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Host plant variation and population limitation of two introduced insects Morrison, Peter D. S. 1986

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HOST PLANT VARIATION AND POPULATION LIMITATION OF TWO INTRODUCED INSECTS by PETER D . S . MORRISON B.S.  Stanford U n i v e r s i t y  1978  A THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept  t h i s t h e s i s as conforming to th r e q u i r e d standard  THE UNIVERSITY OF BRITISH COLUMBIA December 1986 @  Peter D . S . M o r r i s o n ,  1986  In  presenting  degree  this  thesis  in partial fulfilment of  requirements  for  of  department  this thesis for scholarly or  by  his  or  her  I further agree that permission for  purposes  permission.  Department of  7  n  n  - j  n  z  v  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3  r>F-fin/ft-n  advanced  F e b r u a r y 22, 1987  extensive  may be granted by the head of  representatives.  It  is  understood  that  publication of this thesis for financial gain shall not be allowed without  Date  an  at the University of British Columbia, I agree that the Library shall make it  freely available for reference and study. copying  the  copying  my or  my written  ABSTRACT The  response  success  of  f l i e s ,  Urophora  flower  buds  gall  with  larval  oviposition  fewer  temporal  refuge  compensated  per  that  aborted  A  led  production.  to Bud  densities. relative  g a l l s ,  increased  and  fewer  was  observed.  to bud  seeds.  A  Plants  buds.  the  search  simulation  abortion  were  corresponded attack  g a l l  of  may  time  model  between  based  dramatically  on  reduce  this total  formation.  population  limiting  watering  with  an  year-site-treatment  did  for  groups  females  a f f i n i s  g a l l s ,  increase  bud  limited  in  choices  Insect  a f f i n i s U.  among  choices  seed  tephritid  (Asteraceae).  plant  bud  production  ovipositions.  quality  not  U.  more  seed  s l i g h t l y  Plant  and  of to  may  plants,  reduced  females,  long-term  oviposit  maculosa  among  Among  quadrifasciata for  C.  Among  and  the  gall-forming  requirements.  probing  abortion  implied  and  plant.  led  shapes  quadrifasciata,  buds.  densities  U.  U.  chose  abortion,  by  only  successful  gall  buds  sites  abortion,  Bud  species among  bud  variation Two  diffusa  and  caused  Increased  premise  fly  and  developmental  formation,  abortion,  a f f i n i s  both  plant  insects.  Centaurea  plants,  correlated to  of  of  on  host  phytophagous  buds  Females  to  d i f f e r not  larvae  was  manipulated  factors.  d i f f e r  developed  in  Plants  increase  in  bud  combinations,  s i g n i f i c a n t l y  between  their  faster  in  in  an  attempt  responded numbers.  g a l l s  per  treatments.  propensity f e r t i l i z e d  to  abort  plants.  to  to  shift  f e r t i l i z a t i o n  Except  for  developed Treated buds.  three  U.  two  bud  did  plants a f f i n i s  Among y e a r available random in  for  insect  comparisons oviposition  attack,  seed p r o d u c t i o n  limited  gall  showed was  that  density  of  buds  l i m i t e d by p r e c i p i t a t i o n , non-  and, i n t h e l o n g e r  due t o f l y a t t a c k .  densities.  the  t e r m , by t h e Bud d e n s i t i e s ,  reduction in turn,  iv  TABLE OF CONTENTS  ABSTRACT  11  LIST OF TABLES  ix  LIST OF FIGURES  xiii  ACKNOWLEDGEMENTS  XV  INTRODUCTION  1  ORGANISMS  4 Plants  4  Insects  5  GENERAL METHODS  8  Study s i t e s  I.  8  Bud d e s c r i p t i o n s  11  S t a t i s t i c a l methods  14  THE EFFECT OF HOST SELECTION ON THE POPULATION DYNAMICS OF TWO INTRODUCED INSECTS  16  MATERIALS AND METHODS  19  Observation methods  19  Plant c o l l e c t i o n s  21  Calorific  21  content  RESULTS Variation  23 in resources  23  Insect choice  23  Among p l a n t s  23  Among buds on p l a n t s  27  Consequences of  insect  choice  32  Among p l a n t s  32  Among buds on p l a n t s  40  DISCUSSION  47  Variation  i n bud p r o d u c t i v i t y  Bud a b o r t i o n and p o p u l a t i o n l i m i t a t i o n  48  Basis  49  for choice  Insect  interactions  Summary II.  47  51 52  THE EFFECT OF TIMING OF ATTACK ON THE POPULATION DYNAMICS OF TWO INTRODUCED INSECTS  53  MATERIALS AND METHODS  57  O b s e r v a t i o n methods  57  Plant c o l l e c t i o n s  58  Insect density manipulation  59  RESULTS  62  Insect a t t a c k  and bud i n i t i a t i o n  62  Insect a t t a c k  62  Bud i n i t i a t i o n  65  Interaction  65  Changes  in plant a l l o c a t i o n  77  Bud growth and development  77  Compensatory r e p r o d u c t i o n  77  Insect d e n s i t y m a n i p u l a t i o n DISCUSSION  81 85  Changes i n i n s e c t d e n s i t y  85  Seed refuge  87  Compensatory r e p r o d u c t i o n  88  vi  E v o l u t i o n a r y consequences  89  Summary  91  APPENDIX I I A . EFFECT OF COLLECTION DATE  93  APPENDIX I I B . EFFECT OF DENSITY ENCLOSURES  95  III.  BUD ABORTION AND POPULATION LIMITATION OF UROPHORA  AFFINIS (DIPTERA:  TEPHRITIDAE)  IN BRITISH COLUMBIA  MATERIALS AND METHODS  100  Bud c o l l e c t i o n and d i s s e c t i o n  100  RESULTS  102  DISCUSSION  104  O v i p o s i t i o n behaviour  104  Search time between o v i p o s i t i o n s  105  Model f o r m u l a t i o n  107  Model r e s u l t s  109  Summary APPENDIX I I I A . IV.  97  114 LISTING OF THE NUMERICAL MODEL  116  PLANT QUALITY AND THE POPULATION DYNAMICS OF TWO INTRODUCED INSECTS  120  MATERIALS AND METHODS  123  Weather  123  Experimental treatments Nutrient  i n 1 979  analysis  Experimental  treatments  123 125  in 1980  128  Observation of  i n s e c t s i n 1979  129  Observation of  i n s e c t s in 1980  132  Plant c o l l e c t i o n s and d i s s e c t i o n  132  Additional  134  s t a t i s t i c a l methods  vii  RESULTS  135  Response  of p l a n t s  135  Response  to plants  139  Gall  flies  Other Change  139  herbivores  145  in interaction  146  Attack  levels  1979  146  Attack  levels  1980  149  Larval  survival  and development  152  DISCUSSION  154  Response  of p l a n t s  154  Response  to plants  154  Gall  flies  Other Change  154  herbivores  155  in interaction  156  Effect  o f bud a b o r t i o n  156  Larval  survival  158  Effect  of plant  Fertilization  and d e v e l o p m e n t  quality  on p o p u l a t i o n  dynamics  a s a management t o o l  159 160  Summary  161  V. POPULATION LIMITATION OF TWO PROCESSES WITHIN AND  INTRODUCED  BETWEEN YEARS  MATERIALS AND METHODS  INSECTS: 163 166  Weather  166  Plant  collections  i n 1979  166  Plant  collections  i n 1980  167  Plant  collections  i n 1981  168  viii  Plant d i s s e c t i o n s  168  RESULTS  169  Among year d i f f e r e n c e s  169  Effect  173  of  rainfall  DISCUSSION  176  Bud d e n s i t y Effect Gall  of bud d e n s i t y  176 on g a l l d e n s i t y  distributions  I n t e r a c t i o n between g a l l  182 183  fly  species  Summary APPENDIX VA. ESTIMATION OF BUD AVAILABILITY  187 193 194  Methods  194  Results  195  CONCLUDING DISCUSSION  202  LITERATURE CITED  207  ix  LIST OF TABLES  Table  1.1  Calorific  content  of developed d i f f u s e  knapweed  buds by b r a n c h i n g category Table  1.2  24  Observed and p r e d i c t e d d i s t r i b u t i o n s of  U. a f f i n i s  (UA) and U. quadri fasc i a t a  (UQ) a d u l t s among  branching c a t e g o r i e s Table  30  1.3 D i s t r i b u t i o n of U. a f f i n i s  U. quadr i fasc i a t a  (UA) and  (UQ) a d u l t s by s i z e of  diffuse  knapweed buds Table 2.1  31  Dates on which buds were f i r s t  observed and  c o r r e s p o n d i n g bud i n i t i a t i o n c a t e g o r i e s Table 2.2  Mean day of o b s e r v a t i o n for d i f f e r e n t  of Urophora f l i e s Robertson's Table 2.3  diffuse  on d i f f u s e  categories  knapweed p l a n t s ,  1980  62  Counts of Urophora f l i e s  enclosures, Table 2.4  58  Robertson's  observed in  density  1980  81  E f f e c t of g a l l f l y d e n s i t y m a n i p u l a t i o n s on knapweed c h a r a c t e r i s t i c s ,  production,  g a l l p r o d u c t i o n , seed  and bud a b o r t i o n  82  Table 2.5 E f f e c t of p l a n t c o l l e c t i o n date on d i f f u s e knapweed c h a r a c t e r i s t i c s and g a l l f l y Robertson's  attack,  1980  Table 2.6 E f f e c t of Urophora enclosures  94 on d i f f u s e  knapweed  c h a r a c t e r i s t i c s and g a l l f l y attack Table 3.1  Urophora eggs and l a r v a e and p r o p o r t i o n of buds  95  X  aborted  f o r t e r m i n a l buds o f d i f f u s e  Robertson's Table  knapweed,  1980  3.2 D u r a t i o n  102 of p r o b i n g  into  s p o t t e d knapweed  buds by  f e m a l e U. a f f i n i s Table  3.3  Listing  Table  4.1  Soil  Table  4.2  Effect  number  Table  4.3  of the n u m e r i c a l  characteristics  model  at the study  of f e r t i l i z a t i o n  of d i f f u s e  developed  106 117 sites  and w a t e r i n g  128  on t h e t o t a l  knapweed buds a n d t h e number  of  b u d s , 1979  Effect  135  of f e r t i l i z a t i o n  knapweed c h a r a c t e r i