  .07  .04  + +  + + + +  s i g n i f i c a n t d i f f e r e n c e among means from 1975 t o 1978 (a) and between 1977 and 1978 (b) denoted by *  T a b l e IX.  Average numbers o f U_. q u a d r i f a s c i a t a per head on the s p o t t e d knapweed r e l e a s e s i t e from 1975 t o 1978 I 1975  o  X no. o f f i r s t - i n s t a r  •1-1  4->  % in stage  first genet  l a r v a e p e r head third-instar larvae pupae + empty p u p a l cases  1976  .01 - .01  .15  0%  29  100 - 100%  71  +  a  •u  secc genei  c  o X no. o f f i r s t - i n s t a r 004 - .004 .05 l a r v a e p e r head 4-1  •H  X no. o f t h i r d - i n s t a r  l a r v a e p e r head  0  .01  + + + + +  1977 .06  .02  16%  33  16%  67  .02  .10  .01  .06  + + + + +  SIG. a b  1978 .02  .49  33%  8  33%  92  .05  .62  .04  + + + +  .06  A A  3% 3%  .07  A  0  """significant d i f f e r e n c e among means from 1975 t o 1978 (a) and between 1977 and 1978 (b) denoted by *  60  CL  < h-  • 6"i  00  o  1978 X  CO CL  Q ft X CL LU  CL LU CD  LU CO  0-  LU < CL •— > CL LU  •2H  1  Ol  1^76  1975 X, 1  2  X  3  4  5  6  AVERAGE NUMBER OF U. AFFINIS FIRST-INSTAR LARVAE PER HEAD F i g u r e 17.  R e l a t i o n s h i p between the average number of IJ. q u a d r i f a s c i a t a and U_. a f f i n i s f i r s t - i n s t a r l a r v a e p e r head on s p o t t e d knapweed for f i r s t generations of f l i e s .  CL  .6  co  LL. O  I CO CL CL LU r-1 00 U_  1975 X  Q < LU X  <  LU >-"  1976 X  b LU < CO Q> < UJ U_ CL o  > >-  3  1978 X  < CL  -1—  1977 * x  T  1.0 0.5 1.5 2.0 2.5 3.0 AVERAGE NUMBER OF U. AFFINIS FIRST-INSTAR LARVAE PER HEAD Figure  18.  ' C o r r e l a t i o n between the average number of U. q u a d r i f a s c i a t a and U. a f f i n i s f i r s t - i n s t a r l a r v a e p e r head on d i f f u s e knapweed f o r f i r s t g e n e r a t i o n s of f l i e s , ( r = -.98; s i g n i f i c a n t a t 2 D.F.)  61 d ) f i r s t p l u s second U. There was  quadrifasciata  generations:  a s i g n i f i c a n t d i f f e r e n c e i n the mean number of f i r s t - i n s t a r  which hatched per head by  the end  of the growing season on the d i f f u s e  knapweed r e l e a s e s i t e :  d e n s i t i e s increased  s i g n i f i c a n t l y from 1977  to 1978.  t h e r e was  i n c r e a s e i n the mean number of f i r s t - i n s t a r  a significant  per head from 1975  to 1978.  The  On  from 1975  trend.  On  of t h i r d - i n s t a r l a r v a e per head from 1975  and  - 0.06  but  dropped site larvae  mean number of t h i r d - i n s t a r l a r v a e per head  s p o t t e d knapweed t h e r e was  were an average of 0.49  to 1977,  the s p o t t e d knapweed r e l e a s e  on the d i f f u s e knapweed s i t e v a r i e d s i g n i f i c a n t l y w i t h no  larvae  no  time, but  followed  s i g n i f i c a n t d i f f e r e n c e i n numbers  to 1978.  In 1978,  although  g a l l s per head i n August on s p o t t e d  8% of them were t h i r d - i n s t a r l a r v a e , no  diapausing  there  knapweed,  l a r v a e were found i n  September.  4.Discussion: A l t h o u g h t h e r e i s much c o n t r o v e r s y  about t h e o r i e s of p o p u l a t i o n  most workers i n b i o l o g i c a l c o n t r o l f e e l t h a t p o p u l a t i o n s  regulation,  are r e g u l a t e d  density-dependent a c t i o n which " i n c l u d e s the a c t i o n s of r e p r e s s i v e mental f a c t o r s , c o l l e c t i v e l y or s i n g l y , which so i n t e n s i f y as the i n c r e a s e s beyond a c h a r a c t e r i s t i c h i g h l e v e l and that population crease  population falls  i n c r e a s e beyond c h a r a c t e r i s t i c maxima i s prevented and  between d e n s i t y and  and  environ-  so r e l a x as d e n s i t y  to e x t i n c t i o n i s made l e s s l i k e l y . . . T h u s , a n e g a t i v e  E a r l i e r , Varley  by  r a t e of i n c r e a s e i s i n v o l v e d "  (1947) showed t h a t JJ. j a c e a n a  was  (Huffaker,  feed-back  (1947) paper.  process  et^. a l . , 1971).  r e g u l a t e d by  this  process,  because U_. j aceana i s b i o l o g i c a l l y s i m i l a r to U_. a f f i n i s , much of  d i s c u s s i o n w i l l be based on V a r l e y ' s  de-  this  In t h i s study a more  thorough i n v e s t i g a t i o n of TJ. a f f i n i s and U_. q u a d r i f a s c i a t a m o r t a l i t y at each stage was  not p o s s i b l e due  to l a c k of time.  Thus the f o l l o w i n g i s o n l y  a  62 plausible explanation  o f what f a c t o r s may be r e g u l a t i n g f l y p o p u l a t i o n s ;  f a c t o r s , which may n o t be confirmed f o r s e v e r a l y e a r s u n t i l a " c h a r a c t e r i s t i c abundance", which most p o p u l a t i o n s  reach (Huffaker,  e_t. a l . , 1971) i s  attained.  No s p e c i f i c p r e d a t o r s  o f JJ. a f f i n i s were observed, but numerous s p i d e r webs  w i t h dead f l i e s i n them, were seen, m o s t l y on d i f f u s e knapweed. found t h a t the s p i d e r , D i c t y n a major, but  most s p i d e r s a r e n o n - s p e c i f i c p r e d a t o r s ,  1972)  the s p i d e r s c o u l d  f o r food.  Therefore  (1976)  preyed on U. a f f i n i s a d u l t s i n Montana,  he d i d n o t e s t i m a t e the percentage of a d u l t s caught.  density,  Storey  It i s likely  that  and i f g a l l f l i e s were t o d e c l i n e i n  c a t c h the many other  i n s e c t s on t h e s i t e s  (Watson,  s p i d e r s p r o b a b l y do not c o n t r o l f l y p o p u l a t i o n s .  Varley  found t h a t as many as 90% o f JJ. j aceana g a l l s f e l l  winter,  and t h a t the l a r v a e were p r o b a b l y eaten by mice..  a c t i v i t y on the r e l e a s e s i t e s was common:  out d u r i n g the Evidence o f rodent  some p l a n t s were s t r i p p e d o f t h e i r  seed heads and p i l e s o f c h a f f and h a l f - e a t e n  seed heads were o f t e n  found.  Watson (1972) thought t h a t mice f e d on knapweed seeds, but t h e r o d e n t s p r o b a b l y a t e the l a r v a e as w e l l . spotted  fall  out when seed heads, e s p e c i a l l y  knapweed seed heads which open w i d e l y upon m a t u r i t y ,  JJ. a f f i n i s g a l l s i n s p o t t e d JJ.  G a l l s could  dehisce.  Often  knapweed heads a r e n o t anchored to t h e r e c e p t a c l e .  q u a d r i f a s c i a t a g a l l s i n spotted  knapweed heads a r e u s u a l l y h e l d o n l y by  b r a c t s , and few JJ. q u a d r i f a s c i a t a d i p a u s e l a r v a e were found i n September i n spotted  knapweed p r o b a b l y because they f e l l out.  P r e l i m i n a r y work showed  t h a t many g a l l s can be found i n the s o i l i n the s p r i n g , and t h a t a l l diapause l a r v a e i n these g a l l s d i e b e f o r e of g a l l s which f a l l  pupation.  out and a r e d e s t r o y e d  But p r o b a b l y the percentage . by p r e d a t o r s  i s independent o f  63 first-instar are not  Egg  l a r v a l d e n s i t i e s i n the p r e - g a l l s t a g e , and  regulated  by m o r t a l i t y at the  m o r t a l i t y of U.  Varley  j aceana was  a t t r i b u t e d egg m o r t a l i t y  9%  and  15%  i n 1935  and  1936,  He  of egg  d i d not  find  and  U.  q u a d r i f a s c i a t a was  f l i e s were r e l e a s e d f l i e s have e l a b o r a t e The  The  Varley  d i d not  only  time c r o s s - b r e e d i n g f i e l d was  t o g e t h e r from a cage.  Zwblfer  behavioral  consider  j aceana, TJ. a f f i n i s and  Neither  on d e f e c t i v e y o l k s to be  stage,  contribute  between U_.  to  affinis  when s e v e r a l hundred (1974) found t h a t  mechanisms which prevent c r o s s  defective yolks  the  At h i g h d e n s i t i e s unmated  observed i n the  e f f e c t of a d u l t d e n s i t y  mortality  e s t i m a t e s of the death r a t e at the egg  females would be r a r e , so t h i s f a c t o r p r o b a b l y does not regulation.  t h a t egg  batches per head.  were made f o r TJ. a f f i n i s or U_. q u a d r i f a s c i a t a .  population  respectively.  to d e f e c t i v e y o l k s , unmated females, or  with increasing density  cause of egg m o r t a l i t y , nor  populations  t h i r d - i n s t a r stage.  c r o s s b r e e d i n g w i t h TJ. q u a d r i f a s c i a t a . increased  fly  i s not  known.  gall  breeding. But,  because  a r e g u l a t i n g f a c t o r f o r IJ.  TJ. q u a d r i f a s c i a t a p r o b a b l y are not  regulated  by  this factor.  Only 2%  to 3% of U.  jaceana larvae died a f t e r g a l l formation.  a t t r i b u t e d death to "unknown causes" and f u n g i of the l a r v a e o c c u r r e d  after larval  felt  Varley  t h a t a t t a c k by b a c t e r i a  death.  Similarily,  few TJ. a f f i n i s  l a r v a e d i e d a f t e r g a l l f o r m a t i o n e i t h e r i n the f i r s t - or d u r i n g and  t h i r d - i n s t a r stages.  The  highest  t o t a l number of f i r s t - i n s t a r U. i n d i f f u s e knapweed. unrelated  count was  i n 1976,  Death i n the l a r v a l  the  when 10%  a f f i n i s larvae died a f t e r g a l l  and  of  secondthe  formation  stage a f t e r g a l l f o r m a t i o n  was  to f i r s t - i n s t a r d e n s i t i e s , e i t h e r f o r f i r s t - g e n e r a t i o n progeny,  64 or f o r f l y counts 1978  a t the end of the growing season.  death a t second- and  T h e r e f o r e from 1975  to  t h i r d - i n s t a r stages d i d not r e g u l a t e JJ. a f f i n i s  numbers.  JJ. a f f i n i s p o p u l a t i o n s a r e p r o b a b l y for  food and g a l l s i t e s b e f o r e the f i r s t - i n s t a r  c o r r e l a t i o n s between the percentage ation with f i r s t - i n s t a r at  larval  density  u n t i l 1977.  d e n s i t y on both d i f f u s e and  The  to 1978  Although form-  spotted  both l a r v a l m o r t a l i t y and  on the s p o t t e d knapweed s i t e and  plateaued  reason f o r the p l a t e a u - e f f e c t on  diffuse  be the t r a m p l i n g of the knapweed d u r i n g the w i n t e r , which  so severe t h a t few p l a n t s were l e f t  s t a n d i n g by the s p r i n g of  However, V a r l e y ' s p r e d i c t i o n of density-dependent at  l a r v a e form g a l l s .  of l a r v a e which d i e d b e f o r e g a l l  From 1977  i n heads decreased  on the d i f f u s e knapweed s i t e . knapweed may  competition  d e n s i t i e s i n heads were not s i g n i f i c a n t , m o r t a l i t y  t h i s stage i n c r e a s e d w i t h l a r v a l  knapweed from 1975  was  r e g u l a t e d by density-dependent  1978.  c o m p e t i t i o n between l a r v a e  e a r l y stages of development as a c o n t r o l l i n g f a c t o r of U.j_a£eana pop-  u l a t i o n s , i n the absence of n a t u r a l enemies, appears to be t r u e f o r JJ. a f f i n i s as w e l l .  Probably  i f JJ. a f f i n i s a r e a b l e to i n i t i a t e g a l l - f o r m a t i o n ,  most w i l l s u r v i v e to the t h i r d  The of  instar.  f a c u l t a t i v e second g e n e r a t i o n of JJ. a f f i n i s r e g u l a t i n g f a c t o r s of the p o p u l a t i o n d e n s i t y .  t h a t JJ. j aceana produced two  identification  V a r l e y d i d not r e p o r t  g e n e r a t i o n s , but JJ. a f f i n i s may  g e n e r a t i o n s both i n i t s c o u n t r i e s of o r i g i n Columbia.  confounds the  (ZwBlfer, 1970)  produce and  in  two  British  However, the p r o p o r t i o n of f i r s t - g e n e r a t i o n progeny p u p a t i n g i n  August i s extremely  variable.  I f the d e n s i t y of f i r s t - g e n e r a t i o n JJ. a f f i n i s  a d u l t s i s h i g h enough to s u p e r p a r a s i t i z e most of the heads, few  larvae  65 survive be  to the  small.  the  Thus few  g e n e r a t i o n , and be  the  t h i r d i n s t a r and  the  s i z e of the  second g e n e r a t i o n w i l l  a d d i t i o n a l diapause l a r v a e w i l l be produced by the s i z e of f i r s t  g e n e r a t i o n the  following  second  spring w i l l  also  small.  The  r a t e of head s u p e r p a r a s i t i z a t i o n by  the  f i r s t IJ. a f f i n i s  generation  i s r e l a t e d to the number of heads a v a i l a b l e f o r o v i p o s i t i o n and of food and  space i n these heads.  Average head s i z e may  to y e a r , depending on weather c o n d i t i o n s . the appearance of heads i s a l s o an  the amount  change from year  Synchrony of f l y emergence w i t h  important f a c t o r ;  i f the f l i e s  emerge  s l i g h t l y e a r l i e r than heads appear, l a r v a l crowding due  to h i g h d e n s i t i e s  of f l i e s  the expected  i n r e l a t i o n to o v i p o s i t i o n s i t e s , can  of head s u p e r p a r a s i t i z a t i o n . between s u p e r p a r a s i t i z e d  Densities  and  and  heads and  26.6  seeds per  l a r v a l d e n s i t i e s were not  d i f f u s e and mg  and  spotted  1.778  l a r v a e per  at the  second a d u l t  end  of the  d i f f u s e and  mg,  f i r s t - i n s t a r IJ. a f f i n i s l a r v a .  On  significant.  the average, t h e r e  - 0.1  spotted  are  and  (Watson, 1972). 4.9  - 0.2  Thus t h e r e were 5.97  spotted  In  first-  knapweed head, r e s p e c t i v e l y , mg  and  knapweed, r e s p e c t i v e l y , per  I n r e l a t i o n to a v a i l a b l e f o o d ,  IJ. a f f i n i s was  almost t w i c e as dense on d i f f u s e as on  d i f f e r e n c e may  have a r i s e n because g r e a t e r  a knapweed s p e c i e s ,  correlations  head were about twice  respectively  generation.  t o t a l seed weight f o r d i f f u s e and  rate  knapweed head, r e s p e c t i v e l y ,  at peak l a r v a l d e n s i t i e s , t h e r e were 2.3  i n s t a r TJ. a f f i n i s  mg  e x p l a i n why  as i n d i f f u s e knapweed heads.  each seed weighs 1.099  1977,  These f a c t o r s may  of f i r s t - i n s t a r TJ. a f f i n i s l a r v a e per  those i n s p o t t e d 12.5  increase  spotted  9.65 one  therefore, knapweed.  d e n s i t i e s of f l i e s can  coexist  This on  such as d i f f u s e knapweed, which compartmentalizes seeds  66 i n t o s m a l l e r , more numerous u n i t s ( i . e . heads) than s p e c i e s which package seeds i n t o fewer, l a r g e r u n i t s .  In the l a b o r a t o r y the r a t e of d i f f u s e  s p o t t e d knapweed head m a t u r a t i o n  was  i n the f i e l d ,  the same.  then more eggs should be d e p o s i t e d  knapweed to a c h i e v e  similar  i n s p o t t e d than i n d i f f u s e  the same r e s o u r c e u t i l i z a t i o n .  a t t a i n v e r y h i g h a d u l t d e n s i t i e s i n the f i e l d s i t e s , but  I f the r a t e s a r e  G a l l f l i e s appear to  i n r e l a t i o n to o v i p o s i t i o n  some b e h a v i o r a l mechanism must be l i m i t i n g d e n s i t i e s on  knapweed such t h a t the f l i e s are not as e f f i c i e n t knapweed seed as they are i n r e d u c i n g  and  i n reducing  spotted  spotted  seed on the d i f f u s e knapweed  site.  JJ. q u a d r i f a s c i a t a l a r v a l d e n s i t i e s a l s o appear to depend on many f a c t o r s , so t h a t changes i n t h i s i n s e c t ' s d e n s i t y are not e a s i l y e x p l a i n e d . d e n s i t i e s of more than 0.5  At  f i r s t - i n s t a r JJ. a f f i n i s l a r v a e per head, JJ.  q u a d r i f a s c i a t a appears to be suppressed.  At v e r y h i g h JJ. a f f i n i s d e n s i t i e s  o v i p o s i t i o n s i t e s a r e s a t u r a t e d , or even s u p e r p a r a s i t i z e d , because U. can u t i l i z e knapweed heads at younger stages fasciata.  of development than JJ. q u a d r i -  In t h i s s i t u a t i o n , the s u r v i v a l of JJ. q u a d r i f a s c i a t a depends  h e a v i l y on the success  of the second a d u l t g e n e r a t i o n ;  c o n d i t i o n s i n August may  hot dry weather  reduce the number of heads i n the bud  stage,  thus t h r e a t e n i n g JJ. q u a d r i f a s c i a t a w i t h e x t i n c t i o n i n a p o p u l a t i o n . gall-fly  affinis  s p e c i e s , however, appears to be capable  This  of i n c r e a s i n g much more  r a p i d l y than JJ. a f f i n i s from v e r y low a d u l t d e n s i t i e s .  When c o n d i t i o n s  r i g h t , few JJ. a f f i n i s and p l e n t i f u l o v i p o s i t i o n s i t e s , JJ. q u a d r i f a s c i a t a  are  67 numbers can  explode, o n l y  f a s c i a t a may  to c r a s h when JJ. a f f i n i s c a t c h e s up.  TJ'.. q u a d r i -  have many more s u r v i v a l t a c t i c s , adapted to s u r v i v a l i n  same p o p u l a t i o n  w i t h more c o m p e t i t i v e  species  such as U.  the  a f f i n i s and JJ.  jaceana.  The  f i r s t U.  q u a d r i f a s c i a t a l a r v a l i n s t a r causes o n l y a s l i g h t  the ovary w a l l , and could  crush  swelling  of  i f the l a r v a d i e s , d e v e l o p i n g seeds or TJ. a f f i n i s g a l l s  immature TJ. q u a d r i f a s c i a t a g a l l s .  Some immature TJ.  c i a t a g a l l s c o u l d be mistaken f o r n o n - v i a b l e seeds. t h a t the m o r t a l i t y b e f o r e and found i n t h i s study.  I t may  be,  quadrifashowever,  a f t e r g a l l f o r m a t i o n i s indeed v e r y low,  as  Heads w i t h ' a s many as f i v e JJ. q u a d r i f a s c i a t a g a l l s  even i n d i f f u s e knapweed, u s u a l l y do.jnot ,'appear s w o l l e n ,  and  are produced.  have mechanisms  This  i n d i c a t e s t h a t JJ. q u a d r i f a s c i a t a may  which p r e v e n t i n t r a s p e c i f i c c o m p e t i t i o n .  Preliminary  f a s c i a t a to be much more a c t i v e than TJ. a f f i n i s , and t a n t i n the p o p u l a t i o n  r e g u l a t i o n of t h i s  usually  seeds  work showed JJ. q u a d r i d i s p e r s a l may  be  impor-  species.  5.Conclusions: 1.Density-dependent l a r v a l m o r t a l i t y JJ. a f f i n i s numbers i n B r i t i s h 2.On  i n r e l a t i o n to net  denser i n d i f f u s e than i n s p o t t e d  3.JJ. q u a d r i f a s c i a t a appears to be d e n s i t i e s exceed 0.5  restricts  Columbia.  the average JJ. a f f i n i s d e n s i t i e s were g r e a t e r  knapweed heads, but was  i n the p r e - g a l l stage p r o b a b l y  seed weight per  than i n d i f f u s e  head, JJ. a f f i n i s  knapweed heads.  suppressed by U.  first-instar  i n spotted  a f f i n i s when JJ. a f f i n i s  l a r v a e per head, but  the r e g u l a t i o n  JJ. q u a d r i f a s c i a t a appears to depend on many o t h e r f a c t o r s .  of  68 iii.  The  r o l e of h e t e r o g e n e i t y  i n d i f f u s e knapweed head s i z e on  gall-fly  abundance: H a b i t a t s of n a t u r a l animal p o p u l a t i o n s pect  to microweather, food, s h e l t e r and  B i r c h , 1971;  Pajunen, 1971  and  can be v e r y heterogeneous w i t h n a t u r a l enemies (den Boer,  Dempster, 1971).  l e a v e the heads i n which they have hatched and s u r v i v a l may  1971;  G a l l - f l y l a r v a e cannot the p r o b a b i l i t y of  larval  depend not o n l y on numbers hatched per head but a l s o on  amount of o v a r i o l e t i s s u e per head, and  the s i z e of the o v a r i e s .  knapweed the average number of seeds per seed head i n c r e a s e d (r = .68 a t 53 D.F.)  w i t h head diameter when  the s p o t t e d knapweed r e l e a s e s i t e i n 1975  unattacked  were measured.  On  heads, where head s i z e i s a measure of the head i n the bud head s i z e f o r  spotted  t e r m i n a l heads on the  narrow heads, w h i l e o t h e r p l a n t s are " l a r g e - h e a d e d " , p r o d u c i n g  Probably  On  the  significantly  knapweed r e l e a s e s i t e some p l a n t s a r e "small-headed", producing  the head opens to f l o w e r .  res-  diffuse only  short,  l o n g , wide  stage j u s t  before  d i f f u s e knapweed i s a  good i n d i c a t i o n of net o v a r i o l e weight, and/or numbers of seeds per head as i t i s f o r s p o t t e d knapweed. and  T h i s study assumes t h a t t h e r e i s l e s s  space f o r g a l l f l i e s i n s m a l l - than i n large-headed  food  d i f f u s e knapweed, and  compares g a l l - f l y a t t a c k on the r e l e a s e s i t e s between these  two  plant  types.  2.Method: In J u l y , 1977, were chosen and than 8 mm 12 mm  f i v e s m a l l - and tagged.  f i v e large-headed  Heads on the small-headed p l a n t s reached no more  l o n g and heads on large-headed  at anthesis.  p l a n t s reached an average l e n g t h of  A l l the p l a n t s were of s i m i l a r s i z e and  same numbers of heads, were at s i m i l a r stages white f l o w e r s .  d i f f u s e knapweed p l a n t s  shape, had  of development, and  In September, the p l a n t s were h a r v e s t e d  and  the  a l l had  the heads were  -  ... -  69  s y s t e m a t i c a l l y removed from the branches, and c l a s s i f i e d a c c o r d i n g p o s i t i o n , and stage o f development as p r e v i o u s l y .  Superparasitized  (seed, s u p e r p a r a s i t i z e d  to branch  o r undeveloped)  heads were assumed t o c o n t a i n  f o u r dead  f i r s t - i n s t a r TJ. a f f i n i s l a r v a e i n the p r e - g a l l s t a g e , as i n the p r e v i o u s section. and  Seed heads were opened and U_. a f f i n i s and U. q u a d r i f a s c i a t a  seeds were counted.  galls  G a l l - f l y developmental stages were c l a s s i f i e d as  t h i r d - i n s t a r l a r v a e , emerged second g e n e r a t i o n  a d u l t s , dead  first-instar  l a r v a e a f t e r g a l l f o r m a t i o n , dead second- o r t h i r d - i n s t a r l a r v a e , o r dead adults  i n section II B i i .  I n a n a l y s i s , the average number o f f l i e s p e r  head f o r U_. a f f i n i s and TJ. q u a d r i f a s c i a t a were c a l c u l a t e d f o r each s t a g e , where "head" e q u a l l e d fly  the sum of seed and s u p e r p a r a s i t i z e d  heads f o r both  species.  3.Results: G r e a t e r numbers o f heads were s u p e r p a r a s i t i z e d  on s m a l l - than on l a r g e -  headed p l a n t s , and a l t h o u g h the d i f f e r e n c e was not s i g n i f i c a n t , about twice as many heads were undeveloped on s m a l l headed p l a n t s  (Table X ) . A l t o g e t h e r  (62 - 13) than on l a r g e - (36 - 10)  70% of the t o t a l heads on small-headed  p l a n t s , but o n l y 44% o f the t o t a l heads on large-headed p l a n t s , were e i t h e r superparasitized  or undeveloped.  The appearance o f small-headed p l a n t s was  s t r i k i n g l y a l t e r e d because most o f the heads i n d i s t a l p o s i t i o n s were superp a r a s i t i z e d o r undeveloped, but those i n p r o x i m a l p o s i t i o n s developed t o the seed stage ( F i g . 1 9 ) . Large-headed p l a n t s resembled knapweed growing on r a n g e l a n d where there were no g a l l f l i e s , w i t h d i s t a l heads d e v e l o p i n g t o the  seed s t a g e .  there  These heads, however, were s w o l l e n w i t h many g a l l s , and  appeared t o be an i n c r e a s e  i n the number o f p r o x i m a l heads which r e -  mained undeveloped compared to c o n t r o l r a n g e l a n d knapweed.  70 T a b l e X.  Comparison of average numbers of TJ. a f f i n i s and U. q u a d r i f a s c i a t a per head and average head numbers per s m a l l - and large-headed d i f f u s e knapweed p l a n t s on the r e l e a s e s i t e i n 1977. small-headed  total  heads  141 - 22  seed heads undeveloped  heads  % undeveloped  heads of t o t a l  27.1  heads  7-3  - .7  37-7  4.1  - .6  first-instar  2.9  - .6  larvae  3-1 2.8  -  - .2  third-instar larvae  .34 - .08  1.4  empty p u p a l cases  .02  .50 -  - .01  dead f i r s t - i n s t a r j^. g a l l formation  larvae before  „ , + , Z.4-.6  dead f i r s t - i n s t a r g a l l formation  larvae after  , + _„ .04 - .02  T-,  n  .  R  dead second- and t h i r d - i n s t a r l a r v a e dead a d u l t s first-instar  .04 ^ .002  .02  - .002  .4  + „ .5 - .2 c  , + .06 -  .03  .09 -  .06  n  .3 -  .1  .4 - .1  .21 -  .08  third-instar larvae  .3 - .1  .05 -  .03  - .05  .13 -  .05  .01 - .01  0  dead second- and  .07 third-instar larvae  dead pupae  0  dead a d u l t s """significant  .004  d i f f e r e n c e between s m a l l - and  Most small-headed  p l a n t s produced  new  .004  - .004  *  .08  larvae  empty p u p a l cases  3  7-2  43-4  seeds per seed head  CO  36 - 10  38-6 heads  -  .01 -  .004 .01  large-headed p l a n t s denoted  heads u n t i l  l a t e i n the growing  by *  season,  but l a r g e - h e a d e d p l a n t s u s u a l l y ceased head i n i t i a t i o n by the m i d d l e of August.  A l t h o u g h the d i f f e r e n c e between means was  t h a t small-headed  not s i g n i f i c a n t ,  (95 - 12).  There was  no s i g n i f i c a n t  ."  i t appears  p l a n t s i n i t i a t e g r e a t e r numbers of heads (141 - 22)  large-headed p l a n t s  1  52-6  62 - 13  % s u p e r p a r a s i t i z e d heads of t o t a l  SIG.'  95 - 12  40-6  s u p e r p a r a s i t i z e d heads  u  large-headed  than  d i f f e r e n c e i n the  72 average number of seed heads produced by headed p l a n t s , but r e p l i c a t e s had  no  small-  (40 - 6) and  l a r g e - (52 -  6)  s i g n i f i c a n t l y g r e a t e r numbers of seed heads f o r a l l f i v e g a l l s i n small-headed p l a n t s  (55)  compared w i t h l a r g e -  2 headed p l a n t s  (22; % 1 0 . 1 8 ) .  mean number of seeds per  There was  s i g n i f i c a n t l y between s m a l l - and  a t i o n , and cases and  large-headed p l a n t s .  s i g n i f i c a n t l y more IJ. a f f i n i s  large-headed p l a n t s .  l a r v a e per head d i d not  fewer dead IJ. a f f i n i s f i r s t - i n s t a r  differ  However, t h e r e were  larvae before  g a l l form-. ..•  t h i r d - i n s t a r l a r v a e , empty p u p a l  dead a d u l t s per head i n l a r g e - than i n small-headed p l a n t s .  ference between means, was not 1  the average numbers of U. small-  s i g n i f i c a n t d i f f e r e n c e i n the  seed head between s m a l l - and  The mean number of f i r s t - i n s t a r U_. a f f i n i s  significantly  no  (0.4  - 0.1)  supported by  s i g n i f i c a n t , but  there  i s a strong  i n d i c a t i o n that  q u a d r i f a s c i a t a l a r v a e per head are g r e a t e r  than i n l a r g e - (0.21  - 0.08)  headed p l a n t s .  The-dif-  in  This i s  f i n d i n g s i g n i f i c a n t l y more t h i r d - i n s t a r U_. q u a d r i f a s c i a t a  l a r v a e per head i n s m a l l - than i n large-headed p l a n t s , and d i f f e r e n c e between l a r g e - and quadrifasciata  no  significant  small-headed p l a n t s f o r the remaining U_.  stages.  4.Discussion: From e s t i m a t e s of f i r s t - i n s t a r d e n s i t i e s per head, i t appears t h a t U. o v i p o s i t s s i m i l a r numbers of eggs i n s m a l l - and But,  because t h e r e i s l e s s food and  affinis  large-headed d i f f u s e knapweed.  space i n " s m a l l " heads than i n " l a r g e "  heads', g i v e n both heads are a t the same m a t u r i y , the s m a l l heads are more likely  to be  stage,  p r o d u c i n g not  i s great  s u p e r p a r a s i t i z e d , but o n l y U.  l a r g e heads u s u a l l y develop to the  a f f i n i s g a l l s but  a l s o mature seeds.  seed  There  egg wastage i n small-headed d i f f u s e knapweed p l a n t s a t h i g h  popu-  73 l a t i o n d e n s i t i e s , such as i n 1977, when 83% of U. a f f i n i s were e s t i m a t e d t o die  b e f o r e g a l l f o r m a t i o n , compared t o o n l y 23% i n large-headed  plants.  On  the s p o t t e d knapweed r e l e a s e site,' i n 1977, when U_. a f f i n i s was a t peak numbers, 15% o f TJ. a f f i n i s l a r v a e were e s t i m a t e d t o d i e i n the p r e - g a l l stage  (section I I B i i ) .  Spotted knapweed p l a n t s which produced  small  heads were a l s o more s u s c e p t i b l e t o s u p e r p a r a s i t i z a t i o n by U_. a f f i n i s (Fig.  20) than pOsants p r o d u c i n g l a r g e r heads.  Heterogeneity  i n d i f f u s e knapweed head s i z e i s b e n e f i c i a l t o both the g a l l  f l i e s and t h e knapweed.  Some U. a f f i n i s w i l l always s u r v i v e i n large-headed  p l a n t s even when average m o r t a l i t y i n the p r e - g a l l stage i s h i g h . p r e v e n t s & sudden e x t i n c t i o n of the p o p u l a t i o n .  Heterogeneity  This  i n head  size  may a l s o enable U_. q u a d r i f a s c i a t a t o p e r s i s t w i t h TJ. a f f i n i s because h i g h d e n s i t i e s o f TJ. q u a d r i f a s c i a t a were found the progeny o f the second  generation.  i n small-headed  p l a n t s , probably  T h i s aspect i s f u r t h e r discussed i n  the f o l l o w i n g s e c t i o n .  Knapweed b e n e f i t s from h e t e r o g e n e i t y i n head s i z e because some seeds a r e produced  by large-headed  growing season.  p l a n t s even a t h i g h f l y d e n s i t i e s e a r l y i n the  L a t e i n t h e growing season small-headed  p l a n t s compensate  f o r head s u p e r p a r a s i t i z a t i o n d u r i n g the f i r s t g e n e r a t i o n by p r o d u c i n g  similar  numbers o f seeds p e r p l a n t (40 seed heads p e r p l a n t X 4.1 seeds p e r head = 164  seeds p e r p l a n t ) t o large-headed  p l a n t s (52 seed heads p e r p l a n t X 3  seeds p e r head = 156 seeds p e r p l a n t ) .  Thus h e t e r o g e n e i t y i n d i f f u s e knap-  weed head s i z e may be a mechanism f o r s u r v i v a l o f t h i s weed i n c o u n t r i e s o f o r i g i n , where i t i s a t t a c k e d by many head-feeding  insects.  Because h e t e r o -  g e n e i t y i n head s i z e o c c u r s i n knapweed n o t a t t a c k e d by f l i e s ,  and among  74 p l a n t s grown i n the greenhouse from f i e l d - c o l l e c t e d r o s e t t e s , the b a s i s f o r t h i s v a r i a t i o n i s probably genetic. average head s i z e i n f i e l d  Dry weather c o n d i t i o n s may decrease the  populations,  but h e t e r o g e n e i t y  i n head s i z e would  probably s t i l l e x i s t .  5.Conclusions: 1. JJ. a f f i n i s does not appear to show an o v i p o s i t i o n a l p r e f e r e n c e  f o r small-  or large-headed d i f f u s e knapweed. 2. JJ. q u a d r i f a s c i a t a i s more s u c c e s s f u l i n s m a l l - than i n large-headed d i f f u s e knapweed. 3.Similar  numbers of seeds p e r p l a n t were produced by s m a l l - and l a r g e -  headed p l a n t s , even though h i g h percentages of heads on small-headed  plants  were s u p e r p a r a s i t i z e d or undeveloped. 4.Small-headed d i f f u s e knapweed i s more s u s c e p t i b l e to  superparasitism  than i s large-headed d i f f u s e knapweed.  i v . P a r a s i t i s m of d i f f u s e knapweed by f i r s t and second g e n e r a t i o n s flies  of g a l l  i n 1977:  1.Introduction: Earlier  ( s e c t i o n I I B i ) i t was shown t h a t on the d i f f u s e knapweed  s i t e i n 1977, when g a l l f l i e s were a t peak d e n s i t i e s , the r a t i o flies  to heads a c c e p t a b l e  second-generation f l i e s . during  release  of a d u l t  f o r o v i p o s i t i o n was s i m i l a r f o r both f i r s t - and T h i s study determines i f a t t a c k r a t e s a r e s i m i l a r  f i r s t and second g e n e r a t i o n s .  In the p r e v i o u s  s e c t i o n , i t appeared  t h a t g r e a t numbers of heads on small-headed d i f f u s e knapweed p l a n t s were s u p e r p a r a s i t i z e d by f i r s t - g e n e r a t i o n JJ. a f f i n i s , but t h a t  large-headed  75 p l a n t s may  produce seed d u r i n g  compares s m a l l - and  the f i r s t  generation.  T h i s study f u r t h e r  large-headed d i f f u s e knapweed r e a c t i o n to g a l l - f l y  a t t a c k on the r e l e a s e s i t e i n  1977.  2.Method: The  s i x 50 X 50 cm  square p l o t s on the d i f f u s e knapweed r e l e a s e s i t e , which  had  been used to monitor a d u l t f l y d e n s i t i e s ( s e c t i o n I I B i i ) were used  for  t h i s study.  On August 1 s t , 1977,  between f i r s t  and  second a d u l t gen-  e r a t i o n s , the number of heads per p l a n t were counted, and seed, s u p e r p a r a s i t i z e d , undeveloped, and All  the heads i n the bud  the second g e n e r a t i o n , have been a t t a c k e d harvested ding loped  bud  classified  as  stages as i n s e c t i o n I I B i i .  stage were assumed to be a v a i l a b l e f o r a t t a c k  by  but heads i n the remaining stages were assumed to  o n l y by  the f i r s t  i n September, and  each head was  to i t s p o s i t i o n on branches, and or s u p e r p a r a s i t i z e d  generation  stages.  of a d u l t s .  The  p l a n t s were  coded as i n s e c t i o n I I A i , a c c o r -  classified  as being  i n seed, undeve-  Heads i n the seed stage were opened,  and  numbers of seeds and JJ. a f f i n i s and JJ. q u a d r i f a s c i a t a g a l l s were counted. G a l l c o n t e n t s were c l a s s i f i e d  as i n s e c t i o n I I B i i .  i n s e c t i o n I I B i i t h a t o n l y U. t h a t superparasitizediVheads p r e - g a l l formation  I t was  a f f i n i s caused head s u p e r p a r a s i t i z a t i o n , and  contained  f o u r dead f i r s t - i n s t a r  sketched, and  the heads were i n d i c a t e d on  branches by u s i n g d i f f e r e n t symbols f o r each head stage. of heads i n each stage on August 1 s t , and  ches, i t was  l a r v a e i n the  stage.  Each p l a n t s k e l e t o n was  peared d u r i n g  assumed, as  the f i r s t  adult generaiton  p o s s i b l e to i d e n t i f y  a t i o n on the sketches.  the  Knowing the number  assuming t h a t heads, which occupied  d i s t a l p o s i t i o n s on  "heads which developed d u r i n g  Then the average number of seeds and  apbran-  each gener-  flies  i n heads  76 a t t a c k e d by f i r s t second a d u l t  a d u l t g e n e r a t i o n s were compared t o heads a t t a c k e d by  generations.  S i z e s o f the f i r s t  U. a f f i n i s and U.  q u a d r i f a s c i a t a adult generations per  p l o t were found from d a t a c o l l e c t e d f o r e a r l i e r s e c t i o n s  ( T a b l e s VI and V I I I ) .  Average numbers o f t h i r d - i n s t a r l a r v a e p e r seed head were m u l t i p l i e d by the average number o f seed heads p e r p l o t on the s i t e i n the f a l l o f 1976 t o give absolute f i r s t - g e n e r a t i o n population estimates.  The s i z e s o f the s e -  cond g e n e r a t i o n s were e s t i m a t e d from t h e average numbers o f empty p u p a l cases per p l o t , produced by t h e f i r s t  adult generation.  Sex r a t i o s f o r each  g e n e r a t i o n were found from counts o f males and females i n s e c t i o n I I B i i . An e s t i m a t e o f f e c u n d i t y was o b t a i n e d by d i v i d i n g the average number o f f i r s t - i n s t a r l a r v a e per p l o t by the average number o f females per p l o t f o r each g e n e r a t i o n .  