s t i c s  and w a t e r i n g  and i n s e c t  on  diffuse  a t t a c k , Ned's  Creek  1979 Table  4.4  136 Effect  of f e r t i l i z a t i o n  knapweed c h a r a c t e r i s t i c s  and w a t e r i n g  and i n s e c t  attack,  on  diffuse  Robertson's  1979 Table  137  4.5 E f f e c t  of f e r t i l i z a t i o n  knapweed c h a r a c t e r i s t i c s  and w a t e r i n g  and i n s e c t  attack,  on  diffuse  Robertson's  1980 Table  4.6  number  139 Effect  4.7  4.8  of  proportion  and w a t e r i n g  and i n s e c t  of f e r t i l i z a t i o n  characteristics  4.9 E f f e c t  140  of f e r t i l i z a t i o n  characteristics  Effect  knapweed Table  on t h e t o t a l  b u d s , 1979  Effect  knapweed Table  and w a t e r i n g  o f s p o t t e d knapweed buds a n d t h e number  developed Table  of f e r t i l i z a t i o n  of f e r t i l i z a t i o n  a t t a c k , C h a s e 1979  and w a t e r i n g  and i n s e c t  on  1979  .141  spotted  a t t a c k , C h a s e 1980  and w a t e r i n g  of knapweed buds chewed,  on s p o t t e d  .144  on t h e 146  xi  Table 4.10  E f f e c t of  f e r t i l i z a t i o n and watering on the  p r o p o r t i o n of knapweed buds a b o r t e d , Table 4.11  E f f e c t of  E f f e c t of  p r o p o r t i o n of Table 4.13  g a l l s per developed bud, 1979  148  f e r t i l i z a t i o n and watering on the  knapweed buds developed,  E f f e c t of  147  f e r t i l i z a t i o n and watering on the  number of U . a f f i n i s Table 4.12  1979  1979  149  f e r t i l i z a t i o n and watering on the  number of U. q u a d r i f a s c i a t a g a l l s per developed bud, 1979 Table 4.14  150 Contents of Urophora g a l l s from c o n t r o l and  treated diffuse Table 5.1  knapweed p l a n t s ,  Robertson's  1980  D i f f u s e knapweed c h a r a c t e r i s t i c s and Urophora  attack  levels,  Ned's Creek 1979-1980  Table 5.2  Diffuse  knapweed c h a r a c t e r i s t i c s and Urophora  attack  levels,  Robertson's  Table 5.3 attack Table 5.4  169  1979-1981  171  Spotted knapweed c h a r a c t e r i s t i c s and Urophora levels,  Chase 1979-1981  172  Urophora g a l l s per developed bud at the  study s i t e s , Table 5.5  184  P r o p o r t i o n of d i f f u s e  ovipositing gall flies,  knapweed buds unattacked  Ned's Creek  P r o p o r t i o n of d i f f u s e  ovipositing gall flies,  198  knapweed buds unattacked  Robertson's  P r o p o r t i o n of spotted  to  1973-1980  and e s t i m a t e d p r o p o r t i o n of buds u n a v a i l a b l e  Table 5.7  three  1973-1981  and estimated p r o p o r t i o n of buds u n a v a i l a b l e  Table 5.6  152  to  1977-1981  199  knapweed buds unattacked  and estimated p r o p o r t i o n of buds u n a v a i l a b l e  to  xi  ovipositing  gall  f l i e s ,  Chase  1973-1981  200  i  xiii  L I S T OF  Figure  0.1  Location  Figure  0.2  Numbering  Figure  1.1  Distribution  diffuse Figure  of  the  FIGURES  study  scheme  sites  9  f o r knapweed buds  of b o t h  species  12  of g a l l  flies  among  knapweed p l a n t s  1.2  Total gall  25  flies  and  total  buds on  diffuse  knapweed p l a n t s Figure  1.3  T o t a l U.  diffuse Figure U. Figure  bud Figure  affinis  a d u l t s and  U.  affinis  galls  on  knapweed p l a n t s  1.4  T o t a l U.  1.5  Mean U.  1.6  of  galls  1.7  on  affinis  adults  diffuse  galls  per  and  knapweed p l a n t s developed  bud  36  and  buds a b o r t e d  Distribution  across  34  quadri fasc i a t a  quadr i fasc i a t a  proportion Figure  28  branching  Distribution  of  38  galls  and  seeds per  developed  categories of  bud  41  fates across  branching  categories Figure  2.1  C o u n t s on  species Figure  Figure bud Figure  of  2.2  plants  gall  diffuse  f l y at  knapweed p l a n t s of  Robertson's  A v e r a g e numbers of at Robertson's  2.3 by  43  in  2.4  category  initiation  P r o b a b i l i t y of  i n 1980  buds on  diffuse  63 knapweed 66  affinis  category bud  for Robertson's  two  1980  Mean number of U. bud  the  galls  per  developed  for Robertson's  abortion  i n 1980  by  bud  in  1980  .  68  initiation 70  xiv  Figure  2.5 Mean number o f U. q u a d r i f a s c i a t a g a l l s p e r  developed in  bud by bud  initiation  category f o r Robertson's  1980  Figure  72  2.6 Mean number  initiation Figure  2.7  3.1  category for Robertson's  Distribution  branching Figure  of s e e d s p e r d e v e l o p e d bud by bud  of phenology  i n 1980  measures  74 across  categories  78  Sample o u t p u t  from  t h e s i m p l e model of t h e  i n t e r a c t ion Figure  3.2  110  Effect  of v a r y i n g  probes  p e r bud i n t h e  n u m e r i c a l model  112  Figure  4.1  W a t e r i n g and n a t u r a l p r e c i p i t a t i o n  i n 1979  126  Figure  4.2  W a t e r i n g and n a t u r a l p r e c i p i t a t i o n  i n 1980  130  Figure  4.3  Total gall  and c o n t r o l d i f f u s e  flies  observed per plant  knapweed  for treated  p l a n t s at Robertson's i n  1 980 Figure  1 42 5.1  diffuse Figure  5.2  Effect  knapweed  all Figure  174  Creek  5.3 D e n s i t i e s o f s p o t t e d  5.4  g a l l s a t Chase Changes  Urophora  buds and t o t a l  1972-1979 knapweed  178  buds and t o t a l  1971-1979  i n the p r o p o r t i o n  180 o f U. a f f i n i s  g a l l s of 190  distribution  buds a t Ned's  distributions  knapweed  galls  5.5 O b s e r v e d  developed  1 0 - J u l y 27) on buds p e r  plant  g a l l s a t Ned's  Urophora Figure  (June  D e n s i t i e s of d i f f u s e  Urophora Figure  of r a i n f a l l  Creek  o f U. a f f i n i s and t h e  galls in  fitted 196  XV  ACKNOWLEDGEMENTS Any but  undertaking  builds  on  intellectual particular, filling  data.  Northcote,  Michael  Ellen  at  thanks  supported  during  on  in  (No. The  for  cheer.  with  their  Don  part  by  delays  and  Berube  and  Tom  Price,  Geoff and  Scudder,  Norman and  genesis  of  the  constructive this  Agriculture  thesis.  Lai,  mind numbing  completeness.  Tony  Wilimovsky  Hnytka, C h r i s t i n e  with  for  L u d w i g , Jeremy M c N e i l ,  knapweed h e a d s w h i l e  the  thesis  who  last  provided  support  several years  i n ways t o o  task  p u t t i n g up  This  and of  with  research  was  Canada c o n t r a c t t o  Judy  Brett,  and  Alex  Jani  Furniss,  Nancy Hawkins, J e a n  B u r n s , Mag Kirk,  Jane  with  to  completion such  me of  little  Edwards, L i z  Lertzman, Cindy  Lyon,  Sue  M a r c e a u , Dave Marmorek, L i z  P o w e l l , Andrew P u r v i s , L a u r a and  and  Clayton, Linda  Ken  McCormack, C h a r l i e McDermott, M a r c e l  Sutherland,  inspiration  c o n t r i b u t e d to the  numerous t o d e t a i l  reward:  Joan  In  0SU79.-00093).  people  Pope, Rob  the  and  i n the  an  on  i d e a s , comments,  stages  and  the  Denis  criticisms,  precision  relies people.  suffering  Turkington,  helping  and  isolation,  s u p e r v i s o r , Judy Myers,  good  t o D o r o t h y Chen, J e a n  in  many  useful  l a r g e numbers of  insistence  this  various  Roy  done  from  for  Peter  Strong,  Randlesome  Myers  and  generous  encouragement,  dissecting my  roles  Pitt,  i s not  scientists  t o thank my  C h a r l e s Krebs,  Donald  suggestions Special  like  were  one  support  w i t h p a t i e n c e and  unpublished  provided  this  work of o t h e r  these  Harris  Sinclair,  as  emotional  I would  difficulties Peter  the  and  both  such  Templeman.  Richards,  Jens  Thanks  also  Roland, to  the  xvi  management of Cafe Madeleine who refused to charge me  rent  and  to Glen Armstrong who reminded me that knapweed has p o t e n t i a l  as  a cure for insomnia. This scientific was  thesis  i s d e d i c a t e d to the memory of Ann V a l l e e .  discipline  a very d i f f i c u l t  l i v e on.  i s about seeking t r u t h , t r u t h to f a c e .  yet  Ann's  The t r u t h in her l i f e  The death will  1  INTRODUCTION  Scientists outlines  continue  of the e v o l u t i o n a r y  surprising,  given  organisms,  and  minimal insights  the  species  go  populations  about  out  s c a l e , the sheer  the  Since  Darwin's  hardly of  f o r which  and  basis  dim  numbers  changes  the evolutionary  Wallace's  of e v o l u t i o n a r y  process  have  been  o n e : why d o e s one o r g a n i s m do b e t t e r  This question  within  make  I t i s slow g o i n g ;  of the g e n e t i c  a much s i m p l e r  extinct,  to  environmental  exists.  change, many q u e s t i o n s  than a n o t h e r ?  process.  radical  and t h e d i s c o v e r y  to  struggle  t h e enormous t i m e  information  reduced  to  has  when  been  asked  comparing  a species,  when  species  or i n d i v i d u a l  asking  within  organisms  why  groups, within  a  populat ion. The usually size, The  judged  second,  static  by t h r e e  likely  the p o p u l a t i o n  distribution,  i n dealing with  i s widespread  of a s p e c i e s  related c r i t e r i a .  measures  evolutionary  also  persistence.  population  stochastic  are  size,  processes.  