T h i s assumes no death o r movement o f a d u l t s .  Six small-  and s i x large-headed p l a n t s from the p l o t s were a r b i t r a r i l y chosen f o r head and g a l l comparisons between f i r s t  and second g e n e r a t i o n s .  3.Results: There was no s i g n i f i c a n t d i f f e r e n c e i n the average number o f t o t a l heads per p l o t between f i r s t  and second g e n e r a t i o n s (Table X I ) .  But, s i g n i f i c a n t l y  more seed heads were produced d u r i n g t h e second than t h e f i r s t  generation,  w i t h fewer s u p e r p a r a s i t i z e d and undeveloped heads b e i n g produced i n the second than i n the f i r s t  generation.  There was no s i g n i f i c a n t  difference  between g e n e r a t i o n s i n the average number o f seeds per seed head, but because more seed heads were b e i n g produced d u r i n g the second g e n e r a t i o n , i t appears first  t h a t more seeds p e r p l o t were produced d u r i n g the second than t h e  g e n e r a t i o n , even though t h i s d i f f e r e n c e was not s i g n i f i c a n t .  First-  77 T a b l e XI.  Comparison of average head and g a l l p r o d u c t i o n d u r i n g f i r s t second f l y g e n e r a t i o n s on the d i f f u s e knapweed r e l e a s e s i t e first generation  t o t a l heads per p l o t  322  % seed heads  t ±5  heads  53  ±3  seeds per seed head  3  heads  seeds per p l o t  232  total first-instar first-instar CO  fin m  l a r v a e per p l o t  % third-instar  % empty p u p a l cases % dead p r e - g a l l ,  first-instar  Pi  % dead f i r s t - i n s t a r formation  larvae  larvae after  % dead second- and t h i r d - i n s t a r  iata  % dead a d u l t s b e f o r e  uad rif,  CO CCl  cr  ol  total first-instar first-instar  60  gall larvae  emergence  l a r v a e per p l o t  larvae  % empty p u p a l cases % dead t h i r d - i n s t a r % dead  2.0  3 + 1 +  - 78  +  620 - 279  136 .  .9 78  adults  s i g n i f i c a n t d i f f e r e n c e between  first  + .2 +  A A  2%  + 2% + 2% 5  .8%  7  + .3% 1.3 + .4% +  *  52  6  + 9% +  +  135  3  8  + +  1% A  1%  + .4%  1.0  +  93  41  .15 + .04 47 + 13%  + .1 .4 + 1% 97  + 14% .5 + .5% + 3% 5.5  + 1% + .4% .4 +  47  larvae  2.  +  -27 - 3  .7  24  l a r v a e per head  % third-instar  4  2.6  larvae  A  69-3  + .4 + 5% 24 12 + 4%  l a r v a e per head  cd  o  422  SIG.  215 - 61  28 - 5 19  •H  66  +  % superparasitized % undeveloped  second generation  and i n 1977  A  2  .6  and second g e n e r a t i o n s  .6%  denoted by *  i n s t a r TJ.' a f f i n i s ; d e n s i t i e s per p l o t and per head were s i g n i f i c a n t l y greater during  the f i r s t  than the second generation1  head s u p e r p a r a s i t i z a t i o n was h i g h d u r i n g TJ. a f f i n i s  first-instar  the f i r s t  larvae died before  Because "the r a t e of  generation,  g a l l formation'.  60 - 9% of  Therefore  sig-  n i f i c a n t l y more t h i r d - i n s t a r U_. a f f i n i s l a r v a e were found i n heads produced during  the second g e n e r a t i o n ,  when the o v e r a l l death r a t e was  empty p u p a l cases were found i n heads d e s i g n a t e d  low.  Some  as having been produced  78 d u r i n g the second g e n e r a t i o n  (6 - 2%), i n d i c a t i n g t h a t t h e r e was  some e r r o r  by t h i s method i n e s t i m a t i n g f i r s t - v a h d r s e c o n d - g e n e r a t i o n f l y and densities.  U.  head  a f f i n i s l a r v a l death a f t e r g a l l f o r m a t i o n appeared to  h i g h e r d u r i n g the second than the f i r s t s i g n i f i c a n t o n l y f o r second- and g a l l s were found  f o r both  g e n e r a t i o n , but  third-instar larvae.  be  the d i f f e r e n c e was A few  dead a d u l t s i n  generations.  Because U. q u a d r i f a s c i a t a d e n s i t i e s per head were low d u r i n g the f i r s t eration  (.15  - .04 per head), comparisons between f i r s t and  a t i o n s are d i f f i c u l t  to make.  There was  no  gen-  second gener-  s i g n i f i c a n t d i f f e r e n c e between  the average number of U. q u a d r i f a s c i a t a f i r s t - i n s t a r l a r v a e p e r p l o t , and -  per head, but  t h i s s p e c i e s appeared to be more common i n heads produced  d u r i n g the second than the f i r s t l a r v a e pupated d u r i n g the f i r s t stages were low.  During  (2 - 1%)  About 50% U. q u a d r i f a s c i a t a  g e n e r a t i o n , and  death r a t e s i n the  remaining  the second g e n e r a t i o n death r a t e s were a l s o low,  most U. q u a d r i f a s c i a t a (97 - 1%) p u p a l cases  genration.  were found  reached  the t h i r d - i n s t a r s t a g e .  i n heads d e s i g n a t e d  A few  as b e i n g produced  and  empty  during  the second g e n e r a t i o n , i n d i c a t i n g , a g a i n , some e r r o r by  this-method.  Average numbers of empty pupal cases per p l o t were found  f o r both f l y s p e c i e s  by the a d d i t i o n of seed heads c o n t a i n i n g empty punal cases second g e n e r a t i o n s .  These e s t i m a t e s  gave the average number of f l i e s  emerging per p l o t d u r i n g the second g e n e r a t i o n sex r a t i o s were 1.0,  (Table X I I ) .  or g r e a t e r , f o r both g e n e r a t i o n s .  here as the number of f i r s t - i n s t a r s i g n i f i c a n t l y between f i r s t  f o r both f i r s t  second  .  r  Male:female  Fecundity,  defined  l a r v a e produced per female, d i d not  (9.63) and  and  (7.96) U. a f f i n i s  differ  generations  79 Table XII.  E s t i m a t e of f i r s t - and s e c o n d - g e n e r a t i o n g a l l - f l y on d i f f u s e knapweed i n 1977  G  sex  no. o f f e m a l e s emerged p e r  ratio  plot  114 ± 38 39-7  1.6 1.3  43.84 16.96  6 ± 3  1.0 2.0  3 4  second g e n e r a t i o n  (2)  x no. of a d u l t s emerged p e r  A  plot  1 2  affinis  U. quadri- 1 2 fasciata A  first  AA  12-4  generation  F = fecundity  (1) and  (number of f i r s t - i n s t a r  """from counts of d i a p a u s e l a r v a e t  f r o m counts of a d u l t from t a b l e XI  2 TC^J^-  0.16,  1  flies  i n the  s i g n i f i c a n t l y greater 2 generation (23.25) than the f i r s t (8.0;  t h i r d - i n s t a r and  But,  older  fasciata, respectively) the  first  generation  stages  J  8.0 23.25  female)  1976  during  the  second U.  quadrifasciata  7.44).  larvae  (157  and  a r e d i v i d e d by  (24  23.9  TJ. q u a d r i f a s c i a t a ,  a f f i n i s and  to  U.  the number of females per  3 f o r U_. a f f i n i s and  respectively).  the  quadriplot  i n the  (3 ;59  during  the  res-  average  and.7.i96 f o r  Again, during  136)  first-  TJ. q u a d r i f a s c i a t a ,  2 ( X?1.65)  f i r s t - g e n e r a t i o n adults  + -  (422  - 8) were produced by  f o r U.  significant difference  number of progeny produced by a f f i n i s and  AA  9.63 7.96  24 8 93 - 41  i f the number of progeny which s u r v i v e d  (43.84 and  p e c t i v e l y ) , t h e r e i s no  F  136 52  355.17) f i r s t - i n s t a r U_. a f f i n i s l a r v a e  than f i r s t - i n s t a r TJ. q u a d r i f a s c i a t a generation adults.  422 ^ 135.-  k  i n section II B i i  but was  2 S i g n i f i c a n t l y more ( X^y=  x no. o f f i r s t instar larvae per p l o t  l a r v a e produced per f a l l of  fecundities  second  U. gen-  2 e r a t i o n , s i g n i f i c a n t l y more ( X^^  =  quadrifasciata  (93)  7.74)  first-instar  U.  affinis  (135)  l a r v a e were produced.  of s e c o n d - g e n e r a t i o n progeny which s u r v i v e d  to or p a s t the  number of s e c o n d - g e n e r a t i o n females which emerged per  than IJ. But,  the r a t i o  third instar:  the  p l o t was s i g n i f i c a n t l y  80 greater  2 ( ^ ^ ) ~ ^«'98) f o r IJ. q u a d r i f a s c i a t a  (23.16) than f o r U.  affinis  (6.77).  Small-headed  p l a n t s produced  almost e q u a l numbers o f heads d u r i n g both gen-  e r a t i o n s , but large-headed p l a n t s produced the  first  generation (Table X I I I ) .  seed stage d u r i n g the f i r s t  75 - 12% of t h e i r heads d u r i n g  Only 4 - 2% of the heads reached  the  g e n e r a t i o n f o r small-headed p l a n t s , whereas  about h a l f of the heads reached the seed stage f o r large-headed p l a n t s . D u r i n g the second g e n e r a t i o n most o f the heads reached the seed s t a g e on small-headed p l a n t s , and about  61 - 10% d i d so f o r large-headed p l a n t s .  As  a r e s u l t g r e a t e r numbers of seeds per p l a n t , and per seed head, were p r o duced d u r i n g the second than d u r i n g the f i r s t  g e n e r a t i o n by  small-headed  p l a n t s , but more seeds per large-headed p l a n t s were produced d u r i n g the f i r s t generation.  Average numbers of seeds per seed head, and U. a f f i n i s and U.  quadrifasciata  per head were s i m i l a r f o r the two g e n e r a t i o n s f o r large-headed p l a n t s . 2% of the t o t a l number of U_. a f f i n i s f i r s t - i n s t a r  l a r v a e i n small-headed  p l a n t s d i e d i n s u p e r p a r a s i t i z e d heads d u r i n g the f i r s t to o n l y 31 - 6% i n large-headed p l a n t s . i n s t a r i l a r v a e were produced  95 -  As a r e s u l t  g e n e r a t i o n compared few U. a f f i n i s  i n small-headed p l a n t s d u r i n g the f i r s t  thirdgener-  a t i o n , but 79 - 4% were produced d u r i n g the second generation. Large-headed p l a n t s produced 7%)  and second  s i m i l a r numbers o f t h i r d - i n s t a r l a r v a e d u r i n g the f i r s t (64 - 15%)  second g e n e r a t i o n :  generations.  Large-headed  (43 -  p l a n t s a l s o produced  the  16 - 4% U. a f f i n i s empty p u p a l cases were found i n l a r g e -  headed p l a n t s compared to o n l y 2 - 1% i n small-headed p l a n t s .  After  f o r m a t i o n , m o r t a l i t y r a t e s were g r e a t e r d u r i n g the second than the g e n e r a t i o n i n both s m a l l - and large-headed p l a n t s .  In small-headed  gall  first plants  A  81 Table XIII.  Comparison of g a l l - f l y a t t a c k o f .'small- and large-headed knapweed d u r i n g f i r s t and second g e n e r a t i o n s i  head size  *  % seed heads % undeveloped  heads  L  75 44  S L  4 47  S  L  57 46  % s u p e r p a r a s i t i z e d heads  *  S L  39 7  seeds per p l a n t  •k  S L  4 45  S L  .8 1.4  S L  2.8 2.5  S L  2 43  S L  2 16  ' *  S L  95 31  *  S L  1.0 10  S L  .3 .2  S L  58 49  S L  42 27  S L  24  seeds per seed head l a r v a e per head  CO •H  % third-instar  affi  first-instar  % empty p u p a l cases  a  larvae  % dead f i r s t - i n s t a r l a r v a e i n the p f e - r g a l l .'stage: . % dead i n remaining  .adrif ascia  cfl •u  first-instar  stages  *  l a r v a e per head  % third-instar  larvae  A  % empty p u p a l cases  c % dead i n r e m a i n i n g  stages  """significant d i f f e r e n c e a c c o r d i n g to a 2 X 2 by * S = small-headed  p l a n t s ; L = large-headed  X-  plants  + I+I  s  t o t a l heads per p l a n t  first generation  + + + + + + + + + + + + + + + + + + + + + + + + +  diffuse  second generation  12 7  73 14  2 5  73 61  4 6  26 35  5 2  .9 4  2 12  190 9  .4 .7  3.7 1.3  .6 .4  .5 2.1  u  1% 7%  79 ± 64 -  4% 15%  1% 4%  2 11 -  1% 8%  J  2% 6%  6 8  - 8% 13 3% 17 - 8%  .5% 2% .2 .1 42% 21%  l«  .9 .03  J  !•*  J  98 100 -  .03 7% 100%  42% 15%  2 ± 1% 0%  24%  0% 0%  t e s t of a s s o c i a t i o n  denoted  82 most JJ. a f f i n i s d i e d i n the f i r s t - i n s t a r  stage a f t e r g a l l f o r m a t i o n , but  i n large-headed p l a n t s most d i e d i n the a d u l t stage b e f o r e emergence.  A l t h o u g h the d i f f e r e n c e was f a s c i a t a were produced the f i r s t  not s i g n i f i c a n t , i t appears  d u r i n g the second g e n e r a t i o n (.9  g e n e r a t i o n (.3  - .2) i n small-headed  i n large-headed p l a n t s were r a r e .  Due  plants.  t h a t more JJ. q u a d r i - .2) than d u r i n g JJ. q u a d r i f a s c i a t a  t o low numbers of JJ. q u a d r i f a s c i a t a  found i n both s m a l l - and large-headed p l a n t s , e s t i m a t e s of percentages of JJ. q u a d r i f a s c i a t a i n each stage had l a r g e s t a n d a r d e r r o r s . it  appears  From these d a t a  t h a t some s e c o n d - g e n e r a t i o n a d u l t s emerge from both s m a l l - and  large-headed p l a n t s , and t h a t these f l i e s m o s t l y a t t a c k small-headed T h e i r progeny  appear  to have v e r y low death  plants.  rates.  4.Discussion: I f g a l l - f l y m o r t a l i t y a t the egg stage i s not density-dependent e s t i m a t e s of f i r s t - i n s t a r a t t a c k - r a t e , JJ. a f f i n i s generation. second  larval  so t h a t  d e n s i t i e s can be taken as a measure of  i s less efficient  d u r i n g the second than the  first  JJ. q u a d r i f a s c i a t a , i n c o n t r a s t , i s more s u c c e s s f u l d u r i n g the  than the f i r s t g e n e r a t i o n .  H e t e r o g e n e i t y i n head s i z e among d i f f u s e knapweed p l a n t s on the r e l e a s e created great v a r i a b i l i t y between f i r s t  and second g e n e r a t i o n s .  h i g h , such as i n 1977 growing  i n f l y and seed counts when comparisons  were made  On the average, when f l y d e n s i t i e s a r e  on d i f f u s e knapweed, seeds a r e produced  season because most heads d u r i n g the f i r s t  l a t e i n the  g e n e r a t i o n are a t t a c k e d  so h e a v i l y t h a t they are s u p e r p a r a s i t i z e d , and h i g h p r o p o r t i o n s of heads remain undeveloped.  v  unattacked  Seed y i e l d s d u r i n g the second g e n e r a t i o n may  h i g h because JJ. a f f i n i s does not appear  site  t o be as e f f i c i e n t  be  i n a t t a c k i n g heads  83 as d u r i n g the f i r s t  generation.  And, even though d e n s i t i e s o f U_. q u a d r i -  f a s c i a t a a r e much h i g h e r d u r i n g the second than the f i r s t s p e c i e s appears to have about o n e - h a l f affinis body  this  the e f f e c t on seed y i e l d as does U.  because U. q u a d r i f a s c i a t a produces t h i n n e r g a l l s and has a s m a l l e r  size.  U_. q u a d r i f a s c i a t a s u r v i v e the g r e a t c o m p e t i t i o n first  generation,  from U. a f f i n i s d u r i n g t h e  g e n e r a t i o n by l e a v i n g a few progeny i n large-headed  t h e r e i s food and space enough f o r both s p e c i e s  p l a n t s , where  and o f t e n seeds t o o , and  by o v i p o s i t i n g i n the few heads on small-headed p l a n t s t h a t escape p a r a s i t i s m by U. a f f i n i s .  During  super-  t h e second g e n e r a t i o n TJ. q u a d r i f a s c i a t a  takes advantage o f l e s s c o m p e t i t i o n by U. a f f i n i s  and t h e resurgence i n  head i n i t i a t i o n by small-headed p l a n t s , and t h e r e s u l t  i s t h a t U. q u a d r i -  f a s c i a t a appears t o have a h i g h e r f e c u n d i t y d u r i n g the second than the f i r s t generation.  Other " f a c t o r s t h a n r h e a d . s i z e weed heads.  may be i n f l u e n c i n g g a l l - f l y d e n s i t i e s i n knap-  P l a n t s i z e , s p i n e and b r a c t l e n g t h and c o l o u r , and i n t e r n a l  a t t r i b u t e s of the heads which the f l i e s determine by p r o b i n g , may account for  some o f the v a r i a b i l i t y  head s i z e p r o b a b l y larily  i n the d a t a .  Heterogeneity  i n these f a c t o r s and  a f f e c t s g a l l - f l y a t t a c k r a t e on s p o t t e d knapweed s i m i -  t o d i f f u s e knapweed.  I t appears t h a t l i t t l e energy i s expended by d i f f u s e knapweed i n d e v e l o p i n g heads t o the 3 t o 4 mm l o n g bud s t a g e , which i s most s u s c e p t i b l e t o superp a r a s i t i s m by TJ. a f f i n i s .  Because g a l l s and seeds do not develop  i n these  heads, energy,by small-headed p l a n t s a t h i g h f l y a t t a c k - r a t e s , i s a c t u a l l y  v  84 conserved,  and  used l a t e r i n the growing season when JJ. a f f i n i s a t t a c k - r a t e  i s lower.  A s i m i l a r e f f e c t was  c o t t o n buds, and  found  by T a n s k i y  (1969) who  removed t e r m i n a l  determined t h a t head p r o d u c t i o n d u r i n g the l a t t e r p a r t of  the growing season was  s t i m u l a t e d w i t h no  delay i n plant maturation.  l o s s i n ' c o t t o n y i e l d , but w i t h  Some s p e c i e s of p l a n t s , whose f l o w e r s a r e  a  eaten  by i n s e c t s , can compensate f o r t h i s l o s s by the p r o d u c t i o n of a d d i t i o n a l flowers  (Janzen,  1971).  Spotted  knapweed a l s o seems to have the  of r e a c t i n g to head s u p e r p a r a s i t i z a t i o n d u r i n g the f i r s t i n c r e a s i n g the r a t e of head i n i t i a t i o n in-August, commences v e g e t a t i v e r o s e t t e growth.  by  even when i t n o r m a l l y  on s e x u a l r e p r o d u c t i o n ,  c o n t i n u e s head development u n t i l t h i s energy i s spent. s p o t t e d knapweed, i t i s d i f f i c u l t  generation  T h i s i n d i c a t e s t h a t s p o t t e d knapweed  a l l o c a t e s a net amount of energy to be spent  and  capability  For both  to show the resurgence  and  diffuse  i n head  p r o d u c t i o n i n August, when t e r m i n a l heads have been s u p e r p a r a s i t i z e d , because the t o t a l number of heads i n i t i a t e d under normal growing c o n d i t i o n s i s highly variable. than expected  A resurgence  i n head p r o d u c t i o n may  be shown by a g r e a t e r  number of heads produced, e s p e c i a l l y when a,:high p r o p o r t i o n of  these heads a r e produced d u r i n g the second fly-".generation. weather c o n d i t i o n s i n August may  decrease  Hot,  dry  head p r o d u c t i o n , c a u s i n g a c r a s h  i n f l y numbers, because the d e n s i t y of d i a p a u s i n g  l a r v a e may  be  severely  r e s t r i c t e d by fewer and/or s m a l l e r heads.  ZwOlfer Varley  (1970) found (1947) found  their lifetime. 15%.  t h a t JJ. a f f i n i s produced about 120  eggs per female,  t h a t JJ. j aceana c o u l d l a y between 52 and  However, egg m o r t a l i t y f o r JJ. j a c e a n a  was  70 eggs d u r i n g not h i g h e r  I f JJ. a f f i n i s and JJ. q u a d r i f a s c i a t a egg m o r t a l i t i e s i n the f i e l d  s i m i l a r , and  and  each female l a y s 50 or more eggs, then f e c u n d i t y i n t h i s  than are study  85 i s underestimated.  But, a d u l t f l i e s may have d i e d , o r d i s p e r s e d b e f o r e  ovi-  p o s i t i o n , and h i g h a d u l t d e n s i t i e s f o r some T e p h r i t i d s have a l s o been found  to decrease  f e c u n d i t y (Watt, 1960).  Numbers o f TJ. a f f i n i s eggs l a i d  i n s u p e r p a r a s i t i z e d heads c o u l d a l s o have been g r e a t e r than f o u r , as e s t i mated.  Empty pupal cases may have been found  i n heads  designated  as having  been  produced d u r i n g the second g e n e r a t i o n because t h e r e may be a small o v e r l a p between f i r s t  and second g e n e r a t i o n s .  Samples c o u l d have been taken one  week l a t e r , but then some of these'heads'may c o n t a i n second-generation . progeny, w i t h t h e r e s u l t t h a t s e c o n d - g e n e r a t i o n  s i z e would be  underestimated.  5.Conclusions: 1. U. a f f i n i s had a 75% death r a t e i n t h e p r e - g a l l stage i n 1977 d u r i n g the first  g e n e r a t i o n , and on small-headed p l a n t s t h i s percentage was 95% o r  higher. 2. Enough U. a f f i n i s and  and U. q u a d r i f a s c i a t a s u r v i v e i n large-headed  small-headed p l a n t s d u r i n g the f i r s t  plants  g e n e r a t i o n t o produce the  second g e n e r a t i o n even a t peak f l y d e n s i t i e s . 3.Small-headed p l a n t s undergo a resurgence 1  i n head p r o d u c t i o n d u r i n g the  second g e n e r a t i o n i f most o f t h e heads i n i t i a t e d d u r i n g the f i r s t  gener-  ation are superparasitized. 4. TJ. q u a d r i f a s c i a t a appears t o have a h i g h e r f e c u n d i t y d u r i n g t h e second g e n e r a t i o n when U. a f f i n i s numbers a r e low  and t h e r e a r e p l e n t i f u l heads  on small-headed p l a n t s . 5. Even though the g a l l f l i e s destroy many, potential seeds d u r i n g t h e f i r s t g e n e r a t i o n , d i f f u s e knapweed can produce h i g h numbers o f seeds l a t e i n t h e growing season.  86 v. E f f e c t o f g a l l f l i e s on undeveloped  heads:  1.Introduction: Undeveloped  heads i n weedy s p e c i e s such as H i e r a c i u m f l o r i b u n d u m (Thomas  and D a l e , 1975) a r e common, and i n Europe  (Marsden-Jones  and T u r r i l l , 1954)  and i n B r i t i s h Columbia, undeveloped heads on knapweed' a r e common l a t e i n t h e growing season.-  4J.- »aff-inis and TJ. q u a d r i f a s c i a t a a c t l i k e  d r a i n i n g energy i n t o heads w i t h g a l l s  (Shorthouse, p e r s . comm.).  sinks, This  study determines what e f f e c t g a l l f l i e s have on t h e percentage of undeveloped heads produced by d i f f u s e and s p o t t e d knapweed.  2.Method: The average number o f -heads- -in^'seed, s u p e r p a r a s i t i z e d and undeveloped s t a g e s produced by t h e end o f the f i r s t  and second a d u l t g e n e r a t i o n s from 1975 t o  1978 were o b t a i n e d from«samples " c o l l e c t e d on t h e d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e f o r a previous':study on g a l l - f l y abundance ( s e c t i o n I I B i i ) . In 1976 and 1977 s u r v e y s  were made o f r a n g e l a n d p o p u l a t i o n s f o r t h e p e r c e n -  tage heads, where any a b o r t e d head was counted as "undeveloped".  Different  sampling methods were used i n 1976 and 1977, and except f o r r e l e a s e s i t e s and the d i f f u s e knapweed p o p u l a t i o n i n Vernon, d i f f e r e n t p o p u l a t i o n s were each y e a r .  sampled  In' 1976 t h i r t y branches o f d i f f u s e and t h i r t y s t a l k s o f s p o t t e d  knapweed were a r b i t r a r i l y taken.  I n 1977 a 50 X 50 cm square was randomly  thrown on t h e p o p u l a t i o n s , and a l l knapweed w i t h i n f i v e such squares was r e moved.  Heads f o r 1976 and 1977 samples were c l a s s i f i e d as above.  seed heads from e a c h sample were chosen, a t random, and opened whether  g a l l f l i e s had d i s p e r s e d t o t h e p o p u l a t i o n s .  a l a t e r study.  Forty  t o determine  The seeds were used f o r  I n a n a l y s i s , t h e p e r c e n t a g e s o f undeveloped heads  l a n d p o p u l a t i o n s were compared w i t h r e l e a s e - s i t e p o p u l a t i o n s  f o r range-  u s i n g Duncan's  87 New  M u l t i p l e Range T e s t  ( L e C l e r g e , et a l . ,  1962).  On r e l e a s e s i t e s the  e f f e c t on undeveloped heads by JJ. q u a d r i f a s c i a t a was  assumed to be o n e - h a l f  t h a t of JJ. a f f i n i s , because JJ. q u a d r i f a s c i a t a l a r v a e a r e s m a l l e r than JJ_. a f f i n i s larvae  ( s e c t i o n I I B i i a ) and because JJ. q u a d r i f a s c i a t a r e q u i r e  energy f o r l a r v a l and g a l l development  than do JJ. a f f i n i s  less  (Shorthouse, p e r s .  comm.).  3.Results: There was  a s i g n i f i c a n t negative c o r r e l a t i o n  ( r = -.976) between the average  number of f i r s t - i n s t a r JJ. a f f i n i s + ^ JJ. q u a d r i f a s c i a t a l a r v a e per head ( h e n c e f o r t h termed "the average number of g a l l f l i e s per head") and the p e r c e n t a g e of heads i n the seed s t a g e from 1975 weed r e l e a s e s i t e  (Fig. 21i).  on the d i f f u s e knap-  There were s i g n i f i c a n t p o s i t i v e  between the percentage of undeveloped heads s u p e r p a r a s i t i z e d heads  to 1978  correlations  (r = .975) and the percentage of  ( r = .958) w i t h the average number of g a l l f l i e s per  head on d i f f u s e knapweed, but these c o r r e l a t i o n s on s p o t t e d knapweed ( F i g . 2 1 i i ) were not s i g n i f i c a n t  (r = .934 and  .905, r e s p e c t i v e l y ) .  There  was,  however, a s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n between the p e r c e n t a g e o f heads i n the seed stage and the average number of g a l l f l i e s per head on the s p o t t e d knapweed r e l e a s e s i t e  (r = -.954).  G r e a t e r p e r c e n t a g e s o f heads were  2 s u p e r p a r a s i t i z e d on d i f f u s e than on s p o t t e d knapweed ( % 1 3 - 6 7 ) , t h e r e was  no s i g n i f i c a n t d i f f e r e n c e f o r undeveloped heads  2 (^(2)  = z  but  -55).  The percentage of undeveloped heads among r a n g e l a n d knapweed p o p u l a t i o n s varied greatly.  P r o b a b l y the g a l l f l i e s , which were found a t low d e n s i t i e s  on some s i t e s , had not y e t a f f e c t e d the percentage o f undeveloped heads to any g r e a t e x t e n t .  Thus, w i t h few e x c e p t i o n s , r a n g e l a n d p o p u l a t i o n s of  %90  %904  80-  ft  < u  70-  co Q  < LL < LU HH  '3.0  50-  2.5  40-  2.0  30-  1.5  20-  1.0  CL Q CL LU ZD 0_ C  <  LU  .<  ZD > CL  + 00  10-  . JO- - • - • -  -—i 1975  . -  • -0  r~  1976  1977 (i)  Figure  0 •-  1978  .5  1—H  < 1—  00 -ZL u_ HH 1 V00 • H-1  < d z IX  -8.0  C£  ft < HH  Q  ft  o  00 X  <  70-  "7.0  X  LA  60-  80-  60-  •6.0  LL C£  LU  HH  CL CL CD  < <LU gj > PIS  50-  •5.0  40-  •4.0  ft oo z :  30-  3.0  i— oo CL  A" +  i  20. 10  X  X.'  JO  _ • -o1975  2.0 1.0  "0  IX  —r  1976  1977  1978  (ii)  21. R e l a t i o n s h i p between seed heads, undeveloped heads, s u p e r p a r a s i t i z e d heads, and average numbers of f i r s t - i n s t a r IJ. a f f i n i s and U. q u a d r i f asciata. p e r head a f t e r the end o f the f i r s t a d u l t f l y generation. i . d i f f u s e knapweed r e l e a s e s i t e ; i i . s p o t t e d knapweed r e l e a s e s i t e % seed heads + + ; % undeveloped heads X X; % s u p e r p a r a s i t i z e d heads C— •~0; average numbers of TJ. a f f i n i s + % U. q u a d r i f a s c i a t a per head a t the end of the f i r s t a d u l t f l y generation N = 77, 402, 300 and 546 f o r 1975, 1976, 1977 and 1978, r e s p e c t i v e l y on d i f f u s e knapweed, and N = 1 6 3 , 176, 441 and 336 f o r 1975, 1976, 1977 and 1978, r e s p e c t i v e l y , on s p o t t e d knapweed f o r the percentage of heads i n each s t a g e . . Average f l y d e n s i t i e s a r e from T a b l e s V I , V I I , V I I I and IX.  co co  89 T a b l e XIV.  1976 survey f o r undeveloped location  heads i n d i f f u s e knapweed p o p u l a t i o n s  % undeveloped  Boston Bar Lytton Keremeos Penticton Vernon Falkland Sweetsbridge'' release, s i t e k average  heads  27 ± 2% 17 - 2 4-1 10-2 12-2 6-2 20 4 50-5 14-3  1  J  Means o f a l l s i t e s a r e s i g n i f i c a n t l y d i f f e r e n t (p <.01) w i t h the mean o f the r e l e a s e s i t e , a c c o r d i n g t o Duncan's New M u l t i p l e Range T e s t ( L e C l e r g e e t a l . , 1962) U. q u a d r i f a s c i a t a found a t l e s s than .5 g a l l s p e r seed  head  T h i s s i t e was p r o b a b l y sprayed w i t h Tordon. "average f o r s i t e s which had not been sprayed, and where t h e r e were no (N = 6)  T a b l e XV.  1977 survey f o r undeveloped  flies  heads i n d i f f u s e knapweed p o p u l a t i o n s  location -  % undevei  1  11 + 21 + 12 12-2 14-2 14 11 v 1 11 20 + + 9 11 + 12 + + 23 + 25 + 15 + 34 + 16 + 43 + 19  Boston Bar Lytton f Vernon f P r i t c h a r d (grazed) f P r i t c h a r d (ungrazed) (ungrazed) Y e l l o w Lake Falkland Lumby (grazed) Lumby (ungrazed) Summerland White Lake O b s e r v a t o r y Oliver Osoyoos Penticton release.site average''  means of a l l s i t e s a r e s i g n i f i c a n t l y d i f f e r e n t (p < .01) w i t h the mean o f the r e l e a s e s i t e , a c c o r d i n g t o Duncan's New M u l t i p l e Range T e s t ( L e C l e r g e , e t a l . , 1962) """locations preceded by " f " had g a l l f l i e s ''average f o r s i t e s w i t h o u t f l i e s  i n samples  and g r a z i n g  (N = 9)  90 T a b l e XVI.  1976 survey  f o r undeveloped heads i n s p o t t e d knapweed p o p u l a t i o n s  location  % undeveloped h e a d s 35 J 27 30 7 31 ^ 24 r 34 j 31 33 3530-  Barriere Sicamous Barnhartvale HWY 97 (Campbell ranch) Monte Lake Westwold-1 Westwold-2 Lake S u p e r i o r ( O n t a r i o ) release.site average"' X  1  2% 3 ** 2 ** 2 ** 2 ** 2 3 ** 2 * 4 1  s i g n i f i c a n t d i f f e r e n c e w i t h r e l e a s e s i t e i f f o l l o w e d by * (p < .05) o r ** (p < .01) a c c o r d i n g t o Duncan's New M u l t i p l e Range T e s t ( L e C l e r g e e t a l . , 1962)  -'average f o r a l l s i t e s , e x c l u d i n g Lake S u p e r i o r arid-th^ r e l e a s e s i t e  T a b l e XVII.  1977 survey  (N = 7)  f o r undeveloped heads i n s p o t t e d knapweed p o p u l a t i o n s —  location  % undeveloped heads  Westwold-3 Westwold-4 Walachin Keremeos release.site average  _  4^1 61 7 4 18 I 4 21-3 52-2 24 - 12  means o f a l l s i t e s a r e s i g n i f i c a n t l y d i f f e r e n t (p < .01) w i t h t h e mean o f the r e l e a s e s i t e , a c c o r d i n g t o Duncan's New M u l t i p l e Range Test ( L e C l e r g e et^ a l . , 1962) Average  diffuse  f o r a l l s i t e s excluding the r e l e a s e s i t e  (Tables XIV and XV) and s p o t t e d  lower percentages The  (N = 4)  (Tables XVI and XVII) knapweed had  o f undeveloped heads than d i d r e l e a s e s i t e  average percentage of undeveloped heads f o r rangeland  out f l i e s ,  populations.  populations  with-  g r a z i n g o r s p r a y i n g were 14 - 3% and 30 - 1% f o r d i f f u s e and  s p o t t e d knapweed, r e s p e c t i v e l y i n 1976, and 19 - 3% and 24 - 12% f o r d i f f u s e and  s p o t t e d knapweed, r e s p e c t i v e l y , i n 1977.  and Lumby  (Table XV) had s i m i l a r percentages  The grazed  s i t e s at Pritchard  o f undeveloped heads t o un-  91 grazed s i t e s a t these l o c a t i o n s , i n d i c a t i n g t h a t g r a z i n g may  not have a  g r e a t e f f e c t on the percentage of heads t h a t remain*undeveloped. i n t e r s t i n g t o note t h a t the s p o t t e d knapweed p o p u l a t i o n a t Lake Ontario  I t i s also Superior,  (Table XVI) had a s i m i l a r percentage of undeveloped heads as the  average f o r r a n g e l a n d s p o t t e d knapweed p o p u l a t i o n s . •  4.Discussion: P r o x i m a l heads a r e p r o b a b l y developed o n l y when t h e r e a r e s u f f i c i e n t r e s e r v e s and m o i s t u r e l a t e i n the growing season to f i l l are  ovaries.  could adequately s e r v i c e .  i n i t i a t e o n l y the number of seeds which i t  In p r a c t i c e , because e n v i r o n m e n t a l c o n d i t i o n s  v a r y w i t h i n and between seasons, the number o f seeds produced may f a l l s h o r t of t h a t number" (Harper, L o v e l l and Moore, 1970). knapweed must have enough r e s e r v e s to f i l l  exceed or  Presumably,  a l l the o v a r i o l e s i n the heads,  or  the head remains undeveloped.  of  energy r e s e r v e s because t h i s study i n d i c a t e s t h a t g a l l - f l y  G a l l f l i e s may  be r o b b i n g p r o x i m a l heads densities  c o r r e l a t e d w i t h the percentage of undeveloped heads on d i f f u s e and  s p o t t e d knapweed._ but  "Seeds  i n i t i a t e d b e f o r e they a r e s u p p l i e d w i t h r e s e r v e s , and a p e r f e c t l y o r g a -  n i z e d p l a n t would presumably  are  energy  T h i s c o r r e l a t i o n was  the c o r r e l a t i o n c o e f f i c i e n t was  high  not s i g n i f i c a n t on s p o t t e d knapweed, ( r = .934).  Because  undeveloped  and s u p e r p a r a s i t i z e d heads were d i s t i n g u i s h e d m o s t l y on the b a s i s of t h e i r r e s p e c t i v e l y p r o x i m a l and d i s t a l p o s i t i o n s on branches, s l i g h t e r r o r s i n judgement  c o u l d have r e s u l t e d i n the above n o n - s i g n i f i c a n t t e s t .  v e r y p r o b a b l e , however,that of  It is  the g a l l f l i e s a r e i n c r e a s i n g b o t h the percentage  undeveloped and s u p e r p a r a s i t i z e d heads on s p o t t e d knapweed, as they a r e  on d i f f u s e knapweed.  Knapweed i n i t i a t e s 75% or more of the t o t a l number of  heads produced b e f o r e the f i r s t head f l o w e r s  (section II A i ) ,  and the p l a n t s  92 cannot " f o r s e e " t h a t p a r a s i t i s m of t e r m i n a l heads w i l l g r e a t l y energy requirments to these heads. heads are s u p e r p a r a s i t i z e d ,  increase  I t a l s o appears «t«hat even i f d i s t a l  as many were i n 1977,  p l a n t energy above the u s u a l amount r e q u i r e d  i s a depletion  high  in  1977.  to the average number of  JJ. a f f i n i s per numbers of heads at the r i g h t stage of o v i p o s i t i o n . increase  i n the expected s u p e r p a r a s i t i z a t i o n r a t e may'occur i f the  emerge e a r l i e r and  wet,  than knapweed heads appear; i f weather c o n d i t i o n s  promoting r a p i d head development, :but  i f average head s i z e i s s m a l l e r t h i s study i t was  that f l y populations  may  due  assumed that head s i z e was  t h a t f l y emergence and  initiated  than u s u a l  head appearance was  of  f o r p r o x i m a l head development  because the percentage of undeveloped heads was  Head s u p e r p a r a s i t i z a t i o n i s n o r m a l l y . r e l a t e d  there  female  But,  an  flies  are  slowing f l y a c t i v i t y ;  cool or  to dry weather c o n d i t i o n s .  c o n s t a n t from 1975  well-synchronized  to  In  1978,  each y e a r ,  and  were i n c r e a s i n g w h i l e the average number of heads  each y e a r was  the same.  But  a l l of these, and  other v a r i a b l e s  change from year to y e a r , a f f e c t i n g the percentages of heads i n each  stage.  In some y e a r s the d e n s i t y adds v e r y l i t t l e  to the  g a l l - f l y d e n s i t i e s and density had  of IJ. q u a d r i f a s c i a t a i s so low,  t h a t t h i s species-  s i g n i f i c a n c e of the . c o r r e l a t i o n - c o e f f i c i e n t s between the p e r c e n t a g e o f heads i n each s t a g e .  of JJ. q u a d r i f a s c i a t a i n t h i s study and  h a l f the e f f e c t t h a t JJ. a f f i n i s had  Halving  assuming t h a t t h i s  i n seed r e d u c t i o n  the  species  i s supported  by  H a r r i s ' (1980b) f i n d i n g s , where JJ. q u a d r i f a s c i a t a were shown to have h a l f c a l o r i e s as U.  affinis  larvae.  