wide d i s t r i b u t i o n  in  size  the  flexibility  related  i t i s less  habitats,  to  the  third  i s widespread  likely  of the  for i fa  i t  1984).  is The  more first  criterion, and has  t o go e x t i n c t  P e r s i s t e n c e may a l s o be t h o u g h t  past.  T h e s e two  one a n o t h e r  (Brown,  If a species  i n time.  population  i n i t s environment.  several  t o have a l a r g e p o p u l a t i o n  done  the  c o r r e l a t e d with  through  or a population i s  The f i r s t ,  has  indicates  variation  measures a r e r o u g h l y  species  large  success  measures how w e l l  species  two  evolutionary  of  a  through as  a  2  With  an  potential  for  criterion, the  extant  species,  evolutionary  its  population  environment.  I f the  conditions,  the  higher.  On  hand,  insensitive likely  to  other  to changes  o f more o r  the  less  Varley  population  the  population  which to dense, measured  in response size of  a  fourth  to v a r i a t i o n  drops  sharply  extinction  population  size  the  often described  and  is  in  under  is  much  relatively  species  is  more  success  To  i n the  and  The  e c o l o g i s t are  then  as  size  to  potential the  tasks  the  to evaluate  processes how  the  limiting  processes  shift  environment.  sedentary. Thus,  For  weeds a r e  of  ideal  They  organisms  are  broad  may  variation  be in  areas.  phytophagous  biological  with  widespread,  e a c h p l a n t , many c h a r a c t e r s  i t i s p o s s i b l e to q u a n t i f y  over q u i t e  response  limit  t o d e v e l o p a d e s c r i p t i o n of  isolate  background d e s c r i p t i o n .  introduced  fourth c r i t e r i o n ,  set such  which  a population's  environmental v a r i a t i o n .  easily.  a  predation  r e s p o n s e of p o p u l a t i o n  the  s e v e r a l ways, t e r r e s t r i a l study  Those p r o c e s s e s  evaluate  using  variation, and  i n t e r m s of  density-dependent  1960).  c e n t r a l t o the  population  a d e t a i l e d way  this  gauge i t s  a c t i n g f a c t o r s or p r o c e s s e s ,  Gradwell,  size,  changes In  to  examining  environment,  are  variation.  environmental  with  i n the  dispersal,  are  evolutionary  facing  i f the  independently  and  environmental for  dynamics  by  probability  dynamics  reproduction,  (e.g.  success  possible  persist.  Population  as  is  population  changed  the  it  i n s e c t s may  Systems where  c o n t r o l agents  be  insects (Andres,  set  against  have 1977;  been Andres  3  and  Goeden,  1971; W i l s o n ,  addressing  issues  of  p l a n t s and t h e i r  facilitating size.  be  of  importance  o f weeds, h i s t o r i c a l  introduced  identification  the  Finally,  control  good  to  environmental  for  variation. data  on  consumers a r e u s u a l l y a v a i l a b l e ,  of  processes  M o d i f i c a t i o n s of the processes  size  particularly  responses  Because of the economic the  1964) may  agents  limiting  to increase  have  clear  c o n s t r a i n t s on m a n i p u l a t i o n  population  the population  economic  of the p l a n t  benefits.  population are  rare. This  thesis  success,  uses  population  the  fourth  dynamics  introduced  as  description  o f t h e o r g a n i s m s a n d some g e n e r a l  biological  the  behavioural  within  and among h o s t  insect  attack,  in on  the  timing  Chapter  of  bud  limiting  the  response  of  the  observations with  over  a three  the p o p u l a t i o n  Following  a  methods, C h a p t e r I  t h e major consequences limiting  and v a r i a t i o n Chapter  of v a r i a t i o n  in insect density  III  Chapter  discusses  IV  C h a p t e r V draws on flies  year  to  period  the  the  manipulated collected  and combines  link  dynamics of the system.  data  the  processes  describes  to experimentally  of t h e g a l l  of  the i n s e c t  t h e p l a n t s , one o f t h e  insects' attack  flies  of the i n s e c t s t o v a r i a t i o n  population.  the establishment  agents.  II examines the e f f e c t  by  "quality".  environmental  o f two g a l l - f o r m i n g  on two p r o c e s s e s  attack.  abortion  insect  changes i n p l a n t during  response  of i n s e c t a t t a c k  t h e outcome o f i n s e c t  details  control  plants, details  and f o c u s s e s  density.  success  of e v o l u t i o n a r y  to  to  population  the  response  variation,  describes  evaluate  in  criterion  i t with  interaction  4  ORGANISMS  PLANTS  Two  diffusa  species  Lam.)  and  (Asteraceae) , British  are  established area  United are  infested  These  Cranston,  two  bolting  Columbia  o f B.C.  Frankton  variable buds  phase of As  the p l a n t s vertical  Watson, The  branches  h e c t a r e s i n the  million  (Harris  hectares  and  knapweed  Cranston, thrive  in  is typically  knapweed  (Harris  perennials.  usually  i n mid  growth  are  s p e c i e s of p l a n t  conditions, component  initiated  1.1  placed  or s h o r t - l i v e d  b e g i n n i n g o f June u n t i l  soil  firmly  and M u l l i g a n (1977) d e s c r i b e d t h e  from  to  now  estimate  areas than d i f f u s e  lateral  Both  alone  Spotted  supporting  July.  are  species.  stems.  the  States.  million  A potential  species are b i e n n i a l s  reproductive  United  members o f t h e A s t e r a c e a e  wetter  1979).  of t h e  Both  1979).  interior  weeds i n  they  1.5  Lam.)  rangeland  conservative  t h e s e weeds a t  in British  and  Eurasia, A  (Centaurea  (C. maculosa  northwestern  from  thistle-like  in cooler  ranges  by  knapweed  important  the  America.  (Maddox,  semi-arid  found and  i n North  susceptible  the  and  diffuse  knapweed  economically  imported  States  1979).  knapweed,  spotted  Columbia  Accidentally  the  of  of  (Roze,  slows,  initiated.  and  buds  Buds  the p l a n t s  are q u i t e  moisture,  begins  and  are  begin  plastic  May  with their  initiated  flowering in  in their  disturbance.  The  response  The  most  s e e d p r o d u c t i o n i s t h e number of  flower  1981;  1978a;  Schirman,  1981;  Story,  1972). two  species differ  i n g r o w t h form  and  consequently  in  5  the  distribution  produces fewer in  more  seeds per  bolt  the  two  C.  and  spotted  maculosa  European  knapweed  (Moore and the  spp.  Albania, order left  to the  INSECTS Frfld. were  Two and  U.  Frankton,  species  is  name i n t h i s  (1981)  individuals  of has  in  the  sites  diffuse  (1981),  been d e s c r i b e d may  the  not  southern and  C.  except  U.S.S.R,  Romania. usage,  (Urophora  (Diptera:  Peter  spp.  In  I have  maculosa.  fly  of  be  comparable  biebersteinii  the  as  comm.).  (2n=l8),  North American  (Meig.))  four  Roze  knapweed r e f e r r e d  Hungary,  fruit  discussed  ( H a r r i s , pers.  (=C.  t h e s i s as  knapweeds.  were  2n=36, w h i l e  found  true  r e l e a s e s on  but  knapweed  Roze  of  chromosome c o u n t  Dr.  1970's: two  species  has  the  at  stock.  (1980a),  maculosa  part  flies  spotted  species  Columbia  from E u r o p e a s  released  15),  difference  1974), however t h i s  C.  quadr i f a s c i a t a  program a g a i n s t  early  in B r i t i s h  of  vs. The  output  two  Czechoslovakia,  species  introduced  Canada  The  remain c o n s i s t e n t with species  the  micranthos  Bulgaria,  usually  identical.  (1974).  which  of  same r o o t  (1977), H a r r i s  the  (100  1972).  ability  reproductive  have a l o w e r  b i e b e r s t e i n i i D.C.)  the  from t h e  European  Columbia,  maculosa  by  knapweed  knapweed  (Watson,  taxonomy of  Renney  species  25)  i s nearly  Mulligan  to  In B r i t i s h  vs.  lifetime  b i o l o g y and  equivalent  C.  the  Watson and  t o as  (12  Diffuse  spotted  is offset  species  Frankton  and  than  t h a n once  that  The by  bud  more  concluded  seed p r o d u c t i o n .  buds  seed p r o d u c t i o n  to  of  of  a  affinis  Tephritidae)  biological  control  H a r r i s of A g r i c u l t u r e  in B r i t i s h knapweed  Columbia  (1970,  1972)  in  the and  6  two  on  spotted  successfully The  June  and  in  15,  average  to  day  mate a l m o s t  three  days  later  determined  by  observed  that  in  Her  1976.  are (MS  and  timing  flies  females.  established  (Harris,  s p e c i e s of  fly  Zwolfer  beginning  of  their  up  emergence  temperature the g a l l  with  been Adults  June  1  and  M a l e s emerge  When  females  the  ensues  lives  on  emerge  approximately  on  The the  insects knapweed  weeks. of  the g a l l  ( c f . Uvarov,  flies  have  pupation.  adult  to three  1980a).  (1970).  between  Oviposition  flies  appears  1931).  those  of  Berube  temperature-dependent  to  Roze  emerged much e a r l i e r  o b s e r v a t i o n s , and  be  (1981)  i n 1977  than  ( p e r s . comm.),  developmental  rates  in prep.). Eggs a r e  When  the  burrow  laid  on  top  eggs  hatch,  the  florets  into  induction  of  the p l a n t  of 3-4  and  the  form  tissue  1972).  single  bud.  