the  93 The average percentage of undeveloped heads f o r d i f f u s e and s p o t t e d knapweed r a n g e l a n d p o p u l a t i o n s v a r i e d between 1976 p o p u l a t i o n s were sampled were d i f f e r e n t  i n 1976  and 1977 p r o b a b l y because  i n the two y e a r s , and because weather  different  conditions  and 1977, as d i s c u s s e d i n s e c t i o n I I B i .  On  diffuse  knapweed the average percentage of undeveloped heads, when means of the two y e a r s a r e averaged, i s about 17%. weed was  The sample  s i z e i n 1977  f o r s p o t t e d knap-  too s m a l l t o g i v e a r e l i a b l e e s t i m a t e of the percentage of undeve-  loped heads. gall flies  I t i s p r o b a b l y c l o s e to the 30% found i n 1976.  In 1977  the  i n c r e a s e d the expected p e r c e n t a g e of undeveloped heads from the  average of 19 - 3% found on r a n g e l a n d p o p u l a t i o n s to 43 - 2% on the r e l e a s e site.  On s p o t t e d knapweed, i f the expected average of undeveloped heads i s  taken to be 30%, as found i n the r a n g e l a n d survey i n 1976, c r e a s e d the percentage of undeveloped heads by 22%.  gall flies i n -  Thus the f l i e s  reduce  seed numbers not o n l y i n heads which they a t t a c k , but they reduce the number of  heads which develop to the seed s t a g e , and p r e v e n t seed p r o d u c t i o n  alto-  gether i n t h e s e heads.  T h i r t y - y e a r averages of the mean a n n u a l temperature and t o t a l annual p r e c i p i t a t i o n do not appear to be r e l a t e d t o the percentages of undeveloped for  r a n g e l a n d knapweed p o p u l a t i o n s .  loped heads i n Osoyoos (34 - 3%) was  F o r example,  heads  the percentage of undeve-  g r e a t e r than i n Boston Bar  (11 - 2%) f o r  d i f f u s e knapweed even though Boston Bar i s c o o l e r and m o i s t e r (Table X V I I I ) . O l i v e r and Osoyoos a r e b o t h hot and d r y , but the percentage of undeveloped heads on d i f f u s e knapweed i n Osoyoos was Many f a c t o r s p r o b a b l y a f f e c t weather,  a p p r o x i m a t e l y t w i c e t h a t of O l i v e r .  the percentage of undeveloped heads:,: such as  s o i l type, o t h e r v e g e t a t i o n and i n t r i n s i c and g e n e t i c f a c t o r s i n the  population.  Tordon appears to i n c r e a s e the percentage of undeveloped  heads  94 T a b l e X V I I I . Climate * and a l t i t u d e f o r s u r v e y s o f d i f f u s e and s p o t t e d knapweed p o p u l a t i o n s i n 1976 and 1977 0  * location Barnharvale Barriere Bostock r a n c h Boston Bar Campbgll r a n c h Chase Falkland H e l l ' s Gate Kamloops Keremeos Lumby Lytton Monte Lake Oliver Osoyoos Penticton Pritchard Sicamous Sorrento Summerland Sweetsbridge Vernon Walachin Westwold White Lake Observatory Y e l l o w Lake  mean annual temperature (°C)  * . t o t a l annual p r e c i p i t a t i o n (mm)  Altitude  Kamloops 6.7 Kamloops H e l l ' s Gate Westwold Sicamous 7.2 9.5 8.3 9.5 Vernon r H e l l ' s Gate Westwold 8.9 10.0 8.9 Kamloops 7.8 Sicamous Vernon Vernon 7.2 Kamloops 6.1  Kamloops 445 Kamloops H e l l ' s Gate Westwold Sorrento 424 1176 261 249 Vernon Kamloops Westwold 299 342 296 Kamloops 604 515 Vernon Vernon 393 Kamloops 316  375 375 366 228 580 671 600 114 345 549 550 357 670 305 342 610 433 426 390 853 580 555 305 640  Penticton  Penticton  762  Penticton  Penticton  853  * f o r l o c a t i o n s where no d a t a i s a v a i l a b l e , see l o c a t i o n n e a r e s t s i m i l a r weather s t a t i o n  (m)  -• • •  c i t e d , which i s the  **  i s where the a c t u a l sample was taken and not where the A l t i t u d e s gt ia vt ei no n weather was l o c a t e d  diffuse  knapweed r e l e a s e  site  spotted  knapweed r e l e a s e  site  ^ C l i m a t e d a t a from C l i m a t e o f B.C. , p u b l i s h e d by the B r i t i s h Columbia M i n i s t r y o f A g r i c u l t u r e (standard 1941 - 1970 averages)  95 even when the p l a n t i s not k i l l e d . numerous f a c t o r s a f f e c t i n g  On the average rangeland  The g a l l f l i e s  a r e o n l y one of the  the p e r c e n t a g e of undeveloped heads.  s p o t t e d knapweed populations- had h i g h e r  of undeveloped heads than d i f f u s e knapweed p o p u l a t i o n s .  Spotted  percentages knapweed  heads a r e l a r g e r , and produce more numerous, and l a r g e r seeds than d i f f u s e knapweed.  Thus each s p o t t e d knapweed head  the p a r t of the p l a n t to d e v e l o p ' knapweed.  r e q u i r e s a l a r g e r commitment on  the head to m a t u r i t y  than does d i f f u s e  I f energy r e s e r v e s a r e low, and the weather i s d r y , d i f f u s e  knapweed may be a b l e to develop  some o f the heads, w h i l e  may have to a b o r t a l l heads a l r e a d y  spotted  knapweed  initiated.  5.Conclusions: 1. A's w e l l as i n c r e a s i n g the percentage of s u p e r p a r a s i t i z e d heads, flies  gall  can i n c r e a s e the percentage of undeveloped heads i n d i f f u s e and  s p o t t e d knapweed  populations.  2. The p e r c e n t a g e of undeveloped heads v a r i e s g r e a t l y among rangeland  knapweed  p o p u l a t i o n s , but on the average i t i s about 17% f o r d i f f u s e and 30% f o r spotted 3. C l i m a t e  knapweed. does not appear to r e g u l a t e the percentage of undeveloped heads  on rangeland  knapweed  populations.  96 vi.  E f f e c t of g a l l f l i e s on d i f f u s e and s p o t t e d knapweed seed weight, appearance  and  viability:  1.Introduction: Phytophagous i n s e c t s may 1971).  Even u n a t t a c k e d seeds i n f r u i t s which have been p a r t i a l l y e a t e n by  p r e d a t o r s may  have a lower v i a b i l i t y  knapweed heads may may  a l t e r seed s i z e , c o m p o s i t i o n or dormancy (Cavers,  be reduced.  (Janzen, 1971).  D i f f u s e and s p o t t e d  c o n t a i n both g a l l s and mature seeds, but seed v i a b i l i t y  T h i s study d e s c r i b e s some e f f e c t s o f g a l l - f l y a t t a c k on  d i f f u s e and s p o t t e d knapweed seed  attributes.  2.Method: In August,  1976,  undehisced seed heads were a r b i t r a r i l y c o l l e c t e d on the  d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s , and on c o n t r o l s i t e s where t h e r e were no g a l l f l i e s  (Vernon and Westwold f o r d i f f u s e and s p o t t e d knapweed  control sites, respectively).  The heads were s t o r e d a t room temperature f o r  f o u r months b e f o r e they were weighed.  Heads were chosen a t random, and  mature seeds i n each head were counted, weighed to the n e a r e s t 0.01 transferred  be the o p t i m a l  temperature  c l a s s i f i e d as:  germinated  ( r a d i c l e l e s s than 2 mm  The seeds were  A f t e r twelve days the seeds were  ( r a d i c l e g r e a t e r than 2 mm  i n length), non-viable  or i f the seed had become d i s e a s e d ) , or dormant ( i f  the seed d i d not g e r m i n a t e ) . number t e s t e d was  (23°C) , found to  f o r g e r m i n a t i o n (Watson, 1972).  every t h r e e days f o r r a d i c l e growth.  3.Results:  and  to moistened Whatman #2 g e r m i n a t i o n paper i n P e t r i d i s h e s t h a t  were then p l a c e d i n a c l o s e d cupboard a t room temperature  checked  mg,  the  The percentage i n each c l a s s o f the  used i n the a n a l y s e s .  total  97 A s i g n i f i c a n t l y g r e a t e r percentage of seeds from the d i f f u s e knapweed r e l e a s e site  (46%) was n o n v i a b l e  compared w i t h seeds from the c o n t r o l s i t e  (16%).  S i m i l a r i l y a g r e a t e r percentage of seeds from the s p o t t e d knapweed r e l e a s e site  (12%) was n o n v i a b l e  compared w i t h  the c o n t r o l s i t e  (4%) .  Seeds from  both d i f f u s e and s p o t t e d knapweed c o n t r o l s i t e s were s i g n i f i c a n t l y  heavier  than seeds from r e l e a s e s i t e s , but the r e d u c t i o n i n weight f o r d i f f u s e knapweed was o n l y 7% compared to 33% f o r s p o t t e d knapweed  E f f e c t , of g a l l f l i e s o n . d i f f u s e and s p o t t e d knapweed seed v i a b i l i t y and weight i n 1976 knapweed species  . location  % non-viable , seeds  s  '  *  mean seed i. , >. weight (mg)  release s i t e control site  46% 16  0.93 1.01  spotted  release s i t e control site  12 4  1.52 2.27  + I+I  diffuse  I+I +  T a b l e XIX.  (Table X I X ) .  0. 02 0. 04 0. 03 0. 06  s i g n i f i c a n t d i f f e r e n c e between r e l e a s e and c o n t r o l s i t e s  N o n v i a b l e seeds were u s u a l l y grey, or p a r t l y w h i t e i n c o l o u r , and had d u l l , porous seed c o a t s , whereas germinated and dormant seeds were u s u a l l y brown or b l a c k , and had h a r d , waxy seed c o a t s .  N o n v i a b l e seeds from b o t h d i f f u s e  and s p o t t e d knapweed r e l e a s e s i t e s were s i g n i f i c a n t l y l i g h t e r than germinated or dormant seeds  (Table XX).  Germinated and dormant seeds d i d not d i f f e r i n  weight f o r e i t h e r d i f f u s e o r s p o t t e d  There were s i g n i f i c a n t l y knapweed r e l e a s e s i t e but  2 (% ^ =  knapweed.  21.49) more nonviable  seeds from the d i f f u s e  (46%) than from the s p o t t e d knapweed r e l e a s e s i t e (11%)  i 2 t h e r e was no s i g n i f i c a n t d i f f e r e n c e ( % ^ =  1.69) f o r germinated seeds  (51% and 65% f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y ) . A s i g n i -  98 T a b l e XX.  Comparison o f germinated, n o n - v i a b l e and dormant seeds from d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s mean seed weight diffuse knapweed  class germinated  1.06  (mg)  % i n class  spotted knapweed  diffuse knapweed  spotted knapweed  - .03 k  51  65  .80 - .06 j  46  11  *  3  24  *  1  1  - .02 k  non-viable  .77 - .03 j  dormant  .94 - .07 k  1.49  1.54  - .04 k  j  s i g n i f i c a n t d i f f e r e n c e between c l a s s e s i f f o l l o w e d  by d i f f e r e n t l e t t e r s  s i g n i f i c a n t d i f f e r e n c e between d i f f u s e and s p o t t e d  knapweed denoted by *  f i c a n t l y g r e a t e r percentage (X release s i t e (3%).  ^0.05  of seeds fromfhe s p o t t e d  knapweed  (24%) were dormant compared to the d i f f u s e knapweed r e l e a s e  site  Most d i f f u s e knapweed seeds from the r e l e a s e s i t e which germinated or  were dormant, were w e l l - r o u n d e d , or f i l l e d .  Some s p o t t e d  knapweed seeds  which germinated appeared to be much s m a l l e r and s h r i v e l l e d , compared w i t h seeds from the c o n t r o l s i t e sickle-shaped  c  seeds were o f t e n galls.  maculosa  4*14  alt  The s h r i v e l l e d  and were u s u a l l y found i n heads c o n t a i n i n g  C.  3  ( F i g . 22).  Iff!  144 9V  I I I I•I• I  a) U. a ff inis bjseeds parasifi  from zed  c)seeds from sifi zed  galls un — heads paraheads  F i g u r e 22.  Appearance of s p o t t e d knapweed seeds from u n a t t a c k e d and a t t a c k e d heads by IT. a f f i n i s , and f u s i f o r m TJ. affinis galls ( m a g n i f i c a t i o n 1.75X)  99 4.Discussion: The g r e a t e s t e f f e c t of the g a l l f l i e s on d i f f u s e knapweed seed i s one of a decrease i n the percentage of v i a b l e seed, a l t h o u g h t h e r e was c r e a s e i n average seed weight.  Spotted knapweed seed weight was  d r a s t i c a l l y a f f e c t e d than v i a b i l i t y . result  some demore  T h i s d i f f e r e n c e c o u l d occur as a  of the s m a l l e r d i f f u s e than s p o t t e d knapweed o v a r i e s ; any  i n n u t r i e n t s to d i f f u s e knapweed heads may  reduction  cause the seeds to a b o r t , .but  s p o t t e d knapweed seeds would be a b l e to w i t h s t a n d a c o n s i d e r a b l e r e d u c t i o n i n n u t r i e n t s b e f o r e the seeds l o s e t h e i r v i a b i l i t y . appearance  The  shrivelled  of s p o t t e d knapweed seeds i n heads w i t h JJ. a f f i n i s g a l l s  may  be, i n p a r t due to the p r e s s u r e by the woody g a l l s on the immature seeds, squeezing some i n t o s i c k l e  shapes.  The g a l l f l y , JJ. j aceana, which i s s i m i l a r t o JJ. a f f i n i s  (as d e s c r i b e d  e a r l i e r i n s e c t i o n I I B i i ) appears to have a s i m i l a r e f f e c t on C.. n e m o r a l i s (Wadsworth, 1914)  as the g a l l f l i e s  i n t h i s study have on d i f f u s e and s p o t t e d  knapweed (when Wadsworth made h i s s t u d y , C_. n e m o r a l i s was and JJ. j aceana was  c a l l e d JJ. s o l s t i t i a l i s ; V a r l e y , 1947).  c a l l e d C_. n i g r a Wadsworth (1914)  found t h a t " p r o b a b l y the nourishment  t h a t n o r m a l l y goes to the d e v e l o p i n g  seeds became d i v e r t e d to the growing  l a r v a e , and a l s o t o the f o r m a t i o n of  the t h i c k - w a l l e d , woody g a l l " .  He d e s c r i b e d JJ. j aceana g a l l s as h a v i n g a  l a y e r of s o f t , n u t r i t i v e t i s s u e i n s i d e the woody o u t e r e x t e r i o r , and he found t h a t the n u t r i t i v e l a y e r was  "connected a t the base of the chamber w i t h the  v a s c u l a r system o f the p l a n t " .  Only 28.5%  of the seeds from g a l l e d C_.  n e m o r a l i s heads germinated, whereas 89% of the seeds from u n g a l l e d heads germinated.  The o v e r a l l e f f e c t of JJ. j aceana on C_. n e m o r a l i s was  duce v i a b l e seed y i e l d by 50% of the t o t a l number of v i a b l e seeds T h i s e f f e c t i s s i m i l a r to t h a t of JJ. a f f i n i s  to r e produced.  and JJ. q u a d r i f a s c i a t a on d i f f u s e  100 knapweed, where 46% of the seeds were not v i a b l e .  Storey  (1976), working w i t h IJ. a f f i n i s i n Montana, d i d not f i n d a s i g n i -  f i c a n t d e c r e a s e i n s p o t t e d knapweed seed v i a b i l i t y , and the g e r m i n a t i o n percentage was 96.7% from heads w i t h 4 o r more g a l l s . if  In the p r e s e n t study  "dormant" and "germinated" seeds a r e c o n s i d e r e d t o be v i a b l e , the p e r c e n -  tage of seeds which c o u l d p o t e n t i a l l y germinate i s 89% on the s p o t t e d knap-' weed r e l e a s e s i t e .  This result  i s o n l y s l i g h t l y lower than found by S t o r e y .  Storage of weed seeds o f t e n i n c r e a s e s the g e r m i n a t i o n p e r c e n t a g e , and Watson (1972) found t h a t s p o t t e d knapweed seeds, s t o r e d f o r 20 months a t room tempe r a t u r e , had a g e r m i n a t i o n percentage of 93%, whereas those seeds s t o r e d f o r o n l y 3 and 25 days had g e r m i n a t i o n percentages of 20% and 80%, r e s p e c t i v e l y . Seeds i n t h i s study were s t o r e d f o r f o u r months a t room temperature b e f o r e they were moistened, and the g e r m i n a t i o n percentage o b t a i n e d f o r s p o t t e d knapweed on the r e l e a s e s i t e i n 1976 was not u n l i k e percentages found by Watson (1972) f o r seeds s t o r e d f o r 25 days.  T h e r e f o r e the d i f f e r e n c e i n  g e r m i n a t i o n p e r c e n t a g e s between seeds from the r e l e a s e and c o n t r o l s i t e s be m a i n l y due to s i t e d i f f e r e n c e s .  may  Even i f g a l l f l i e s do lower the germin-  a t i o n r a t e of s p o t t e d knapweed seed, the n e t e f f e c t  seems s m a l l (see a l s o  Storey,- 1976) .  S i t e d i f f e r e n c e s p r o b a b l y d i d not e n t i r e l y account f o r the g r e a t decrease i n d i f f u s e knapweed seed v i a b i l i t y on the r e l e a s e s i t e because of the seed coat appeared  t o be changed.  the a t t r i b u t e s  Seeds from the r e l e a s e s i t e were  l i g h t brown o r grey i n c o l o r , and had d u l l and porous c o a t s , whereas seeds from the c o n t r o l s i t e were dark brown, and had h a r d , waxy seed c o a t s . and Cavers  (1971a) found s i m i l a r r e s u l t s by d e f o l i a t i n g Rumex c r i s p u s .  Maun  101 Seeds from n o n d e f o l i a t e d p l a n t s were "plumper, and v e r y s h i n y . brown i n c o l o r " .  b r i g h t reddish-brown i n c o l o r ,  Seeds from d e f o l i a t e d p l a n t s were d u l l ,  s m a l l e r , and  light  They found a l s o t h a t "the average t h i c k n e s s of the i n -  v e s t i n g s t r u c t u r e s of seeds was  reduced from 62.2 u i n seeds from c o n t r o l  p l a n t s to 52.6 u i n seeds from d e f o l i a t e d p l a n t s " and t h a t the seeds from the d e f o l i a t e d p l a n t s took up water more r a p i d l y and germinated than seeds from c o n t r o l p l a n t s .  faster  Thus one e f f e c t o f the g a l l f l i e s  d i f f u s e knapweed may be to decrease the seed bank i n the s o i l , because from t h i s i . s i t e appeared t o have t h i n n e r seed c o a t s , and would germinate f a s t e r than seeds from c o n t r o l  seeds  therefore  sites.  Small seeds tend to germinate more r e a d i l y than l a r g e seeds t h e r e f o r e the g a l l f l i e s may  on  (Harper, 1963),-  a l s o be d e c r e a s i n g the seed bank on the s p o t t e d  knapweed r e l e a s e s i t e because s p o t t e d knapweed seed weight was<reduced by 33%.  Some of t h i s d i f f e r e n c e i n weight between the c o n t r o l and  s i t e may 1.78  mg  2.27 mg  release  be due to s i t e d i f f e r e n c e s , and Watson (1972) found an average of . f o r s p o t t e d knapweed seeds, which i s lower than the average of found i n t h i s study f o r the c o n t r o l s i t e .  knapweed r e l e a s e - s i t e seeds was  Average weight f o r s p o t t e d  lower than Watson's (1972) weight,  t h a t the g a l l f l i e s a r e r e d u c i n g average seed weight.  indicating  P r o b a b l y seeds i n  heads w i t h g a l l s a r e more s e v e r e l y a f f e c t e d , w h i l e seeds i n u n a t t a c k e d heads may  s u f f e r o n l y s l i g h t weight l o s s .  However, average seed weight  would  be g r e a t l y reduced at peak f l y "population, i d e n s i t i e s , such as i n 1977, when v e r y few heads were found w i t h o u t g a l l s .  S e e d l i n g s produced by s m a l l seeds s u f f e r a g r e a t e r m o r t a l i t y than s e e d l i n g s produced by l a r g e r seeds, when seeds of b o t h s i z e s a r e found i n the same  102 population.  However, i f o v e r a l l seed  growth can be a c h i e v e d from l a r g e seeds. seed  s i z e i s s m a l l , then the same p o p u l a t i o n  from the s m a l l e r s i z e s as f o r p o p u l a t i o n s s t a r t e d  (Harper, L o v e l l and Moore, 1970).  On both r e l e a s e s i t e s  s i z e v a r i e d f o u r f o l d f o r the c l a s s of seeds which germinated i n 12 days.  Thus t h e r e was a m i x t u r e  of s m a l l and l a r g e seeds,  and a long-term  e f f e c t of  the g a l l f l i e s c o u l d be an i n c r e a s e i n s e e d l i n g m o r t a l i t y by i n c r e a s i n g the p r o p o r t i o n of s m a l l seeds produced on the r e l e a s e s i t e s .  The  c o l l e c t i v e e f f e c t s of the g a l l f l i e s on seed a t t r i b u t e s w i l l not r e s u l t  i n a decrease  i n knapweed p o p u l a t i o n d e n s i t y u n l e s s the s u r v i v i n g s e e d l i n g s  cannot r e p l a c e a l l those  i n d i v i d u a l s which d i e d .  T h i s q u e s t i o n demands a  l e n g t h y study of tte decay-rate o f the seeds i n the s o i l , and knapweed p o p u l a t i o n dynamics.  5.Conclusions: l . G a l l f l i e s appear to reduce both v i a b i l i t y and weight of d i f f u s e and s p o t t e d knapweed seeds, • crease weight  vii.  but d i f f u s e knapweed seed has a c o m p a r a t i v e l y  i n v i a b i l i t y , whereas s p o t t e d knapweed seed  g r e a t e r de-  suffers a greater  loss.  Survey o f rangeland  d i f f u s e and s p o t t e d knapweed seed y i e l d  i n 1977:  1.Introduction: Young g a l l - f l y  l a r v a e f e e d d i r e c t l y on knapweed o v a r i e s  (Shorthouse,  comm.) b e f o r e c e l l s p r o l i f e r a t e and form n u t r i t i v e t i s s u e .  E a r l i e r i t was  shown t h a t head s i z e w i t h i n d i f f u s e knapweed p o p u l a t i o n s a f f e c t s s u r v i v a l at high population d e n s i t i e s . s i t i e s per head f o r rangeland  Therefore  pers.  gall-fly  c h a r a c t e r i s t i c f l y den-  knapweed p o p u l a t i o n s may depend on the average  103 numbers o f seeds produced p e r seed head.  And, a l t h o u g h most a u t h o r s agree  t h a t seed s i z e i s one of the l e a s t p l a s t i c c h a r a c t e r s o f a p l a n t 1963;  Palmblad,  populations.  1968),  (Harper,  t h e r e c o u l d be v a r i a t i o n i n knapweed seed s i z e among  T h i s -study surveys d i f f u s e and s p o t t e d knapweed seed weight  and y i e l d : on r a n g e l a n d .  2. Method: Seed heads from f o u r t e e n d i f f u s e and f o u r s p o t t e d knapweed p o p u l a t i o n s , and from the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s , were o b t a i n e d from knapweed c o l l e c t e d i n 1977 f o r the survey i n head a b o r t i o n All  the seed heads from each s i t e were counted, and the average number of  seed heads per p l o t  (50 X 50 cm) were found.  were chosen, a t random, and opened. was  (section II B v ) .  F o r t y undehisced seed heads  The number of v i a b l e seeds i n each head  counted, where v i a b l e seeds were d i s t i n g u i s h e d from n o n - v i a b l e seeds  and u n f e r t i l i z e d o v a r i e s as noted i n the p r e v i o u s s e c t i o n  (II B v i ) .  any s t e r i l e seed heads were found, they were c l a s s e d as s e e d l e s s .  If  I f any  TJ. a f f i n i s o r TJ. q u a d r i f a s c i a t a g a l l s were found, t h e i r d e n s i t y per seed was r e c o r d e d .  head  Seed heads w i t h g a l l s were i n c l u d e d i n the e s t i m a t i o n o f the  mean number of seeds per seed head.  A l l v i a b l e seeds from the f o r t y heads  were p o o l e d and spread over a g r i d .  S i x t y seeds, c l o s e s t to predetermined  p o i n t s on the g r i d , were weighed to the nearest 0-01 mg.  3. R e s u l t s : D i f f u s e knapweed seeds from the r e l e a s e s i t e ranked s e c o n d - h e a v i e s t out of the d i f f u s e knapweed p o p u l a t i o n s surveyed, w i t h the Y e l l o w Lake s i t e h a v i n g s i g n i f i c a n t l y h e a v i e r seeds  (Table X X I ) .  The Y e l l o w Lake s i t e had been  h e a v i l y grazed d u r i n g the m i d d l e and l a t t e r p a r t s o f the growing  season.  104 Seeds from a l l o t h e r d i f f u s e knapweed s i t e s were s i g n i f i c a n t l y l i g h t e r those from the d i f f u s e knapweed r e l e a s e s i t e .  than  Seeds from the Lumby-2 s i t e ,  which was moderately g r a z e d , were s i g n i f i c a n t l y h e a v i e r than those from the ungrazed Lumby-1 s i t e , but the d i f f e r e n c e between grazed and ungrazed P r i t c h a r d - 2 and P r i t c h a r d - 1 p o p u l a t i o n s , r e s p e c t i v e l y , was not s i g n i f i c a n t . The P r i t c h a r d - 2 s i t e had been grazed o n l y i n the e a r l y s p r i n g , b e f o r e r o s e t t e s had s t a r t e d to b o l t , w h i l e the Lumby-2 s i t e had been moderately grazed throughout the growing  season.  F o r a l l but two d i f f u s e knapweed p o p u l a t i o n s , the mean number of seeds p e r head was s i g n i f i c a n t l y g r e a t e r than on the r e l e a s e s i t e . where t h e r e were no g a l l f l i e s , was found a t a low d e n s i t y 3.3 seeds per head.  But a t Osoyoos,  and a t Summerland, where U. q u a d r i f a s c i a t a  (0.3 - 0.1 g a l l s per seed head), t h e r e were o n l y  T h i s average was almost the exact d e n s i t y found on the  d i f f u s e knapweed r e l e a s e s i t e  (3.2 seeds per head).  I f n e t seed weight i s  d e f i n e d as the weight of the t o t a l number of seeds p e r seed head, and i s found by m u l t i p l y i n g  the mean seed weight by the mean number of seeds per  head, then f o r the d i f f u s e knapweed p o p u l a t i o n s surveyed, t h e r e was a s i x f o l d g r a d a t i o n i n n e t seed weight. and few per head  A t Osoyoos the. seeds were l i g h t  (0.90 mg)  ( 3 . 3 ) , so n e t seed weight was o n l y 2.97 mg per head.  at Y e l l o w Lake, seeds were both heavy (1.37 mg) and many per head net seed weight was 17.67 mg per head. i a t i o n i n n e t seed,  weight  But,  (12.9), so  S i m i l a r i l y , t h e r e was a l a r g e v a r -  f o r s p o t t e d knapweed.  The p l o t s a t Lumby-1 and Boston Bar had s i g n i f i c a n t l y g r e a t e r numbers of seeds per p l o t than the d i f f u s e knapweed r e l e a s e s i t e , but t h e r e were s i g n i f i c a n t l y fewer seed heads per p l o t on f o u r s i t e s  ( O l i v e r , Osoyoos, Lumby-2,  T a b l e XXI.  sxte  Vernon Summerland M Penticton Oliver' " Osoyoos . Falkland Lytton Pritchard-1 Pritchard-2 H Lumby-1 Lumby-2 M White Lake Observatory H Y e l l o w Lake H Boston Bar release s i t e  seed weight" (mg)  1.02..+ 1.07 + 1.02 + 1.12 + .90 + 1.10 + .97 + .99 + -'.99 + ,04 + ,10 + -  .02 ** ,03 ** ,03 ** ,03 ** ,03 ** ,03 ** ,03 ** ,03 ** .03 ** ,02 ** .02 **  +  05 - .03 **  + 37 ,04 ** + .93 ,02 ** +  1.21  ,04  s i t e was grazed moderately  Survey o f d i f f u s e knapweed seed weight  seeds"  5.5 5.0 9.2 9.1 8.  + + + + + + + + + + ±1 +  number per seed head U. a f f i n i s U. q u a d r i f a s c i a t a galls galls  1 .5 .8 .5 .7 .7 .8 .5  **  ** ** **  , 9  * *  ** **  .7 ** . 9  0 0 0 0 0 0  * * •k*  ,9 * * 12.9 + ,7 ** 8.0 + 3.2 ,6  $  o o  .2 .1  .6 - .1  •9  .15 - .07 0 0 0 0  .08 .08 - .06  0  0  1.2 - .2  .20 - .08  0  1.0 - .2  and y i e l d  i n 1977  number o f seed-' heads p e r p l o t (50 X '50 'cm),.  308 149 243 130 105 279 258 237 198 728 67  J J J J T  r T  r -  80 74 94 27 15 48 70 58 47 135 ** 20 **  9± 262 t 61 380 - 82 235 - 51  number o f seedsper p l o t (50 X 50 cm)  2768 492 2209 622 345 2289 1417 1184 1820 6628 724  | r J T T  r -  714 244 852 130 51 390 383 291 433 1228 108  ** ** **  ** **  66 ± 13 2345 t 732 3038 - 652 751 - 163  ** **  (M) o r h e a v i l y (H)  ^ s i g n i f i c a n t d i f f e r e n c e w i t h r e l e a s e s i t e i f f o l l o w e d by * (p <.05) o r ** (p <.01) a c c o r d i n g t o Duncan's New M u l t i p l e Range T e s t (LeClerge e t a l . , 1962)  T a b l e XXII.  site'  seed weight'' (mg)  Keremeos Walachin Westwold-1 Westwold-2 release s i t e  1.82 2.00 1.62 1.52 1.68  J .03 ** T -  .05 ** .03 .04 ** .04  Survey o f s p o t t e d knapweed seed weight  seeds''  number per seed head U. a f f i n i s U. q u a d r i f a s c i a t a galls galls  19 t. 2 ** 6 + 1 11-2 ** 13-2 ** 7.0 - .9  .02 - .02 0 0 4.7 - .5  <?  1.0 - .3  4.4 - .2  and y i e l d i n 1977 number o f seed> heads p e r p l o t (50 X 50 cm)  J  54 26 28 108 72  J 14 j 8 ** - 7 : *•*'• T 18 ** - 15  number o f seeds^ per p l o t (50 X 50 cm) 1034 155 312 1407 507  ^ T -  273 ** 49 * 75 230 ** 102  s i g n i f i c a n t d i f f e r e n c e w i t h r e l e a s e s i t e i f f o l l o w e d by * (p <.05) o r ** (p <.01) a c c o r d i n g t o Duncan's New M u l t i p l e Range T e s t (LeClerge et^ a l . , 1962)  o ON  107 and White Lake O b s e r v a t o r y ) .  Seven out o f t h e f o u r t e e n d i f f u s e knapweed  p o p u l a t i o n s surveyed produced more seeds p e r p l o t than the r e l e a s e - s i t e p o p u l a t i o n , but the seed y i e l d on the remaining s i t e s d i d not d i f f e r  sig-  n i f i c a n t l y w i t h the r e l e a s e s i t e .  JJ. q u a d r i f a s c i a t a was found i n Vernon, Summerland and F a l k l a n d , the c l o s e s t of  these s i t e s b e i n g 60 km from the d i f f u s e knapweed r e l e a s e s i t e .  The f l i e s  on the P r i t c h a r d - 1 and Lumby s i t e s came from e a r l i e r r e l e a s e s made f o r o t h e r studies.  Seeds on the Westwold-2 s i t e , where JJ. q u a d r i f a s c i a t a g a l l s were found a t a d e n s i t y o f 0.1 - 0.1 per seed head, were s i g n i f i c a n t l y from the s p o t t e d knapweed r e l e a s e s i t e  (Table X X I I ) .  on the Westwold-1 s i t e d i d not d i f f e r s i g n i f i c a n t l y  lighter  than seeds  The mean seed weight from the r e l e a s e  site,  and seed weight o f the r e m a i n i n g two p o p u l a t i o n s i n the survey, a t Keremeos and W a l a c h i n , had s i g n i f i c a n t l y h e a v i e r seeds than the p o p u l a t i o n s on the release s i t e . significantly  The number o f seeds per seed head a t Walachin d i d not v a r y from the number o f seeds p e r head on the r e l e a s e s i t e , but on  a l l o t h e r s i t e s , t h e r e were more seeds per seed head than on the r e l e a s e site.  Similarily,  the number o f seed heads per p l o t , and t h e number o f  seeds p e r p l o t exceeded averages found f o r the s p o t t e d knapweed r e l e a s e on o n l y one and two s i t e s ,  Because o n l y ' w e l l - f i l l e d  site  respectively.  seeds were weighed  i t was assumed t h a t the average  seed weight was not a f f e c t e d by the o c c a s i o n a l g a l l found i n the seed head samples.  The average weight o f d i f f u s e knapweed r a n g e l a n d seed was 1.05 -  .03 mg, and t h e r e were an average o f 7.4 - .7 seeds per seed head, 240 - 46  108 seed heads per p l o t and 1853 - 447 seeds per p l o t . average seed weight was  1.7  - .1 mg,  For s p o t t e d knapweed the  and t h e r e were an average of 12 - 3  seeds per seed head, 54 - 19 seed heads per p l o t and 727 - 297 seeds per plot.  4.Discussion: There was  c o n s i d e r a b l e v a r i a t i o n i n the average number of seeds per seed  head and i n average seed weight between knapweed p o p u l a t i o n s .  Thus average  f l y d e n s i t i e s per head, which a r e a f f e c t e d by n e t seed weight per head, w i l l p r o b a b l y v a r y from one p o p u l a t i o n to another when the g a l l d i s p e r s e d throughout the I n t e r i o r . weight per head i s low w i l l  f l i e s have  Knapweed p o p u l a t i o n s where net seed  support lower average numbers of g a l l s per head  than knapweed w i t h many, heavy seeds per. head, because s m a l l e r heads, a r e more e a s i l y s u p e r p a r a s i t i z e d than l a r g e r ones . the  percentage of undeveloped and s u p e r p a r a s i t i z e d heads, and the r a t i o of  TJ. a f f i n i s net  It  Other phenomena, such as  to TJ. q u a d r i f a s c i a t a w i l l p r o b a b l y be a f f e c t e d by the changes i n  seed weight per head.  i s i n t e r e s t i n g to note t h a t , a l t h o u g h the g a l l  sities  f l i e s were a t peak den-  on r e l e a s e s i t e s i n 1977, o t h e r r a n g e l a n d p o p u l a t i o n s o f knapweed  w i t h none or o n l y a few f l i e s produced fewer or the same number of seeds per  seed head, and per p l o t .  T h i s i n d i c a t e s t h a t r e l e a s e - s i t e knapweed  p o p u l a t i o n s a r e v e r y f e r t i l e and a r e p r o b a b l y p r o d u c i n g seed f a r i n excess of may is  t h a t needed  f o r the maintenance  of the e x i s t i n g p o p u l a t i o n s .  Gall  flies  a f f e c t knapweed p o p u l a t i o n s o n l y a h a r s h s i t e s , where s u r p l u s of seed smaller.  109 V a r i a t i o n i n seed weight and y i e l d a r e a f f e c t e d by many f a c t o r s , p o o l e d under "the environment" by G o o d a l l (1970). fertility  could a f f e c t  seed y i e l d :  Harper  (1960) found t h a t  soil  i n l e s s f e r t i l e s o i l Papaver rhoeas  produced an average o f f o u r seeds p e r c a p s u l e and one c a p s u l e per p l a n t , but i n more f e r t i l e s o i l 2,000 seeds were produced per c a p s u l e and t h e r e were 400 c a p s u l e s per p l a n t . in per  S i m i l a r i l y , d i f f u s e and s p o t t e d knapweed, which grew  i r r i g a t e d p a s t u r e produced more seeds p e r seed head, and more seed heads p l a n t than knapweed growing on r a n g e l a n d (Watson, 1972).  may be a f f e c t e d by s e a s o n a l weather and by  defoliation  changes  Seed weights  (Harper, L o v e l l and Moore, 1970),  (Maun and Cavers, 1971a).  Where p l a n t s grow i n mixed  p o p u l a t i o n s , s t r e s s due t o i n t e r s p e c i f i c c o m p e t i t i o n a t the time when the seeds a r e " f i l l e d "  can a f f e c t  seed weight and number  (Harper, L o v e l l and  Moore, 1970).  The time o f h a r v e s t can a f f e c t average seed weight.  F o r example,  i f Rumex  c r i s p u s i s c o l l e c t e d e a r l y , average seed weight w i l l be h i g h e r than the r e a l averages f o r the p o p u l a t i o n because seeds, which mature f i r s t  are heavier  than l a t e - m a t u r i n g seeds (Maun and Cavers, 1971b).  D i f f u s e knapweed seed i n t h i s study appears t o be a f f e c t e d by g r a z i n g . Y e l l o w Lake g r a z i n g o c c u r r e d d u r i n g mid-summer flowering.  At  when- d i f f u s e knapweed was  A r e d u c t i o n i n the number o f heads p r o b a b l y r e s u l t e d i n an i n -  c r e a s e d s u p p l y o f n u t r i e n t s to seeds'which escaped d e s t r u c t i o n and were being f i l l e d ,  because averagerseed weight appeared to be very heavy.  still  On the  P r i t c h a r d - 2 s i t e g r a z i n g o c c u r r e d o n l y i n the s p r i n g , so t h a t o n l y the r o - .. s e t t e s were damaged, and p l a n t s , t h a t b o l t e d , produced and f i l l e d the  p l a n t s growing on the ungrazed P r i t c h a r d - 1  site.  seeds  like  ,  110  Because so many f a c t o r s may i n f l u e n c e seed weights and y i e l d s , e s t i m a t e s f o r t h e same s p e c i e s can be found i n the l i t e r a t u r e . Stevens  (1932) r e p o r t e d seed weights  f o r C i r s i u m arvense from  sources r a n g i n g from 0.900 t o 1.575 mg. of d i f f u s e  different F o r example, different  I n t h i s study, average seed  weights  (1.05 mg) and s p o t t e d (1.74) knapweed were s i m i l a r t o Watson's  (1972) e s t i m a t e s o f 1.10 mg and 1.78 mg f o r d i f f u s e and s p o t t e d knapweed. T h i s i n d i c a t e s t h a t the s p o t t e d knapweed c o n t r o l s i t e i n the p r e v i o u s section  ( I I B v i ) produced  e x c e p t i o n a l l y heavy seeds  t h a t u n l e s s the s p o t t e d ^ k n a p w e e d ' r e l e a s e - s i t e  seeds  (2.27 - .06 mg) and ' were a l s o h e a v i e r  than average, g a l l - f l i e s may be r e d u c i n g seed''weigHfi.'less- than e s t i m a t e d . Fewer seeds p e r d i f f u s e knapweed seed head than by Watson (1972; 12.5).  (7.36) were found i n t h i s  Watson (1972) a l s o found a l a r g e r v a l u e f o r  the average number o f s p o t t e d knapweed seeds p e r seed head t h i s study low  study  (26.6) than i n  (12.25), but the sample s i z e f o r s p o t t e d knapweed here,was , too  ( o n l y f o u r s i t e s ) t o c o n f i r m t h a t Watson's e s t i m a t e i s d e f i n i t e l y h i g h e r .  U. a f f i n i s was n o t found a t any new s i t e s where i t had not been p r e v i o u s l y r e l e a s e d , but U. q u a d r i f a s c i a t a was found a t s e v e r a l new l o c a t i o n s .  This  i n d i c a t e s t h a t IJ. q u a d r i f a s c i a t a d i s p e r s e s much f a s t e r than U_. a f f i n i s , and may be a b l e t o a t t a i n h i g h p o p u l a t i o n s i z e s b e f o r e U. a f f i n i s c a t c h e s up.  5.Conclusions: 1. Net  seed weight p e r seed head v a r i e s c o n s i d e r a b l y among rangeland knapweed  p o p u l a t i o n s because weight  t h e r e were s i g n i f i c a n t d i f f e r e n c e s i n average  seed  and average numbers of seeds p e r seed head among these p o p u l a t i o n s .  2."Average seed d e n s i t i e s p e r head and p e r u n i t a r e a f o r some rangeland popul a t i o n s were l e s s than o r e q u a l t o those on the d i f f u s e and s p o t t e d knap--- . -  -  Ill weed p o p u l a t i o n s on the r e l e a s e s i t e s i n 1977, a t peak g a l l - f l y  densities.  3.JJ. q u a d r i f a s c i a t a d i s p e r s e s f a s t e r than U_. a f f i n i s .  viii.  V a r i a t i o n i n seed weight and numbers i n a s p o t t e d knapweed p o p u l a t i o n :  1.Introduction In the p r e v i o u s of  s e c t i o n i t was shown t h a t seed weight and average numbers  seeds p e r seed head v a r i e d among rangeland  s p o t t e d knapweed.  p o p u l a t i o n s of d i f f u s e and  Here comparisons a r e made of average seed weights and  numbers of seeds p e r seed head among i n d i v i d u a l p l a n t s i n a s i n g l e knapweed p o p u l a t i o n , and between i n d i v i d u a l seed heads on s i n g l e knapweed  spotted  spotted  stalks.  2.Method: . T h i s study was made on a s p o t t e d knapweed rangeland i n 1976.  S i n g l e s t a l k s , a l l of which came from s e p a r a t e p l a n t s , were tagged  w h i l e the heads were s t i l l to  p o p u l a t i o n i n Westwold,  the n e a r e s t cm.  i n the bud s t a g e , and s t a l k h e i g h t s were measured  A mature seed head was d e f i n e d as one which had turned  y e l l o w and d r i e d , i n d i c a t i n g t h a t the v a s c u l a r t i s s u e had been b l o c k e d , and the seeds were r e c e i v i n g no a d d i t i o n a l n u t r i e n t s .  When the heads were h a r -  v e s t e d they were coded a c c o r d i n g to t h e i r p o s i t i o n on branches as i n s e c t i o n I I A i , and s t o r e d i n separate envelopes. v e s t e d , but a f t e r w a r d s  i t was found  heads on f i f t e e n of the s t a l k s . forty-five r e p l i c a t e s . counted. those  Heads on s i x t y s t a l k s were h a r -  t h a t U. q u a d r i f a s c i a t a had a t t a c k e d some  These s t a l k s were d i s c a r d e d , l e a v i n g o n l y  The seed heads were opened and v i a b l e seeds were  V i a b l e seeds were d e f i n e d as p r e v i o u s l y ( s e c t i o n I I B v i ) , as  seeds w i t h hard,  s h i n y , brown or b l a c k c o a t s .  V i a b l e seeds from each  seed head were weighed t o g e t h e r and d i v i d e d by the number o f seeds per head  112 for  an e s t i m a t e o f average seed weight per head.  3.Results: There was  a s i g n i f i c a n t d i f f e r e n c e i n average seed weight and average num-  b e r s of seeds per head.  U s u a l l y the seed head on the f i r s t  p r i m a r y branch,  which a l s o f l o w e r e d f i r s t , had the h i g h e s t seed count and the h e a v i e s t seeds for (a  the  stalk.  The r e s u l t s v a r i e d from 9 to 41 seeds per t e r m i n a l head  2 ^ - f o l d range) and from 0.93  to 2.57  mg  f o r seed weight  (a 3 k - f o l d r a n g e ) .  The average seed weight and numbers of seeds per seed head f o r heads  on  primary branches u s u a l l y decreased from the top to the bottom of the s t a l k , as d i d the o r d e r of f l o w e r i n g . of  F o r one t y p i c a l s t a l k , the average numbers  seeds per head were 20, 20, 18, and 17 f o r I , I I , I I I and IV head  t i o n s , and average seed weights were 1.87, tively.  However t h e r e were e x c e p t i o n s .  1.76,  1.61  and 1.38 mg, r e s p e c -  On another s t a l k the number of seeds  per  seed head decreased w i t h i n c r e a s i n g o r d e r of f l o w e r i n g  for  heads  1.47  If  (24, 19, and  i n I , I I and I I I p o s i t i o n s ) , but seed weight was v a r i a b l e  and 1.77  mg  posi-  f o r heads i n I , I I and I I I p o s i t i o n s ,  heads i n t e r m i n a l p o s i t i o n s on the f i r s t  11  (1.52,  respectively).  f o u r p r i m a r y branches a r e con-  s i d e r e d to be be i n d i s t a l p o s i t i o n s , whereas any head on a secondary branch i s i n a p r o x i m a l p o s i t i o n , then d i s t a l heads appeared to have g r e a t e r numbers of  seeds per seed head  (26.3 - 6) than those heads i n p r o x i m a l p o s i t i o n s  (19 - 1). A l t h o u g h t h i s d i f f e r e n c e was if  sample  larger. heads  not s i g n i f i c a n t , i t might have been  s i z e f o r p r o x i m a l heads which reached m a t u r i t y  (N = 14) had  The r e a s o n f o r the s m a l l proximal-head sample s i z e was  i n t h i s class aborted.  seed weight was  been  t h a t many  And, a l t h o u g h t h e r e were e x c e p t i o n s , average  h i g h e r i n d i s t a l than i n p r o x i m a l heads.  The end  result  4oH  X , 1  X  X  30' X  x  X  x  x  x  x  X  x  X X  x, x  2 0 H  x  X x x  10  x  x  H  10 Figure 23.  —r—  20  —i— 30  — I  40 50 STALK HEIGHT (CM)  60  70  80  C o r r e l a t i o n between the number of seeds per terminal seed head and s t a l k height f spotted knapweed. (r = .39; s i g n i f i c a n t at 43 D.F.)  114 was  t h a t net seed weight was  t h i s was  g r e a t e r i n d i s t a l than p r o x i m a l heads, and  o f t e n v i s u a l l y apparent  by the s m a l l e r seed-head s i z e f o r p r o x i m a l  than f o r d i s t a l heads.  There was  a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between the mean number of  seeds per seed head w i t h s t a l k h e i g h t when o n l y f i r s t - f l o w e r i n g seed heads i n p o s i t i o n I were c o n s i d e r e d .  But, the c o r r e l a t i o n c o e f f i c i e n t was  (0.39) i n d i c a t i n g o n l y a weak r e l a t i o n s h i p nificant  c o r r e l a t i o n between s t a l k h e i g h t and average  heads (r = 0.26;  N = 45).  (r = .51, N = 45) was per head  ( F i g u r e 23).  There was  no  low sig-  seed weight i n t e r m i n a l  However, a s i g n i f i c a n t c o r r e l a t i o n c o e f f i c i e n t  o b t a i n e d between s t a l k h e i g h t and net seed weight  (numbers of seeds per head X average  weight per  seed).  4.Discussion: The  food r e s o u r c e f o r g a l l f l i e s ,  i n the form of o v a r i o l e  tissue,  varies  among i n d i v i d u a l s t a l k s i n a s p o t t e d knapweed p o p u l a t i o n , as w e l l as w i t h the o r d e r of f l o w e r i n g and head p o s i t i o n on i n d i v i d u a l s t a l k s .  Because a l l  e x p e r i m e n t a l s t a l k s were from d i f f e r e n t p l a n t s , t h i s v a r i a t i o n p r o b a b l y o c c u r s among p l a n t s . in  The number of g a l l s and mature seeds which can  s p o t t e d knapweed heads p r o b a b l y depends to some e x t e n t on the net  weight,  as d i s c u s s e d p r e v i o u s l y .  a r e caged w i t h f l i e s on seed r e d u c t i o n . tions  develop seed  Thus g r e a t c a r e must be taken when s t a l k s  f o r the purpose of d e t e r m i n i n g the e f f e c t of f l y a t t a c k Storey  (1976) had  to c a l c u l a t e  s e p a r a t e r e g r e s s i o n equa-  f o r each of t h r e e , s e p a r a t e l y - c a g e d s t a l k s w i t h JJ. a f f i n i s i n o r d e r  to determine yield.  _-  the e f f e c t of i n c r e a s i n g  He found  21.36, 26.10  and  g a l l numbers on s p o t t e d knapweed seed  t h a t when t h e r e were no g a l l s , t h e r e were  respectively  28.07 seeds per seed head f o r the t h r e e r e p l i c a t e s .  He  115 a l s o found t h a t t h e r e was heads produced  by each  a great v a r i a b i l i t y  i n the t o t a l number of seed  replicate.  The average number of seeds per head and net seed weight p o s i t i o n s p r o b a b l y i n c r e a s e s w i t h p l a n t h e i g h t because appear  to be produced  first  to ensure s e e d - f i l l i n g  weather c o n d i t i o n s s e t i n .  energy  stalks  Net seed  weight  flows i n t o heads which  f o r a t l e a s t some heads i n case adverse  Heads i n p r o x i m a l p o s i t i o n s u s u a l l y have lower  seed weights p r o b a b l y because  little  energy  is left  by the time t h e i r t u r n comes f o r development. undeveloped.  the t a l l e r  by l a r g e r , more v i g o r o u s r o s e t t e s .  decreases w i t h the o r d e r of f l o w e r i n g because appear  f o r t e r m i n a l head  L a r g e r heads produced  f o r sexual reproduction  O f t e n p r o x i m a l heads  remain  by knapweed e a r l i e r i n the growing  son g i v e f i r s t - g e n e r a t i o n g a l l f l i e s an advantage  sea-  over s e c o n d - g e n e r a t i o n  flies.  O v a r i o l e number, as w e l l as o v a r i o l e s i z e , i s p r o b a b l y c o n t r o l l e d by g e n e t i c f a c t o r s as w e l l as by e n v i r o n m e n t a l c o n d i t i o n s , hence the e x c e p t i o n s to the above p a t t e r n s of seed weight  and number.  Harper, L o v e l l and Moore (1970)  found t h a t p l a n t s w i t h a d e t e r m i n a t e type of growth p a t t e r n have a g r e a t e r v a r i a t i o n i n seed s i z e than those p l a n t s w i t h i n d e t e r m i n a t e growth  forms.  A l s o s p e c i e s which f l o w e r more s y n c h r o n o u s l y have a g r e a t e r v a r i a t i o n i n seed weight  than s p e c i e s which f l o w e r c o n t i n u o u s l y .  Both d i f f u s e and s p o t t e d  knapweed are d e t e r m i n a t e , but v a r i a t i o n i n seed weight  among heads i n a  d i f f u s e knapweed p l a n t would p r o b a b l y be l e s s than i n a s p o t t e d knapweed p l a n t because  s p o t t e d knapweed has a s h o r t , c o n c e n t r a t e d p e r i o d of f l o w e r i n g  compared to d i f f u s e knapweed.  Harper, L o v e l l and Moore (1970) c i t e d  numerous examples of v a r i a t i o n i n seed s i z e w i t h i n p l a n t s .  They found  t h a t i n some cases the h e a v i e r seeds are shed l a t e r , germinate  later  and  116 produce  l a r g e r c o t y l e d o n s than t h e l i g h t e r  can a l t e r many seed p r o p e r t i e s  seeds.  Biological control  agents  (Cavers, 1971), but i n o r d e r t o determine  those a f f e c t e d , normal d i s t r i b u t i o n p a t t e r n s of these a t t r i b u t e s f o r i n d i v i d u a l p l a n t types must be found, o r e l s e sample sizes:must be v e r y l a r g e .  5.Conclusions: l.Seed weight and number o f seeds per seed head v a r y among i n d i v i d u a l s p o t t e d knapweed p l a n t s i n a p o p u l a t i o n , and w i t h head p o s i t i o n and o r d e r o f f l o w e r i n g on i n d i v i d u a l  stalks.  2. T a l l e r s p o t t e d knapweed s t a l k s u s u a l l y produce more seeds per head and h e a v i e r seeds  i n t e r m i n a l heads than do s h o r t e r  3. D i s t a l heads appear head  ix.  stalks.  t o produce h e a v i e r and more numerous seeds per seed  than do p r o x i m a l heads.  E f f e c t of g a l l f l i e s  on knapweed seed number on the r e l e a s e s i t e s  from  1975 t o 1977: 1.Introduction: T h i s i s a study o f the e f f e c t s o f U_. a f f i n i s and TJ. q u a d r i f a s c i a t a on the seed y i e l d s o f d i f f u s e and s p o t t e d knapweed p o p u l a t i o n s on the r e l e a s e  sites  from 1975 t o 1977.  2.Method: In  1975 and 1977 a 50 X 50 cm square was thrown a t random on t h e d i f f u s e and  s p o t t e d knapweed r e l e a s e s i t e s and a l l the heads w i t h i n the square were h a r v e s t e d a t the end o f the growing  season.  I n 1975 t h e r e were f o u r  replicates  and i n 1977 t h e r e were f i v e . - ' Numbers o f heads i n seed, s u p e r p a r a s i t i z e d and undeveloped  stages were counted.  Samples o f a t l e a s t f i f t y undehisced seed  117 heads, chosen a t random from the c o l l e c t e d heads, were opened, and the v i a b l e seeds  (defined  fasciata.  as p r e v i o u s l y )  were counted, as were JJ. a f f i n i s and JJ. q u a d r i -  S t e r i l e heads, i . e . , those heads which f l o w e r e d , but produced no  seed and were u n a t t a c k e d , were counted as "seed heads" w i t h n i l seeds. 1976 numbers o f seed heads were e s t i m a t e d by m u l t i p l y i n g  In  the mean number o f  s t a l k s p e r 50 X 50 cm p l o t by the mean number o f seed heads p e r s t a l k . Counts of seeds and g a l l s p e r seed head were o b t a i n e d from p l a n t m a t e r i a l f o r the study o f g a l l - f l y d e n s i t i e s on r e l e a s e assumptions were made i n e s t i m a t i n g be a t t r i b u t e d t o g a l l f l i e s : not  collected  sites (section I I B i i ) .  the percentage o f seed l o s s which  Two could  the average number o f t o t a l heads p e r p l o t was  a f f e c t e d by g a l l - f l y a t t a c k ,  and the expected percentage of undeveloped  heads was the average f o r knapweed growing on r a n g e l a n d i n 1977, where t h e r e were no f l i e s ,  found t o be 14 - 3% and 30 - 1% f o r d i f f u s e and s p o t t e d  weed, r e s p e c t i v e l y  (section I I B i v ) .  p l o t was found by s u b t r a c t i n g the  knap-  The expected number o f seed heads p e r  the expected number o f undeveloped heads  t o t a l number o f seed heads + s u p e r p a r a s i t i z e d  heads + undeveloped  from  heads.  The expected number o f seeds p e r seed head was found by a r b i t r a r i l y c o l l e c t i n g undehisced seed heads on nearby c o n t r o l s i t e s i n 1977 and 1975, o n l y , f o r diffuse  (Pritchard)  and s p o t t e d  (Chase) knapweed, r e s p e c t i v e l y .  Preliminary  work had i n d i c a t e d t h a t average numbers o f seeds p e r seed head were s i m i l a r i n u n a t t a c k e d heads. -  G a l l f l i e s on c o n t r o l s i t e s were a t low d e n s i t i e s (0.07  .02 and 0.21 - .03 JJ. a f f i n i s g a l l s p e r seed head on d i f f u s e and s p o t t e d  knapweed, r e s p e c t i v e l y , and 0.14 - .03 and 0 . 0 5 - .01 JJ_. q u a d r i f a s c i a t a g a l l s per  seed head on d i f f u s e and s p o t t e d  containing per  knapweed, r e s p e c t i v e l y ) .  Any seed heads  g a l l s were not used i n t h e - e s t i m a t e s o f expected numbers o f seeds  seed head, and these e s t i m a t e s were used i n a n a l y s i s  I t was assumed t h a t i n u n a t t a c k e d heads.  from 1975 t o 1977.  the few heads t h a t were g a l l e d d i d not a f f e c t seed counts The a c t u a l and ex-  118 p e c t e d seed y i e l d s per p l o t were c a l c u l a t e d by m u l t i p l y i n g  the a c t u a l and  expected number o f seed heads per p l o t by the a c t u a l and expected number of seeds per seed head, r e s p e c t i v e l y . i s defined  The "percentage r e d u c t i o n  here as the (expected number of seeds per p l o t —  i n seed  yield"  the a c t u a l  number  of seeds p l o t ) / (the expected number o f seeds per p l o t ) X 100%.  U. q u a d r i f a s c i a t a was d e t e c t e d i n Vernon JJ. a f f i n i s .  i n 1976, i n a p o p u l a t i o n  without  Branch samples were a r b i t r a r i l y c o l l e c t e d from the same d i f f u s e  knapweed p o p u l a t i o n  i n 1977 and 1979, and t h e seed heads were opened, and  g a l l s and v i a b l e seeds were counted.  3.Results: On the a v e r a g e - 1 0 V 7 - . 0.3 and 25.3 T 0; 4-seeds-per  seed Ahead we're found on  the d i f f u s e and spotted" knapweed c o n t r o l s i t e s , r e s p e c t i v e l y . t h a t i n 1971, b e f o r e the f l i e s were r e l e a s e d f l y numbers were s t i l l release  Assuming  on d i f f u s e knapweed, and when  low a t Chase, the numbers o f seeds per head on t h e  s i t e s were the same as on the c o n t r o l s i t e s , t h e r e was a s i g n i f i c a n t  decrease i n t h e mean number o f seeds per 'seed head both r e l e a s e  s i t e s ( F i g . 24).  The s l o p e  from 1971 t o 1977 on  o f the r e g r e s s i o n  f i c a n t l y l e s s f o r d i f f u s e (-1.28) than f o r s p o t t e d c a t i n g that on s p o t t e d  the r a t e  l i n e was  signi-  (-2.80) knapweed,  o f decrease i n seed numbers per seed head was  than on d i f f u s e knapweed.  shown t h a t d e n s i t i e s o f U. a f f i n i s  Previously  indigreater  ( s e c t i o n I I B i i ) i t was  f i r s t - i n s t a r larvae  c a n t l y from 1975 t o 1977 on both d i f f u s e and s p o t t e d  increased  signifi-  knapweed r e l e a s e  sites.  From 1975 to 1977 t h e r e was a s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n between the mean number o f U. a f f i n i s of seeds per seed head  first-instar  f o r spotted  l a r v a e per head and the mean number  knapweed ' ( F i g . 26), but t h i s r e l a t i o n s h i p  00  c  ro  611  AVERAGE NUMBER OF SEEDS PER SEED HEAD  H-  TO 3 K (D  <  ^ •  iVd  CD 3 H* fu  Hi fD fo H- CL CL  OJ  -4 XI  o pa Hi fD 1 Hi t-j hHi ;<=i co c & • rt  X to  . PL XI H- fD  rn 73  I CD fD fD CO Co O V_O CL Hi 3 Hi CO vo IV N> 3 CO H- 3* •3 < • • " » •' 3 H-  1  H-  O  3  X)  3 C  1  CL H- T) CO cr p- Hi fD fD H- rt H C 3 CO fD fD fD 3 Co  O fD rt rt  s!  fD fD  fD CL  CD H- CD TO fD 3 fD H- CL Hi CD H-  3  rt  3* fD  o i3 CO fD 3 H  3  fD CO  3 3 3 3  co Co fD rt fD CL  fD cr H fD  13 TO 3 s: 3* H- fD fD  PER HEAD N3  N3 Ul  3* Hi 1— fD H- CU 3 rt  cr fD rt  LARVAE  fD  K3  fD H g HfD CO CO p fD 3 Hi fD HCu 3 1-1 D 3 C 3* S rt fD o - 1 CO fD H* CL l-t 3 CD • O rt to s s Hi H H CD II X) M 1 O Co • rt VO rt VO fD CO CL fD  FIRST-INSTAR  H  ON CD Ci n fD 3 o (D CL H CL fu i-i CO rt Hi fD  X NUMBER O F U. A F F I N I S  TO 3  • CO HJ  o Hi  CL  3 3  i fD H  o Hi  . tO  IX)  m m o  1  to  •u m to  m m o  rt  3* fD  x ^°  zz  3  fD CO  3 3  C  §• fD H  O  CO  3  rt  X NUMBER  OF U. A F F I N I S F I R S T - I N S T A R  Co rt  _JL_  H-  1  LARVAE  to i  PER HEAD  -P-  Ul  I  a  ^—  X  o  -i XtO cn  X  ho  o  031  -«  vO  121 was not s i g n i f i c a n t f o r d i f f u s e knapweed  ( F i g . 25).  However t h e c o r r e l a t i o n  c o e f f i c i e n t on d i f f u s e knapweed was h i g h (-.992), i n d i c a t i n g t h a t T J .  affinis  p r o b a b l y does decrease average numbers o f seeds per seed head._ on t h i s  site  as w e l l . TJ.  There was no s i g n i f i c a n t  quadrifasciata  first-instar  per seed head on e i t h e r  In  c o r r e l a t i o n between t h e mean number o f  l a r v a e per head and t h e mean number o f seeds  site.  1976 f o r d i f f u s e , and by 1977 f o r s p o t t e d knapweed, seed y i e l d had de-  c r e a s e d t o 80% o f the expected y i e l d , but i n 1977 about  800 t o 900 d i f f u s e ,  and 500 t o 600 s p o t t e d knapweed seeds were s t i l l b e i n g produced per p l o t (Table X X I I I ) .  From 1975 to 1977 the number o f t o t a l heads and seed heads  produced per p l o t on t h e s p o t t e d knapweed r e l e a s e s i t e d e c l i n e d , but on the  d i f f u s e knapweed r e l e a s e s i t e head numbers were lowest i n 1976.  For  a l l y e a r s the mean number o f seeds per seed head d e c r e a s e d  w i t h i n c r e a s i n g d e n s i t i e s o f U. a f f i n i s g a l l s per seed head on the d i f f u s e and s p o t t e d knapweed r e l e a s e s i t e s . seed head v a r i e d c o n s i d e r a b l y on both s i t e s . counts were s t i l l  significantly  ( F i g s . 27 t o 32)  Numbers o f seeds per  F o r example, i n 1975, when g a l l '  low, t h e r e were as few as-one and as many as twenty-four  seeds i n u n a t t a c k e d d i f f u s e knapweed heads, and t h e r e was was a range o f seven t o t h i r t y - o n e seeds i n u n a t t a c k e d s p o t t e d knapweed heads. t h e r e was g r e a t v a r i a t i o n i n . t h e r a t i o of seeds produced w i t h i n one seed head. one six  Similarily,  t o numbers o f g a l l s  I n 1977 some d i f f u s e knapweed seed heads c o n t a i n e d o n l y  TJ. a f f i n i s g a l l , but produced no seed, but one seed head was found w i t h JJ.  a f f i n i s g a l l s and e l e v e n seeds.  On s p o t t e d knapweed i n 1977, a seed  head was found w i t h one g a l l and no seeds, but another was found f o u r t e e n g a l l s and two seeds.  containing  Table XXIII.  knapweed  year  Expected arid a c t u a l seed y i e l d s per p l o t on d i f f u s e and s p o t t e d knapweed r e l e a s e and the estimated r e d u c t i o n i n y i e l d from 1975 t o 1977 t o t a l number of heads counted  A*  •. a c t u a l number o f seed heads  actual-number of. seeds per seed head  V actual number o f seeds-  % reduction i n seed-, yield  5.37 - .03  2857 - 828  51%  /;  •cu,.  1975  651 - 175  560 - 270  5832 - 2970  532 - 149  ffu  expected number o f seeds  1976  299 - 29  257 - 128  2754 - 1455  140 - 36  4.1 ± .5  574 - 219  81  1977  537 - 126  462 - 45  4941  230 - 47  3.2 -  852 - 287  83  13  1975  306 - 22  256 - 21  6482 - 633  251 - 28  17.8 - .3  4468 - 13  31  tte  1  A  expected number o f seed heads  sites,  1976  275 - 43  192 - 32  4869 - 881  180 - 26  11.8 - .9  2124 - 459  56  ods  1977  170 - 42  119 - 31  3011  68 - 14  7.8 ± .9  530 - 32  82  CD  •H 13  -  - 2322  - 813  +  .3  p l o t s i z e wass50 X 50 cm A  +  assumption: AA  the % aborted heads o f the t o t a l heads produced and 30 - 1% f o r s p o t t e d knapweed (Table XVI) _  assumption:  +  =14-3%  f o r d i f f u s e knapweed (Table XIV) +  ;the x number o f seeds p e r seed head = 10.7 - .3 f o r d i f f u s e and 25.3 - .4 f o r s p o t t e d knapweed (see t e x t f o r source o f data)  NUMBER OF SEEDS PER SEED HEAD cn  >< x  xte*  oo  I—'  o  I—'  ho  I—'  00 1  -F"  7 ^ ^ g# x xx xx *  *  O  _1_  to to  _J  X-  X X  a* * a *  X X  NUMBER OF SEEDS PER SEED HEAD  to 00 c l-(  fD to 00 h- cr W fD Hi fu Hi ON Cu fD • O o rt 3 —s O CO rt Hi H- Cr 00 fD a 3 1  1  H- Cu Hi Hn fa 3 rt  HHi Hi C co fD  i-i 7T fD 3 oo fo i-i T) fD s! CO fD CO fD  fo Hi Hi H3 Hcn O 3  cn fD fD  H- Cu Cu o 3  i-i 3 fD C fu H 3 rt fD cr fu fD u> CO ON fD cn  a • •  cn T3 H" fD rt H fD cn H- fD 3 fD  Cu  £31  cn  _L_  (-> CO  _]  to o  L_  to to  _L_  to 4^  J  18 o 16 -k  I UJ LU  *  12 +  g  10 +  LU CL  X  UJ LU CO  u_ o LU CD  *x  "*x  tx  X,  3  H  5  X  6  10  NUMBER OF U. A F F I N I S G A L L S PER SEED HEAD  F i g u r e 29.  E f f e c t of U. a f f i n i s on seed numbers p e r seed.head on t h e d i f f u s e knapweed r e l e a s e s i t e i n 1977 ( s i g n i f i c a n t r e g r e s s i o n a t 151 D.F.) Symbols f o r number o f d a t a p o i n t s : X 10 p o i n t s ; X 5 points; x 1 point.  hho 1  4>-  125  35n X X  30H x  x  GXX  X  EX c  CX  2?X X X  X  XX X X  25'1?*xx  X X X  Pxxxxxxx  r ~ xx k x xxx xx 1 x Q UJ UJ CO OL  kxxx X  3x  J 2 0  "F xx K  x  X x  X  x  X  X X  X  xx  UJ  D_ U~l  Q UJ UJ to U_ O  ( XX bcX Xx 15-i  X  x xxxxx:  OC.XX X X X XX  X cxxxxxx X c xxx X x xxxx  C£  C  UJ  CD  x  X XXXx x  10' XX  X  X  x  X X K X  x  XX X  X  X  4  30.  8  10  12  14  —r-  16 1 20 16 NUMBER OF U. AFFINIS GALLS PER SEED HEAD Figure  6  —r  -  22  i 24  E f f e c t o f IJ. a f f i n i s on seed numbers p e r seed head on t h e s p o t t e d knapweed r e l e a s e s i t e i n 1975 ( s i g n i f i c a n t r e g r e s s i o n a t 252 D.F.) Symbols f o r number o f d a t a p o i n t s : X 5 points; x 1 point  126 x  35H X X  X  3CH X X X  X X  25  *  X  X  X  X  XX  X  X X X X Q LU LU CO  XX  20  CL LU O.  CO Q LU LU CO  15  H  CL LU CD  io  H  X XX  XX X  X X  X  5  X  X  X  X  X  X  XX  H X X XX  X  X X 4  6  8  10  12  14  16  18  20  22  24  NUMBER OF U. AFFINIS GALLS PER SEED HEAD Figure  31.  E f f e c t o f JJ. a f f i n i s on seed numbers p e r seed head on t h e s p o t t e d knapweed r e l e a s e s i t e i n 1976 ( s i g n i f i c a n t r e g r e s s i o n a t 113 D.F.) Symbols f o r number o f d a t a p o i n t s : X 5 points; x 1 point  127  35'  30i  25-  Q  20H  UJ UJ  If)  xx  OL UJ  X  CL  I/J  Q UJ UJ  X  15'  X  I/O  U_ O  X  ry  X  UJ CO  X  X  10H  x  ^  v  y y y v y VTrffy  4  6  8  -y YY  10  y ^  12  14  16  18  20  ~22~  —i  NUMBER OF U. AFFINIS GALLS PER SEED HEAD Figure  32.  E f f e c t o f JJ. a f f i n i s on seed numbers p e r seed head on t h e s p o t t e d knapweed r e l e a s e s i t e i n 1977 ( s i g n i f i c a n t r e g r e s s i o n a t 65 D.F.)  24  128 The percentage of seed heads a t t a c k e d per sample decreased from 1975 to 1977 on the d i f f u s e knapweed r e l e a s e s i t e  (41%, 18% and 11% f o r 1975, 1976  and 1977, r e s p e c t i v e l y ) and decreased from 1975 to 1976 on the s p o t t e d knapweed r e l e a s e s i t e  (22% and 2%, r e s p e c t i v e l y ) and remained  knapweed i n 1977 (4%) .  low on s p o t t e d  The maximum number of U_. a f f i n i s g a l l s per seed head  i n c r e a s e d on both r e l e a s e s i t e s from 1975 t o 1977:  from f o u r to n i n e on  d i f f u s e knapweed, and from n i n e to e i g h t e e n on s p o t t e d knapweed.  Y-inter-  c e p t s on d i f f u s e and s p o t t e d knapweed r e g r e s s i o n s of numbers o f seeds per seed head on numbers of TJ. a f f i n i s g a l l s per seed head were g r e a t e r i n 1975 (7.2 - .3 and 19.7 - .7 f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t i v e l y ) than i n 1977 (4.5 - .4 and 9.2 - .2 f o r d i f f u s e and s p o t t e d knapweed, r e s p e c t tively),  i n d i c a t i n g t h a t numbers of seeds i n u n a t t a c k e d heads d e c l i n e d  1975 to 1977 on both  from  sites.  When o n l y those heads c o n t a i n i n g U. q u a d r i f a s c i a t a and unattacked seed heads a r e c o n s i d e r e d , t h e r e was a s i g n i f i c a n t decrease i n numbers o f seeds per seed head w i t h i n c r e a s i n g numbers of TJ. q u a d r i f a s c i a t a g a l l s p e r seed head i n 1977 on the d i f f u s e knapweed r e l e a s e s i t e r e g r e s s i o n l i n e was s i g n i f i c a n t l y l e s s knapweed i n the same year quadrifasciata  ( F i g . 33).  The s l o p e of the  (-1.37) than f o r U. a f f i n i s on d i f f u s e  (-0.87), but the Y - i n t e r c e p t was h i g h e r f o r U_.  (7.67) than f o r U. a f f i n i s  (4.54).  Average numbers of U. q u a d r i f a s c i a t a g a l l s per seed head i n 1977 on the Vernon s i t e  (0.5 - .2) d i d not v a r y s i g n i f i c a n t l y w i t h the average  count  i n 1979 (0.46 - .06), but the mean number of seeds per seed head i n unatt a c k e d heads was s i g n i f i c a n t l y l e s s i n 1979 (7.5 - .4) than i n 1977 (12 1).  There appeared  to be a decrease i n numbers of seeds per seed head w i t h  i n c r e a s i n g d e n s i t i e s of U. q uadr i f as c i a t a  i n Vernon i n 1977 ( F i g . 34), but  T  22  lex c 20-5C  15H x  Q UJ UJ  184f x 16-f  Kx 10 +  14  00 ry  UJ  a.  12.^x  oo a UJ UJ  00  x  5 + 8-&  UJ CO  XX  X  h~ ex NUMBER OF U. QUADRIFASCIATA GALLS PER SEED HEAD  2-< X  F i g u r e 33,  E f f e c t of U. q u a d r i f a s c i a t a on numbers of seeds per seed head on the d i f f u s e knapweed r e l e a s e s i t e i n 1977 ( s i g n i f i c a n t r e g r e s s i o n a t 32 D.F.) F i g u r e 34.  NUMBER ..OF U . QUADR IFASCI ATA GALLS PER SEED HEAD E f f e c t o f U. q u a d r i f a s c i a t a on d i f f u s e knapweed seed numbers p e r seed head i n Vernon,. 1977 (no s i g n i f i c a n t r e g r e s s i o n )  K3 VO  130  17 4CX 16  154c 14-KX  12 ir-kxx  Q UJ UJ  ioi<  x  00 oc UJ  0_  00  8+  x  Q UJ UJ  00 DC UJ  co  1  2  3  NUMBER OF U. OUADRIFASCIATA GAULS PER SEED HEAD F i g u r e 35.  E f f e c t o f U. q u a d r i f a s c i a t a on d i f f u s e knapweed seed numbers p e r seed head i n Vernon, 1979. ( s i g n i f i c a n t r e g r e s s i o n a t 146 D.F.) Symbols f o r number o f d a t a p o i n t s : X 10 p o i n t s ; X 5 p o i n t s ; and x 1 point.  131 the sample s i z e was  s m a l l (40 h e a d s ) , so t h e r e g r e s s i o n was not  However, i n 1979, when sample r e l a t i o n s h i p was  significant  unattacked seed heads was  s i z e was  i n c r e a s e d to 148 heads, the same  ( F i g . 35).  V a r i a t i o n i n numbers of seeds per  g r e a t i n both y e a r s :  as two and as many as twenty-two  significant.  i n 1977  t h e r e were as  seeds per seed head, and i n 1979  few  the v a r -  i a t i o n ranged from one to seventeen seeds per seed head.  4.Discussion: The d e c r e a s e i n average numbers of seeds per seed head from 1975 as average numbers of f i r s t - i n s t a r IJ. a f f i n i s l a r v a e p e r head may  1977  increased  be a t t r i b u t e d to an e f f e c t on d i f f u s e and s p o t t e d knapweed by t h i s  f l y species. 1975  to  to 1977  gall-  E v i d e n c e f o r an average r e d u c t i o n i n seeds per seed head  from  i s t h a t f o r each year numbers of seeds per seed head decreased  w i t h i n c r e a s i n g number-s-of  JJ. a f f i n i s g a l l s per seed head. U.  a l s o reduces average seed numbers, but i t s e f f e c t  quadrifasciata  i s minimal compared w i t h  TJ. a f f i n i s , because o f lower numbers of JJ. q u a d r i f a s c i a t a and because JJ. q u a d r i f a s c i a t a l a r v a e a r e s m a l l e r and form t h i n n e r g a l l s , thereby u s i n g p l a n t r e s e r v e s than do JJ. a f f i n i s l a r v a e .  less  At d e n s i t i e s o f f i v e or more g a l l s  f o r e i t h e r s p e c i e s , few seeds escaped d e s t r u c t i o n , but a t lower g a l l  densities  more seeds escaped in^'heads w i t h TJ. q u a d r i f a s c i a t a than w i t h JJ. a f f i n i s . T h i s may  e x p l a i n why  w i t h JJ. a f f i n i s  the a b s o l u t e  s l o p e o f the r e g r e s s i o n l i n e was  less  than w i t h JJ. q u a d r i f a s c i a t a on d i f f u s e knapweed i n 1977.  Harris  (1980b) found t h a t on d i f f u s e knapweed JJ. a f f i n i s d e s t r o y e d an average  of 2.4  seeds f o r every g a l l and JJ. q u a d r i f a s c i a t a reduced y i e l d by an average  of 1.9  seeds f o r every g a l l , and on s p o t t e d knapweed JJ. a f f i n i s reduced y i e l d  by 1.1  seeds per g a l l .  The e a r l i e r assumption t h a t d i f f u s e and s p o t t e d knap-  132 weed heads a r e s u p e r p a r a s i t i z e d l a r v a e per head, r e s p e c t i v e l y 1977,  a t an average o f f o u r and e i g h t JJ. a f f i n i s  ( s e c t i o n I I B i i ) appears v a l i d , because i n  when head s u p e r p a r a s i t i z a t i o n was most s e v e r e , few seeds were produced  at h i g h e r TJ... a f f i n i s " d e n s i t i e s than those e s t i m a t e d f o r s u p e r p a r a s i t i z e d 1  v  .  heads.  T h i s study supports the t h e o r y t h a t g a l l s a c t l i k e s i n k s , u t i l i z i n g reserves located.  energy  from o t h e r p a r t s o f the p l a n t o t h e r than i n heads were the g a l l s a r e As f l y d e n s i t i e s i n heads on both r e l e a s e s i t e s i n c r e a s e d ,  seed numbers i n u n a t t a c k e d heads d e c r e a s e d .  P o s s i b l y competition  average  f o r nu-<  t r i e n t s a l s o e x i s t s among heads w i t h g a l l s , and heads w i t h IJ. a f f i n i s  may  be r o b b i n g energy from heads w i t h JJ. q u a d r i f a s c i a t a , as w e l l as from unat-tacked heads.  This  could  create  error i n estimating  t h e a c t u a l e f f e c t JJ.  q u a d r i f a s c i a t a had on seed y i e l d on the d i f f u s e knapweed r e l e a s e  site.  How-  ever a s i g n i f i c a n t r e g r e s s i o n was o b t a i n e d i n Vernon, where JJ. q u a d r i f a s c i a t a occurred cept  As  a l o n e , the e f f e c t appears t o be much the same as f o r JJ_. a f f i n i s ex-  t h a t i t i s not as s e v e r e .  i n p r e v i o u s s e c t i o n s , t h i s study shows the g r e a t v a r i a t i o n i n c a r r y i n g  c a p a c i t i e s among knapweed heads f o r g a l l - f l y a t t a c k . only  Some heads support not  l a r g e numbers o f g a l l s and a l s o produce v i a b l e seeds, but o t h e r heads  y i e l d no seed even though t h e r e may be o n l y one o r two g a l l s i n them. t h i s v a r i a t i o n sample s i z e s had be l a r g e t o show any e f f e c t on seed by  the f l i e s .  I t i s p r o b a b l e t h a t the r e g r e s s i o n  e q u a t i o n o f JJ.  Due to-  reduction  quadrifasT..  c i a t a on d i f f u s e knapweed on t h e Vernon s i t e i n 1977 would have been s i g n i f i c a n t had more than 40 seed heads been  dissected.  E n v i r o n m e n t a l c o n d i t i o n s may a l s o a f f e c t seed head.  the average number of seeds per  T h i s i s w e l l - i l l u s t r a t e d by the s i t u a t i o n i n Vernon, where a v e r -  age IJ. q u a d r i f a s c i a t a counts p e r seed head were the same i n 1977 and 1979, but average numbers of seeds per seed head were lower i n 1979 than i n 1977. T h e r e f o r e fewer g a l l f l i e s head s i z e s a r e s m a l l .  c o u l d reduce seed y i e l d  to n i l i n y e a r s when  However, from 1975 to 1977, when samples were taken on  r e l e a s e s i t e s , head s i z e s on c o n t r o l s i t e s d i d not appear to v a r y .  There-  f o r the r e a s o n f o r the r e d u c t i o n i n seed y i e l d on the r e l e a s e s i t e s from 1975 to 1977 was p r o b a b l y due to f l y a t t a c k a l o n e .  Seed head numbers c o u l d have i n c r e a s e d from 1976 to 1977 on the d i f f u s e knapweed r e l e a s e s i t e because of the apparent r e s u r g e n c e i n head p r o d u c t i o n i n the growing season o f 1977 ( s e c t i o n I I B i v ) .  Harris  late  (1980b) a t t r i b u t e d  the d e c l i n e i n average numbers o f heads on t h e s p o t t e d knapweed r e l e a s e  site  to e n v i r o n m e n t a l c o n d i t i o n s .  Wadsworth (1914) found t h a t U_. s o l s t i t i a l i s  ( i . e . , U. j a c e a n a ; V a r l e y , 1947)  reduced the seed y i e l d o f C. n i g r a  ( i . e . , C_. n e m o r a l i s ; V a r l e y , 1947) by  50% of the expected y i e l d , and f e l t  t h a t i f t h i s f l y were encouraged to  i n c r e a s e i n d e n s i t y , i t c o u l d be used as a n a t u r a l c o n t r o l agent a g a i n s t weed.  this  I f TJ. a f f i n i s and U. q u a d r i f a s c i a t a reduce knapweed seed p r o d u c t i o n by  50% i n c o u n t r i e s o f o r i g i n , where t h e i r e f f e c t i s l i m i t e d by n a t u r a l  enemies,  then these b i o l o g i c a l c o n t r o l agents a c h i e v e d about a 30% i n c r e a s e i n seed d e s t r u c t i o n i n B r i t i s h Columbia.  