The  l a r v a e f e e d on  until  they  cases,  larvae  the  inside  Zwolfer  More  than the  reach the t h i r d  larvae the  galls,  presumably  overwinter  1969;  one  gall  nutritive  instar as  knapweed  oviposition,  (Dieleman,  Osborne,  gall  immature  days a f t e r  1964;  all  The  m u l t i p l e matings are observed.  of  consistent  two  (1981) and  immediately.  Females l i v e  The  1971).  t h r e e weeks a f t e r  t o s p e n d most  plants.  the  by Roze  b e f o r e the  they  appear  of  summer, u s u a l l y  two  one  histories  detail  in early  (1970,  t h e p o p u l a t i o n s grew r a p i d l y  natural  discussed emerge  knapweed  be  layer  several  the  by  Hori, may  florets. larvae  chemical  1974;  Mani,  formed  in a  inside  the  weeks l a t e r .  diapausing  third  In  instar  galls.  (1970)  suggests  that  the  size  of t h e  immature  7  tubular Buds  above  despite U.  florets  of  1970).  factor  females  their  eggs  Berube  l a r v a e develop  in  knapweed plant  4-6 mm s i z e range  in  a  size  range  of  generation by a  is  pers.  facultative  temperature  cue.  (Zwolfer, diffuse  2-8 mm,  i n l a r g e r buds, 6-10  In U. q u a d r i f a s c i a t a , a second g e n e r a t i o n (Berube,  laid  (1978) concluded that U. a f f i n i s  U. quadr i fasc i a t a l a r v a e develop  obligate  female.  s t u d i e s of both spotted and  Harris  buds  choice.  not r e c e i v e any eggs,  spotted  in buds i n the  and  oviposition  a v a i l a b l e to a f e r t i l e  caged on a s i n g l e  Based on greenhouse  knapweed,  in  a certain size threshold w i l l  being the only s u b s t r a t e  affinis  93%  i s the c r i t i c a l  while  mm l o n g .  i s b e l i e v e d to be  comm.).  In  (Zwolfer,  1970), presumably determined  While  U. a f f i n i s ,  relatively  few  the  second  temperate-zone  i n s e c t s have been shown to use temperature as a primary diapause inducing the  few  stimulus  (Tauber et  environmental  Photoperiod  cues  ajL. ,  1986),  available  to  temperature i s one of U. a f f i n i s  larvae.  i s u n l i k e l y to be used by l a r v a e i n s i d e woody  i n s i d e unopened flower  buds.  galls  8  GENERAL METHODS  STUDY SITES F i e l d which, sites  Ned's f o r the  and  gall  diffuse  will  be  1979  and  was  t o as Ned's C r e e k  was  sprayed with  between Kamloops and  Chase  r e c e i v e s more r a i n  the The  the a v e r a g e )  summer)  than  Ned's C r e e k  and  between Chase and Only  on  at  Ned's  pers.  (1980), H a r r i s  during  above  the  the and  site,  site  i n 1980  South  Columbia  the p e r i o d  is cooler  in when  Thompson  (Figure  from A p r i l  to  km  0.1). August  ( a p p r o x i m a t e l y 1°C  sites  is  nearest  of d i f f u s e  during  to the  sites  1965  west.  halfway  t h e Ned's C r e e k  i s a pure  cm  s t a n d of  (MeantS.E.) a t  (Harris,  Roze  pers.  spotted  was  higher  Robertson's  been p r e s e n t  at  Comm.; R o b e r t s o n ,  i n more d e t a i l  (1981).  and  d i s t a n c e s measured i n  Knapweed has  are described  ( 1 9 8 0 a ) , and  at  knapweed a t R o b e r t s o n ' s  a t Ned's C r e e k ) .  The  found  neighbour  (6.34±0.26  since at l e a s t  comm.).  third  knapweed  knapweed s i t e  British  the Chase s i t e  Creek  8 . 0 8 ± 0 . 2 9 cm  Chase,  knapweed  Based  than  apart  are approximately  knapweed.  the d e n s i t y  m  of  Kamloops.  diffuse  1979,  diffuse  release  result  Robertson's  and  sites  the  r o u g h l y 60  sites  all  is  of  herbicide. terraces  and  two  knapweed,  Kamloops A i r p o r t ,  Robertson's  vs.  spotted  h e r e a f t e r . ) The  u s e d as an a d d i t i o n a l  t h r e e s i t e s a r e on  on  sites,  were o r i g i n a l  and  Creek-Pritchard  River  (3.5 cm  Chase,  became the p r i m a r y d i f f u s e  Ned's C r e e k All  on  study  s e p a r a t e r e l e a s e s a p p r o x i m a t e l y 200  referred  Robertson's,  flies  (Ned's  o f two  done a t t h r e e  Creek-Pritchard  respectively. merging  work was  by  Berube  9  Figure 0.1. L o c a t i o n of the study s i t e s . The two d i f f u s e knapweed s i t e s , Ned's Creek and R o b e r t s o n ' s , are l o c a t e d at a p p r o x i m a t e l y 1 1 9 ° 5 0 ' W , 5 0 ° 4 2 ' N and 1 1 9 ° 5 0 ' W , 50°40'N, respectively. The spotted knapweed s i t e , Chase, i s l o c a t e d at approximately 1 1 9 ° 4 2 ' W , 5 0 ° 4 8 ' N . The top of the f i g u r e i s due n o r t h .  • 1 Ned's Creek • 2 Robertson's • 3 Chase  Metres  0  1000 2000 3000 4000 • 4  11  Chapters only;  BUD  Chapters  II,  IV and  DESCRIPTIONS The  describe Any  I,  bud  the that  described  initiated  enough r e s o u r c e s large  The  first  of  buds on  t o be  lateral  Lateral  buds  subtending  can bud  It  is  lateral  Locations  the  or  bud  The  the  apical  first  to  receives  collection  is  i s described  as  developed, as  is  initially  I f a bud  the  mm)  categories:  are  but  is  not  aborted.  knapweed s i m p l i f i e s bud  is  flower  recording  ( i n the  the  absence  of As  stem.  branches elongate,  lateral  buds d e v e l o p  on  and  branches This  can  pattern  centripetally, directional  "1".  o f f the  The  first  flies  (1981) u s e d a s i m i l a r  be  repeats until  identified itself  lateral  were r e c o r d e d  (see  Figure  lateral branch  bud is  relative  Buds may  be  by  their  initiated.  individual  0.2).  The  i s "2". "2-1"  so  buds.  in a  buds  apical  The  and  to these placed  them.  recursively,  a l l buds a r e  g r o w t h means t h a t  first  scheme.  also  the  typically  buds down t h e  a unique d e s i g n a t i o n  of  buds  of  be  2.0  three  time  seeds,  (>  to  buds.  lateral  denoted bud  All  used  by  and  given  of  sites.  knapweed  measured  i t is described  i s followed  r e c u r s i v e and be  and  by  Robertson's  are  l o c a t i o n of  i n t o one  normally  plants.  bracts.  basipetally This  would  growth of  initiated  attack).  these  of  methods  in that category.  galls  insect attack, pattern  location  fly  aborted.  from  from a l l t h r e e  be  or  t o m a t u r e and  bud  to  placed  remain  If the  b e c a u s e of  s t a t e and  and  enough t o c o n t a i n  developed.  results  l a r g e ' enough  some  results  f o l l o w i n g t e r m s and  undeveloped, developed, undeveloped;  III present  V present  developmental is  as  and  first on. Roze  branching  12  F i g u r e 0.2. Numbering scheme for knapweed buds. are given in the t e x t .  Details  1 4  category  based  location  o f t h e bud ( e . g .  category  a n d "4-1-1" would be i n t h e t h i r d ) .  The  on t h e number o f i n d i c e s  determinate  possible  to identify  plant.  Aborted  to  developed  be  aborted  aborted  developmental  buds  were  those  4-3  the  f o l l o w i n g bud was d e v e l o p e d numbers  relationship  of a b o r t e d  on  location  since aborted  the  relative  the f i r s t  three  would  not developed, i t  s i n c e i t does More  followed  in  not  precisely, the  larger  normal  by 2.0 mm  (flowered, or c o n t a i n e d  to developed  buds  can  buds.  i t  i f buds 4, 4-1, a n d 4-2  category,  buds e s t i m a t e d  in this only  Aborted  when  galls).  way a r e p r o b a b l y  be  identified  in  buds a r e e q u i v a l e n t t o  (1981) " s u p e r p a r a s i t i z e d " buds.  S T A T I S T I C A L METHODS U n l e s s regression  coefficients  Mean±S.E.).  distributions, combined are  makes  o r t h e bud under c o n s i d e r a t i o n was n o t d e v e l o p e d  underestimates  (e.g.  by t h e i r  were  branching  position  s e q u e n c e by a bud t h a t was e i t h e r  more,  Roze's  their  i n development.  that  or  The  by  first  growth  I f 4-1-1 was a l s o  i n the aborted bud  the  knapweed  F o r example,  as a b o r t e d .  precede  buds  of  a n d 4-3 h a d f l o w e r e d ,  n o t be p l a c e d  necessarily  pattern  (=good) b u d s .  identified  could  "2" would be i n  buds were d e t e r m i n e d  were n o t d e v e l o p e d  required to d e s c r i b e the  with  (Sokal and R o h l f ,  g i v e n by an e x a c t  0.001, o t h e r w i s e  indicated,  when  are reported the standard  When  cells  otherwise  x  2  tests  fewer 1969).  probability,  by t h e i n e q u a l i t y  than  means  error to  i s given  are  used  compare  five  observations  R e s u l t s of s t a t i s t i c a l p,  if p  p<0.00l.  is  or  greater  are tests than  I t was n o t p o s s i b l e  1 5  to  assign  tests.  exact Square  probabilities root  and  t o the r e s u l t s  of groups b e i n g  different  the  if  degrees of freedom Satterthwaite's significantly 1982).  for  formula  different  statistical  logarithmic transformations  when t h e v a r i a n c e s or  o f some  variance Student's  compared  are  a r e used  significantly  i s a f u n c t i o n o f t h e mean. t-test  i f the variances  was  adjusted  The using  o f t h e two g r o u p s were  by t h e F - t e s t a t a=0.05  (SAS  Institute,  1  I.  THE EFFECT OF HOST SELECTION ON THE POPULATION DYNAMICS TWO  Phytophagous variation 1975;  selecting  1976).  