But r e l e a s e s i t e p o p u l a t i o n s produced such  c o p i o u s amounts of seed t h a t i n 1977, a t peak f l y d e n s i t i e s , an average of 800 d i f f u s e and 500 s p o t t e d knapweed seeds per 50 X 50 cm were b e i n g shed. Whether o r not these seed d e n s i t i e s w i l l be s u f f i c i e n t  to m a i n t a i n knapweed  134 p o p u l a t i o n d e n s i t i e s on r e l e a s e s i t e s depends on knapweed s u r v i v a l from seed  to mature-plant  s t a g e s , and w i l l be d i s c u s s e d i n a l a t e r s e c t i o n .  5.Conclusions: 1. G a l l f l i e s a c h i e v e d d i f f u s e and  about an 80% r e d u c t i o n i n p o t e n t i a l seed y i e l d on  both  s p o t t e d knapweed r e l e a s e s i t e s at peak p o p u l a t i o n d e n s i t i e s i n  1977. 2. Fewer seeds a r e produced by unattacked  heads as g a l l d e n s i t i e s i n a t t a c k e d  heads i n c r e a s e . 3. U. q u a d r i f a s c i a t a i s not as e f f e c t i v e as U. a f f i n i s i n r e d u c i n g  seed.  135 III  KNAPWEED DEMOGRAPHY  A. EFFECTS OF SEED REDUCTION ON KNAPWEED POPULATIONS 1.Introduction: Population  s i z e and ground cover o f p l a n t p o p u l a t i o n s  t h a t produce greater;  numbers o f seeds than r e q u i r e d f o r the maintenance o f e x i s t i n g d e n s i t i e s , ' may  be r e g u l a t e d by one o r more o f t h r e e f a c t o r s :  1.mortality:  an i n -  c r e a s i n g p r o p o r t i o n o f p l a n t s d i e as d e n s i t y i n c r e a s e s , and a d e c r e a s i n g p r o p o r t i o n d i e as d e n s i t y d e c r e a s e s ;  2.plasticity:  as p l a n t d e n s i t y  changes,  i n d i v i d u a l p l a n t s i z e , seed y i e l d p e r p l a n t , seed y i e l d p e r pod o r c a p s u l e , or type of r e p r o d u c t i o n and  (eg., v e g e t a t i v e as opposed t o s e x u a l ) may change;  3.controlled germination:  fewer  germinate.  as numbers o f seeds i n t h e s o i l  increase  (Harper, 1960; Harper and G a j i c , 1961; and Palmblad,  1968).  Most weedy s p e c i e s s t u d i e d produce seeds f a r i n excess o f t h e numbers needed for  the maintenance o f p o p u l a t i o n s ;  e.g.,  sowing seeds i n t o p o p u l a t i o n s o f  the same s p e c i e s d i d n o t i n c r e a s e p o p u l a t i o n Harper, 1960).  Knapweed p o p u l a t i o n s  size  (Putwain et^ a l . , 1968;  commonly produce over 1,000 seeds p e r  50 X 50 cm ( s e c t i o n I I B v i i ) , and t h e r e f o r e produce more seed than i s needed to r e p l a c e i n d i v i d u a l s which d i e d .  Gall flies  ( s e c t i o n I I B v i i ) , but i s t h a t s u f f i c i e n t q u e s t i o n was examined by a r t i f i c i a l l y  can reduce seed y i e l d by 80%  t o a f f e c t p l a n t stands?  thinning  This  seedlings.  2.Method: T h i s study was begun i n 1976 and continued test plots.  u n t i l 1977,  Work i n 1976 was l a r g e l y p r e l i m i n a r y .  d e t a i l s found i n 1977 were used t o c o n s t r u c t  using  t h e same  Some o f t h e l i f e h i s t o r y  t h e s u r v i v o r s h i p and f e r t i l i t y  136 schedules described  The  i n the next s e c t i o n .  d i f f u s e knapweed study s i t e was l o c a t e d on f l a t  e l e v a t i o n , near P r i t c h a r d , B.C. 1965 (Robertson, p e r s . t e c t e d from g r a z i n g northeast  comm.).  r a n g e l a n d , 380 m i n  D i f f u s e knapweed invaded the s i t e The study a r e a had been e n c l o s e d  s i n c e 1970.  circa  and p r o -  The l o c a t i o n of t h i s s i t e was 3 to 4 km  from the d i f f u s e knapweed r e l e a s e s i t e .  The s p o t t e d knapweed  •  s i t e was l o c a t e d i n Westwold, B.C., a p p r o x i m a t e l y 48 km south from the d i f f u s e knapweed s i t e , a t an e l e v a t i o n of 610 m. c i r c a 1970 ( B u f f , p e r s .  comm.).  caging  There was a v e r y  invaded the area  The study s i t e was not grazed f o r f o u r  y e a r s p r i o r to 1976, and was e n c l o s e d grazing.  Knapweed  w i t h a fence to p r e v e n t  small g a l l - f l y population  further  on both s i t e s because  s t u d i e s had been c a r r i e d out nearby, and some f l i e s had escaped.  In 1976 t h i r t y 50 X 50 cm square plots were e s t a b l i s h e d on the d i f f u s e and spotted  knapweed s i t e s by throwing a square, and d e l i n e a t i n g square p e r i -  meters w i t h b a l e r twine. Three s t r a n d s  Corners were h e l d i n p l a c e w i t h f e n c i n g  of b a l e r twine were s t r e t c h e d a c r o s s  the p l o t s i n t o f o u r 50 X 12.5 cm r e c t a n g l e s , The  staples.  each p l o t , s u b d i v i d i n g  to f a c i l i t a t e  seedling  treatments were 0%, 25%, 50%, 75% and 100% removal o f the t o t a l  of s e e d l i n g s which appeared. treatment.  counting. number  S i x r e p l i c a t e s were chosen a t random f o r each  In 1976, the s e e d l i n g s were thinned  once every two weeks, when  s e e d l i n g s were removed a t the r a t e of each treatment, 0%, 25%, 50%, 75% and 100%  of the number p r e s e n t  by u s i n g  forceps.  A s e e d l i n g was d e f i n e d as  a p l a n t h a v i n g f i v e o r fewer t r u e l e a v e s , none of which were d i s s e c t e d . r o s e t t e was d e f i n e d  A  a s - a p l a n t which had not p r e v i o u s l y b o l t e d , and which had  s i x o r more t r u e l e a v e s  i n a s i n g l e " r o s e t t e " arrangement.  t h a t i f a s e e d l i n g was p r e s e n t  during  I t was assumed  one sampling time, i t would r e a c h the  137 r o s e t t e stage by the next sampling time, two weeks l a t e r .  In 1977 s e e d l i n g s were s u b d i v i d e d  i n t o two c l a s s e s :  s m a l l and l a r g e .  s e e d l i n g s were d e f i n e d as p l a n t s which ranged i n m a t u r i t y stage  Small  from the d i c o t y l e d o n  t o the t h r e e - t r u e - l e a f stage, w i t h no l e a v e s l o n g e r than 2 cm, and none  dissected.  Large s e e d l i n g s were c l a s s i f i e d as p l a n t s w i t h f o u r o r f i v e  true  l e a v e s , w i t h a t l e a s t one l e a f g r e a t e r i n l e n g t h than 2 cm, but none d i s s e c ted.  Small r o s e t t e s were c l a s s i f i e d as p l a n t s w i t h s i x or more t r u e l e a v e s ,  of which a t l e a s t one was l o n g e r than 2 cm, and d i s s e c t e d .  Small and l a r g e s e e d l i n g s were counted once every  two weeks, and a t the same  time any p l a n t i n the s m a l l r o s e t t e stage was marked by i n s e r t i n g a l e t t e r e d p l a s t i c p i n d i r e c t l y behind  i t i n t o the ground.  which had appeared i n the p r e c e d i n g  Then the number o f s e e d l i n g s  two-week i n t e r v a l , i . e . , "newly-appeared  s e e d l i n g s " , was c a l c u l a t e d as f o l l o w s : if  t h e r e was an i n c r e a s e i n the number o f l a r g e s e e d l i n g s d u r i n g the p r e v i o u s  two weeks, i t was assumed t h a t i n d i v i d u a l s which had e n t e r e d s e e d l i n g c l a s s i n the p r e v i o u s a t the l a s t count.  Small  the l a r g e  two weeks had been counted as s m a l l  s e e d l i n g s i n the p r e v i o u s  seedlings  count which d i d not  e n t e r t h e l a r g e s e e d l i n g stage e i t h e r d i e d o r remained i n the s m a l l s e e d l i n g stage.  These l a t t e r i n d i v i d u a l s were c a l l e d  " o l d small seedlings".  Newly-  appeared s m a l l s e e d l i n g s were c l a c u l a t e d by the e q u a t i o n NA = SS^ - (SS^_^ A L S ) , where NA = the number o f newly-appeared s m a l l s e e d l i n g s , SS^ = the number o f s m a l l s e e d l i n g s i n the c u r r e n t week's count, SS.  ^ = the number o f s m a l l s e e d l i n g s i n t h e p r e v i o u s week's count,  zjk LS = the number of l a r g e s e e d l i n g s i n the c u r r e n t week's count - t h e number of l a r g e s e e d l i n g s i n the l a s t  count,  138 SS. ., - A LS = the number of o l d s m a l l s e e d l i n g s , l-l  if  t h e r e was  a decrease i n the number of l a r g e s e e d l i n g s d u r i n g the  two weeks, i t was  assumed t h a t no  s m a l l s e e d l i n g s , which had  previous^  been counted  two weeks e a r l i e r , grew-enough f o l i a g e to e n t e r the l a r g e s e e d l i n g c l a s s , the number of newly-appeared s m a l l s e e d l i n g s was NA  The  = SS.  1  c a l c u l a t e d from the  l a t e d from the number of newly-appeared s m a l l s e e d l i n g s and removal r a t e .  The  s m a l l s e e d l i n g s were removed by p u l l i n g  s e e d l i n g s was  g i v e n a c h o i c e of two  sampling  interval.  Rosettes  were d e f i n e d as p l a n t s whichhad not  f o r e c o n s i s t e d of o n l y one had  " r o s e t t e " formation  with  cm were counted.  (September and  s e e d l i n g s , the youngest-  f o r l o n g e r than the two-week  cm,  When d i f f u s e and  there-  from a s i n g l e r o o t crown. at which time a l l the r o s e t t e s  i n s e r t i n g numbered p l a s t i c p i n s d i r e c t l y behind  diameters were measured to the n e a r e s t  recorded  them out  p r e v i o u s l y b o l t e d , and  at l e a s t s i x t r u e l e a v e s i n May,  were tagged by  than two  designated  always removed because i t soon became apparent t h a t  some s m a l l s e d l i n g s c o u l d s u r v i v e i n t h i s stage  Rosettes  the  then c a l c u -  More s m a l l s e e d l i n g s were removed from t h i c k e r than t h i n n e r •• ...  patches o f s e e d l i n g s and, appearing  equation  - SS. , . l - l  number of s m a l l s e e d l i n g s to be removed from each p l o t was  forceps.  and  and  them.  the number of l e a v e s  s p o t t e d knapweed reached  Rosette greater maturity  August, r e s p e c t i v e l y ) , f a t e s of each numbered r o s e t t e were  as e i t h e r :  "dead" i f a l l the l e a v e s had  been l o s t , and no new  "regrowing" i f a l l the l e a v e s had  ones appeared;  been l o s t , but s h o r t , d i s s e c t e d l e a v e s  with  139 s h o r t p e t i o l e s had "vegetative"  sprouted  afterwards;  i f the r o s e t t e had  " a r r e s t e d " i f the r o s e t t e had "unsuccessful"  not  attempted to b o l t ;  b o l t e d , but had  i f the r o s e t t e had  " s u c c e s s f u l " i f the r o s e t t e had  b o l t e d but  b o l t e d and  not produced any  heads;  produced' o n l y a b o r t e d heads; or  produced at l e a s t one  mature  seed head.  Diameters of v e g e t a t i v e  r o s e t t e s were measured to the n e a r e s t  number of l e a v e s  than two  longer  cm were counted.  r o s e t t e s were measure to the n e a r e s t  cm,  and  cm,  Stalk heights  numbers of seed and  and  the  of b o l t e d aborted  heads per b o l t e d r o s e t t e were counted.  P e r e n n i a l d i f f u s e knapweed was bolted.  defined  P e r e n n i a l p l a n t s u s u a l l y had  each of which c o u l d b o l t .  as any  bolted.  crown,  Those p e r e n n i a l p l a n t s w i t h s i n g l e r o s e t t e s  had  y e a r s when r o s e t t e s , coming from  P e r e n n i a l p l a n t s were tagged i n May  numbered p l a s t i c p i n s d i r e c t l y behind them. recorded  previously  numerous"rosettes a t the r o o t  the remains of dead s t a l k s from p r e v i o u s same r o o t , had  p l a n t which had  In the f a l l ,  by  inserting  t h e i r f a t e s were  as:  "dead" i f a l l l e a v e s had  been l o s t from a l l r o s e t t e s ;  "regrowing" i f a l l l e a v e s d i s s e c t e d l e a v e s had  from a l l r o s e t t e s had  been l o s t , but  short,  sprouted from the c e n t r e of at l e a s t one of the  "dead"  rosettes; "vegetative"  i f none of the r o s e t t e s had  " a r r e s t e d " i f at l e a s t one "unsuccessful"  r o s e t t e had  i f a t l e a s t one  were a b o r t e d ; or  bolted;  b o l t e d , but  r o s e t t e had  no heads were produced;  b o l t e d , but  a l l heads produced  the  140 " s u c c e s s f u l " i f at l e a s t one mature seed head.  r o s e t t e had  Numbers of seed and  b o l t e d and  produced a t l e a s t  a b o r t e d heads per b o l t e d  one  perennial  p l a n t were counted.  F a t e s of p e r e n n i a l  spotted  knapweed p l a n t s were c l a s s i f i e d  e n n i a l d i f f u s e knapweed p l a n t s .  Spotted knapweed was  on the b a s i s of numbers of r o s e t t e s a t t a c h e d p e r e n n i a l " p l a n t had f o u r , and In May,  one  or two;  further subclassified  to the r o o t crown:  a "medium p e r e n n i a l " p l a n t had  a " l a r g e p e r e n n i a l " R i a n t had  each p e r e n n i a l s p o t t e d  a "small, three  f i v e or more r o s e t t e s p e r  knapweed p l a n t was  or  crown.  tagged w i t h a numbered  p l a s t i c p i n , i n s e r t e d d i r e c t l y behind i t i n t o the ground. of s p o t t e d  s i m i l a r l y to p e r -  knapweed p e r e n n i a l p l a n t s were r e c o r d e d  and  In August, f a t e s  head p r o d u c t i o n  was  counted the same as f o r d i f f u s e knapweed.  3.Results:  In 1976 than two  i t appeared t h a t s e e d l i n g s  remained i n the s e e d l i n g stage  weeks because they developed t h i c k r o o t crowns and  when l e a f numbers were fewer than f i v e .  Therefore  percentage of t o t a l s e e d l i n g s which appeared was  leaves  designated  p r o b a b l y removed i n  1976.  made to p u l l i t out,  o f t e n regrew a s i n g l e r o s e t t e , or numerous i n d i v i d u a l r o s e t t e s from  crown.  These regrowing r o s e t t e s were soon d i s t i n g u i s h e d from other  i n t h a t they c o n s i s t e d of s h o r t , v e r y and  dissected  more than the  I f a s e e d l i n g broke at the crown when an attempt was it  longer  were' l a t e r removed..  leaves,  the c e n t r e  of the  crown.  plants  dissected leaves, with short p e t i o l e s ,  Both s e e d l i n g s and  thereby a p p e a r i n g dead, and  the  rosettes could lose a l l t h e i r  l a t e r sprout  new,  healthy  leaves  from  141 In 1977 numbers of s m a l l d i f f u s e and s p o t t e d decreased s i g n i f i c a n t l y w i t h removal r a t e s m a l l d i f f u s e and s p o t t e d  knapweed s e e d l i n g s per p l o t  (Table XXIV).  The percentage of  knapweed s e e d l i n g s which d i e d decreased w i t h i n -  c r e a s i n g t h i n n i n g , but the decrease was s i g n i f i c a n t o n l y f o r s p o t t e d  knapweed.  S i m i l a r l y , " there-.was a d e c r e a s i n g  spotted  knapweed l a r g e s e e d l i n g s  trend  i n the number of d i f f u s e and  and s m a l l r o s e t t e s w i t h i n c r e a s i n g t h i n n i n g  but  the decrease was s i g n i f i c a n t o n l y f o r l a r g e d i f f u s e knapweed  and  small spotted  knapweed r o s e t t e s .  rate,  seedlings  No p l a n t s i n the l a r g e s e e d l i n g or  s m a l l r o s e t t e s t a g e s were found on the p l o t s where a l l s e e d l i n g s were r e moved because a l l i n d i v i d u a l s had been removed w h i l e they were s t i l l s m a l l s e e d l i n g stage.  i n the  There was no s i g n i f i c a n t d i f f e r e n c e i n the percentage  of l a r g e d i f f u s e knapweed s e e d l i n g s which d i e d , o r s m a l l d i f f u s e and  spotted  knapweed r o s e t t e s which d i e d w i t h i n c r e a s i n g t h i n n i n g r a t e , but the p e r centage o f l a r g e s p o t t e d with thinning  knapweed s e e d l i n g s which d i e d v a r i e d  significantly  rate.  There was no s i g n i f i c a n t d i f f e r e n c e between t h i n n i n g r a t e s i n the number of d i f f u s e knapweed p l a n t s i n r o s e t t e o r p e r e n n i a l c l a s s e s , nor i n the number of s p o t t e d  knapweed p l a n t s i n s m a l l , medium o r l a r g e p e r e n n i a l  the s p r i n g of 1977 (Table XXV).  However, t h e r e was a s i g n i f i c a n t  w i t h t h i n n i n g r a t e i n the number o f s p o t t e d stage.  But, i f one p l o t w i t h u n u s u a l l y  (85 compared w i t h the average of 2 8 - 3 than t h e r e  vegetative,  high spotted  knapweed r o s e t t e counts-  f o r a l l t h i r t y p l o t s ) i s omitted, The percentage  knapweed p e r e n n i a l p l a n t s which entered -.dead, regrowing,  arrested, unsuccessful  of 1977 d i d not v a r y  difference  knapweed p l a n t s i n the r o s e t t e  i s no s i g n i f i c a n t d i f f e r e n c e w i t h t h i n n i n g r a t e .  of d i f f u s e o r s p o t t e d  classes i n  o r s u c c e s s f u l f a t e c a t e g o r i e s by the f a l l  s i g n i f i c a n t l y with thinning rate.  Numbers of seed,  T a b l e XXIV.  Average numbers of d i f f u s e and s p o t t e d  knapweed p l a n t s per p l o t f o r each t h i n n i n g r a t e i n 1977  small seedlings large seedlings small rosettes t r e a t - d i f f u s e knapweed s p o t t e d knapweed d i f f u s e knapweed s p o t t e d knapweed d i f f u s e knapweed s p o t t e d knapweed ment % dead number % dead number % dead number % dead number % dead number % dead number 0% '337 J 38 147 J 15 25 124 I 9 50 85 - 10 75 5 0-2 100 . * SIG. 1  73 6 376 J 90 63 T 8 192 - 43 72 - 5 120 - 28 46 --10 91 - 19 63 - 16 *  84 t 3 89-3 76-4 60-6 *  76 J 37 | 1612-  10 8 3 1  18 J 6 33 - 10 34 - 7 23-9  56 t 21 21-5 17-7 11-2  76 J 62 | 8363-  *  5 5 8 7  53 t 7 29-9 10-1 10-1  21 J 5 27 - 5 27 J 6 29-9  13 t 5 6-2 + 4-2 2  1  36 ~t 10 52 - 12 67 T 24 57 - 14  *  *  s i g n i f i c a n t d i f f e r e n c e among t h i n n i n g r a t e s denoted by * treatments a r e 0%, 25%, 50%, 75% and 100% removal o f s m a l l  T a b l e XXV.  spotted  diffuse  knapweed  1  seedlings  Average numbers o f d i f f u s e and s p o t t e d knapweed p l a n t s p e r p l o t f o r each s i z e c l a s s i n t h e s p r i n g of 1977, and t h e i r f a t e s by the f a l l o f 1977. Average head p r o d u c t i o n f o r each s i z e c l a s s i n the f a l l o f 1977. i  size class r P r sp mp IP  r=rosette;  number of plants  % p l a n t s i n f a t e c a t e g o r y i n f a l l o f 1977 revegeunsucsucdead arrested growing t a t i v e cessfull ' cessfull  123 J 8 1 8 2 1.6 - .7 1 5 - 7 + * 28-3 28 J 4 15-4 + 6.7 - .9 8 - 2 2.3 - .3 2 - 1 9  1  2-2 0 0  6  0  66 t 6 38-7 46 J 4 13-3 9-2 1-1  0 0 8 ± 1 31- 5 20-4 32- 7  1-1  1*1 2 44-2  17- 4 18- 5 7-3  l l | 2 24-5 45-6 58-8  p = p e r e n n i a l ; sp=small p e r e n n i a l ; mp=medium p e r e n n i a l ;  lp=large  heads per b o l t e d seed  aborted  total  .8 t .1 .8 - .2  14.3 ^ .8 11-4  | .05 . 7 ± . l .7 - .2 - .4 7 .4 1.3 - .2 - .9 2.8 - .6  1.2 | . l 1.7 - .5 3.0 - .6 8-1  13.2 J .9 11-3 .49 1.0 1.7 4.7  plant  perennial  s i g n i f i c a n t d i f f e r e n c e between treatments due t o one p l o t w i t h e x c e p t i o n a l l y h i g h r o s e t t e counts; i f t h i s p l o t i s o m i t t e d there i s no s i g n i f i c a n t d i f f e r e n c e between treatments and the x No. o f r o s e t t e s p e r p l o t i s 26 - 2  143 undeveloped and t o t a l heads p e r b o l t e d d i f f u s e or s p o t t e d  knapweed r o s e t t e ,  or d i f f u s e o r s p o t t e d knapweed p e r e n n i a l p l a n t , a l s o d i d not v a r y  signifi-  cantly with thinning rate.  Neither  d i f f u s e nor spotted  knapweed r o s e t t e diameters v a r i e d  w i t h t h i n n i n g r a t e i n May, 1977.  A g a i n , i n the f a l l  o f 1977, t h e r e was no  s i g n i f i c a n t d i f f e r e n c e w i t h t h i n n i n g r a t e among s p o t t e d width c l a s s e s .  significantly  knapweed r o s e t t e  But f o r d i f f u s e knapweed there was a s i g n i f i c a n t  w i t h t h i n n i n g r a t e f o r r o s e t t e diameters i n the f a l l  difference  o f 1977 ( F i g . 3 6 ) .  There was, however, no s i g n i f i c a n t d i f f e r e n c e between average s p r i n g and average f a l l  d i f f u s e knapweed r o s e t t e diameters f o r p l o t s where a l l s e e d l i n g s  were removed.  The  f o l l o w i n g i s based on a measure o f r o s e t t e s i z e , where the s i z e i s  r o s e t t e diameter  (cm) X the number o f l e a v e s  percentage o f d i f f u s e and s p o t t e d  greater  d i f f u s e and s p o t t e d  The  knapweed r o s e t t e s which b o l t e d o f the  number o f r o s e t t e s i n t h e s p r i n g o f 1977, i n c r e a s e d creasing rosette size  than 2 cm l o n g .  s i g n i f i c a n t l y with i n -  ( F i g s . 37 and 38, r e s p e c t i v e l y ) .  The percentage o f  knapweed r o s e t t e s which d i e d o r remained  vegetative  during  the summer of 1977 decreased s i g n i f i c a n t l y w i t h i n c r e a s i n g r o s e t t e  size.  There was no s i g n i f i c a n t d i f f e r e n c e w i t h t h i n n i n g r a t e f o r d i f f u s e  knapweed r o s e t t e s which regrew.  Bolted and  s p o t t e d knapweed r o s e t t e s had t h r e e  successful.  I f only  spotted  fates:  knapweed r o s e t t e s  arrested,  which b o l t e d  s i d e r e d , then the percentage which was a r r e s t e d decreased with increasing rosette size  unsuccessful, a r e con-  significantly  ( F i g . 39). The percentage o f r o s e t t e s which  144 8T  7H LU LU  Q  LU  P  6H  0  UJ  cn O OL  UJ  O LU  0  ,1  0  —r—  25  0  T" 50  75  100  % SEEDLINGS REMOVED OF TOTAL WHICH APPEARED Figure  36.  Average d i f f u s e knapweed r o s e t t e diameter i n t h e s p r i n g and f a l l of 1977 f o r each t h i n n i n g r a t e s p r i n g 0; f a l l X  were u n s u c c e s s f u l  d i d not vary  s i g n i f i c a n t l y with rosette s i z e .  d i f f u s e knapweed r o s e t t e s which b o l t e d i n 1977 a r e c o n s i d e r e d , s t a l k height  then average  and numbers o f seed heads p e r b o l t e d s t a l k i n c r e a s e d  c a n t l y w i t h r o s e t t e s i z e ( F i g . 40). correlation  I f only  There was a s i g n i f i c a n t  ( r = .907; 4 D.F.) between s t a l k h e i g h t  heads p e r s t a l k . are c o n s i d e r e d ,  I f only spotted  signifi-  positive .  and the number o f seed  knapweed r o s e t t e s which b o l t e d i n 1977  t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n the mean number o f  seed heads produced w i t h i n c r e a s i n g  rosette  size.  %100'i  % 100-1  0-20 ROSETTE  SIZE  CLASS (NO. LEAVES X SPRING,  Figure  1977  DIAMETER)  ROSETTE  .  3 7 . The percentage of d i f f u s e knapweed r o s e t t e s i n each f a t e c l a s s r e l a t e d t o s p r i n g size classes Fates: bolted 0 0; v e g e t a t i v e X X; dead and regrowing A A  SIZE  21-40  41-60  CLASS (NO. L E A V E S X SPRING,  Figure  61-80  81-100  +100  cm  DIAMETER)  1977  38. The p e r c e n t a g e o f s p o t t e d knapweed r o s e t t e s i n each f a t e c l a s s r e l a t e d t o s p r i n g size classes Fates: bolted 0 0; v e g e t a t i v e X X; dead and regrowing A* • • - A  4>-  %  Hi  IN F A T E C L A S S OF TOTAL NO. ROSETTES WHICH  BOLTED  TO e  H  fD  r - r h CO Co 3 c fD OJ 1 rt rt vO h- rt 1 CfDO fD fD CO CD O 1 H X P* o C P* CO cn H P fD Co c H3 r N Si O -3 Cu fD P Hi  X  1  70  O  .  1  .  CO  m  rn co  4  CO O cn M O l-h CCO C M CD  p*  O  1  C  o o fD  cn cn O H1  e  3 cr 3  rt fD Cu  rn CO  7?  x o  3  Co X)  cn  I  fD CU  m H m  ro  er  rt  cr  CO X)  cn K 3 fD  o h- o 3 n fD H 1  o  co $> -o co ?o co  3 O O rh  c ffi  3 cn  3  rt rt fD Co Cu TO fD CD  Co l-h CD rt rt rt P^ e a fD M xi H rt rt V ! fD O >« Cu rt Co c rt M 3  •  N rn  o fD  Ot  * O  o r-  ce sf  CO H H fD O Z CO 3* It fD n Cu  • T  fD cr  er  er  ce  CO H H fD CO rt fD Cu  4  70  AVERAGE S T A L K HEIGHT 0-0 AVERAGE NUMBER OF SEED HEADS PER S T A L K  TO 3 H fD  o  Cu Co O  H- <! rh rh  70  O  CO  3 Co cn TOfD  m  TO l-i  5^ 3 fD 3 cj CD fo  3  CD  fD  o  cr H-  o  o o r h l-h  cn CO Co  <  fD fD rt (D fD rt CU l-l fD Co P TO cn fD fD H< CO N CU CD fD CO rt Cu cn -d M fD !^  3*  CD fD rt r CO r- P ?T rt  N  m o  o  3  9n  TO 4  I  -p o  CO J> "0 CO 70 CO  i—t  I O  H-• <£> I—•  I _ > oo <  m o CO X  oo H-•  1  1  I  HH  4  i-t  o  m o co  fD ri 3 fD CO CD CU H  HH  1 -  t—»  CU  o m o  Cu  m  3  o  O  _l_  •  fD  fD fD  O  70  o o o 3  -X-  X  X  o  147 G a l l s were found o n l y on the d i f f u s e knapweed s i t e .  There were averages of  0.03 - .02 and 0.44 - . 09 U_. a f f i n i s and U. q u a d r i f a s c i a t a g a l l s per seed head, r e s p e c t i v e l y , i n 1976, and 0.07 - .02 and 0.14 - .03 U. a f f i n i s and  U. q u a d r i f a s c i a t a g a l l s per seed head i n 1977.  5.Discussion: D i f f u s e and s p o t t e d  knapweed p o p u l a t i o n s  are regulated  to some extent  by  density-dependent m o r t a l i t y a t the s m a l l e s t p l a n t stage measured: the s m a l l s e e d l i n g stage.  On the average fewest s m a l l s e e d l i n g s  t h i n n i n g r a t e s were h i g h e s t  d i e d on p l o t s where  s h o r t of complete s e e d l i n g removal.  The d i f f e r -  ence i n average m o r t a l i t y between t h i n n i n g r a t e s f o r d i f f u s e knapweed s e e d l i n g s was not s i g n i f i c a n t because of u n f o r s e e n p a t c h i n e s s  of the seed-  l i n g s , and the i n f l u e n c e of p l a n t s i n r o s e t t e and p e r e n n i a l p l a n t Milthorpe  small  stages.  (1961) s t a t e s t h a t " C o m p e t i t i o n a r i s e s when one i n d i v i d u a l i s  s u f f i c i e n t l y c l o s e to another t o modify i t s s o i l o r atmospheric environment and  thereby decrease i t s r a t e of growth".  Where seeds had been washed i n t o  hollows and seedlings* grew-as t h i c k as moss, the m o r t a l i t y r a t e was p r o b a b l y g r e a t e r w i t h a t h i n n i n g r a t e of 75% than on other d i s t r i b u t e d more evenly  Harris  p l o t s where s e e d l i n g s  were  , but where the t h i n n i n g r a t e was lower.  (1973b) suspected t h a t "most of the n a t u r a l m o r t a l i t y of the weed  [spotted knapweed] between s e e d l i n g s  i n B r i t i s h Columbia i s from i n t r a s p e c i f i c and r o s e t t e s .  I f t h i s i s so, then the most e f f e c t i v e  b i o l o g i c a l c o n t r o l agent would be one t h a t a t t a c k e d mortality.  competition  immediately a f t e r t h i s  The e f f e c t of agents t h a t feed on seeds or s e e d l i n g s ,  though a p o t e n t i a l p l a n t i s e a s i l y d e s t r o y e d  a t t h i s stage,  reduce the m o r t a l i t y from i n t r a s p e c i f i c c o m p e t i t i o n " .  even  i s merely to  Here, r o s e t t e numbers  148 were not a f f e c t e d by s e e d l i n g removal, even on p l o t s where a l l s e e d l i n g s had been removed f o r two y e a r s .  The s i g n i f i c a n t d i f f e r e n c e between r o s e t t e  d e n s i t i e s w i t h removal r a t e f o r s p o t t e d h i g h r o s e t t e d e n s i t i e s on one p l o t .  knapweed i s a t t r i b u t e d to u n u s u a l l y  Therefore  s u r v i v a l of e i t h e r d i f f u s e  or s p o t t e d knapweed r o s e t t e s i s not a f f e c t e d by p l a n t s i n the s m a l l r o s e t t e , or younger stages of development.  However, o l d e r p l a n t s c o u l d a f f e c t the  s u r v i v a l of the younger ones i n p o p u l a t i o n s older plants are high.  where d e n s i t i e s of r o s e t t e s and  But, most s m a l l s e e d l i n g s  a r e surrounded o n l y by  s m a l l s e e d l i n g s , and s m a l l s e e d l i n g s u r v i v a l p r o b a b l y depends m o s t l y on i n t r a s p e c i f i c competition  between i n d i v i d u a l s i n t h i s  stage.  I t appears t h a t s e e d l i n g removal, even a t the lowest r a t e , can decrease the number of p l a n t s s u r v i v i n g to the l a r g e ; s e e d l i n g and s m a l l r o s e t t e stages i n two y e a r s ,  and i f t h i n n i n g c o n t i n u e d ,  be t h i n n e d .  r o s e t t e and o l d e r p l a n t d e n s i t i e s c o u l d  However, knapweed would:probably respond to a'decrease i n  several:ways.  D i f f u s e knapweed a l r e a d y showed s i g n s of an i n c r e a s e 1  s e t t e s i z e a f t e r two y e a r s of s e e d l i n g removal. more l i k e l y  to bolt"and/produce more seed heads.  Larger  inro-  r o s e t t e s would be  Although spotted  knapweed  d i d not show these: r e l a t i o n s h i p s i n t h i s study, p r e l i m i n a r y work on other s i t e s showed t h a t t h e p r o b a b i l i t y of b o l t i n g and p r o d u c i n g more numerous seed heads i n c r e a s e s w i t h s p o t t e d spotted  knapweed r o s e t t e s i z e .  knapweed has e x i s t e d f o r many y e a r s ,  On s i t e s where  crowding by p e r e n n i a l  plants  c o u l d decrease average r o s e t t e diameter, and r o o t s i z e c o u l d be a b e t t e r i n d i c a t i o n of spotted leaves  and l e a f  knapweed r o s e t t e v i g o u r  r a t h e r than the number of  length.  Werner (1975) found;that t h e , p r o b a b i l i t y of b o l t i n g f o r the b i e n n i e l ,  149 Dipsacus was  fullonum  ( t e a s e l ) , i n c r e a s e d w i t h i n c r e a s i n g r o s e t t e diameter,  not r e l a t e d to the age of i n d i v i d u a l r o s e t t e s .  b i e n n i e l s which grow i n suboptimal  Werner.felt  that  c o n d i t i o n s or where c o m p e t i t i o n i s g r e a t  e i t h e r from the same, or o t h e r s p e c i e s , remain i n the r o s e t t e stage than p l a n t s growing i n good c o n d i t i o n s . marginal  p r o b a b l y reached  A critical  before b o l t i n g .  s i z e , based  D i f f u s e and  knapweed appear to be s i m i l a r to Werner's (1975) o b s e r v a t i o n s . about o n e - t h i r d d i f f u s e , and 1977, f  these weeds spend a t l e a s t one  r o s e t t e stage. and  one-half  spotted  Because o n l y  s p o t t e d knapweed r o s e t t e s b o l t e d i n growing season,  probably  two,  i n the  Some i n t r a s p e c i f i c c o m p e t i t i o n between p l a n t s i n r o s e t t e  o l d e r stages o c c u r s , but c o m p e t i t i o n a t t h i s stage does not  survival.  longer  O f t e n r o s e t t e s growing i n the more  l o c a t i o n s died before reaching maturity.  on food r e s e r v e s , was  but  I n s t e a d average p l a n t s i z e and average seed y i e l d per  affect individual  p l a n t would decrease w i t h i n c r e a s i n g i n t r a s p e c i f i c c o m p e t i t i o n . I f g a l l do a c h i e v e a r e d u c t i o n i n knapweed density-,-\t>a4-l they may  do i s a l l e v i a t e  i n t r a s p e c i f i c c o m p e t i t i o n among r o s e t t e s , and the end r e s u l t s would be but l a r g e r p l a n t s , w i t h no decrease  i n knapweed cover on r a n g e l a n d .  knapweed, because of i t s s h o r t e r l i f e s p a n , would respond d e n s i t y w i t h a p l a s t i c response c r e a s e i n p l a n t d e n s i t y may  r o s e t t e s t a g e because " c r i t i c a l s i z e " may  the l e n g t h of time spent be reached  f a s t e r due  fewer,  Diffuse  to a decrease  f a s t e r than would s p o t t e d knapweed.  a l s o decrease  flies  A  in de-  i n the  to l e s s  i n t r a s p e c i f i c c o m p e t i t i o n among r o s e t t e s .  C o n t r o l l e d g e r m i n a t i o n may 1976,  p l a y a p a r t i n knapweed p o p u l a t i o n r e g u l a t i o n .  a l t h o u g h the d i f f e r e n c e was  not s i g n i f i c a n t , i t appeared t h a t as more  s e e d l i n g s were r e m o v e d a - g r e a t e r percentage their place.  In 1977  In  of seeds germinated  the o p p o s i t e t r e n d o c c u r r e d :  to take  s i g n i f i c a n t l y fewer s m a l l  150 s e e d l i n g s appeared w i t h knapweed s i t e s . highest  The  i n c r e a s i n g " t h i n n i n g r a t e s on both d i f f u s e and  seed bank seems to have been d e p l e t e d  thinning rates.  T h i s may  have o c c u r r e d  on p l o t s w i t h  because the s o i l  is slightly  d i s t u r b e d when s e e d l i n g s are removed, or because s e e d l i n g s c o n t i n u e d germinate i n 1976  as l o n g as t h e r e was  space f o r them.  spotted  to  C o n t r o l l e d germi-  n a t i o n i s s t u d i e d i n a l a t e r s e c t i o n where seeds are a c t u a l l y sown on s u r f a c e of the s o i l , are  and  germination  the  r a t e s over a range of sowing d e n s i t i e s  compared.  T h i s study demonstrates s e v e r a l ways i n which knapweed i s drought- and damage-tolerant. s e e d l i n g stage, season, and  P l a n t s i n any  stage of development, even i n the  _'  small  can lose**teheir l e a v e s d u r i n g dry p e r i o d s of the growing  regrow them when t h e r e i s s u f f i c i e n t m o i s t u r e .  S m a l l and  large  s e e d l i n g s can remain i n t h e i r r e s p e c t i v e stages  f o r n e a r l y one month, and  continue  When s e e d l i n g s are damaged  growth i n more f a v o u r a b l e  conditions.  they o f t e n s u r v i v e i f some of the r o o t remains i n t a c t .  Although  spotted  knapweed b o l t s more r e a d i l y than d i f f u s e knapweed, b o l t e d s p o t t e d knapweed p l a n t s may  not produce any  small-bud s t a g e ,  and  p l a n t s produce new seed heads.  heads, or they may  then abort  them.  heads o n l y to the .  f o l l o w i n g s p r i n g these b o l t e d  r o s e t t e s at t h e i r bases, and u s u a l l y b o l t and  T h i s i s an example of an advantage which s p o t t e d  a s h o r t - l i v e d p e r e n n i a l , has  over d i f f u s e knapweed.  set  i n i n midsummer, i . e . a hot,  and  bear seed the f o l l o w i n g y e a r , but  nothing  The  develop  attempt" at r e p r o d u c t i o n  d i f f u s e knapweed has  sufficient  seed heads even i n v e r y dry  dry s p e l l ,  knapweed,  I f adverse  conditions  s p o t t e d knapweed can cease growth  f o r d i f f u s e knapweed i t i s an " a l l or  f o r most b o l t e d p l a n t s . stored root reserves  years.  bear mature  U s u a l l y , however,  to produce some mature  151 5. C o n c l u s i o n s : 1. D i f f u s e and  s p o t t e d knapweed p o p u l a t i o n s  are c o n t r o l l e d to some  by density-dependent s e l f - t h i n n i n g at the s m a l l s e e d l i n g 2. Because at l e a s t one-half vegetative,  d i f f u s e and  spotted  these weeds p r o b a b l y spend one  extent  stage.  knapweed r o s e t t e s remain  y e a r , or more, i n the  stage i n a d d i t i o n to the year i n s e e d l i n g and  rosette  small r o s e t t e stages,  before  bolting. 3. The  p r o b a b i l i t y of b o l t i n g i n c r e a s e s and  the p r o b a b i l i t y o f d y i n g  w i t h i n c r e a s i n g r o s e t t e s i z e f o r d i f f u s e and 4. D i f f u s e and  spotted  t h e i r leaves  spotted  knapweed.  knapweed are so drought t o l e r a n t t h a t they can l o s e a l l  even at young stages of development, and  c o n d i t i o n s are  decreases  regrow them when  favourable.  5.Spotted knapweed r o s e t t e s bolt'more r e a d i l y than do d i f f u s e knapweed .. • r o s e t t e s , but  spotted  knapweed o f t e n does not -produce seed heads even when  i t bolts. 6. D i f f u s e knapweed may rosette  B.  show a p l a s t i c response to t h i n n i n g by an i n c r e a s e  in  size.  SURVIVAL AND  FERTILITY SCHEDULES  1.Introduction: Demography i s the branch of ecology which d e s c r i b e s i n numbers of p o p u l a t i o n s  (Harper and White, 1974).  b i r t h , death, i m m i g r a t i o n and ment of death r a t e s ship schedules. He  emigration  and  explains  tabulated  The  ( s t a t i c ) and  examples from animal e c o l o g y .  h o r i z o n t a l (cohort)  Horizontal l i f e  measure-  into survivor-  Deevey (1947) c a l l e d s u r v i v o r s h i p s c h e d u l e s " l i f e  reviewed both v e r t i c a l  changes  Demographers measure  r a t e s of p o p u l a t i o n s .  (or s u r v i v o r s h i p r a t e s ) can be  the  life  tables".  tables, with  t a b l e s f o l l o w the s u r v i v a l  152 of  a c o h o r t of i n d i v i d u a l s from b i r t h to death, whereas m o r t a l i t i e s o f i n d i -  v i d u a l s o f a known age, and s p e c i f i c time, a r e measured f o r s t a t i c tables.  I n s e c t e c o l o g i s t s have found t h a t developmental  convenient time u n i t s f o r l i f e a stage-specific l i f e  tables.  life  stages a r e the most  For example, Dempster  (1975) compiled  t a b l e f o r the moth, T y r i a j a c o b a e a .  There a r e numerous examples of animal l i f e  tables.  Most p l a n t  ecologists,  however, have s t u d i e d the s u r v i v a l of o n l y s p e c i f i c stages i n the l i f e of  a plant:  1965),  f o r example, seed  seedling  and shoot  (Sarukhan,  (Amor and H a r r i s , 1975;  (Hutchings and Barkham, 1976;  1974;  Harper, W i l l i a m s and  P i g g i n , 1976;  Bernard, 1976).  1972),  Harper and White (to grow,  f l o w e r , to remain v e g e t a t i v e , to d i e ) has been undertaken by few p e o p l e "  some work has been done by Tamm (1956), Sagar of  Sagar,  Ross and Harper,  (1970) found t h a t a l t h o u g h " C h a r t i n g the f a t e of i n d i v i d u a l p l a n t s to  history  Rabotnov and co-workers  dynamics of some annuals 1979)  and a p e r e n n i a l  from 1940,  (Watkinson  (1959) and by the Moscow S c h o o l  onwards.  and Harper,  ( B a s k i n and B a s k i n , 1979)  R e c e n t l y the p o p u l a t i o n 1978;  Regehr and  Bazzaz,  have been s t u d i e d .  " O b s e r v a t i o n s on the l o n g e v i t y of p o p u l a t i o n s , r a t e s of t u r n o v e r i n t h e i r v e g e t a t i v e and r e p r o d u c t i v e c o m p o s i t i o n , e t c . a r e extremely (Harper and White, 1970).  The term " p o p u l a t i o n t u r n o v e r " has been l o o s e l y  used by s e v e r a l p l a n t e c o l o g i s t s of  l i f e s p a n of i n d i v i d u a l s i n the p o p u l a t i o n .  l o n g e v i t y of p l a n t s , may  i n h i s study  a n d ' i s a measure of the  The average l i f e s p a n , or  v a r y g r e a t l y from one h a b i t a t  ( c i t e d by Harper and White, 1970) a  ( f o r example, A n t o n o v i c s , 1972,  the p o p u l a t i o n dynamics of Anthoxanthum odoratum),  average  laborious"  to another.  R  botnov  found t h a t T r i f o l i u m p r a t e n s e (red clover) had  s h o r t l i f e s p a n ; i . e . , a r a p i d p o p u l a t i o n t u r n o v e r , on a f l o o d p l a i n , where  \  153 the p l a n t s grew from s e e d l i n g s to m a t u r i t y ered once b e f o r e  t h e i r death.  i n two to t h r e e y e a r s , and f l o w -  In c o n t r a s t , r e d c l o v e r which grew i n a sub-  a l p i n e meadow, d i d not f l o w e r u n t i l i t was 5 to 10 y e a r s repeatedly  f o r 10 y e a r s .  the t u r n o v e r ,  The  i n age, and  o r replacement, i n t h i s p o p u l a t i o n was slow.  f o r both d i f f u s e and s p o t t e d knapweed i s an  p o p u l a t i o n a t t r i b u t e i n * t h i s study because g a l l f l i e s a f f e c t the  p l a n t s by d e c r e a s i n g \  Thus some i n d i v i d u a l s reached 20 y e a r s  r a t e of p o p u l a t i o n turnover  important  o l d , and reproduced  the number of v i a b l e seeds, and thus the p o t e n t i a l  number of s e e d l i n g s and mature p l a n t s . produce o n l y from seed.  D i f f u s e and s p o t t e d knapweed r e -  I f the f l i e s d e s t r o y a l l the seeds every y e a r ,  the minimum l e n g t h o f time r e q u i r e d f o r e r a d i c a t i o n of the knapweed t i o n would be the turnover  r a t e of the p o p u l a t i o n .  d i f f u s e and s p o t t e d knapweed t u r n o v e r structing v e r t i c a l l i f e  popula-,.  Due to l a c k of time  r a t e s on rangeland  t a b l e s , r a t h e r than cohort  then  life  a r e found by contables.  This section  a l s o compares the p o p u l a t i o n dynamics of d i f f u s e and s p o t t e d knapweed i n s m a l l s e e d l i n g , l a r g e s e e d l i n g and s m a l l r o s e t t e stages  d u r i n g the 1977  growing season.  2.Method: Except where noted, c o n t r o l p l o t s ( i . e . , 0% removal of s e e d l i n g s ) from the previous and  study  ( s e c t i o n I I I A) on the e f f e c t s of t h i n n i n g r a t e s on d i f f u s e  s p o t t e d knapweed were used.  The s u r v i v a l r a t e s and f e r t i l i t y  schedules  f o r p l a n t s i n s m a l l r o s e t t e and o l d e r stages were determined f o r each v i d u a l p l a n t because they were tagged w i t h a number.  indi^  But s u r v i v a l r a t e s f o r  p l a n t s i n s m a l l and l a r g e s e e d l i n g stages were determined from the t o t a l numbers which appeared i n each stage and the number which d i e d d u r i n g the 1977 growing season.  154 S u r v i v a l and f e r t i l i t y  t a b l e s were formulated  a f t e r S h a r i t z and McCormick  (1973), where x = plant  stage,  D^ = d u r a t i o n o f stage  (months),  Months = c a l e n d a r months spent  i n the stage,  A  = t o t a l age o f t h e s t a r t i n g c o h o r t  (months),  1  = number o f i n d i v i d u a l s e n t e r i n g the stage,  d  = number o f i n d i v i d u a l s dying d u r i n g the s t a g e ,  q  = the percentage o f i n d i v i d u a l s dying d u r i n g each  L  = the p r o p o r t i o n o f i n d i v i d u a l s s u r v i v i n g t o the b e g i n n i n g  stage, of a stage,  = 1 /1000, X  m^ = the average number o f seeds produced per p l a n t f o r each V  = L m , X X  X  R  stage,  0  = 2V , i . e . , the average number o f seeds produced by each p l a n t t h a t v i v e d to m a t u r i t y  out of the s t a r t i n g c o h o r t o f seeds.  the net r e p r o d u c t i v e r a t e (adapted G = A ^ /R » 0  i -  e  « 5  t  n  e  mean g e n e r a t i o n  from W i l s o n  (Krebs,  This i s called  and B o s s e r t ,  1971),  time, which i s the mean p e r i o d o f  time e l a p s i n g between the b i r t h of p a r e n t s spring  sur-  and the b i r t h o f t h e i r  off-  1972).  D i f f u s e and s p o t t e d knapweed p l a n t s were assumed t o i n c r e a s e i n age as thev increased i n s i z e .  Therefore  d i f f u s e knapweed grew c o n s e c u t i v e l y  through  s m a l l s e e d l i n g , l a r g e s e e d l i n g , s m a l l r o s e t t e , r o s e t t e and p e r e n n i a l p l a n t s t a g e s , where each stage Likewise,  i s d e f i n e d as i n the p r e v i o u s  section (III A).  s p o t t e d knanweed grew from s m a l l s e e d l i n g t o r o s e t t e s t a g e s , and  then developed through s m a l l , medium, and l a r g e p e r e n n i a l p l a n t s t a g e s , where these  stages  a r e d e f i n e d as i n the p r e v i o u s  section (III A).  155 A l t h o u g h p r e l i m i n a r y work showed that both s p e c i e s c o u l d germinate e i t h e r in  the s p r i n g o r i n the f a l l ,  spring. but  here they were assumed t o germinate i n the  Spotted knapweed seeds a r e shed from seed heads upon m a t u r i t y ,  d i f f u s e knapweed seeds c o u l d remain i n s i d e seed heads u n t i l the f o l l o w i n g  s p r i n g , when they f a l l  to the ground, and germinate.  Watson (1972) found  t h a t d i f f u s e knaoweed seeds, c o l l e c t e d from seed heads which had remained in  the f i e l d d u r i n g the w i n t e r , were 88% v i a b l e .  T h e r e f o r e the d i f f u s e  knapweed s u r v i v o r s h i p s c h e d u l e was s t a r t e d w i t h a c o h o r t of 1000 seeds, which had a death r a t e o f 12% from November u n t i l A p r i l .  Because s p o t t e d knapweed  seed has a h i g h e r percentage v i a b i l i t y than does d i f f u s e knapweed  (section  I I B v i ) , the death r a t e f o r the s t a r t i n g c o h o r t of 1000 s p o t t e d knapweed seeds was a r b i t r a r i l y a s s i g n e d as 10% from November u n t i l  April.  D i f f u s e and s p o t t e d knapweed seeds were assumed to germinate a t the b e g i n n i n g of May and to spend one month  (May) i n the s m a l l s e e d l i n g s t a g e , and the  f o l l o w i n g month i n the l a r g e s e e d l i n g s t a g e .  The r e s t of the growing season  ( J u l y to October) was spent i n the s m a l l r o s e t t e s t a g e . each stage were e s t i m a t e d from c o n t r o l p l o t s .  Mortalities for  In May, 1978, tagged s m a l l  r o s e t t e s were c l a s s i f i e d as a l i v e o r dead t o f i n d m o r t a l i t y r a t e s f o r t h e s m a l l r o s e t t e stage from November u n t i l A p r i l . all  Bv the b e g i n n i n g of A p r i l  s u r v i v i n g s m a l l r o s e t t e s were assumed to e n t e r the r o s e t t e s t a g e .  Previously  ( s e c t i o n I I I A) i t was found t h a t 66% o f d i f f u s e and 46% of  s p o t t e d knapweed p l a n t s i n the r o s e t t e stage remained v e g e t a t i v e . t h i s stage was s u b d i v i d e d i n t o v e g e t a t i v e and b o l t e d s t a g e s .  Therefore  Both s p e c i e s  were assumed to remain i n each of these sub-stages f o r one y e a r .  The m o r t a l i t y r a t e f o r d i f f u s e knapweed i n the v e g e t a t i v e r o s e t t e stage was  156 e s t i m a t e d f o r two p e r i o d s observing  o f time, May to October and November  the f a t e s of tagged r o s e t t e s i n October and May.  to A p r i l , by  The death r a t e  of d i f f u s e knapweed i n the b o l t e d r o s e t t e stage from May t o October was found by o b s e r v i n g  the f a t e s of b o l t e d r o s e t t e s i n O c t o b e r .  d i f f u s e knapweed r o s e t t e s d i e d u r i n g stalks i n following years. the p r e v i o u s  section  the w i n t e r ,  Preliminary  Most b o l t e d  but some may produce mature  a n a l y s i s of the d a t a p r e s e n t e d i n  ( I I I A) showed t h a t 8 - 3% o f the b o l t e d p l a n t s  (bolted  r o s e t t e s + p e r e n n i a l p l a n t s ) on the d i f f u s e knapweed s i t e were i n the p e r e n n i a l stage.  Therefore  i t was assumed t h a t from November u n t i l A p r i l  of the b o l t e d d i f f u s e knapweed r o s e t t e s d i e d . assumed t o e n t e r by  The  92%  The s u r v i v i n g p l a n t s were  the p e r e n n i a l stage i n May, b o l t d u r i n g  the summer, and d i e  October.  m o r t a l i t y rates f o r spotted  knapweed i n v e g e t a t i v e  and o l d e r  plant  stages were e s t i m a t e d from May to October, and from November u n t i l by r e c o r d i n g were o b t a i n e d  f a t e s of tagged p l a n t s i n May and October. by c o n s i d e r i n g  or s i z e f o r v e g e t a t i v e  These e s t i m a t e s  a l l t h i r t y p l o t s i n the p r e v i o u s  cause s e e d l i n g removal had had no e f f e c t on s p o t t e d r o s e t t e and o l d e r s t a g e s .  April,  s e c t i o n , be-  knapweed s u r v i v a l  A l l spotted  were assumed to d i e a f t e r b o l t i n g i n the l a r g e p e r e n n i a l p l a n t  knapweed  plants  stage.  In September, 1977, d i f f u s e knapweed seed heads were a r b i t r a r i l y c o l l e c t e d from p l a n t s o u t s i d e  the study p l o t s .  The heads were opened and the number  of seeds i n heads c o n t a i n i n g no g a l l s were counted.  I t was assumed t h a t  the average number o f seeds p e r seed head, thus found, was not a f f e c t e d by g a l l - f l y a t t a c k a t low d e n s i t i e s .  The average number of seeds produced per  p l a n t f o r each stage was found by m u l t i p l y i n g the average number of seed  157 heads per p l a n t by the average number o f seeds p e r seed head.  Because  d i f f u s e knapweed p e r e n n i a l p l a n t s were so few ( o n l y 1.6 - .7 per p l o t ) and s e e d l i n g removal had not a f f e c t e d them, a l l t h i r t y p l a n t s i n the p r e v i o u s s e c t i o n were used t o e s t i m a t e the average number o f seed heads p e r p l a n t f o r this  stage.  Watson's (1972) e s t i m a t e o f 26.6 seeds per seed head was taken t o be the average number o f seeds per seed head on the s p o t t e d no counts were made on the study s i t e i n 1977.  knapweed s i t e because  Few s p o t t e d  knapweed  plants  were found i n the o l d e r stages and s e e d l i n g removal had had no e f f e c t on seed yield,  t h e r e f o r e a l l t h i r t y p l o t s i n the p r e v i o u s  mate the average number o f s p o t t e d r o s e t t e and o l d e r  s e c t i o n were used t o e s t i -  knapweed seed heads per p l a n t f o r b o l t e d  stages.  Numbers of s m a l l s e e d l i n g s , l a r g e s e e d l i n g s , and s m a l l r o s e t t e s had been counted once every two weeks on c o n t r o l p l o t s i n the p r e v i o u s  section (III A).  These d a t a a r e p r e s e n t e d here as average numbers o f p l a n t s i n each stage throughout the growing season.  3.Results: Survivorship  o f d i f f u s e and s p o t t e d knapweed f o l l o w s a Deevey type I I I c u r v e  (Deevey, 1947) where m o r t a l i t y i s h i g h d u r i n g  e a r l y l i f e , but the few i n d i -  v i d u a l s t h a t do s u r v i v e t o o l d e r stages of development have a constant  expectancy o f f u r t h e r l i f e  more s p o t t e d  (Tables XXVI and XXVII).  than d i f f u s e knapweed p l a n t s d i e d d u r i n g  of development.  F o r both s p e c i e s  stage was g r e a t e s t  relatively On t h e average,  the f i r s t  three  the m o r t a l i t y r a t e a t the s m a l l  (73 - 6% and 84 - 3% f o r d i f f u s e and s p o t t e d  stages  seedling  knapweed,  r e s p e c t i v e l y ) , but by the s m a l l r o s e t t e stage m o r t a l i t y r a t e s had dropped  158 T a b l e XXVI. D  X  S SS LS SR SR R R  6 1 1 4 6 6 6 6 6 6  V  P  b  Months  x  A  Nov-Apr May June Jul-Oct Nov-Apr May-Oct Nov-Apr May-Oct Nov-Apr May-Oct  Survivorship 1  X  d  X  6 7 8 12 18 24 30 36 42 48  1000.00 880.00 237.60 194.83 153.92 132.37 107.22 94.35 92.47 7.40  and f e r t i l i t y  X  o f d i f f u s e knapweed m  X AA  120. 00 642. 40 42. 77 40. 91 21. 55 25. 15 12. 87 1. 89 85. 07 7. 40  12 + 73 + 18 + 21 + 14 + 19 + 12 + 2 AAA 92 100  L.00000 .88000 .23760 .19483 .15392 .13237 .10722 .09435 .09247 .00740  V  X  0 0 0 0 0 0 148  A V  X  X  X  0 0 0 0 0 0 0 13.96 0 .84  0 0 0 0 0 0 0 502. 70 0 40. 14  Ro = 14.80  542. 84  23 +> 1  113 - 37  G = 36.68 months A  plant stages: S=seed; SS=small s e e d l i n g ; LS=large s e e d l i n g ; SR=small r o s e t t e ; R = v e g e t a t i v e r o s e t t e ; R^=bolted r o s e t t e ; P = p e r e n n i a l p l a n t AA  V  B  seed m o r t a l i t y e s t i m a t e d f rom  AAA  Watson (1972)  B o l t e d r o s e t t e m o r t a l i t y e s t i m a t e d t o be t h e p e r c e n t a g e o f b o l t e d (R^) o f the t o t a l number o f b o l t e d p l a n t s (R^ + P)  T a b l e XXVII. x  D  S SS LS SR SR R R  6 1 1 4 6 6 6 6 6 6 6 6 6 6  V  % SP SP MP MP LP  G  x  Months Nov-Apr May June Jul-Oct Nov-Apr May-Oct Nov-Apr May-Oct Nov-Apr May-Oct Nov-Apr May-Oct Nov-Apr May-Oct  A  Survivorship  and f e r t i l i t y  x  6 7 8 12 18 24 30 36 42 48 54 60 66 72  of spotted m  x 1000. 00 900. 00 144. 00 34. 56 22. 12 15. 48 9. 75 9. 47 9. 09 8. 37 7. 11 6. 54 6. 02 5. 78  AA  100 .00 1.00000 + 756 .00 .90000 84 J 3 109 .44 .14400 76-5 12 .44 .34560 36 - 10 6 .64 .22120 30 - 16 5 .73 .15480 37 - 5 .09750 .28 2.9 J .9 .09470 .38 4 + 2 .09090 .73 8^2 .08370 1 .25 15-4 .07110 .57 8 + 3 .06540 .52 8-2 .06020 .24 4-4 .05780 5 .78 100 1  knapweed  x  x  0 0 0 0 0 0  0  A V x x  0 0 0 0 0 0 0 1 .23 0 2 .26 0 3 .01 0 7 .23  0 0 0 0 0 0 0 44.28 0 108.48 0 180.60 0 520.56  Ro = 13 .73  853.92  13- 1 27 - 9 46  rosettes  10  125 - 25  62.19 months  A  plant stages: S=seed; SS=small s e e d l i n g ; LS=large s e e d l i n g ; SR=small r o s e t t e ; R^=vegetative r o s e t t e ; R ^ b o l t e d r o s e t t e ^ g P , MP, and LP=small, medium and l a r g e p e r e n n i a l p l a n t , r e s p e c t i v e l y ; from Watson (1972)  159  4001  300'  200J  1001  AUGUST F i g u r e 41.  Average numbers of d i f f u s e and s p o t t e d knapweed s m a l l per p l o t i n 1977 d i f f u s e knapweed 0 0; s p o t t e d knapweed X X  KEPTFMBFR seedlings  OCT.  160  +  +  considerably  (21 - 5% and 36 - 10% f o r d i f f u s e and s p o t t e d knapweed, r e s -  pectively) .  When d i f f u s e and s p o t t e d knapweed reached r o s e t t e and o l d e r  p l a n t s t a g e s , m o r t a l i t y r a t e s were l e s s than 20%, except f o r s p o t t e d knapweed v e g e t a t i v e r o s e t t e s , o f which 37 - 5% d i e d d u r i n g the summer. knapweed had a l o n g e r average l i f e mately f i v e y e a r s ) three y e a r s ) .  expectancy  than d i d d i f f u s e knapweed  Spotted  (62.19 months, o r a p p r o x i (36.68 months, o r  approximately  The mean number o f seeds per seed head on the d i f f u s e knapweed  s i t e was 10.7 - .3.  G i v e n t h a t the mean number o f s p o t t e d knapweed seeds p e r  head was 26.6 (Watson, 1972), r e p r o d u c t i v e r a t e s f o r d i f f u s e and s p o t t e d knapweed p o p u l a t i o n s were s i m i l a r :  14.8 and 13.73, r e s p e c t i v e l y .  D i f f u s e and s p o t t e d knapweed s m a l l s e e d l i n g s were p r e s e n t April  on the s i t e s i n  ( F i g . 41). These were i n d i v i d u a l s which had germinated d u r i n g t h e  previous  f a l l because c o t y l e d o n e s  were l a c k i n g , o r w i t h e r e d ,  and s e e d l i n g  hue was dark green o r r e d r a t h e r than the b r i g h t green t y p i c a l o f newlygerminated p l a n t s .  D i f f u s e and s p o t t e d knapweed s m a l l s e e d l i n g s appeared a t  almost a l l times d u r i n g the growing season, but t h e i r numbers were  sig-  n i f i c a n t l y g r e a t e r i n May, a f t e r which time they d e c l i n e d t o n i l i n t h e middle o f August.  I n the f a l l  t h e r e was a f l u s h i n s e e d l i n g  D i f f u s e and s p o t t e d knapweed c o u l d a l s o s u r v i v e t h e w i n t e r  germination.  i n the large  s e e d l i n g stage because numerous l a r g e s e e d l i n g s were a l r e a d y p r e s e n t  on the  p l o t s i n A p r i l , b e f o r e any newly germinated s m a l l s e e d l i n g s had appeared (Fig.  42). There was no s i g n i f i c a n t d i f f e r e n c e between average l a r g e  s e e d l i n g counts throughout the growing season, b u t , l i k e s m a l l  seedlings,  g r e a t e s t numbers o f l a r g e s e e d l i n g s appeared to occur  Average l a r g e  s e e d l i n g counts,  i n May.  however, d i d n o t drop t o n i l i n August as d i d s m a l l s e e d l i n g  161  60-i  50 40302010-  4- ' " MAY  F i g u r e 43.  |  JUNE  JULY  AUGUST  SEPTEMBER OCTOBER  Cumulative numbers of d i f f u s e and s p o t t e d knapweed s m a l l r o s e t t e s per p l o t i n 1977 d i f f u s e knapweed 0 0; s p o t t e d knapweed X X  counts.  The  first  the f i r s t cumulative  d i f f u s e knapweed s m a l l r o s e t t e s appeared i n the m i d d l e of Mav f o r s p o t t e d knapweed appeared i n the m i d d l e of June ( F i g . 43) . t o t a l d i f f u s e and  s p o t t e d knapweed s m a l l r o s e t t e s i n c r e a s e d  the middle of August, a f t e r which few The  s i g n i f i c a n t l y g r e a t e r , and  The  until  a d d i t i o n a l s m a l l r o s e t t e s appeared.  r a t e of appearance of d i f f u s e compared w i t h  s e t t e s was  and  by the end  d i f f u s e than s p o t t e d knapweed s m a l l r o s e t t e s had  s p o t t e d knapweed s m a l l r o of the growing season more been produced  ( F i g . 44).  5.Discussion: Krebs (1972) compared a t t r i b u t e s of r - ("big-bang") and p r o d u c e r s ) s e l e c t e d organisms.  The  terms r - and  K-  (repeated  K - s e l e c t i o n are  re-  relative,  w i t h r - s e l e c t e d organisms having  a more r a p i d developmental time,  reproducing  once, r e p r o d u c i n g  having  little  early in l i f e ,  i n t r a s p e c i f i c a l l y and  having  a s m a l l e r s i z e , competing  a low density-dependent m o r t a l i t y compared  with  LOG  F i g u r e 44.  1 Q  CTIME)  D i f f u s e and s p o t t e d knapweed r e g r e s s i o n s o f t h e c u m u l a t i v e number of s m a l l r o s e t t e s produced per p l o t i n 1977 (Y), where X = log^ (time). F o r d i f f u s e knapweed time = 1, 2, 3...11, where 1 = May 18th; 2 = June 1; 3 = June 15th ... 11 = October 5 t h . F o r s p o t t e d knapweed time = 2.5, 3.5, 4.5...10.5, where 2.5 = June 8 t h ; 3.5 = June 22nd; 4.5 = J u l y 6th ... 10.5 = September 28th. Both r e g r e s s i o n s a r e s i g n i f i c a n t , and t h e r e i s a s i g n i f i c a n t d i f f e r e n c e between "b", where Y = a + bX. d i f f u s e knapweed 0 0; s p o t t e d knapweed X X -  163 K - s e l e c t e d organisms.  In the P l a n t Kingdon,  r - s e l e c t e d organisms  are u s u a l l y  annuals, which must r e c o l o n i z e every year, and have Deevey type I I I s u r v i v a l curves ( i . e . , m o r t a l i t y i s g r e a t e s t d u r i n g e a r l y s t a g e s of l i f e ,  but o l d e r  i n d i v i d u a l s have r e l a t i v e l y c o n s t a n t e x p e c t a n c i e s of s u r v i v a l ) .  K-selected  organisms  a r e p e r e n n i a l s and have Deevey type I s u r v i v a l c u r v e s  t a l i t y i s low d u r i n g e a r l y l i f e ,  ( i . e . , mor-  but i n c r e a s e s w i t h age), o r Deevey type I I  s u r v i v a l curves ( i . e . , m o r t a l i t y i s c o n s t a n t throughout  life).  Diffuse  and  s p o t t e d knapweed a r e n e i t h e r annuals, nor p e r e n n i a l s , and have a t t r i b u t e s of both r - and K - s e l e c t e d organisms.  They both have Deevey type I I I s u r v i v a l  c u r v e s , but s p o t t e d knapweed, w i t h a l o n g e r l i f e  expectancy,  repeated r e -  p r o d u c t i o n , and a l a r g e r p l a n t s i z e i s more t y p i c a l o f a K - s e l e c t e d organism than i s d i f f u s e knapweed.  Harper  and White (1974) c l a s s i f y b i e n n i e l s as "big-bang"  reproducers:  " w i n t e r a n n u a l s , a l s o b i e n n i a l s , have a more or l e s s l o n g v e g e t a t i v e stage t h a t changes under p e r i o d i c s t i m u l i to a f l o w e r i n g phase; v e g e t a t i v e a p i c e s a r e c o n v e r t e d to a f l o w e r i n g c o n d i t i o n and a "big-bang" of r e p r o d u c t i o n is  f o l l o w e d by d e a t h . "  p l a n t s may  Harper  and White (1974) c i t e s e v e r a l examples where  grow v e g e t a t i v e l y i n the r o s e t t e stage f o r s e v e r a l y e a r s b e f o r e  f l o w e r i n g , but c l a s s i f y them as b i e n n i e l s because d e a t h f o l l o w s b o l t i n g copious seed p r o d u c t i o n .  They m a i n t a i n t h a t the b i e n n i e l h a b i t i s p a r t i c u -  l a r l y advantageous, compared w i t h the annual h a b i t , i n environments seedling establishment i s r i s k y . growing year. in  and  Even i f a l l s e e d l i n g s p e r i s h d u r i n g  season, r o s e t t e s are l i k e l y In t h i s study i t was  where  to s u r v i v e  and produce  seed i n a  one later  assumed that d i f f u s e knapweed spent o n l y one  the v e g e t a t i v e r o s e t t e s t a g e , but because 66% of the r o s e t t e s i n 1977  not b o l t , t h i s phase of l i f e  is likely  to l a s t  two  o r more y e a r s , and  the  year did  164 mean g e n e r a t i o n time may  be g r e a t e r than t h r e e  years.  Spotted knapweed b o l t e d more r e a d i l y than d i d d i f f u s e knapweed because o n l y 46%  of the r o s e t t e s remained v e g e t a t i v e i n 1977.  the f i r s t year of m a t u r a t i o n  was  much l e s s  However, seed y i e l d  (13 - 1 seeds per i n d i v i d u a l )  than f o r d i f f u s e knapweed (148 - 23 seeds per i n d i v i d u a l ) . knapweed may  produce e v e r - i n c r e a s i n g amounts of seed  compensated f o r , and  knapweed was study may  i n t h i s study  the r e p r o d u c t i v e e f f o r t of  f i n d t h a t s p o t t e d knapweed has  e t a t i v e growth may  "on"  and  a b i l i t y of p l a n t s to p e r s i s t  maturation  spotted  However, f u t u r e  " o f f " y e a r s of f l o w e r i n g ,  and White, 1974), such t h a t y e a r s of v e g -  occur between y e a r s of s e x u a l  p l a n t s on v e r y low n u t r i e n t and to  year of  almost i d e n t i c a l to t h a t of d i f f u s e knapweed.  as does Centaurea j aceana (Harper  "The  Because s p o t t e d  i n f o l l o w i n g growing  seasons, the weak attempt at r e p r o d u c t i o n d u r i n g the f i r s t is  during  reproduction.  f o r long p e r i o d s as j u v e n i l e or immature  l i g h t r e s o u r c e s , i s c o n s i d e r e d by Rabotnov  be of g r e a t importance i n the s t r u c t u r e of p e r e n n i a l herbaceous p l a n t  populations.  The  d i v e r s i t y of  'age  stage' composition  i n plant  (and the spectrum i n c l u d e s the b u r i e d , v i a b l e seed p o p u l a t i o n s )  populations enable  s p e c i e s , i n s p i t e of c o n s i d e r a b l e changes of environment, to p e r s i s t  as  components of communities, sometimes w i t h q u i t e s m a l l changes i n the numbers of  individuals."  (Harper  and White, 1970)  D i f f u s e and  s p o t t e d knapweed  p l a n t s , which a r e i n v e g e t a t i v e r o s e t t e s t a g e s , or which grow v e g e t a t i v e l y between y e a r s of f l o w e r i n g , comprise 25% than the s m a l l r o s e t t e stage. space, and prevent  to 75% of the i n d i v i d u a l s o l d e r  Even i f they produce no  o t h e r s p e c i e s from e s t a b l i s h i n g .  seed,  they  occupy  Therefore, g a l l  which can a t t a c k o n l y p l a n t s which f l o w e r , a f f e c t , what may  be l e s s  flies, than  165 half of  the p o p u l a t i o n o l d e r than the s m a l l r o s e t t e s t a g e .  'age  stage' c o m p o s i t i o n "  (Harper and White, 1970)  p l a n t p o p u l a t i o n to p e r s i s t plants.  The  timated  to be t h r e e and  pectively.  Therefore  M i n i m a l turnover f i v e years  "diversity  a l s o enable  i n s p i t e of i n t e n s e a t t a c k by  l e n g t h i e r the v e g e t a t i v e stage,  of the p l a n t p o p u l a t i o n .  may  Thus the  the  i n s e c t s of mature  the slower i s the t u r n o v e r  r a t e s f o r these  f o r d i f f u s e and  s t u d i e s were e s -  s p o t t e d knapweed, r e s -  the f l i e s would have to e l i m i n a t e a l l seeds f o r  p e r i o d s b e f o r e the p l a n t p o p u l a t i o n s  rate  c o u l d be e r a d i c a t e d .  those  In o t h e r h a b i t a t s ,  where l o n g e v i t y i s even g r e a t e r , complete seed d e s t r u c t i o n would have to occur  f o r even l o n g e r p e r i o d s .  Werner (1975) found t h a t D i p s a c u s  r o s e t t e s c o u l d remain v e g e t a t i v e f o r as long as f i v e y e a r s . could conceivably p e r s i s t average i t has seed-reducing  f o r f i v e years  fullonum  D i f f u s e knapweed  i n a v e g e t a t i v e s t a g e , but on  a s h o r t e r l i f e s p a n than does s p o t t e d knapweed.  the  Therefore  a  b i o l o g i c a l c o n t r o l agent, which t h e o r e t i c a l l y d e s t r o y s a l l  seeds, would e r a d i c a t e a d i f f u s e knapweed p o p u l a t i o n f a s t e r than a  spotted  knapweed p o p u l a t i o n .  The  g a l l f l i e s were a b l e to reduce the p o t e n t i a l seed y i e l d by o n l y about  80%  on both d i f f u s e and  numbers i n 1977 (R ) 0  (section II B i x ) .  f o r the d i f f u s e and  g r e a t e r than one  s p o t t e d knapweed r e l e a s e s i t e s at peak p o p u l a t i o n  and  At t h i s r a t e the r e p r o d u c t i v e  s p o t t e d knapweed p o p u l a t i o n s  the p l a n t p o p u l a t i o n s  or g i v e n t h a t R =  94%  of the seed y i e l d on the d i f f u s e and  and  93%  0  tions, respectively. some y e a r s  For R  0  are to  be  0.999, the g a l l f l i e s would have to reduce  I t i s p o s s i b l e that R  even without  i n t h i s study  are i n c r e a s i n g .  decreasing,  efforts  the g a l l f l i e s .  0  s p o t t e d knapweed  c o u l d be  In 1977,  l e s s than 1.0  populaduring  the average number of seeds  per seed head f o r a s p o t t e d knapweed p o p u l a t i o n i n Westwold, c l o s e to  this  166 study  s i t e , was  only 1 1 - 2  (Table X X I I ) ,  and  i f t h i s v a l u e i s used i n s t e a d  of  Watson's (1972) e s t i m a t e of 26.6  if  c o n d i t i o n s t h a t d i d not i n c r e a s e the seed y i e l d p e r s i s t e d , t h i s  tical  seeds per seed head, then R =  s p o t t e d knapweed p o p u l a t i o n would decrease  i s l e s s than 1.0  f o r most y e a r s  i n density.  f i v e years) which produces a r e s e r v o i r of seeds,  crop  Thus  theore-  Possibly  f o r some knanweed p o p u l a t i o n s , and  p e r s i s t e n c e of these p o p u l a t i o n s depends on a bumper seed in  0.86.  a  R  0  the  (say, once  r o s e t t e s and j u v e n i l e  perennial plants.  Because g a l l f l i e s  decrease  seed y i e l d  i n unattacked  heads i f some heads on  the same p l a n t have been a t t a c k e d , the e s t i m a t e of 10.7 seeds per seed head i s p r o b a b l y underestimated. in  Although  R  c  low i n t h i s study,  f o r d i f f u s e and  and R  - .3 d i f f u s e knapweed D  may  be  s p o t t e d knapweed  t h i s study were s i m i l a r , R„ v a l u e s p r o b a b l y  slightly  populations  f l u c t u a t e g r e a t l y with  vear,  l o c a t i o n and knapweed s p e c i e s .  Plant l i f e was  t a b l e s should be made over l e n g t h v p e r i o d s .  considered  spp.  (Harper  too s h o r t to develop  and White, 1974).  Anthoxanthum odoratum mine s i t e .  of  tables f o r Plantago  Antonovics  and  years  Ranunculus  (1972) s t u d i e d p o p u l a t i o n s  of  "Measures of p o p u l a t i o n t u r n o v e r . . . are r e v e a l e d . . . o n l y i f p l a n t s observations... Stable vegetation i s . . . i n  f l u x i n which the r a t e s of turnover a r e c r i t i c a l  the s t a b i l i t y . "  r o s e t t e and  to t h r e e  f o r s i x years to o b t a i n r a t e s of t u r n o v e r on a z i n c  are marked f o r r e p e a t e d continuous  life  Two  (Harper,  1967).  In t h i s study,  a s t a t e of  characteristics  only plants i n small  o l d e r stages were marked f o r o b s e r v a t i o n , but more u s e f u l i n f o r -  mation c o u l d be o b t a i n e d their lifespan.  i f s e e d l i n g s were a l s o marked and  S e e d l i n g s of some s p e c i e s develop  followed  through  i n t o mature p l a n t s f a s t e r  167 if  they germinate i n the f a l l ,  germinate i n the f a l l  r a t h e r than i n the s n r i n g , but those  r i s k death d u r i n g the w i n t e r .  that  I f seedlings are not  marked, then they must be counted f r e q u e n t l y enough to e s t a b l i s h death r a t e s for  a l l c o h o r t s which germinate (Harper and White, 1974).  I n t e r v a l s o f two  weeks appear t o be s h o r t enough to determine death r a t e s o f d i f f u s e and s p o t t e d knapweed s e e d l i n g s , p r o v i d e d  the r e s e a r c h e r  can d i s t i n g u i s h between  newly-germinated s m a l l s e e d l i n g s and s m a l l s e e d l i n g s which may be o l d e r than two weeks.  Age  i s u s u a l l y based on p l a n t s i z e .  P l a n t age, however, i s o f t e n u n r e l a t e d ,  or o n l y weakly r e l a t e d , t o seed y i e l d , e s p e c i a l l y i n b i e n n i e l s , where r o s e t t e s must a t t a i n a c r i t i c a l  s i z e before b o l t i n g .  This c r i t i c a l  s i z e can  be a t t a i n e d q u i c k l y under good growing c o n d i t i o n s , but i f c o m p e t i t i o n f o r n u t r i e n t s , l i g h t and space a r e g r e a t , the c r i t i c a l attain  (Werner, 1976).  Thus l i f e  s i z e may take  t a b l e s f o r some p l a n t s may be termed  s p e c i f i c " r a t h e r than " s t a g e - s p e c i f i c " as i n i n s e c t e c o l o g y , as i n animal  longer to "size-  or "age-specific"  ecology.  D i f f u s e and s p o t t e d knapweed m o r t a l i t y a t the s m a l l s e e d l i n g stage appears to be dependent on weather c o n d i t i o n s to some degree. hot  s p e l l s without  I n 1977 t h e r e were two  r a i n f a l l d u r i n g the growing season;  J u l y 19th to 27th (Table XXVIII),  the f i r s t was from  when the mean temperature was 17 - 1 °C i n  Kamloops (the n e a r e s t weather s t a t i o n t o the d i f f u s e knapweed s i t e ) , and 19 l"C  i n Westwold (Table XXXIX).  The second hot, d r y s p e l l o c c u r r e d  from  August 5 t h to 17th, when the mean d a i l y temperatures i n Kamloops and Westwold were 24.3 - .5°C and 19.4 - .5°C, r e s p e c t i v e l y .  During  the l a t t e r h o t s p e l l  s m a l l s e e d l i n g numbers dropped to n i l f o r both d i f f u s e and s p o t t e d knapweed,  168 T a b l e XXVIII.  Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31  April K w T 0.2 0 0 0 0 0 T 2.6 T 0 0 5.8 0.7 0.7 2.7 0 T T 0 0 0 0 0 0 1.8 0 0 T 0  -  May K  0.8 0 0 0 0 0 0 7.6 0 0.5 0 0 0 0.5 0.3 0.5 0 0 2.0 0 0 0 0 0 1.0 0 0 0 0 0  -  T o t a l d g i l y p r e c i p i t a t i o n (mm) f o r Kamloops and Westwold i n 1977 June w  0 0.3 4.1 3.1 0.8 2.0 T 0.5 T 2.5 0.6 0 0 0 0 0 0 0 0.2 2.0 1.1 0 0 0 0.2 T T 0 T 0 T 0 0 0 0 0 T 0 T 0 0 0 0 0 5.7 11.4 0 8.9 0 1.3 0.6 0 0 1.0 T 0.3 0 0 0 0 0.4 0.8  w  0 T T 0.4 0 0 0 T T 0 0 0 6.7 2.5 T 0 0 0 6.9 T 0 0 0 0 0 0 T 0 0 0  0 0 0 3.8 0 0 0 T 0 0 0 0.7 0 2.0 0 0 0 0 1.5 0 0 0 0 0 0 0 0 0 0 0  -  -  K  w  0 0 1.2 0.5 2.6 2.3 0.2 1.3 0.5 1.8 T 0 0 0 0 0 0 0 0 9.9 7.1 1.5 1.4 2.8 0.7 2.0 0 0 0 0 T 1.9 0 0 T 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9.0 10.9 0 0 0 0 0 0  September K w  August K W  July  K  0 0 5.4 T 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 1.5 0.6 1.7 3.4 T 12.5 T 2.2 0.5 4 0  0 2.8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 T 0.8 2.5 T 0.5 6.1 0 7.4 2.5 T 0  0 1.2 1.2 1.4 0 0 4.4 0 0 0 0 0 0 2.4 0 0 T T 1.4 T 0.9 0.8 12.1 0.7 0 0 0 0 0 0  -  0 2.3 0 T 0 0 2.8 0 0 0 0 0 0 0 0 0 0.8 1.5 4.3 2.3 0 5.8 1.0 0.5 0 0 0 0 0 0  -  C l i m a t e o f B r i t i s h Columbia, pub. by the B.C. M i n i s t r y o f A g r i c u l t u r e T = t r a c e ; K= Kamloops, W= Westwold  but  i f the summer had been c o o l e r and w e t t e r , such as i n 1976, l a r g e  of replacement r o s e t t e s  c o u l d have been produced.  p e t i t i o n may p l a y a p a r t weather c o n d i t i o n s  appear a t any time d u r i n g have to f a l l  Thus i n t r a s p e c i f i c com-  i n the r e g u l a t i o n o f knapweed  f a v o u r g e r m i n a t i o n and s e e d l i n g  numbers  populations  survival.  the growing season, but a g r e a t  o n l y when  Seedlings  may  d e a l o f r a i n may  i n midsummer a f t e r a drought t o r a i s e the s o i l m o i s t u r e  level  169 T a b l e XXIX.  Mean d a i l y temperature  April K 5.5 5.1 12.6 13.2 9..8 9..9 15.,3 13. 8. 6.8 5.8 8.3 9.9 5.9 10.1 7.4 4.0 7.1 5.0 5.4 8.0 17.1 17.6 18.3 18.7 14.7 10.5 12.7 14.2 12.6  May W  2.0 2.0 8.6 8.9 7.5 8.3 10.3 10.0 5.0 3.1 4.7 5.3 8.6 4.1 4.4 1.7 2.8 4.0 2.8 4.4 4.2 15. 12. 15.0 14.7 10.6 14.6 8.9 14.2 9.7  K 13.9 13.7 12.4 11.3 8.0 12.1 15.5 16.0 14.7 12.2 11.4 11.7 13.2 12.1 9.1 14.5 14.1 14.2 15.9 15.3 18.6 15.5 13.1 12.9 12..2 15.,1 10..4 10.6 14.9 15.8 16.0  (°C) f o r Kamloops and Westwold i n  June W  10. 8. 9. 8. 6. 8. 12. 8. 11. 9. 10.0 7.8 9.5 8.3 6.1 10.3 11.1 9.5 12.0 12.8 12.5 10.0 10.3 10.6 8.1 11.4 5.6 7.8 11.4 10.0 12.2  C l i m a t e of B r i t i s h Columbia, K = Kamloops, W = Westwold  K 17.2 14.7 13.3 16 18 24 24 18 15 16.4 19.1 18.4 18.8 18.3 18.0 21.6 22.1 23.8 24.3 19.6 19.2 18.6 20.4 22.0 17.7 20.6 18.6 20.9 18.7 19.6  pub.  July W  12.2 11.4 14.5 13.6 13.4 19.2 20 18 11 11 13 14 15 14 14 16 16.7 19.2 19.7 17.8 16.4 18.6 16, 19. 16. 16. 14. 16. 15. 14.  K 23.0 15.4 13.6 15.0 15.7 17.5 18.6 22. 20. 21. 19. 17.0 20.1 19.2 22.2 18.8 16.6 16.4 16.8 21.1 23.9 21.2 23.1 22.6 25 26 25 21 17 19.0 21.5  by the B.C.  s u f f i c i e n t l y f o r g e r m i n a t i o n , because "The  W 18.9 13.9 11.4 9.5 10.3 14.2 13 18 17 17 16 15.3 17.5 15.8 19.2 16.7 13.9 13.6 12.2 15.3 19.2 16.7 17.2 18.6 24.2 22.8 20.6 31.6 13.9 17.0 18.3  August K W 23.4 25.5 25.6 22.9 23.2 22.5 24.0 23.3 25.5 23.6 25.3 26.3 28.5 25.4 22.5 22.5 23.7 24.8 27.5 25 23 23 18 16 15 15 16.0 17.9 13.6 13.4 14.5  September K  17.5 18.8 22 19 18, 17, 18, 20.0 20.3 19.5 20.8 22.2 22.5 20.8 17.5  15 13 17 18 15 15 14 15 15.8 15.9 15.3 16.5 17.3 13.8 12.2  16 18 19 21 21.1 20.3 21.4 17.5 15.0 13.9 13.3 12.5 12.5 11.4 9.2 10.3  11.,1 15.,3 14.,3 13.,8 13.,3 11..4 12,.4 10.1 10.8 9.9 10.3 8.6 9.3 12.6 10.3  M i n i s t r y of A g r i c u l t u r e  l o n g e r and more severe the d r o u t h  the g r e a t e r the q u a n t i t y of r a i n f a l l t h a t w i l l be r e q u i r e d s u b s e q u e n t l y break i t . " (Daubenmire,  1911*  1959)  5.Conclusions: 1 . D i f f u s e and s p o t t e d knapweed have Deevey type I I I s u r v i v a l  curves.  to  170 2. D i f f u s e knapweed i s more t y p i c a l of an " r - s e l e c t e d " organism, and s p o t t e d knapweed i s more t y p i c a l o f a " K - s e l e c t e d " organism. 3. D i f f u s e knapweed, w i t h a f a s t e r p o p u l a t i o n t u r n o v e r s m a l l r o s e t t e s each year 4.In  r a t e , produces more  than does s p o t t e d knapweed.  t h i s study r e p r o d u c t i v e e f f o r t s of d i f f u s e and s p o t t e d knapweed were  similar. 5.Small s e e d l i n g s u s u a l l y appear i n the s p r i n g o r i n the f a l l . 6. Dry,  hot weather i n t h e summer i n c r e a s e s s m a l l s e e d l i n g death,  but a few  l a r g e s e e d l i n g s and s m a l l r o s e t t e s u s u a l l y s u r v i v e t o take t h e p l a c e o f mature p l a n t s which d i e . 7. D i f f u s e and s p o t t e d knapweed can s u r v i v e the w i n t e r  i n any stage o f develop-  ment .  C. KNAPWEED SEED SOWING TRIALS 1.Introduction: P o p u l a t i o n d e n s i t i e s o f some p l a n t p o p u l a t i o n s a r e r e g u l a t e d by " c o n t r o l l e d germination", densities  where g e r m i n a t i o n  (Palmblad,  v a r y i n g seed  1968).  r a t e s a r e suppressed  w i t h i n c r e a s i n g seed  D i f f u s e and s p o t t e d knapweed produce w i d e l y  d e n s i t i e s on r a n g e l a n d .  F o r example, a t White Lake  Observatory  t h e r e were o n l y 66 - 13 d i f f u s e knapweed seeds p e r 50 X 50 cm, w h i l e i n Lumby-1 t h e r e were 6628 - 1228 d i f f u s e knapweed seeds p e r 50 X 50 cm ( s e c t i o n II B v i i ) .  Preliminary observations  i n the f i e l d  showed t h a t , even i f av-  erage seed y i e l d s were low, d e n s i t i e s of s e e d l i n g s i n s m a l l p a t c h e s c o u l d be very high.  One purpose o f t h i s study was t o determine i f d i f f u s e and s p o t t e d  knapweed e x h i b i t e d a c o n t r o l l e d g e r m i n a t i o n density.  response t o an i n c r e a s i n g seed  171 Watson (1972) found t h a t s p o t t e d knapweed i s more p r e v a l e n t i n mesic i n t h e I n t e r i o r of B r i t i s h Columbia, w h i l e d i f f u s e knapweed drier locations.  habitats  i s more common i n  T h i s study compares the s u c c e s s o f knapweed e s t a b l i s h m e n t  from seed i n two h a b i t a t s , one h o t t e r and d r i e r than t h e o t h e r . order to compare the e f f e c t s o f weather on knapweed t r i a l s on one s i t e were made a t two d i f f e r e n t  Also, i n  e s t a b l i s h m e n t , seed  sowing  times d u r i n g t h e 1976 growing  season.  2.Method: D i f f u s e and s p o t t e d knapweed  seeds were sown a t t h e A g r i c u l t u r e Canada Re-  s e a r c h S t a t i o n i n Kamloops, and a p p r o x i m a t e l y 70 km from Kamloops, i n Westwold. site  The Kamloops s i t e has a h o t t e r and d r i e r c l i m a t e than t h e Westwold (Table XXX).  D i f f u s e knapweed i s more p r e v a l e n t i n t h e Kamloops a r e a  w h i l e s p o t t e d knapweed  i s most common i n Westwold.  No knapweed was found on  the Kamloops s i t e , but s p o t t e d knapweed was found i n s p a r s e patches a few meters  from t h e Westwold s i t e .  Other s p e c i e s commonly  p r e s e n t on t h e Kam-  l o o p s s i t e were S a l s o l a k a l i and A r t e m e s i a t r i d e n t a t a , whereas i n Westwold, Amelanchier a l n i f o l i a ,  Shepherdia c a n a d e n s i s , Pseudotsuga m e n z i e s i i , P i n u s  c o n t o r t a l a t i f o l i a , Poa p r a t e n s i s and C a l a m a g r o s t i s rubescens were common. The Kamloops s i t e was l o c a t e d i n an open f i e l d , w h i l e t h e Westwold s i t e was i n a c l e a r i n g i n t h e midst o f regrowth from a p r e v i o u s l y logged  T a b l e XXX.  Comparison  o f Kamloops and Westwold seed sowing  *  *  t o t a l annual precipitation (mm) Kamloops 260 Westwold 316  x daily temperature (°C) 8.3 6.1  Site  C l i m a t e of B r i t i s h Columbia,  sites  * x No. o f days with frost 130 192  Altitude (m) 350 646  s t a n d a r d 1941 - 1970 average  forest.  172 Both s i t e s were m e c h a n i c a l l y worked to a depth of about 10 cm and then raked smooth. cm.  P l o t s were e s t a b l i s h e d i n g r i d s 75 cm a p a r t .  G r i d s i z e and shape v a r i e d between s i t e s .  Plot  s i z e was 25 X 25  B o r d e r s o f p l o t s were d e l i n -  eated w i t h b a l e r twine, h e l d i n p l a c e w i t h f e n c i n g s t a p e s .  Sowing r a t e s  were chosen a t random f o r each p l o t .  Seeds f o r the Kamloops 1976 sowing had been c o l l e c t e d  i n 1975 i n the Kamloops  a r e a d u r i n g August, and s t o r e d d u r i n g the w i n t e r a t room temperature. b o t h 1976 f a l l the  Pritchard  For  sowings a t Kamloops and a t Westwold seeds were c o l l e c t e d i n ( d i f f u s e knapweed) and Westwold ( s p o t t e d knapweed) a r e a s ,  s t o r e d a t room temperature u n t i l they were used i n O c t o b e r .  and  Seeds were  s p r i n k l e d e v e n l y over the s u r f a c e of the s o i l and p r e s s e d f i r m l y i n t o the ground because Watson (1972) found that g e r m i n a t i o n was b e s t on the s o i l surface.  P l o t s were not watered.  The Kamloops s i t e was seeded t w i c e , i n A p r i l and October o f 1976.  I n the  s p r i n g of 1976 sowing r a t e s were 0, 78, 156, 625 and 1250 d i f f u s e knapweed seeds per p l o t , and 0, 39, 156 and 625 s p o t t e d knapweed seeds per p l o t (because t h e r e were not enough s p o t t e d knapweed seeds f o r o t h e r d e n s i t i e s ) . the  fall  In  of 1976 seeds were sown a t r a t e s of 0, 69, 104, 625, 1875 and 5625  seeds per p l o t f o r b o t h d i f f u s e and s p o t t e d knapweed.  These r a t e s  corres-  ponded to r a t i o s of 0, 9:1, 6:1, 3:1, 1:1, 1:3 and 1:6 square c e n t i m e t e r s of  space t o the number of seeds sown.  Westwold.  T h i s was i n t h e f a l l o f 1976, a t the same time t h a t seeds were  sown i n Kamloops. fall  rates.  f i v e times.  Only one sowing took p l a c e i n  Sowing r a t e s i n Westwold were the same as the Kamloops  Each sowing r a t e , f o r a l l l o c a t i o n s and t i m e s , was  replicated  Counts of knapweed were made i n the s p r i n g and f a l l  of 1977,  when the p l a n t s were c l a s s i f i e d  a c c o r d i n g to t h e i r s i z e , as s m a l l  seedlings,  173 large seedlings  or rosettes  c l a s s ) as i n the p r e v i o u s not  counted.  ( s m a l l r o s e t t e s were i n c l u d e d  section.  Knapweed  found o u t s i d e  i n the r o s e t t e t h e p l o t s was  In September, 1977, counts of seed heads p e r p l o t , and seeds  per head were made f o r knapweed which had b o l t e d i n t h e s p r i n g  1976 t r i a l  i n Kamloops.  3.Results: a)Kamloops, s p r i n g 1976 t r i a l : By t h e s p r i n g o f 1977, one year a f t e r t h e seeds were sown, a l l s u r v i v i n g d i f f u s e and s p o t t e d knapweed p l a n t s were i n t h e r o s e t t e s t a g e . of d i f f u s e and s p o t t e d  knapweed r o s e t t e s i n c r e a s e d  r a t e , w i t h sowing r a t e  ( F i g . 45).  1977,  t h e r o s e t t e s had a l r e a d y  l i n e a r l y , and a t t h e same  When t h e p l a n t s were counted i n May o f  started to b o l t .  synchronously i n n a t u r a l p o p u l a t i o n s ,  B o l t i n g occurs  of b o l t i n g r o s e t t e s p e r p l o t f o r e i t h e r knapweed s p e c i e s  s i g n i f i c a n t l y w i t h sowing r a t e . and  spotted  relatively  t h e r e f o r e most r o s e t t e s which were des-  t i n e d to b o l t would p r o b a b l y have s t a r t e d t o do so i n May. ber  Mean numbers  The average numd i d not d i f f e r  On the average 0.7 - .3 and 0.7 - .2 d i f f u s e  knapweed r o s e t t e s p e r p l o t , r e s p e c t i v e l y , were b o l t i n g i n t h e  s p r i n g , and there was no s i g n i f i c a n t d i f f e r e n c e between t h e s e means.  There  was no s i g n i f i c a n t d i f f e r e n c e , i n r e l a t i o n t o sowing r a t e , i n t h e percentage of r o s e t t e s which d i e d d u r i n g  t h e 1977 growing season o f t h e number  shed i n t h e s p r i n g o f 1977 f o r e i t h e r d i f f u s e o r s p o t t e d  knapweed  establi-  (Table  XXXI).  Only a few o f t h e b o l t e d r o s e t t e s produced seed i n t h e f a l l o f 1977. The r e s t were a r r e s t e d  ( d i d not produce any heads) or b o l t e d u n s u c c e s s f u l l y  duced only a b o r t e d h e a d s ) .  Most of the d i s t a l heads on p l a n t s which  (pro-  174 50-i  -r 400 600 800 .1000 200 NUMBER OF SEEDS SOWN PER PLOT, SPRING 1977 F i g u r e 45.  1200  Average numbers of d i f f u s e and s p o t t e d knapweed r o s e t t e s per p l o t i n the s p r i n g of 1977. f o r the Kamloops, 1976 sowing t r i a l d i f f u s e knapweed-0 0; s p o t t e d knapweed X X  produced mature seed heads, had d e h i s c e d b e f o r e the p l a n t s were h a r v e s t e d . p r o x i m a l seed heads on these p l a n t s appeared s m a l l e r than the d i s t a l  The  heads,  and p r o b a b l y c o n t a i n e d fewer seeds, as shown p r e v i o u s l y f o r a n a t u r a l s p o t t e d knapweed p o p u l a t i o n  (section I I B v i i i ) .  There was a l s o c o n s i d e r a b l e v a r -  i a t i o n i n average numbers of seeds p e r head among i n d i v i d u a l p l a n t s .  There-  fore numbers of seeds f o r each d e h i s c e d seed head were e s t i m a t e d on the b a s i s of head s i z e , p o s i t i o n on the branch, and average numbers of seeds per head i n u n d e h i s c e d heads on the same p l a n t , and t h e t o t a l seed y i e l d per p l o t was found.  A l t h o u g h o n l y s i x d i f f u s e , and two s p o t t e d knapweed p l o t s produced  seeds, i t appears t h a t lowest seed y i e l d s were produced on p l o t s w i t h the  175 T a b l e XXXI.  Percentage dead d i f f u s e and s p o t t e d knapweed by the f a l l of 1977, of the number counted i n the s p r i n g of 1977, on the Kamloops, s p r i n g 1976 sowing t r i a l No. seeds sown per plot  knapweed^" species  2 % dead from May to September, 1977  39  d s  10 J 10% 67 - 33  78  d s  33 - 17  156  d s  13 J 13 51 - 23  313  d s  59 - 15  625  d s  53 J 18 79-8  1250  d s  68 - 14  d = d i f f u s e knapweed; s = s p o t t e d knapweed 2 no s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r e i t h e r d i f f u s e o r s p o t t e d knapweed  highest  r o s e t t e counts i n the s p r i n g of 1977 ( F i g . 46).  b)Kamloops, f a l l  1976 sowing:  Seeds on t h i s s i t e p r o b a b l y germinated i n the f a l l  o f 1976 because by May  of 1977 some p l a n t s had reached the r o s e t t e stage.  Most p l a n t s , however,  were i n the l a r g e s e e d l i n g stage. for  d i f f u s e and s p o t t e d  Large s e e d l i n g numbers i n c r e a s e d  knapweed w i t h sowing r a t e .  There was no s i g n i f i c a n t  d i f f e r e n c e i n r e g r e s s i o n c o e f f i c i e n t s between s p e c i e s appears t h a t a t h i g h e r  sowing r a t e s more s p o t t e d  s e e d l i n g s were produced. per p l o t  ( F i g . 47), but i t  than d i f f u s e knapweed  In May average numbers of s p o t t e d  (8 - 2) d i d not. d i f f e r  linearly  knapweed  large  rosettes  s i g n i f i c a n t l y w i t h sowing r a t e , but average  numbers of d i f f u s e knapweed r o s e t t e s per p l o t i n c r e a s e d  significantly  with  176  500-  0  cn 4001 < U_  O °~  300-\  LU Q. CO Q LU LU  co  200i  LL.  O  ac LU  100 < ho h-  10  20  —T" 30  T" 40  1 50  TOTAL NUMBER OF ROSETTES PER PLOT, SPRING Figure  46.  sowing r a t e  1977  T o t a l number of d i f f u s e and s p o t t e d knapweed seeds produced per p l o t by the f a l l o f 1977 f o r the Kamloops, s p r i n g 1976 sowing trial d i f f u s e knapweed 0 — 0 ; s p o t t e d knapweed XX  (Table XXXII).  In the f a l l  of 1977  t h e r e was no  d i f f e r e n c e i n mean numbers of d i f f u s e (0.2 - .1) or s p o t t e d weed r o s e t t e s per p l o t i n r e l a t i o n to sowing r a t e . weed m o r t a l i t y d u r i n g t o t a l number o f p l a n t s  significant (0.4 - .3)  D i f f u s e and s p o t t e d  knapknap-  the 1977 growing season was between 87% and 100% of the (large seedlings + r o s e t t e s ) present  i n the s p r i n g of  1977, and t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n m o r t a l i t y w i t h sowing r a t e .  c)Westwold, f a l l By May  1976  sowing:  1977 knapweed had developed o n l y as f a r as the l a r g e s e e d l i n g  i n d i c a t i n g t h a t the seeds had germinated i n the s p r i n g of 1977.  stage,  Numbers of  177  200,  1000  2000  3000  4000  5000  6000  NUMBER OF SEEDS SOWN PER PLOT, FALL 1976 Figure  47.  Average numbers o f d i f f u s e and s p o t t e d knapweed l a r g e s e e d l i n g s per p l o t i n the s p r i n g of 1977 f o r the Kamloops, f a l l 1976 sowing trial d i f f u s e knapweed 0 0; s p o t t e d knapweed X -X  d i f f u s e and s p o t t e d  knapweed l a r g e s e e d l i n g s  same r a t e , w i t h the sowing r a t e do b e t t e r a t h i g h e r  increased  l i n e a r l y , and a t the  ( F i g . 4 8 ) , but d i f f u s e knapweed appeared t o  seed d e n s i t i e s .  In the f a l l  of 1977 d i f f u s e and  knapweed were found i n s m a l l s e e d l i n g , l a r g e s e e d l i n g and r o s e t t e The  spotted  stages.  s m a l l s e e d l i n g s had germinated i n the f a l l because they s t i l l had c o t -  yledons attached.  I t was assumed t h a t any l a r g e s e e d l i n g or'.rosette was a  s u r v i v o r of the s p r i n g c o h o r t .  In the f a l l  t h e r e was no s i g n i f i c a n t  ence between mean numbers of d i f f u s e o r s p o t t e d  differ-  knapweed l a r g e s e e d l i n g s  +  r o s e t t e s per p l o t i n r e l a t i o n to sowing r a t e , nor was t h e r e a s i g n i f i c a n t d i f f e r e n c e between mean numbers of d i f f u s e (7 - 1) o r s p o t t e d  (8 - 2) knap-  178 T a b l e XXXII.  No. seeds sown per p l o t , f a l l , 1976 69 104 208 625 1875 5625  Comparison o f d i f f u s e and s p o t t e d knapweed r o s e t t e e s t a l i s h m e n t d u r i n g the 1977 growing season f o r the Kamloops, f a l l 1976 sowing t r i a l knapweed"*" species d s  x number o f r o s e t t e s per p l o t s p r i n g , 1977 2.4 4.4  + +  fall, 0 .4  •£ .9  + 1.6 + .6  d s  4  5.0  d s d s  9  + 100 + 0  0  0  100  0  .5  0  0  100  0  2  2  91  8  0  0  100  0  0  0  100  0  10  + 0 + 0  3  17  4  + 100 + 0  + 0 + 0  + 19 + 6  + .8 + .5  + 18 + 7  + .4 + .4  9 — 7  "d = d i f f u s e knapweed; s = s p o t t e d  + +  1  + 5 + 2  d s  .2 °^  100 87  + 0 + 0  + 1.4 + .8  d s  + +  1977  % dead r o s e t t e s d u r i n g 1977 o f number i n -spring  + 100 + 0 + 98 + 1 + 99 + 1  knapweed  s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r d i f f u s e knapweed  (p <.01)  no s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r d i f f u s e knapweed 'no s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r s p o t t e d  weed r o s e t t e s a l o n e ,  i n r e l a t i o n t o sowing r a t e  knapweed  (Table X X X I I I ) .  The p e r -  centage o f d i f f u s e knapweed l a r g e s e e d l i n g s + r o s e t t e s which d i e d d u r i n g the 1977 growing season i n c r e a s e d w i t h sowing r a t e , but the percentage o f s p o t t e d knapweed l a r g e s e e d l i n g s + r o s e t t e s which d i e d d u r i n g  1977 d i d not v a r y  n i f i c a n t l y w i t h sowing r a t e , and t h e average death r a t e was 22 - 3%. g e r m i n a t i o n r a t e was d e f i n e d  The g e r m i n a t i o n r a t e i n May, 1977, d i d  d i f f e r s i g n i f i c a n t l y w i t h sowing r a t e f o r d i f f u s e knapweed  decreased s i g n i f i c a n t l y w i t h sowing r a t e f o r s p o t t e d knapweed the f a l l  The  as the number o f l a r g e s e e d l i n g s per p l o t / the  number o f seeds sown per p l o t X 100%. not  sig-  o f 1977 the. g e r m i n a t i o n r a t e , d e f i n e d  ( F i g . 49), but ( F i g . 50).  as the number o f s m a l l  In '*  s e e d l i n g s p e r p l o t / t h e number o f seeds sown per p l o t X 100%, decreased s i g -  179 o _i  4ooH  Q_ 0£ LU D_  to  ^  _1  cn  300H  O r-l LU LU  to tJ2 LU  i—i  j§ QL 2 0 0 1 <r to  LL. o  LU CD  1  IOOH  1000  2000  3000  6000  4000 . : 5000  NUMBER OF SEEDS SOWN PER PLOT, FALL 1.9.76 F i g u r e 48/ '•• Average- numbers-of ' d i f f u s e and s p o t t e d "Knapweed l a r g e s e e d l i n g s per p l o t i n t h e - s p r i n g of 1977 f o r the Westwold, f a l l 1976 sowing t r i a l d i f f u s e knapweed 0 0; s p o t t e d knapweed X-•——X  n i f i c a n t l y w i t h i n c r e a s i n g sowing r a t e f o r both d i f f u s e and s p o t t e d  knapweed.  4.Discussion: During the f i r s t  year of growth d i f f u s e and s p o t t e d knapweed e s t a b l i s h e d  e q u a l l y w e l l on e x p e r i m e n t a l at  s i t e s i n Kamloops and i n Westwold.  In f a c t ,  young stages o f development, s p o t t e d knapweed appeared t o do b e t t e r i n  Kamloops, where d i f f u s e knapweed was most common, and d i f f u s e knapweed appeared to do b e t t e r i n Westwold, where s p o t t e d knapweed was more common. Mixed p o p u l a t i o n s  of d i f f u s e and s p o t t e d knapweed i n B r i t i s h Columbia a r e  r a r e , so t h a t s t r o n g i n t e r s p e c i f i c c o m p e t i t i o n stages  probably  e x i s t s at older  of development, and/or s l i g h t changes i n h a b i t a t and c l i m a t e  gives  180 Table  XXXIII.  No. of seeds sown per p l o t  1  Average numbers p l a n t s produced wold, f a l l 1976 d u r i n g the 1977  knapweed species  of d i f f u s e and s p o t t e d knapweed by the f a l l of 1977 on the Westsowing t r i a l , and the death r a t e s growing season  number per p l o t , f a l l 1977 large seedlings rosettes + rosettes  :  8-6% 14-4  69  d s  6 ± 2 13-5  104  d s  17 J 3 11-3  11 J 2 7- 2  208  d s  21 J 7 15 - 3  6 ± 3 8- 3  625  d s  64 J 10 31-7  15 ± 5  16 J 7 27-9  1875  d s  65 ^ 9 76 - 11  11-  5  50 J 4 29-3  5625  d s  130 J 45 107 - 13  6-  3  71 t 8 25-5  12knapweed  8  d = d i f f u s e knapweed; s = s p o t t e d  4 ± 2 5- 2  % dead d u r i n g the\1977 •' growing season  14-4 31 ± 12 24 - 14  s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r d i f f u s e knapweed; no s i g n i f i c a n t d i f f e r e n c e w i t h sowing r a t e f o r a l l o t h e r cases  one  s p e c i e s an advantage over the o t h e r .  Consequently, i f these  were monitored for s e v e r a l more y e a r s , one s p e c i e s may d i s p a c e S i n c e the temperature ranges f o r d i f f u s e 28°C) knapweed seed g e r m i n a t i o n tablishment of h a b i t a t s . and  i s probably Spotted  populations  the o t h e r .  (13°C to 28°C) and s p o t t e d  a r e so s i m i l a r  (10°C to  (Watson, 1972), s e e d l i n g e s -  e q u a l l y s u c c e s s f u l f o r both s p e c i e s i n a wide v a r i e t y  knapweed p e r s i s t s i n the h o t , d r y c l i m a t e of Walachin,  d i f f u s e knapweed grows w e l l i n the c o o l , wet c l i m a t e of Boston Bar,  p o s s i b l y because t h e i r r e s p e c t i v e c o u n t e r p a r t s  have not d i s p e r s e d to these  sites yet.  Seedling establishment  and s u c c e s s i v e growth of some p l a n t s may depend on  whether the s e e d l i n g s germinated i n the f a l l  o r i n the s p r i n g (Harper and  i T  T  1000  2000  3000  NUMBER OF SEEDS  F i g u r e 49.  4000  SOWN PER PLOT,  5000  6000  F A L L 1976  Percentage d i f f u s e knapweed appeared o f t h e number o f seeds sown on t h e Westwold, f a l l 1976 sowing t r i a l l a r g e s e e d l i n g s , s p r i n g 1977 0 0; s m a l l s e e d l i n g s , f a l l 1977 X X  %40l7  30'  20  10  4  I  " ! 1000  2000  NUMBER OF SEEDS  F i g u r e 50.  3000 SOWN PER PLOT,  4000  5000  6000  F A L L 1976  Percentage s p o t t e d knapweed appeared o f t h e number o f seeds sown on the Westwold, f a l l 1976 t r i a l l a r g e s e e d l i n g s , s p r i n g 1977 0 0 s m a l l s e e d l i n g s , f a l l 1977 X X  182 White, 1974).  Those which germinated i n t h e f a l l would be o l d e r , and b e t t e r  e s t a b l i s h e d the f o l l o w i n g summer, than those which germinated i n the s p r i n g . T h i s phenomenon would have a f f e c t e d the s u r v i v a l o f knapweed which was p r o duced from seed sown i n the s p r i n g o f 1976 compared w i t h f a l l Kamloops. but  The f a l l  cohort s h o u l d have the advantage over the s p r i n g  the o p p o s i t e t o the expected o c c u r r e d :  1976  growing season, but the f a l l  season.  cohort,  the s p r i n g cohort s u r v i v e d the  c o h o r t d i e d out d u r i n g the 1977 growing  Weather caused t h i s r e v e r s a l .  and c o l d e r  o f 1976 i n  The 1976 growing season was w e t t e r  (the mean temperature from A p r i l u n t i l September was 15°C and the  t o t a l r a i n f a l l was 221.23 mm)  than the 1977 growing season (the mean temp-  e r a t u r e from A p r i l u n t i l September was 16.4°C and the t o t a l r a i n f a l l was 139.50 mm;  T a b l e XXXIV).  The weather  i n 1977 was s i m i l a r t o the t h i r t y - y e a r  average from 1941 t o 1970, f o r which the mean temperature from A p r i l September was 16.3°C and the t o t a l r a i n f a l l was 140.97 mm, growing season was e x c e p t i o n a l l y wet. in  but the 1977  T h e r e f o r e s e e d l i n g s , which germinated  the f a l l o f 1976, grew i n t o l a r g e h e a l t h y r o s e t t e s , some of which  s u r v i v e d the t y p i c a l l y from t h e f a l l ,  h o t , d r y summer o f 1977.  even  But, a l t h o u g h some p l a n t s  1976 cohort had reached the r o s e t t e stage by the f o l l o w i n g  s p r i n g , they d i d not s u r v i v e the h o t 1977 summer.  T h e r e f o r e knapweed may be-  come e s t a b l i s h e d i n Kamloops o n l y d u r i n g e x c e p t i o n a l l y good growing tions.  until  condi-  Once e s t a b l i s h e d , however, i t c o u l d w i t h s t a n d normal y e a r s .  The Westwold 1976 f a l l  c o h o r t s u r v i v e d the 1977 growing season even  the  cohort d i d n o t .  Kamloops 1976 f a l l  though  I n Westwold the t o t a l r a i n f a l l from  A p r i l u n t i l September i n 1977 (139.31 mm) was s i m i l a r to Kamloops (139.50 mm), but  t h e mean temperature was c o o l e r i n Westwold (12.8°C) than i n Kamloops  (16.4°C).  Even though the seeds i n Westwold p r o b a b l y d i d n o t germinate u n t i l  183 T a b l e XXXIV.:. 1976  and  1977  weather d a t a f o r Kamloops and Westwold  Kamloops x tempera t u r e (°C) 1976 1977  month  January February March April May June July August September October November December  -2.78 .56 2.22 9.45 13.89 16.11 19.45 17.78 15.56 8.33 2.78 0.56  -.41 2.50 4.70 10.50 13.50 19.30 19.90 21.90 13.50 8.30 0.30 -6.60  Westwold  x temperature (°C) 1977 1976  total precipitation (mm) 1976 1977 19.56 10.16 18.80 3.81 21.08 33.02 32.26 122.17 8.89 20.07 14.22 38.10  -3.33 -1.11 0.00 5.56 10.56 12.22 16.11 15.0 12.78 5.56 0.56 -.56  20.0 5.4 11.7 14.5 22.6 16.5 24.6 34.8 26.5 8.3 50.1 63.3  -6.13 -.02 1.96 7.11 9.72 15.56 16.33 17.89 10.45 5.43 -1.67 -8.22  :'total precil p i t a t i o n (mm) 1977 1976 19.55 10.16 18.80 13.21 31.50 44.70 45.97 110.74 4.75 25.15 24.64 31.24  40.39 30.73 28.70 13.21 25.15 25.15 31.85 22.61 21.3421.34 50.04 74.68  ft C l i m a t e of B r i t i s h Columbia, p u b l i s h e d M i n i s t r y of A g r i c u l t u r e  the f o l l o w i n g s p r i n g , p l a c i n g the s e e d l i n g s appeared i n Kamloops i n the f a l l of 1976, more r u n o f f  from the g r e a t e r  moister s o i l conditions  by  the B r i t i s h  Columbia  at a disadvantage to those which  the c o o l e r summer temperatures  and  snow cover i n Westwold p r o b a b l y r e s u l t e d ' i n ....  i n Westwold than i n Kamloops, w i t h b e t t e r knapweed  s u r v i v a l i n Westwold.  Earlier,  i n a study of p o p u l a t i o n  ( s e c t i o n I I I ' A ) , i t was regulatory  r e g u l a t i o n of n a t u r a l knapweed i n f e s t a t i o n s  shown t h a t density-dependent c o m p e t i t i o n  f a c t o r o n l y at the s m a l l s e e d l i n g stage.  acted  r o s e t t e stages.  seedling  In Westwold, the percentage of d i f f u s e knapweed l a r g e  s e e d l i n g s which d i e d i n 1977  increased  w i t h the number of l a r g e s e e d l i n g s  significantly  w i t h sowing r a t e ,  e s t a b l i s h e d i n the s p r i n g of 1977.  growing season was' lower f o r the s p a r s e r  sowing r a t e s  (10%,  33%  and In  Kamloops the percentage of d i f f u s e knapweed r o s e t t e s which d i e d d u r i n g 1976  a  Here, density-dependent  m o r t a l i t y f o r d i f f u s e knapweed appeared to o c c u r b o t h a t the l a r g e and  as  the  and  13%  184 f o r 39, rates  78 and  (59%,  There was  53%  no  156  seeds per p l o t , r e s p e c t i v e l y ) than f o r the denser sowing  and  68%  f o r 313,  625  and  1250  seeds per p l o t , r e s p e c t i v e l y ) .  s i g n i f i c a n t d i f f e r e n c e i n the percentage of d i f f u s e knapweed r o -  s e t t e s which d i e d w i t h i n c r e a s i n g sowing r a t e , but a  the above r e s u l t s do  show  trend.  Spotted knapweed d i d not appear to be r e g u l a t e d  by density-dependent  e i t h e r i n Westwold or i n Kamloops a t the l a r g e s e e d l i n g  and  rosette  density-dependent r e g u l a t i o n p r o b a b l y o c c u r s o n l y at the s m a l l stage.  Other s t u d i e s of p l a n t p o p u l a t i o n  dependent p o p u l a t i o n  seedling  stage.  greater  spp.  S i m i l a r i l y Marshall  Avena spp.  (oats).  An  i n death r a t e w i t h an  exception  to these s t u d i e s  (1961) study of a weed of c e r e a l c r o p s , where no  change i n p l a n t m o r t a l i t y was  density-  Harper  McNaughton (1962) found t h a t m o r t a l i t y was (poppies) were sown at denser r a t e s .  stages;  seedling  dynamics have shown t h a t  r e g u l a t i o n o c c u r s at the  (1968) o b t a i n e d an i n c r e a s e  competition-  and  on p l o t s where Papaver and  Jain  i n c r e a s i n g sowing r a t e f o r i s Harper and  Agrostemma g i t h a g o  Gajic's  (corn  cockle),  observed w i t h sowing r a t e .  In t h i s study i t appears t h a t seed y i e l d per u n i t a r e a d e c r e a s e s w i t h i n creasing  rosette density.  In o t h e r s i m i l a r s t u d i e s , r e p r o d u c t i v e  such as c a p s u l e s or pods which c o n t a i n per  i n d i v i d u a l p l a n t as p l a n t d e n s i t y  Agrostemma g i t h a g o McNaughton, 1962)  (Harper and and  seeds, u s u a l l y decrease i n number increases.  G a j i c , 1961)  pods of V i c i a f a b a  decreased per p l a n t as p l a n t d e n s i t y  structures,  and  For example, c a p s u l e s of of Papaver spp.  (beans'; Hodgson and  increased.  (Harper  Blackman,  Numbers of seeds per  a l s o decreased f o r the above study w i t h Papaver spp.  found.  T h i s r e l a t i o n s h i p d i d not  1956) capsule  I f more work were done  w i t h knapweeds a decrease i n the number of seed heads per p l a n t and might be  and  occur here because few  per  plot  rosettes  185 b o l t e d a f t e r o n l y one season i n the v e g e t a t i v e s t a g e , and sample s i z e s were small.  D i f f u s e and s p o t t e d knapweed p o p u l a t i o n s are r e g u l a t e d , to some degree, by c o n t r o l l e d germination.  The decrease i n g e r m i n a t i o n r a t e f o r s e e d l i n g s  appeared by the s p r i n g o f 1977  i n Westwold was  which  not s i g n i f i c a n t p r o b a b l y be-  cause of the l a r g e s t a n d a r d e r r o r s of the means, but t h e r e was  a decreasing  t r e n d i n the percentage o f seeds which germinated w i t h i n c r e a s i n g sowing Palmblad  (1968) found t h a t c o n t r o l l e d g e r m i n a t i o n was  e x h i b i t e d by Bromus  imermis, Conyza c a n a d e n s i s , P l a n t a g o l a n c e o l a t a and S i l e n e a n g l i c a . fall,  rate.  In the  on the Westwold s i t e , the d e c r e a s e i n the g e r m i n a t i o n r a t e w i t h i n -  c r e a s i n g sowing r a t e may  a l s o have been i n f l u e n c e d by numbers of p l a n t s a l -  ready e s t a b l i s h e d on the p l o t s .  A l t h o u g h the d i f f e r e n c e among means was  not s i g n i f i c a n t , numbers o f l a r g e s e e d l i n g s + r o s e t t e s per p l o t appeared i n c r e a s e w i t h sowing-rate, and s e e d l i n g s may denser p l o t s due to l a c k of space.  to  not have germinated on the  Very low percentages of seed  germinated  a t any one time - u s u a l l y l e s s than 30% o f the o r i g i n a l number o f seeds sown. The remaining seeds p r o b a b l y were blown away, b u r i e d , e a t e n by i n s e c t s , r o dents or b i r d s , or washed out of the p l o t s .  The p r o b a b i l i t y of r o s e t t e e s t a b l i s h m e n t and the subsequent r o s e t t e s i s independent of the number of seeds sown.  b o l t i n g of the  T h e r e f o r e , even i f  g a l l f l i e s d e s t r o y e d 80% of the seeds, as found on the r e l e a s e s i t e s i n 1977 ( s e c t i o n I I B i x ) the chance of knapweed e s t a b l i s h m e n t on a new  s i t e would  depend on weather c o n d i t i o n s and h a b i t a t r a t h e r than the number of seeds d e p o s i t e d on the s i t e . i n B r i t i s h Columbia  I t i s p r o b a b l e t h a t many of the knapweed i n f e s t a t i o n s  s t a r t e d from o n l y a few seeds because knapweed was  first  186 introduced  i n t o the p r o v i n c e as a contaminant of a l f a l f a  seed.  5.Conclusions: 1. D i f f u s e and s p o t t e d knapweed r o s e t t e e s t a b l i s h m e n t  i s independent of  numbers of seeds sown, but s e e d l i n g and r o s e t t e s u r v i v a l a r e dependent on s i t e and weather f a c t o r s . 2. When growing c o n d i t i o n s a r e f a v o u r a b l e d i f f u s e knapweed i s r e g u l a t e d by density-dependent m o r t a l i t y a t the l a r g e s e e d l i n g and r o s e t t e s t a g e s , but s p o t t e d knapweed does not appear to be r e g u l a t e d a t these  stages.  3. Both d i f f u s e and s p o t t e d knapweed may be r e g u l a t e d by c o n t r o l l e d germination. 4. Knapweed c o o l , wet  w i l l e s t a b l i s h i n h o t , d r y l o c a t i o n s , such as Kamloops, o n l y i n summers.  187 IV CONCLUDING DISCUSSION A. INTRODUCTION U_. a f f i n i s and IJ. q u a d r i f a s c i a t a e s t a b l i s h e d e a s i l y , and reached peak i n d e n s i t i e s i n 5 to 7 y e a r s a f t e r t h e i r r e l e a s e . f l i e s on seed p r o d u c t i o n on d i f f u s e and peak p o p u l a t i o n d e n s i t i e s , i n 1977: was  d e s t r o y e d on both the d i f f u s e and  appearance of the p l a n t s was  spectacular at  80% of the expected v i a b l e seed  yield  s p o t t e d knapweed r e l e a s e s i t e s .  The  s t r i k i n g l y a l t e r e d , w i t h d i s t a l heads a b o r t i n g There was  s p o t t e d knapweed seed weight and a 30% decrease  seed v i a b i l i t y .  