food  these  and o t h e r  1978;  Moore,  choice  stage  respond  to  (Bach,  1981),  enormous  (e.g.  this  Chew,  variation  (Brues,  Crawley,  by  1920),  1959; M c N e i l l and  size  (Whitham, 1978;  ( C a l c o t e , 1975), a n d c o m b i n a t i o n s  (e.g.  between  is critical  host  where  life  reflect  suitability  (Chew,  form  an  resources  ( D e t h i e r , 1941; F r a e n k e l ,  factors  another  it  food  with  1983; H a r e a n d  of  Futuyma,  1978b).  link  (Rausher,  confronted  of  Insects  1978), g r o w t h  developmental  The  are  OF  INSECTS  r e s o u r c e s on t h e b a s i s o f s p e c i e s  composition  Southwood, 1980),  insects  i n the s u i t a b i l i t y  Dixon,  chemical  INTRODUCED  6  stage.  1979b;  one  plant insect  I n some c a s e s , for  larval  Wiklund,  1977; C o u r t n e y ,  variation life  and o v i p o s i t i o n  stage  oviposition survival  see  may  for  c h o i c e s may n o t  and  1975), a n d i n d e e d  1981; t h o u g h  chooses  development run counter t o  Rausher  and  Papaj,  1983). The  two  introduced  U. q u a d r i f a s c i a t a the  immature  Lam.  (Meig.)  insects,  (Diptera: Tephritidae),  f l o w e r buds o f d i f f u s e  (Asteraceae). buds  The young  within  the  and  plant.  Thus t h e o b s e r v e d  plants  and  Urophora a f f i n i s  larvae stimulate  distribution  among buds on p l a n t s , s h o u l d females.  lay  eggs  knapweed, C e n t a u r e a  f e e d on n u t r i t i v e  c h o i c e s made by t h e a d u l t  F r f l d . and  tissue of  gall  diffusa formation  produced  galls,  in  both  be c o r r e l a t e d  by t h e among  with the  17  Two  possible  oviposition have  been  site found  developmental reflected  contrasts  L a r v a e of  to  gall  complete  the  second c o n t r a s t  clarify  selection.  stages  in  will  ( B e r u b e and choice  of  i s between  the  two  formation Harris,  buds by  sexes.  If  the  insect  i n buds of  1978).  This  ovipositing females are  males must c h o o s e  the  females  the  gall  flies  near  (Zwolfer-,  1970).  oviposition  sites  tephritids  are  Varley,  1947)  exception  and  may  flies,  mating compared  of  knapweed buds  high  levels do  not  buds w i l l the  number o f Attack  future enough,  seed  reduced. density  the  are to  fly  i n the gall If  production seed  and  next  by  as  eventual of  many  Parker,  1974; no  Territorial of  male  males that  may  Roze they  are  reduce  (1981)  the  observed  were e x p o s e d  laboratory.  Because  d i s t r i b u t i o n of  to  aborted  attack  g a l l s p r o d u c e d and,  also  level the  production  h e n c e of  choices  among hence,  generation.  flies the  of  attack  develop a f t e r  g a l l s , the  The  mating.  sites.  i n the  the  distributions  not  be  males are  1974).  distributions  t o t a l number of  density.  plants  to  attack  the  in  i n the  should  males  1981;  Zwolfer,  different  same buds  quadrifasciata  oviposition  failed  adults  A drop of  the  plants  p r o d u c e any  by  insect  in  the  insect  affect  U.  differences  buds as  Burk,  M y e r s , MS;  or  of  that  of  and  w i t h males that  response  suitability  buds  to  However, t h e  (e.g.  affinis and  lead  female  One  U.  (Berube  behaviour and  territorial  or  species  making  s i t e s , the  mate on  of  females.  among o v i p o s i t i o n because  process  has of  plants may  oviposition  a delayed  fly  attack  may in  be turn  sites  impact is  on  high  significantly affect  i n the  the  future.  18  This selection  Chapter  of o v i p o s i t i o n  suitability and  (1)  of  (2) a s s e s s e s  suitability  those  examines sites  sites  relationship  by t h e two for larval  the consequences  f o r the p o p u l a t i o n  the  of  dynamics  gall  flies  growth and  the  and  the  development,  selection  of the  between  insects.  and  site  19  MATERIALS AND METHODS  OBSERVATION  METHODS  Robertson's points  The  to  bolt  The  observations two  days,  plant.  adult  f l y was  wings  plants  provided  sexes  not  obviously altered  surveys  between  9:30  The s u r v e y s on  necessary  and  27 a n d J u l y  activity  where  count  over  a  so  basis  was s t a k e d . that  for  staked  detailed  visual  survey  sex, and a c t i v i t y  pattern  by t h e p r o m i n e n t  docile  which  Approximately  by t h e b a n d i n g  are quite  for adult  lasted  flies  from  number o f f l i e s  t o survey adults 1 and 7).  strongly  case  plant  and t h e i r  every of each  of  each  The two on  the  oviscape of  behaviour  was  on p l a n t s  were  usually  8:30 a.m. and 11:30 a.m., w i t h most begun a t  the  was  The  by an o b s e r v e r .  conducted  depending  with a  apart  by b r a n c h  are distinguished  The f l i e s  visual  of the f i e l d  on t h e g r i d  hosts.  species,  distinguished  females.  a.m.  a branch  (5x10)  r e c o r d e d a t t h e moment o f o b s e r v a t i o n .  the  The  and t h e i r  The l o c a t i o n ,  are easily and  point  neighbours.  I conducted  established at of f i f t y  knapweed.  were f a r enough  of the f l i e s  staked  species  of d i f f u s e  nearest  staked  was  A rectangular grid  n e a r e s t each  p o i n t s on t h e g r i d were r a r e l y  plot  a 3 m x 6.5 m p o r t i o n  uniform density  begun  plants  observation  1, 1980.  was p l a c e d o v e r  visually had  on J u n e  An  affected  counts a l l fifty  were  one h a l f  observed.  i n the e a r l y  It i s unlikely the counts made  hour  twice  to  one  In f o u r  cases, i t  afternoon  that  hour,  (June  17  daily  p a t t e r n s of  o f U. a f f i n i s .  In t h e one  i n one day (June  p l a n t s a t 8:40 a.m. was 10  13),  U. a f f i n i s  the  and  20  at  2:00  p.m.  the  same p l a n t s The  time  the  counts  two  species  indication the  14 U.  of  U.  of  longest  experiment  ground  posts at the v e r t i c e s interior  of  trademark  o f The  from  was  r e f r e s h e d every  give  affinis  patterns  August  24.  affect  f o r the  r e c o r d e d the  the  plants The  on  This picture  number,  interval  two  As  was  constructed.  sides.  between  flies  The  (registered  Rapids,  over  wooden  Michigan)  were  removed  the  first  the e n t i r e  daily  quadr i fasc i a t a  adults  of  the  (7.1%)  and  sticky  suggests of  the  trap  that  the  relative  Differences among  in  visual  numbers of activity  p l a n t s o r among  species.  location,  times  by  days d u r i n g  comparisons  same i n s e c t  19-21  trap.  (6 m on i t s  the  Gall  integrate  quadri fasc i a t a .  not  times  every  similar  (7.8%).  of  Grand  t h r e e weeks.  very  with  sticky  netting  An  comparing  m high, supported  Company,  reasonable U.  will  I also on  a  and  observation  buds  surveys  on a  i f the  surveys  coated with Tanglefoot  p r o p o r t i o n o f U.  was  comes from  the v i s u a l  the m i d p o i n t s  trap counts  The  flies  from v i s u a l  U.  Sticky  on  affect  patterns.  in prep.), a large  t o 0.5  approximately  cycle.  gall  surveys  at  Tanglefoot  the n e t t i n g  activity  and  from  fibreglass  level  however,  activity  caught  (MS  t h e hexagon was  generation.  all  flies  d i a g o n a l ) hexagon o f from  observed  quadrifasciata  difference  recorded  of  may,  t o U.  daily  of t h i s  composition  another  extended  which  relative  different  the e x t e n t  were not  surveys.)  affinis  species composition  part  (Insects  s u r v e y s were c o n d u c t e d  have  of  affi n i s .  i n t h e two  the  species  the  It  was  and  size  of  d u r i n g the p e r i o d the  observations  all  the  June  1 to  of  buds  21  increased Bud  as  the  number  of buds i n c r e a s e d d u r i n g the  season.  s i z e s were measured with c a l i p e r s as d e s c r i b e d by Berube and  Harris  (1978) to the nearest m i l l i m e t e r .  became  possible  to  c a l i p e r s confirmed height,  v i s u a l l y estimate the  accuracy  developmental s t a t e ,  noted.  One  plant  died  c o n t i n u e d to a t t r a c t  of  With some p r a c t i c e sizes.  these  and evidence  Spot checks with estimates.  Plant  of h e r b i v o r y were  also  during the p e r i o d of o b s e r v a t i o n ,  flies.  It was  it  excluded  from  but  statistical  a n a l y s i s when a p p r o p r i a t e .  PLANT 23,  COLLECTIONS  1980,  stored  P l a n t s were c o l l e c t e d  by c l i p p i n g them off  in  folded  and  until dissection. plant  was  at ground l e v e l .  stapled  measured  and  bud  the  were  size,  then  the height of  each  developmental s t a t u s ,  recorded.  Buds  large  and  enough  e i t h e r g a l l s or seeds were i n d i v i d u a l l y d i s s e c t e d .  these,  the number of seeds and g a l l s present  galls  of  the  two  U. af f i n i s g a l l s are  They were  paper bags at room temperature  When they were d i s s e c t e d ,  l o c a t i o n of each contain  i n d i v i d u a l l y on August  insect  species  are  were  easily  to For  noted.  The  distinguished;  are hard and woody and U . quadri fasc i a t a  galls  t h i n and papery.  