apparent  e f f e c t of these  s p o t t e d knapweed was  and p r o x i m a l heads d e v e l o p i n g to the seed s t a g e . average  The  an  a 33% decrease i n  i n d i f f u s e knapweed  However, these e f f e c t s have not been severe enough to  c o n t r o l knapweed.  L i k e most b i o l o g i c a l c o n t r o l systems the knapweed/gall f l y system i s a v e r y simple system compared w i t h n a t u r a l phytophagous i n s e c t communities t h e i r host p l a n t s .  The o n l y source of food f o r g a l l - f l y l a r v a e i s o v a r i o l e  t i s s u e i n knapweed heads, and enemies. i s grazed.  the l a r v a e and a d u l t s have no : s p e c i f i c  Knapweed i s not s e r i o u s l y t h i n n e d by o t h e r animals u n l e s s i t But  the f a i l u r e of the f l i e s to c o n t r o l d i f f u s e and  spotted  knapweed can be a t t r i b u t e d not o n l y to i n h e r e n t p r o p e r t i e s of the f l i e s and  the knapweed, but a l s o to the n a t u r e of the responses  p l a n t s to a t t a c k . of two  and  gall-fly  The  system i s f u r t h e r  c o m p l i c a t e d by the  s p e c i e s , each a t t a c k i n g heads a t d i f f e r e n t  m a t u r i t y ; a f a c u l t a t i v e second  gall  of the -  presence  stages of  f l y g e n e r a t i o n ; and h e t e r o g e n e i t y i n  head s i z e s among knapweed such t h a t p l a n t s  183 of one s p e c i e s and i n one p o p u l a t i o n r e a c t d i f f e r e n t l y to the same r a t e o f gall-fly  attack.  IJ. a f f i n i s p o p u l a t i o n s for  appear t o be r e g u l a t e d by density-dependent  competition  food and space i n t h e f i r s t - i n s t a r , p r e - g a l l s t a g e , as was p r e d i c t e d f o r  IJ. j a c e a n a  i f predator  p r e s s u r e were to be l i f t e d  ( V a r l e y , 1947).  Super-  numerary U. a f f i n i s l a r v a e i n d i f f u s e and s p o t t e d knapweed heads causes t h e head t o a b o r t . hard,  E v i d e n c e o f t h i s phenomenon a r e the 4 mm long heads, w i t h  dark-grey o u t e r  U_. a f f i n i s .  Some o f these heads c o n t a i n e d  l a r v a e , but without tified  s h e l l s observed i n the l a b o r a t o r y a f t e r o v i p o s i t i o n by s i n g l e t h i r d - i n s t a r U. a f f i n i s  the t y p i c a l f u s i f o r m g a l l s .  About 57, o f t h e heads i d e n -  as s u p e r p a r a s i t i z e d were o f e i t h e r the above type.  Some l a r g e r super-  p a r a s i t i z e d heads had grown to t h e f l o w e r i n g p o i n t , but c o u l d not f l o w e r because the f l o r e t s had been r e p l a c e d by m u l t i l o c u l a r g a l l complexes, c o n t a i n ^ : r ing  dead l a r v a e a t a l l i n s t a r s and dead a d u l t s which f a i l e d  t o emerge from  the woody g a l l s .  Most s u p e r p a r a s i t i z e d heads (95%)  were d i s t i n g u i s h a b l e from undeveloped heads  o n l y on t h e b a s i s of t h e i r d i s t a l p o s i t i o n s on branches, where heads develop t o the seed stage.  normally  T h i s study d i d n o t c o n c l u s i v e l y e s t a b l i s h t h a t  d i s t a l head a b o r t i o n was caused by s u p e r p a r a s i t i z a t i o n by U. a f f i n i s . Probing  by females b e f o r e o v i p o s i t i o n may have i n j u r e d t h e young heads, o r ."  the p l a n t may'have d e t e c t e d p r o b i n g comm.).  and aborted  t h e head  (Shorthouse, p e r s .  T h i s i s s u b s t a n t i a t e d by t h e f a c t t h a t d i s t a l head a b o r t i o n  occurs  more f r e q u e n t l y on "small-headed" than on " l a r g e - h e a d e d " d i f f u s e knapweed p l a n t s , and i t stands  to reason  t h a t s m a l l heads a r e more e a s i l y i n j u r e d  than l a r g e heads, g i v e n both head types a r e a t t h e same stage of development.  189 But,  g i v e n e q u a l numbers o f eggs l a i d i n s m a l l and l a r g e heads, t h e r e s u l t i n g  l a r v a e have l e s s room and food many eggs o r f i r s t - i n s t a r s  i n the s m a l l heads.  c o u l d abort  containing  as a r e s u l t o f a " s t i m u l a t i o n  the head c o u l d n o t t o l e r a t e " (Shorthouse, p e r s . loped  Small heads  comm.).  that  Sometimes undeve-  heads cannot be d i s t i n g u i s h e d from heads known t o be s u p e r p a r a s i t i z e d  because l a b o r a t o r y work, where s p o t t e d  knapweed was caged w i t h U. a f f i n i s ,  showed t h a t even l a r g e r heads (4 t o 6 mm long) c o u l d a b o r t when exposed t o the f l i e s .  A l l o f these heads shrunk t o a p p r o x i m a t e l y 3 t o 4 mm l o n g , and  resembled undeveloped heads. not 'cause these heads t o abort  I n j u r y due to p r o b i n g  by females p r o b a b l y d i d  because they were o l d e r and l a r g e r ; too many  eggs or l a r v a e per head seems t o be the reason f o r head a b o r t i o n . (ZwBlfer,  1970) and U. j a c e a n a  ( V a r l e y , 1947) both commonly o v i p o s i t f a r  g r e a t e r numbers of eggs p e r head i n t h e l a b o r a t o r y than t h e r e food  forlarval  eggs a l r e a d y  development.  the p a r t o f TJ. a f f i n i s  Females p r o b a b l y cannot determine numbers o f  f u t u r e o v i p o s i t i o n s i t e s simply  f o r egg d e p o s i t i o n .  may be damaged, as a r e f l o w e r  P o s s i b l y , some o f the f l o r e t s  I n t h i s t h e s i s i t i s assumed t h a t  have been s u p e r p a r a s i t i z e d by U. a f f i n i s .  TJ. q u a d r i f a s c i a t a numbers appear to be r e g u l a t e d i t s n a t u r a l enemies.  by many f a c t o r s even  with-  T h i s s p e c i e s never reaches h i g h d e n s i t i e s , but  p e r s i s t s i n s p i t e o f severe c o m p e t i t i o n  by such g a l l f l i e s as TJ. a f f i n i s and  ( V a r l e y , 1947) and o t h e r ' h e a d - f e e d i n g i n s e c t s .  d e n s i t i e s are greater  by t e s t i n g  heads of Sonchus a r v e n s i s when a t t a c k e d by  T e p h r i t i s d i l a c e r a t a (Shorthouse, 1980). d i s t a l heads which a b o r t  ovi-  Furthermore, i t seems a poor s u r v i v a l t a c t i c on  to destroy  the heads f o r s u i t a b i l i t y  U. j a c e a n a  i s room and  l a i d i n heads when they probe, and many females p r o b a b l y  p o s i t i n t o the same head.  out  TJ. a f f i n i s  When JJ. a f f i n i s  than 0.5 f i r s t - i n s t a r l a r v a e p e r head, U. q u a d r i -  f a s c i a t a i s suppressed because U. a f f i n i s , which o v i p o s i t s i n younger  190  heads than U.  quadrifasciata, saturates  o v i p o s i t i o n s i t e s w i t h l a r g e numbers  of woody g a l l s b e f o r e the heads a r e mature enough f o r U. q u a d r i f a s c i a t a utilize. during  At v e r y h i g h U. a f f i n i s d e n s i t i e s many of the heads i n i t i a t e d  the f i r s t f l y g e n e r a t i o n a b o r t and  f a s c i a t a are f u r t h e r r e s t r i c t e d .  o v i p o s i t i o n s i t e s f o r U.  quadri-  But U. q u a d r i f a s c i a t a f i r s t - g e n e r a t i o n  progeny s u r v i v e i n l a r g e - h e a d e d p l a n t s , and  emerge i n August to  on the many heads i n i t i a t e d by small-headed p l a n t s l a t e i n the season.  to  capitalize growing  However, when f i r s t - g e n e r a t i o n U. a f f i n i s d e n s i t i e s are low  most heads a t t a c k e d  i n June and  and  J u l y d e v e l o p to the seed s t a g e , few new  a r e i n i t i a t e d i n A u g u s t , e s p e c i a l l y on s p o t t e d  knapweed.  I f hot,  heads  dry  weather i n August i s combined w i t h the above s i t u a t i o n , second g e n e r a t i o n s of U. q u a d r i f a s c i a t a may  l e a v e v e r y few d i a p a u s i n g l a r v a e .  of U. q u a d r i f a s c i a t a can i n c r e a s e i n the s p r i n g . may  The  But  populations  r a p i d l y from o n l y a few a d u l t s  emerging  e a r l i e r emergence of U. q u a d r i f a s c i a t a i n the  spring  a l s o be a s u r v i v a l t a c t i c by t h i s s p e c i e s , a l t h o u g h i t i s a t a c e r t a i n  d i s a d v a n t a g e because few heads a r e a v a i l a b l e a t t h a t t i m e , and have appeared a r e v e r y young. q u a d r i f a s c i a t a was  These early-emerging f l i e s may  found more f r e q u e n t l y  i n new  those that •  disperse;  l o c a t i o n s than U.  U.  affinis,  (  and  p r e l i m i n a r y work on f l y a c t i v i t y showed U. q u a d r i f a s c i a t a t o be more  a c t i v e than U_.  affinis.  B. REASONS FOR  THE  i.  FAILURE OF THE  GALL FLIES TO  CONTROL KNAPWEED  R e s i l i e n c e of knapweed:  Knapweed heads a r e i n d i v i d u a l u n i t s i n the sense t h a t the amount of  net  o v a r i o l e t i s s u e i n each head appears to l i m i t the number of g a l l s t h a t form.  Heads w h i c h a r e s u p e r p a r a s i t i z e d  p l a n t does not d i e .  do not y i e l d seed, but  the  When the r a t e of s u p e r p a r a s i t i z a t i o n d u r i n g  can  entire  the  first  191 fly  g e n e r a t i o n i s h i g h , the p l a n t responds by i n c r e a s i n g the r a t e o f p r o x i m a l  head i n i t i a t i o n l a t e r i n the growing appears  t o be l e s s e f f i c i e n t  season.  But, i n August  TJ. a f f i n i s  i n a t t a c k i n g heads, and U. q u a d r i f a s c i a t a  cannot use a l l the o v a r i e s t h a t U. a f f i n i s m i s s e s .  T h e r e f o r e seed  can be h i g h i n these l a t e - a p p e a r i n g , f l y - i n d u c e d heads. r e s t r i c t e d by s u p e r p a r a s i t i z a t i o n d u r i n g the f i r s t d e n s i t y may s t i l l be 20% o f the expected y i e l d .  F l y numbers a r e  g e n e r a t i o n , but the seed  T h i s amounted t o 800 and 500  v i a b l e seeds p e r 50 X 50 cm on the d i f f u s e and s p o t t e d knapweed s i t e s , r e s p e c t i v e l y , i n 1977. produce  yield  release  From l i f e t a b l e s , these numbers of seeds can  74 d i f f u s e and 5 s p o t t e d knapweed mature, b o l t e d  plants.  H e t e r o g e n e i t y i n head s i z e among p l a n t s o c c u r s i n both d i f f u s e and s p o t t e d knapweed p o p u l a t i o n s , b u t i t i s most s t r i k i n g i n d i f f u s e knapweed. g e n e i t y i n head s i z e accounted  f o r both r e s t r i c t i o n o f U. a f f i n i s  and h i g h seed y i e l d l a t e i n the growing on small-headed  season.  densities,  More than 95% o f the heads  d i f f u s e knapweed a b o r t e d d u r i n g the f i r s t  whereas o n l y 53% a b o r t e d on large-headed p l a n t s . c i a t a , and some seed were produced  Hetero-  f l y generation,  U. a f f i n i s , U. q u a d r i f a s - ,  by the large-headed p l a n t s d u r i n g t h i s  i n t e r v a l , but fewer new heads were i n i t i a t e d by these p l a n t s when the second g e n e r a t i o n emerged and o n l y 61% o f these l a t e - a p p e a r i n g heads developed to the seed s t a g e .  I n c o n t r a s t , as many heads were i n i t i a t e d  September by small-headed  i n August and  p l a n t s as d u r i n g June and J u l y , and 73% of these  developed t o the seed s t a g e .  i i .Phenology  of TJ. a f f i n i s and TJ. q u a d r i f a s c i a t a :  A l t h o u g h U. q u a d r i f a s c i a t a emerges 5 t o 7 days e a r l i e r than U. a f f i n i s i n June,  the second g e n e r a t i o n s of both s p e c i e s appear  t o be s y n c h r o n i z e d .  192 There i s an i n t e r v a l of one week d u r i n g e a r l y August when f i r s t e r a t i o n s have a l l but d i e d o f f , and to emerge.  The  r a t i o s of f l i e s  f l y gen-  the second g e n e r a t i o n has j u s t s t a r t e d  to heads at s u i t a b l e stages f o r o v i p o s i t i o n  are so low at t h i s time t h a t many heads escape a t t a c k e n t i r e l y , or a r e lightly  iii.  attacked.  Longevity  and  aggressiveness  of v e g e t a t i v e  stages:  D i f f u s e and  s p o t t e d knapweed have been c l a s s i f i e d as b i e n n i e l s or  (Watson and  Renney, 1974;  rangeland two  only  d i f f u s e and  Anonymous, 1962), but  t h i s study  showed t h a t  s p o t t e d knapweed can remain i n the r o s e t t e stage f o r  o r more y e a r s b e f o r e b o l t i n g .  D i f f u s e knapweed may  f o u r months out of i t s t h r e e - to f o u r - y e a r l i f e  spend o n l y the  span r e p r o d u c i n g  B o l t e d s p o t t e d knapweed spends l e s s time then d i f f u s e knapweed heads, and  trienniels  sexually. producing  s p o t t e d knapweed can grow v e g e t a t i v e l y between y e a r s of  reproduction.  The  stage.  Knapweed can become f i r m l y e s t a b l i s h e d i n new The  sexual  g a l l f l i e s a t t a c k o n l y when the p l a n t s have b o l t e d , and  then o n l y when they are i n the bud  a t t a c k them.  last  first  l o c a t i o n s b e f o r e the f l i e s  can  r o s e t t e s to b o l t u s u a l l y produce a few heads, but  these a r e o n l y l i g h t l y a t t a c k e d or missed because f l y p o p u l a t i o n s a r e T h i s ensures a supply of seed  f o r coming y e a r s .  become more v i g o r o u s , and as they develop,  low.  Meanwhile knapweed r o s e t t e s  hundreds of heads w i l l be  duced b e f o r e t h e r e a r e s i g n i f i c a n t numbers o f f l i e s a v a i l a b l e , except  proby  immigration.  Storey  (1976) a l s o f e l t  that  "U. a f f i n i s by i t s e l f may not reduce adequately the d e n s i t y of s p o t t e d knapweed i n western Montana. T h i s suggested because the type of c o n t r o l  193 e f f e c t e d by JJ. a f f i n i s (the r e d u c t i o n i n seed p r o d u c t i o n ) i s not a d i r e c t c o n t r o l of s p o t t e d knapweed ( i . e . , i t does n o t c o n t r o l e x i s t i n g plants). Consequently, wlthough the number of seeds produced c o u l d be reduced, t h e r e would s t i l l be a r e l a t i v e l y l a r g e number of seeds being d i s p e r s e d by the p l a n t s . S i n c e s p o t t e d knapweed i s not an annual, any s u c c e s s f u l s e e d l i n g s c o u l d be s e r v i n g as p o p u l a t i o n a d d i t i v e s i n s t e a d -of p o p u l a t i o n replacements; thus, a s p o t t e d knapweed i n f e s t a t i o n c o u l d c o n c e i v a b l y i n c r e a s e d e s p i t e the presence of JJ. a f f i n i s . " The  r o s e t t e stage of d i f f u s e knapweed i s the most a g g r e s s i v e and  stage of the l i f e c y c l e . ground and d i s c o u r a g e s  competitive  The c i r c u l a r arrangement of l e a v e s shades the  germination  of o t h e r s e e d l i n g s .  Allelopathic  compounds a r e produced not o n l y by the growing l e a v e s , but a l s o by l e a f L'L'zz litter  (Hajak, p e r s . comm.).  The l a r g e tap r o o t uses most of the a v a i l a b l e  s o i l m o i s t u r e i n the v i c i n i t y o f the p l a n t , f u r t h e r d i s c o u r a g i n g growth of other  species.  Rosettes  a r e v e r y drought t o l e r a n t , even when s m a l l , and  can l o s e a l l t h e i r l e a v e s d u r i n g h o t , d r y weather, and regrow new ones when conditions are favourable. be grazed  Preliminary observations  down to the l a s t l e a f without  a f t e r the c o m p e t i t i v e  r o s e t t e stage  the b o l t e d p l a n t s a r e i n the bud  Spotted  killing  them.  show t h a t r o s e t t e s can However, i t i s o n l y  the f l i e s a t t a c k , and then o n l y when  stage.  knapweed i s s i m i l a r t o d i f f u s e knapweed i n t h a t the r o s e t t e stage i s  v e r y a g g r e s s i v e , but i t b o l t s e a r l i e r i n l i f e .  Probably  s p o t t e d knapweed can  take a chance and b o l t w i t h a s m a l l e r c r i t i c a l r o s e t t e s i z e because i n the advent of poor growing c o n d i t i o n s , s t a l k e l o n g a t i o n can cease, or a l l heads may a b o r t , w i t h subsequent p e r e n n i a l i t y and seed p r o d u c t i o n In August head i n i t i a t i o n t e r m i n a t e s  i n later  u n l e s s d i s t a l heads a r e s u p e r p a r a s i t i z e d ,  and v e g e t a t i v e b a s a l growth of r o s e t t e s around maturing s t a l k s Again,  years.  commences.  the f l i e s a t t a c k o n l y d u r i n g the non-competitve stage of s p o t t e d  knapweed.  H a r r i s (1973b) f e l t  t h a t " I t may  ... be rewarding to  194 synchronize  the a t t a c k by the b i o c o n t r o l agent w i t h the p e r i o d of r a p i d  growth by competing v e g e t a t i o n .  T h i s should make maximum use of the compe-  t i t i o n between p l a n t s p e c i e s f o r l i g h t , water, or m i n e r a l s the weed."  in  suppressing  H a r r i s (1973b) c i t e d an example where the stem w e e v i l ,  Ceutor-  hynchus l u t t u r a F. a t t a c k s the t h i s t l e Cirsi'um arvense (L) Scop, i n ' ' e a r l y s p r i n g when g r a s s e s  are most c o m p e t i t i v e w i t h  the t h i s t l e .  In f o u r  years  a f t e r r e l e a s e s were made, the t h i s t l e s d e c l i n e d to 3% of t h e i r former density.  The  problem i s t h a t a s a f e agent may  a g a i n s t d i f f u s e and  not be a v a i l a b l e f o r  s p o t t e d knapweed which a t t a c k s w i t h  importation  sufficient severity  i n the s p r i n g , when r o s e t t e s a r e growing most v i g o r o u s l y .  i v . P l a s t i c r e a c t i o n s by knapweed to a decrease i n seed d e n s i t y : Given a decrease i n s e e d l i n g d e n s i t y , t h e r e i s some i n d i c a t i o n t h a t knapweed r o s e t t e s i n c r e a s e i n s i z e , but must be great - p r o b a b l y eventually result depleted  and  over 95%.  Thus a r e d u c t i o n i n seed d e n s i t y  fewer s e e d l i n g s s u r v i v e to the r o s e t t e stage  death a f t e r m a t u r a t i o n . to 100%  But  to death i n the v e g e t a t i v e s t a g e ,  r e d u c t i o n i n seed d e n s i t y every y e a r .  reduced.  of knapweed p o p u l a t i o n s  a l l e v i a t i n g i n t r a s p e c i f i c competition  secretions  s p e c i e s even when p l a n t c o v e r . i s  d i d not  take p l a c e f o r a s u f f i n .  c i e n t l y l o n g p e r i o d to determine the r e a c t i o n by weeds.  weed, c o u l d be a f a s t e r turnover  a decade  t h i n n i n g of  Furthermore, a l l e l o p a t h i c  the i n v a s i o n of u s e f u l r a n g e l a n d  Thinning  But,  or  not decrease p l a n t cover because l a r g e r  r o s e t t e s produce l a r g e r mature p l a n t s . prevent  should  than the number of  t h i s p r o c e s s would take y e a r s , p r o b a b l y  knapweed p o p u l a t i o n s w i l l p r o b a b l y  may  the r e d u c t i o n i n s e e d l i n g d e n s i t y  i n an i n c r e a s e i n average r o s e t t e s i z e i f the seed bank i s  r o s e t t e s l e a v i n g the p o p u l a t i o n due  w i t h a 95%  diffuse  Another e f f e c t of'  i n knapweed,: e s p e c i a l l y d i f f u s e knap-  r a t e of the p o p u l a t i o n because l e s s  time  195 would have to spent i n the r o s e t t e stage b e f o r e c r i t i c a l  v. Knapweed e s t a b l i s h m e n t from Plant establishment  seed:  i n t h i s study o c c u r r e d i n d e p e n d e n t l y of seed d e n s i t y  sown, down to the lowest (1960) f e l t  s i z e i s reached,  t h a t "The  seeding r a t e of 39 seeds per 50 X 50 cm.  Harper  seed p o p u l a t i o n bears no d i r e c t r e l a t i o n s h i p to the  d e n s i t y of weed i n f e s t a t i o n i t w i l l produce;  t h i s depends on the  frequency  w i t h which i n d i v i d u a l seeds meet m i c r o s i t e s s u i t a b l e f o r e s t a b l i s h m e n t " . T h e r e f o r e , i f e n t i r e , knapweed p l a n t s a r e t r a n s p o r t e d i n the u n d e r c a r r i a g e of a v e h i c l e , as commonly o c c u r s  ( S t r a n g , et a l . , 1979), the p r o b a b i l i t y t h a t  knapweed e s t a b l i s h e s w i l l be the same given t h a t a l l seeds a r e d e p o s i t e d , or t h a t g a l l f l i e s had a l r e a d y reduce  the expected  y i e l d by  80%.  C. FUTURE ASPECTS OF KNAPWEED CONTROL "...the most e f f e c t i v e stage a t which a weed p o p u l a t i o n may  be a t t a c k e d i s  at the e a r l y phases of i t s spread, not when i t has become an obvious tation."  (Harper, 1960).  Although no r e c e n t surveys of the a r e a o c c u p i e d  by knapweed have been undertaken scheduled new  (aerial  photography programmes are ,~  f o r the near f u t u r e ) , d i f f u s e and  areas s i n c e the l a s t survey i n 1972  s p o t t e d knapweed have spread  made by Watson and Renney  D i f f u s e knapweed i s a l r e a d y i n A l b e r t a ( H a r r i s and C r a n s t o n , northwestern 1.5  U n i t e d S t a t e s a l o n e , d i f f u s e and  m i l l i o n ha  (Maddox, 1979).  slow p r o c e s s s : on the average weed ( H a r r i s , 1979).  infes-  1979)  (1974). and  i n the  s p o t t e d knapweed occupy some  B i o l o g i c a l c o n t r o l i n Canada i s a . r e l a t i v e l y i t takes 20 y e a r s to a c h i e v e s u c c e s s f o r one  T h e r e f o r e knapweed can c o n c e i v a b l y spread to new  t i o n s , d e s p i t e the e f f o r t s of s p r a y i n g crews to c o n t a i n t h i s p e s t u n t i l logical control i s successful.  to  locabio-  196 Usually  f i v e b i o l o g i c a l c o n t r o l agents must be r e l e a s e d , and  e s t a b l i s h e d to c o n t r o l one and  spotted  weed ( H a r r i s , 1979).  be  However, because d i f f u s e  knapweed are c l o s e l y r e l a t e d , the e s t a b l i s h m e n t  agents i n 28 y e a r s should  f o u r must  b r i n g about c o n t r o l ( H a r r i s and  of o n l y  six  C r a n s t o n , 1979).  M u l t i p l e i n t r o d u c t i o n s against weeds must be made because, u n l i k e i n s e c t p e s t s which are a t t a c k e d  and  k i l l e d by  t h e i r enemies, weeds are u s u a l l y  weakened by phytophagous i n s e c t s u n t i l c o m p e t i t i o n dary a t t a c k by pathogens, or lowered r e p r o d u c t i v e densities  (van den  A moth, Metzaeria  from other p l a n t s ,  on s p o t t e d  Bosch and Messenger, 1973).  paucipunctella Zeller  knapweed, and  l o c a t i o n s , i t has  ( L e p i d o p t e r a t G e l i c h i i d a e ) , whose  failed  introduced  i n 1976,  introduced  in  a l t h o u g h t h i s agent became e s t a b l i s h e d i n some  to become e f f e c t i v e .  j u g o s l a v i c a Obenberger ( C o l e o p t e r a : B u p r e s t i d a e ) , was  secon-  c a p a c i t y u l t i m a t e l y reduces  l a r v a e a l s o cause seed r e d u c t i o n , but by d i r e c t f e e d i n g , was 1973  only  A f o u r t h agent, Sphenoptera —j s p e c i f i c to d i f f u s e knapweed,  and 'survived on a s i t e near P e n t i c t o n .  This  beetle  r e q u i r e s a r i d h a b i t a t s t h a t a r r e s t r o s e t t e growth i n mid-summer, because l e a f growth d i s l o g e s eggs and  l a r v a e t h a t develop between them.  Galls  are  produced i n the r o o t s , where development to the a d u l t stage i s completed, r o s e t t e s seldom d i e when a t t a c k e d , d u c t i o n may  not be p r e v e n t e d .  and  subsequent b o l t i n g and  (ZwBlfer,  Myers, p e r s .  seed head p r o -  comm.)  agents a g a i n s t  d i f f u s e and  Among them are  the r o o t - b o r i n g moths, ' Pseudocosma caecimaculana  Agapete zoegana L., centaureae DC.  A l t h o u g h U.  spotted  1976:  knapweed are c u r r e n t l y being  and P t e r o l o n c h e i n s p e r s a S t g . , and  and P.  jaceae Otth.  a f f i n i s and  U.  ( H a r r i s and  two  New  screened. Dup.,  rusts, Puccinia  C r a n s t o n , 1979).  q u a d r i f a s c i a t a have not,  but  to date, c o n t r o l l e d  197 d i f f u s e and s p o t t e d knapweed, they may have weakened t h e p l a n t s t o a degree where a t t a c k by a d d i t i o n a l agents w i l l  r e s u l t i n complete c o n t r o l .  The  s i n k - e f f e c t , whereby f l y l a r v a e i n g a l l s a t t r a c t n u t r i e n t s which would have gone i n t o the development of other heads, may a l s o draw on r e s e r v e s a l l o c a t e d to  v e g e t a t i v e growth by s p o t t e d knapweed i n August, thus g r a d u a l l y d e c r e a s i n g  perennial plant size.  Spotted knapweed s e e d l i n g v i g o u r may decrease as a  r e s u l t o f the 33% r e d u c t i o n i n average t h i s decrease  seed weight caused by t h e f l i e s , and  i n s e e d l i n g v i g o u r may a l s o have the long-term  d u c i n g average  plant size.  The percentage  e f f e c t of r e -  o f dormant seeds i n the s o i l  decrease as a r e s u l t o f f l y a t t a c k because i t appears  t h a t seed-coat  may  pro-  p e r t i e s , e s p e c i a l l y f o r d i f f u s e knapweed, have been a l t e r e d by the f l i e s . However, s t u d i e s o f seed-bank dynamics and s e e d l i n g s u r v i v a l should be undertaken  over l o n g p e r i o d s b e f o r e i t can be determined  that the g a l l  flies  a r e c o n t r i b u t i n g to the c o n t r o l of knapweed.  The k n a p w e e d / g a l l - f l y  system i s a u s e f u l system to study from the p o i n t o f  i n s e c t p o p u l a t i o n ecology because a s p e c t s o f e c o l o g i c a l t h e o r y can be t e s t e d w i t h few measurements.  No o t h e r i n s e c t s a t t a c k knapweed heads, and few o t h e r  i n s e c t s damage the r e s t o f the p l a n t s . plants  . -•  developmental  S p i d e r mites  can d e s t r o y b o l t e d  , when the p l a n t s a r e i n t h e bud s t a g e , but t h i s i s r a r e . A l l stages o f the f l i e s  s p e c i f i c enemies.  can be sampled, and to date they have no  V a r l e y (1947) on the o t h e r hand, had t o contend w i t h 8  o t h e r phytophagous i n s e c t s which a t t a c k e d C. n e m o r a l i s head-feeding  i n s e c t s ) and 14 p a r a s i t i c and 1 p r e d a t o r y s p e c i e s of U. j aceana.  He had t o m o n i t o r ' t h e jaceana. chosen,  (some o f them were  s u r v i v a l and f e r t i l i t y  of n i n e of the enemies of U.  I t i s from e c o l o g i c a l theory t h a t new b i o l o g i c a l c o n t r o l agents a r e t h e r e f o r e i t stands t o r e a s o n t h a t as much should be l e a r n e d  from  198 these simple system i n f i e l d  D. RECOMMENDATIONS  c o n d i t i o n s as p o s s i b l e .  FOR THE BIOLOGICAL CONTROL OF WEEDS  E a r l y attempts a t c l a s s i c a l b i o l o g i c a l c o n t r o l were based on the r e s e a r c h e r ' s i n t u i t i o n , and thus c l a s s i c a l b i o l o g i c a l c o n t r o l was more of an a r t than a science  ( H a r r i s , 1973a).  More r e c e n t l y , recommendations f o r choosing  agents  (Watt, 1965; T u r n b u l l , 1967; van den Bosch, 1968 and 1971; L e v i n s , 1969; F r a z e r , 1972; and H a r r i s , 1973a and 1971), the s c r e e n i n g and r e l e a s i n g o f agents and ness  (van den Bosch and Messenger, 1973; ZwBlfer  ZwBlfer,  and H a r r i s , 1971; H a r r i s  1968; and B e i r n e , 1975) and the e v a l u a t i o n o f t h e i r  effective-  (DeBach and H u f f a k e r , 1971; and van den Bosch and Messenger, 1973) have  been made t h a t should make t h e p r o c e s s more s c i e n t i f i c .  A s c i e n t i f i c p r o c e s s s , however, i n v o l v e s t h e p r e d i c t i o n o f the b e s t agent t o c o n t r o l the p e s t .  To a c e r t a i n e x t e n t , non-promising  e s p e c i a l l y where weedy p e s t s a r e concerned, stages.  i f they a t t a c k  non-vulnerable  But r e l i a b l e p r e d i c t i o n s o f the performance o f a new agent cannot  be made y e t . gall-fly  Laboratory  stystem  s i t l z e heads. source  agents can be s h e l v e d ,  s t u d i e s i n d i c a t e d e a r l y i n the study o f the knapweed/  t h a t the f l i e s  can saturate o v i p o s i t i o n s i t e s , and s u p e r p a r a -  B u t , o f t e n i n s e c t s d i s p e r s e r a t h e r than d e p l e t e t h e i r food r e -  i n the f i e l d ,  and a l t h o u g h V a r l e y (1947) p r e d i c t e d t h a t the g a l l f l y ,  TJ. j a c e a n a , c o u l d be c o n t r o l l e d by density-dependent  competition f o r food,  o t h e r f a c t o r s i n B r i t i s h .Columbia c o u l d have r e g u l a t e d U. a f f i n i s Even i f TJ. a f f i n i s proved  to follow Varley's  densities.  (1947) t h e o r y , as i t subse-  q u e n t l y d i d , the amount o f seed r e d u c t i o n c o u l d n o t be f o r e t o l d i n terms o f the more p r a c t i c a l , weed-control s i z e , and the g r e a t e f f e c t  standpoint.  Heterogeneity  i n knapweed head  t h i s f a c t o r has i n r e g u l a t i n g U. a f f i n i s and U.  q u a d r i f a s c i a t a numbers, as w e l l as i n the p o t e n t i a l seed y i e l d o f knapweed  199 at  peak f l y d e n s i t i e s , was not r e c o g n i z e d  their population  maxima.  I t remains to be  ever become more of a s c i e n c e  To  u n t i l the f l i e s were  seen, i f b i o l o g i c a l c o n t r o l w i l l  than an a r t .  take f u l l advantage of the unique o p p o r t u n i t i e s  agents, and introduced  reaching  f o r studying  the e f f e c t s these agents have on weeds, each agent should s i n g l y so t h a t i t s i n d i v i d u a l e f f e c t s can be determined.  r e t i c a l l y , wherever s e v e r a l s p e c i e s are i n t r o d u c e d ,  (van den  Bosch, 1968).  But,  weight, but 1971a one  and  1971b).  together  By  i n s e c t s may  studying  p l a n t , the r e s e a r c h e r  may  increase  seed weight  simple systems i n v o l v i n g one foresee  agents  reduction  in  attack  the o v e r a l l r e s u l t might  For example, f o l i a g e - f e e d i n g i n s e c t s may  flower-feeding  Theo-  i n a s i t u a t i o n where agents t h a t  d i f f e r e n t p a r t s of a p l a n t are r e l e a s e d counter-productive.  be  the more e f f i c i e n t  r e p l a c e or suppress the l e s s e f f i c i e n t ones, presumably w i t h no control  introduced  be  reduce seed (Maun and  Cavers,  insect attacking  the outcome i n a more  complicated  system.  Harris  (1973b) f e l t  that g a l l - f o r m i n g  i n s e c t s may  l o g i c a l c o n t r o l agents because they have "evolved host  t h a t r e n d e r s them i n c a p a b l e  of i n f l i c t i n g  study support's H a r r i s ' p r e d i c t i o n . Pamakani, by in  stems, was  be poor c h o i c e s  bio-  a homeostasis w i t h  s e r i o u s damage to i t " .  their This  However, c o n t r o l of the r a n g e l a n d weed,  a t e p h r i t i d g a l l f l y , Eupatorium adenophorum, which forms g a l l s s u c c e s s f u l i n some p a r t s o f Maui (Bess and  Shorthouse (1980) c i t e d  s e v e r a l exampls of g a l l - f o r m i n g  warranted c o n s i d e r a t i o n as b i o l o g i c a l c o n t r o l agents. f u r t h e r p r e d i c t e d t h a t f l o w e r - and value  as  f o r b i o l o g i c a l c o n t r o l and  Haramoto, 1959), i n s e c t s which  Harris  (1973a)  b u d - f e e d i n g i n s e c t s would be of  little  t h i s study supports h i s g e n e r a l i z a t i o n .  and  200 The wide d i s t r i b u t i o n of b i o l o g i c a l c o n t r o l agents b e f o r e t h e i r success can be demonstrated monitored owners who  on a few t y p i c a l s i t e s , and t h e i r i n i t i a l d i s p e r s a l can be  i s a waste of money and may may  a l s o f a l s e l y r a i s e the hopes of l a n d -  be d e s p e r a t e f o r a low-cost means of p e s t c o n t r o l . '  The  a b i l i t y of agents to s e a r c h f o r t h e i r h o s t s i s an important a t t r i b u t e which s h o u l d be e v a l u a t e d .  I f one agent were d i s t r i b u t e d  initially  to a l l .  l o c a t i o n s , then e f f e c t s of i n d i v i d u a l agents t h a t might be imported i n the f u t u r e i s . ' " d i f f i c u l t a t best-, and'.of ten i m p o s s i b l e ' t o determine 1  o r i g i n a l agent cannot be kept out of the study a r e a s .  i f the  There must be  ' . control  s i t e s where the e c o l o g y of the weed can be monitored without i t s enemies to e s t a b l i s h a b a s e l i n e f o r e s t i m a t i n g the e f f e c t s of i n s e c t a t t a c k . a l t e r s the n a t u r a l p l a n t growth and the m i c r o - e c o l o g y of the t e s t  Caging  site.  "The p l a n t demographer s h o u l d . . . i d e a l l y concern h i m s e l f not o n l y w i t h the numbers of but a l s o the s i z e d i s t r i b u t i o n of i n d i v i d u a l s w i t h i n a p o p u l a t i o n ; he s h o u l d d i s t i n g u i s h between g e n e t i c and p h y s i o l o g i c  i n d i v i d u a l s ; he  have to make a r b i t r a r y d i s t i n c t i o n s about when a p l a n t becomes a p l a n t ; he s h o u l d attempt  to measure r e a l d e n s i t i e s w i t h i n ,  d e n s i t i e s over an a r e a " (Harper, 1960).  may and  an a r e a r a t h e r than mean  The importance  of l o o k i n g a t the  i n d i v i d u a l i n a p l a n t p o p u l a t i o n was"'shown i n t h i s study by the more f r e q u e n t head s u p e r p a r a s i t i s m by U. a f f i n i s of " s m a l l " than " l a r g e " heads, g i v e n both head types a r e a t the same stage of m a t u r i t y .  Weeds may  form  monocultures,  and a l t h o u g h i n t r o d u c e d b i o l o g i c a l c o n t r o l agents a r e u s u a l l y monophagous, the environment  can s t i l l be heterogeneous  i n terms of the d i s t r i b u t i o n of  p r e f e r r e d s i t e s of f e e d i n g or o v i p o s i t i o n .  These s p e c i a l u n i t s can become  s a t u r a t e d w i t h o u t weed' "control;-.-... .  201 R e d u c t i o n o f weedy p e s t s by b i o l o g i c a l c o n t r o l agents i s more d e s i r a b l e than c h e m i c a l treatment because p e s t i c i d e s pose dangers t o human no matter how c a r e f u l l y they a r e used.  The p u b l i c has become s u f f i c i e n t l y  educated about the dangers o f p e s t i c i d e s t h a t e n v i r o n m e n t a l i s t o f t e n s u c c e s s f u l i n stopping of E u r a s i a n Canyon.  health,  planned s p r a y i n g  groups a r e  programs, e.g., t h e s p r a y i n g  m i l f o i l i n Okanagen Lake, and t h e spruce budworm i n the F r a s e r  There a r e i n c r e a s i n g demands f o r the supposedly s a f e r and more  e f f e c t i v e a l t e r n a t i v e , b i o l o g i c a l c o n t r o l . "But t h i s .method should careful'.follow-up.istudies  t o make i t t a r m o r e l s c i e h t i f i c p r o c e s s .  involve  202 V LITERATURE CITED Amor, R. L. and R. V. H a r r i s . 1975. S e e d l i n g e s t a b l i s h m e n t and v e g e t a t i v e spread of C i r s i u m arvense (L) Scop, i n V i c t o r i a , A u s t r a l i a . Weed Research 15 (16): 407 - 411. Andres, L. A. and R. D. Goeden. 1971. 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