CALORIFIC  CONTENT  One  l a r v a l development, produce,  could  produced seeds. value of p o s s i b l e  measure  of the s u i t a b i l i t y of buds for  the maximum number  not  be  evaluated  Using H a r r i s ' bud  of  galls  directly  a  because  bud  could  buds a l s o  (1980b) measurements of c a l o r i f i c  contents,  the  "carrying  capacity"  of  22  developed knapweed  buds  may  seeds  have  calories.  The  calorific  value of  does  be  calculated  an  average  combination 28.0±1.1  common u n i t s .  energy  content  of U . a f f i n i s calories  Diffuse  of  6.5±0.1  l a r v a and g a l l has a  (Harris,  1980b).  Harris  not give a value for U . quadr i fasc i a t a l a r v a and g a l l ,  the value for the l a r v a alone since  little  gall  tissue  measure of s u i t a b i l i t y of  in  the  season  among buds that choices  and  thus  larval  may be  used,  feeding.  measure estimated at the  represents  should t r y to  season.  calories)  remains a f t e r  is a static  females  d u r i n g the  (4.27±0.14  but  This end  the accumulated v a r i a t i o n match  by  their  dynamic  23  RESULTS  VARIATION  Plants  RESOURCES  varied considerably  buds p e r of  IN  plant  was  v a r i a t i o n of  i n the  16-180, w i t h  59.5%  (cf.  number of  a mean of  62%  buds.  71.7  based  on  The  and  a  range  in  coefficient  Schirman's  (1981)  data). Using  Harris'  (1980b)  calorific  distribution  of c a l o r i f i c  value  buds  a  57.3  gives  range of again exact are  mean  of  0-279 c a l o r i e s and  a  high  d e g r e e of  representation not  of  identical  primary  branching  resources  than  among the  a coefficient  the  category  the  other  The  gall  three  bud  bud  of v a r i a t i o n  galls  t o bud.  significantly  categories  with  of not and  a  69%, be  an  seeds  Buds  in  more  (Table  the  developed  T h i s measure w i l l  from  had  of  developed  v a r i a t i o n because  weight  to estimate  contents  c a l o r i e s per  variation.  in  values  the  energy  1.1).  INSECT CHOICE  AMONG  PLANTS  total  numbers of  that  the  X =510,  f l i e s observed  distribution df=49,  2  f l i e s c h o s e among p l a n t s .  was  not  p<0.001;  U.  on  individual  uniform  A x  2  plants  among p l a n t s  quadrifasciata,  (U.  test  of  reveals affinis,  x =338,  df=8,  2  P<0.001). Contrasting species  will  the  clarify  d i s t r i b u t i o n s of the  basis  for  the  choice  two  s e x e s and  among  the  plants.  two The  24  Table  1.1  - C a l o r i f i c content of developed d i f f u s e buds by branching category  Branching Category  Calor i f ic Content *  1 2 3 4  knapweed  N 269 782 448 34  7 5 . 6 ± 3 . 1 ** 5 4 . 3 ± 1 .3 4 8 . 6 ± 1 .6 44.8±5.7  *  C a l o r i e s ( M e a n i S . E . ) . Based on H a r r i s ' (1980b) measurements. ** A n a l y s i s of v a r i a n c e on l o g transformed data g i v e s F=9.88, df=3,1529, p<0.001.  numbers plants  of  males  and  females  were h i g h l y c o r r e l a t e d  df=48,  p<0.00l).  related)  Males  of  the two species observed on  (log  and  transformed  females  c r i t e r i a for p o s i t i o n i n g  differed  from  the  heterogeneity plants plant  between  distribution  2  the  removed  (x =48.26, 2  df=3,  from  analysis,  p<0.001),  (log  P<0.001).  plant  any of  The anomalous  the other p l a n t s  proportionally flies,  larger  U. a f f i n i s .  The  p<0.00l),  during  however  response to If  heterogeneity  the  As a r e s u l t ,  flies  r=0.53,  oviposition  the  the the this  persists  buds  period  per  df=47,  i n i t i a t e d buds much e a r l i e r  twice as many  difference  among  observed  (Figure 1.1).  transformed d a t a ,  observed.  and a t t r a c t e d almost  the  all  but o v e r a l l the counts of  p l a n t are w e l l c o r r e l a t e d  same (or  adults  of  two s p e c i e s in t h e i r  i s p r i m a r i l y due to a s i n g l e p l a n t is  the  U. a f f i n i s  ( x = l 9 0 . 2 , df = 4,  U. quadr i fasc i a t a a d u l t s  use  r=0.73,  themselves.  The d i s t r i b u t i o n of a l l observed plants  may  data,  than were  of  the  U. quadr i fasc i a t a  as  in bud s i z e preference  between  fly  25  Figure  1.1. of g a l l plants.  T o t a l number o f a d u l t f l i e s o f t h e two s p e c i e s f l y o b s e r v e d on e a c h o f t h e d i f f u s e knapweed Each p o i n t represents a s i n g l e p l a n t .  T,  o >  25.  ©  2 20. TO CO  o 15J (0 CO  =!  10J  a) 5E 3  in . i r  10  »JL  •• •  •  ••  ••  20 30 40 Number of U. affinis observed  —r-  50  —r—  60  27  species  (see  initiation  below) and  heterogeneity  that  of  growth  there  flies  plant  separately,  differences probably  observed  (Figure  d i s c u s s e d above,  the  p<0.001,  df=1,47,  in  regressions in  for U . a f f i n i s -  of  Figure  the  total buds on  two  species  relationship  plant  is:  1.86(±0.55),  r=0.55.  These r e g r e s s i o n s  and  Variability  of  counts  unaccounted for  among p l a n t s not  t r a c k the number  explain  U. q u a d r i f a s c i a t a  may be due to d i f f e r e n c e s  to p e r f e c t l y  species.  Removing the anomalous  -  U. aff i n i s 1.1.  remaining  0.94(±0.44),  r = 0.78.  p<0.00l,  bud  is:  the numbers of buds per p l a n t or to the  flies  the  the  for U. quadr i fasc i a t a the  correlation  observed  the two  Considering  ln(UQ+l) = 0 . 5 9 ( ± 0 . 1 3 ) l n ( B U D S + 1 ) F=19.98,  for  in  on p l a n t s and the number of  1.2).  the r e g r e s s i o n  df = 1,48,  plants  i s a s t r o n g r e l a t i o n s h i p between  ln(UA+1) = 0 . 9 1 ( ± 0 . 1 1 ) l n ( B U D S + 1 ) F=72.32,  among  account  in the d i s t r i b u t i o n s of  Overall, number  and  the  reflected  i n a b i l i t y of  oviposition  in  the  gall  sites  per  plant.  AMONG If  BUDS  ON PLANTS The f l i e s  buds are d i v i d e d i n t o t h e i r  secondary,  etc.),  a l s o chose s i t e s w i t h i n branching  and the numbers of  flies  compared with the numbers of buds i n the adjusted  by  the  distribution  were observed on the p l a n t , P<0.001)  and  both  U. q u a d r i f a s c i a t a  categories  (primary,  observed on buds are  respective  categories  of buds at the time the U. a f f i n i s  df=2,  2  2  on  insects  (x =21.65,  ( X = 3 9 . 5 1 , df=1,  observed d i s p r o p o r t i o n a t e l y more often  plants.  primary  p<0.00l) buds  were  (Table  28  Figure  1.2. T o t a l number of g a l l f l i e s and t o t a l number of buds for each of the d i f f u s e knapweed p l a n t s . Each p o i n t represents a s i n g l e p l a n t .  60  40J c (0  (0  ®  20J  20  i  40  i  60  i  •  1  1—  80 100 120 Buds per plant  —i  140  1—  160  180  200  30  1.2).  Table  (The e f f e c t  1.2  of  the temporal d i s t r i b u t i o n of  the  flies  is  - Observed and p r e d i c t e d d i s t r i b u t i o n s of U. a f f i n i s (UA) and U. q u a d r i f a s c i a t a (UQ) a d u l t s among branching c a t e g o r i e s BRANCHING CATEGORY 1  2  UA Obs. UA P r e d .  463 (0.56)a 411.6 b  UQ Obs. UQ P r e d .  53 (0.67) 26.6  3  324 (0.40) 350.6  34 (0.04) 63. 8  23 (0.29) 52.4  3 (0.04) c  a - T o t a l observed ( P r o p o r t i o n ) b - P r e d i c t e d numbers of f l i e s in branching c a t e g o r i e s are based on the t o t a l number of f l i e s observed on a l l buds weighted by the d i s t r i b u t i o n s of buds among branching c a t e g o r i e s as the d i s t r i b u t i o n s change in time. c - C a t e g o r i e s 2 and 3 were combined because of the s m a l l number of o b s e r v a t i o n s i n category 3.  treated  separately  significant adult  in  the  difference  between  f l i e s among b r a n c h i n g  df = 2,  p=0.511,  p=0.291,  N=65).  observed  if  the  N=690; The  next  Chapter.) sexes  categories  in  There  for  (U. a f f i n i s ,  buds  females a l s o p r e f e r r e d primary buds  df=1,  This preference  calorific  content of  t e r t i a r y buds  (Table  primary 1.1).  buds  to  also  separately (N=26), (x =4.89,  i s c o n s i s t e n t with the compared  df=1,  is  i s small  probing U . a f f i n i s p=0.027).  2  2  primary  Though the sample s i z e  x =1.342,  x = 1 - 117,  sexes of each s p e c i e s are c o n s i d e r e d  (p<0.01 in a l l c a s e s ) .  no  the d i s t r i b u t i o n of  U. quadrifasciata,  preference  was  2  higher  secondary  or  31  There among  was  branching  behaviour.  no evidence categories  the d i s t r i b u t i o n of male  was  affected  two f l y s p e c i e s a l s o d i f f e r e d  Table 1.3  territorial males was not  bud s i z e s  were  p=0.645, N=573).  2  for  flies  from the d i s t r i b u t i o n of males that  not mating (x =0.878, df=2,  preference  by  The d i s t r i b u t i o n of mating U . a f f i n i s  significantly different  The  that  significantly  (Table 1.3).  As e x p e c t e d ,  in U.  their affinis  - D i s t r i b u t i o n of U. a f f i n i s (UA) and U. quadr i fasc i a t a (UQ) a d u l t s by s i z e of d i f f u s e knapweed buds  Insect Category  Bud S i z e  UA males UA females UA mating p a i r  2.91±0.07 a 3.01±0.13 a 3.22±0.23 c  519 171 54  UQ males UQ females UQ mating p a i r  3.60±0.27 b 4.66±0.34 b 5.35±0.98 c  40 25 3  (mm)  N  L e t t e r s i n d i c a t e s t a t i s t i c a l comparisons: a - t=0.061, df=582, p=0.952. b - t=1.75, df=57, p=0.085. c - Mann Whitney U t e s t , U=139, 0.02<p<0.05.  sat on or near buds that U. q u a d r i f a s c i a t a  were  (overall  The bud s i z e s chosen by  male  differ  but  significantly,  slightly preference reflected  bigger  buds  than  smaller  t-test, and  than  t=4.96, female  those df=842,  males.  for l a r g e r buds by U . quadr i fasc i a t a  by  p<0.00l).  U. a f f i n i s  U. q u a d r i fasc i a t a conspecific  chosen  did  not  females  picked  The  slight  females  in the buds on which mating p a i r s were observed  is  also  (Table  32  1.3).  The bud s i z e s U . q u a d r i f a s c i a t a females chose are  to the  s i z e s p r e f e r r e d for o v i p o s i t i o n  and H a r r i s , The  distributions  fly  of mating and non-mating males significantly  (U. a f f i n i s ,  U. quadr i fasc i a t a , difference  laboratory  (Berube  1978) than the bud s i z e s males chose.  to bud s i z e d i d not d i f f e r gall  in the  closer  for e i t h e r  t=1.59,  t=1 .33,  df = 36,  relative  species  df=480,  p=0.l9l).  of  p=0.1l3; Again,  no  that c o u l d be a t t r i b u t e d to t e r r i t o r i a l behaviour was  detected. The flies  sizes  i n the  observed  of  field  i n the  Zwolfer,  3.7 mm (N=32),  and  by  between  than  small and the  to  the  bud  size  female  preferences  1978; Roze, 1981;  The mean s i z e of buds probed by U . a f f i n i s  df = 36, p=0.002). smaller  correspond  l a b o r a t o r y (Berube and H a r r i s ,  1970).  difference  buds which I observed being probed by  U . quadr i fasc i a t a  the The  that  two  species  size  probed  5.1 mm  (N=6).  was s i g n i f i c a n t by  p r e v i o u s l y observed,  was The  (t=3.34,  U. quadr i fasc i a t a  was  but the sample s i z e  females may not have been o v i p o s i t i n g  (see  is  below).  CONSEQUENCES OF INSECT CHOICE  AMONG  PLANTS  consequence  GALL of  FORMATION  oviposition  formation.  The number of  correlated  with  (log  the  transformed d a t a ,  Figure  The  from the  galls  number of  formed  flies' per  most  important  perspective plant  is  is  p<0.00l  for  U.  gall  strongly  females observed on those  r=0.70, df=47,  1.3; untransformed d a t a ,  single  plants  affinis,  Spearman r=0.52, df=47, p<0.001  33  for  U. quadr i fasc i a t a , Since  the  number of  the number of buds, depend  on  Figure 1.4).  the  the  flies  number of  number  g a l l s as a f u n c t i o n of  per p l a n t  of  is well  g a l l s per  buds.  plant  For the  the number of  buds,  correlated should  number of U. the  with also  affinis  regression  is:  ln(UAG+1) = 0.80(±0.18)ln(BUDS+1) + 0 . 0 6 ( ± 0 . 7 6 ) , F=19.54, df=1,47, p<0.00l, r=0.54. regression  For  U. q u a d r i f a s c i a t a  the  is:  ln(UQG+1) = 0.99(±0.25)ln(BUDS+1) - 2 . 4 ( ± 1 . 1 ) , F=15.53, df=1,47, p<0.00l,  BUD  ABORTION  attack.  If  attack,  then  Bud  bud  r=0.50.  abortion  abortion  is  an  an  alternative  increasing  number  of  aborted  c o r r e l a t e d with the number  of  U. a f f i n i s  observed  (log  r=0.5l).  If  exclusive, of  the  is  transformed the  then  two  outcomes  for a given  buds aborted per p l a n t  average  data,  buds  level  fly of  fly  F=8.08, df=1,47, indicates  that  the p r o p e n s i t y  SEED  p=0.007, r=-0.38  there  are s i g n i f i c a n t  to abort  REDUCTION  from the p l a n t ' s  (Figure  of  fly fly  This  df=1,47, are  attack  was  p<0.00l, mutually  the p r o p o r t i o n  p r o p o r t i o n a l to  g a l l s per developed  PROP. ABT = -0.054(±0.019)UA GALLS/BUD +  of  per p l a n t w i l l be  attack  w i l l be i n v e r s e l y  number of U . a f f i n i s  function  females.  F=16.44, of  outcome  the  bud:  0.346(±0.028), 1.5).  differences  F i g u r e 1.5 a l s o among p l a n t s  in  buds.  The most important consequence of perspective  is  the  reduction  in  insect seeds.  choice Since  34  Figure  1.3. T o t a l number of U. a f f i n i s a d u l t s observed and t o t a l number of U. a f f i n i s g a l l s for each of the d i f f u s e knapweed p l a n t s . D e t a i l s of the c o r r e l a t i o n are given in the t e x t .  35  Lo CO  in  o  < / > £> O CO  C  .o r CO  CO  o -° CM E  *  •  *  z  Lo  o CM  O O  O CO  o  S||B6 Bujiinsau  O  5t  o CM  36  Figure  1.4. T o t a l number of U . q u a d r i fasc i a t a a d u l t s observed and t o t a l number of U . quadr i fasc i a t a g a l l s for each of the d i f f u s e knapweed p l a n t s . D e t a i l s of the c o r r e l a t i o n are given i n the t e x t . Note that nine p o i n t s were recorded at ( 0 , 0 ) .  •o 25. CD > <D CO  •g 20. CO CD  o 15J  CO CO  10J  $ 5•U  E  • •  3  1.  . tit  1  10  - «  • .  «  20 30 40 Number of U. affinis observed  38  Figure  1.5. Mean number of U. a f f i n i s g a l l s per developed bud and p r o p o r t i o n of buds aborted for each of the d i f f u s e knapweed p l a n t s . D e t a i l s of the c o r r e l a t i o n are given in the t e x t .  39  •9 T3 3  3  •a CD  a o  CD > CD  CD CM <n  "co O)  .Q CM  II .-I  =1  ••  •  I  —I IT)  d  T rt  1 CO  1 CM  I T  o d d ^ pajjoqe spnq jo uojjjodojd  UQ  40  seeds  will  regressed  be  p r o p o r t i o n a l to the number of developed  the number of  developed  seeds per p l a n t a g a i n s t  the  buds, I  number  buds per p l a n t and the number of U . a f f i n i s  of  g a l l s per  plant: SEEDS = 4 . 7 4 ( ± 0 . 4 8 ) D B U D S F=51.9, df=2,46, number of number  - 0.97(±0.28)UAG  p<0.00l,  r=0.83.  -  3.3(±14.3),  Thus for any given p l a n t ,  seeds produced w i l l be p o s i t i v e l y  of  developed  number of  buds  U. a f f i n i s  U. q u a d r i fasc i a t a significantly  and  galls.  galls  increase  in  c o r r e l a t e d with  negatively The  the  multiple  the  c o r r e l a t e d with  inclusion  the p r o p o r t i o n of  the  of  a  term  regression  the v a r i a n c e  the for  d i d not accounted  for. Given  the  average  (36.9±4.0),  the average  (30.7±2.4)  and  the  number  of  number  of  regression  U. a f f i n i s developed  above,  As  discussed  does  the  effect  take  differences  account  of  buds  galls will  p r o d u c t i o n per p l a n t by 27%. not  g a l l s per p l a n t  below,  per  plant  reduce this  seed value  of bud a b o r t i o n or of  i n bud p r o d u c t i v i t y .  AMONG BUDS ON PLANTS The r e l a t i o n s h i p s  between f l y  formation,  p r o d u c t i o n observed among  plants  bud  also  (Figures  abortion,  hold 1.6,  across  (Figure  are no declines  aborted  1.7). buds  seed  branching  1.7).  Branching  p r o p o r t i o n s of developed buds  and  buds,  the  categories  aborted  For comparison, and  categories  buds,  attack,  within differ and  plants in  w i t h i n c r e a s i n g branching category  of  buds  number.  the  undeveloped  in unattacked p l a n t s  proportion  gall  there  developed F l y choice  41  Figure  1.6. D i s t r i b u t i o n of g a l l s and seeds per developed bud across branching c a t e g o r i e s . V e r t i c a l l i n e s give ± one standard e r r o r . Unattacked d i f f u s e knapweed buds have approximately 12 seeds per developed bud (Watson, 1972).  6.0.  TJ 3 A  "|5.0. O >  o  "° 4.0_ L. o a  U affinis galls per developed bud  •  .1.0I  Seeds per developed bud  O  per developed bud  •0-8| a  "g3.0. o  .0.6 (0  (0  ro O) ro  2.0-  .0.4-2  (0  OT ro  (0  O) OT  'E  TJ <D  a  ijijijiA quadrifasciata galls  (0  c  3 13  i  1.0.  0.23 Dl  =1  T"  2 Branching category  T  4  ro  43  Figure  1.7. D i s t r i b u t i o n of bud f a t e s a c r o s s branching categories. A l l buds f a l l i n t o one of three f a t e categories. The sample s i z e for each branching category i s shown i n parentheses above the c o r r e s p o n d i n g proport i o n s .  1  2 3 Branching category  4 £  45  as measured by l o c a t i o n of a d u l t s was p o s i t i v e l y formation and  bud  abortion  and  negatively  r e l a t e d to g a l l  related  to  seed  product i o n . Fewer  galls  were o b t a i n e d from primary buds than  based on the d i s t r i b u t i o n s of a d u l t both  U. a f f i n i s  U. q u a d r i f a s c i a t a  (x =835, df=2,  2  preferred  primary  relatively  lower  buds,  This  df=2,  2  (x =846,  flies.  but  was  p<0.00l)  p<0.001).  gall  expected true  for  and  for  Both  formation  per  species i n s e c t was  i n these buds, presumably because of the  higher  bud a b o r t i o n . Of the (63%)  were  eight a  The  into  (25%)  bud  (The  32 probings by female U . a f f i n i s  matured,  remainder of s i z e of  galls  but  smaller  than  ( 3 . 4 7 ± 0 . 1 5 mm v s .  U=128.5,  into  d i d not c o n t a i n a U . a f f i n i s  gall.  the buds (9%)  were damaged  0.01<p<0.02).  correlation  mm;  probing  only one of  U. quadr i fasc i a t a contained possibility U. a f f i n i s  U. a f f i n i s that  none  galls.  were These  U . quadr i fasc i a t a  eggs or l a r v a e .  They  are  U  test,  smaller buds are  probes.  Of the  s i x probings I  the probed buds subsequently  gall,  contained  and g a l l production for  U. quadr i f a s c i a t a was not n e a r l y so good. observed,  subsequently  Mann-Whitney  These data suggest that  between  grasshoppers.)  subsequently  more l i k e l y to abort for a given number of The  by  that were  of buds that  4.21±0.15  (3%)  galls,  was  the buds probed by U . a f f i n i s  was  twenty  which l a t e r c o n t a i n e d U . a f f i n i s  were i n t o buds which a b o r t e d , and one  which  aborted  buds  I observed,  aborted,  and  observations  contained three  later  raise  the  can d e t e c t the presence also  a  consistent  with  of a  46  rejection state.  of  the buds on the b a s i s of u n s u i t a b l e developmental  47  DISCUSSION  VARIATION  IN  BUD  capacity"  of  buds  PRODUCTIVITY and  the  p r o d u c t i v e buds e x p l a i n s on  seed  production  Zwolfer,  1969,  Story  noted  (1978b)  reduction by  in seed set  U. a f f i n i s  the n o n l i n e a r  1978). effect  in  by  This  for  knapweed  of  in  "carrying  attack  impact of g a l l  in more  formation  other workers ( S t o r y ,  may  also  account  1978b;  for  the  of U . q u a d r i f a s c i a t a on seed p r o d u c t i o n . a  highly  significant,  by s p o t t e d  field  i n Europe.  but  nonlinear  knapweed with i n c r e a s i n g  cages  i d e n t i f i e d a similar nonlinear spotted  variation  concentration  observed  nonsignificant  The  in  Montana.  impact  on  An analogous  attack  Zwolfer  seed  (1978)  production  p a t t e r n was  observed  Urophora s i r u n a - s e v a a t t a c k i n g Centaurea s o l s t i t i a l i s  Europe.  The  r e d u c t i o n i n seed set  buds, but l e s s than 50% for  was 50% for s i n g l y  multiply  attacked  buds  of  L . in attacked  (Zwolfer,  1969) . Harris nutrients 1970) .  (1980b) argues  (cf. He  used  a  comparison for the  regression  of the e f f e c t  had a lower  intercept  seeds)  difference fly  galls  Fourcroy and Braun,  knapweed as evidence  (26.6  that  for  1967;  of  of U . a f f i n i s  (19.9  seeds)  away  unattacked  p r o d u c t i v i t y and s e l e c t i v e a t t a c k  e_t  al. ,  spotted  He observed that  galls  Watson  (1972)  H a r r i s suggests that of  n u t r i e n t s by  buds.  on more  the  on seed p r o d u c t i o n  than found by  unattacked p l a n t s .  from  Jankiewicz  seed production in  sink e f f e c t .  i s due to the s e q u e s t e r i n g  larvae  act as a "sink" for p l a n t  Variation productive  the  the gall  in  bud  buds  can  48  a l s o e x p l a i n the d i f f e r e n c e  BUD C.  ABORTION  (cf.  LIMITATION  (Roze,  1981)  are the  abortion something  production  result  resources Bud  of from  a  Pyrrhic  aborted  victory  buds  for  the  the  Faeth et a l . early  mortality  leaf  for  (1981) suggest abscission,  leaf  miners and g a l l  The  reduction  if  that  the  the  gall  a  similar  may be an important kinds  of  sedentary  from the  of  buds  number of g a l l s  distribution  aborted.  of  plant insects  due to bud galls  same  number  of g a l l s  have been an average of  the p l a n t s had  conservative  not  because  aborted  they do not  have  per bud as unaborted buds.  72% and 71% h i g h e r , buds.  and  I used the b r a n c h i n g  number of U. af f i n i s and U. quadr i fasc i a t a g a l l s  would  to  d i s t r i b u t i o n s and assumed that aborted buds would the  the  formers.  in the p o t e n t i a l  proportion  seed  however  r e p r o d u c t i v e output of  reduces  a b o r t i o n may be estimated  The  as  abortion  against  produced  plant  It  1981).  defence w i l l be p a r t i c u l a r l y e f f e c t i v e  category  attack).  small compared  These  the  fruits example  insect  is also eliminated,  foliovores.  from  or  (Stephenson,  defence",  source of  of  in  documented  r e q u i r e d to develop i t  populations.  like  first  appears to be f u n c t i o n i n g as a p l a n t defence.  c o s t of a b o r t i n g a bud may be r e l a t i v e l y  "plant  abortion  1981; Hare and Futuyma (1978) g i v e an  seed a b o r t i o n in a cocklebur as the  fly  Bud  of members of the Asteraceae a b o r t i n g flowers  Stephenson,  The is  POPULATION  d i f f u s a and C . maculosa  examples  of  AND  observed by H a r r i s .  These  per  plant  respectively,  percentages  i n c l u d e the e f f e c t s  are  discussed  49  in  the next C h a p t e r s . If  the g a l l f l i e s  plant,  the  density)  of  i n subsequent  estimate of  density  significantly  reduce seed p r o d u c t i o n  oviposition  sites  (and  years may a l s o drop.  It  is  the p o t e n t i a l seed p r o d u c t i o n per plant in the  by  branching  category.  have  absence  developed  the t o t a l  as  developed  buds  in  the  number of c a l o r i e s that would  been a v a i l a b l e for seed p r o d u c t i o n i n the average p l a n t  2986.  D i v i d i n g by the  knapweed  seeds  average  (6.5±0.1),  p r o d u c t i o n of 459 seeds. seeds  per  plant  of  calorific  gives  an  content  observation  that  of  both  species  no  the  gall  category.  the proximal b a s i s  of  per  between  The  plants plant. the  Zwolfer's  choose p l a n t s on the  the p l a n t . on  with  numbers  were  directly  Moore  intensity  of  (1978b) of  seed  size.  Both s p e c i e s of branching  flies  observed  relationship  p r e d a t i o n and p l a n t  number  f l y a t t a c k of 77%.  p r o p o r t i o n a l to the number of buds found  seed  g i v e s an estimated r e d u c t i o n in seed  b a s i s of the p h y s i c a l s t r u c t u r e of flies  is  diffuse  estimated p o t e n t i a l  BASIS FOR CHOICE The o b s e r v a t i o n s are c o n s i s t e n t (1970)  of  Compared with the observed  (106±11),  p r o d u c t i o n as a r e s u l t  also  of  to  Assuming that aborted buds would  have had the same c a l o r i f i c content same branching c a t e g o r y ,  insect  possible  f l y a t t a c k from the observed c a l o r i f i c content  buds  at  hence  per  gall  fly  preferred  buds  in  Z w o l f e r ' s (1970) o b s e r v a t i o n s  for s e l e c t i o n  is  the l o c a t i o n of  the  first  suggest  that  these  buds  the ends of the branches, however primary buds are a l s o more  50  suitable (Table  for l a r v a l growth. 1.1),  grow  They have a higher  faster  (Roze,  combined  selection  with  requirements, nearly that;  bud  of  size  of  acting  alone,  but  classes  be it  flies  buds to  appear to be  not  is  larval  making  a  Bud a b o r t i o n changes  "ideal" is  of  corresponding  decisions.  the sequence may s t i l l  flies  and  selection  sequence  to  attack.  plants  the o v i p o s i t i n g g a l l  "ideal"  content  1981), and are l e s s l i k e l y  abort buds for a given l e v e l of f l y When the  energy  for for  individual the  gall  population in  aggregate. In the face of t h i s density-dependent  p l a n t response,  there  i s a p o s s i b i l i t y for other behaviour to be i n c o r p o r a t e d i n t o oviposition selection males  would  selectivity may  reduce  the  overall  would d i s t r i b u t e the  reduce  territory  insect  insect  size  density.  of  Reduced  a t t a c k more evenly  (but  of buds a b o r t e d ) .  The use of  marking pheromones (Prokopy, 1981)  on probed buds or  buds  received  evenly  eggs would a l s o d i s t r i b u t e the  (Monro,  There  be  severe  informative  order to make the  restrictions  inputs  the  a t t a c k more  "correct" d e c i s i o n ,  Morse and F r i t z  the best f o r a g i n g s i t e ,  on  the  number  especially  g i v e n the  (Huber,  1974).  (1982) found that not a l l s p i d e r s  p r i m a r i l y because  employed for s i t e s e l e c t i o n .  of the simple  of  decisions  may  be  tight For used  stimulus  The apparent use by the g a l l  of a r e l a t i v e l y simple sequence  of  i n s e c t s can respond to i n  space l i m i t a t i o n s on t h e i r n e u r a l systems example,  insect  that  1967).  may  potentially  the  Increased  proportion  had  not  process.  the  a  flies good  51  compromise, d e s p i t e  INSECT  INTERACTIONS  "optimal" (1978, the  t h e impact  Selection  i f insects  MS; p e r s .  interactions  on  behaviour  ovipositions oviposition appear  to  because  the  influence time  Whitham  aphids.  Despite  one a n o t h e r  no e f f e c t  o f males  of  compared the  lag  buds  which  have  The  one; i t a p p e a r s  to females, rather  eggs  "territoriality"  (Berube  aggressive to females.  distribution  between  received  t o be p r i m a r i l y  from t h e  as  o b s . ; Z w o l f e r , 1970) and b e c a u s e  p e r s . comm.).  fluid  access  of  deviate  another,  towards  I detected  the d i s t r i b u t i o n  (pers.  one  f l y males  obs.),  may  for gall-forming  i s unlikely  t o guard  Berube, very  with  1980) h a s d e m o n s t r a t e d  and M y e r s ,  patterns  interact  a g g r e s s i v e n e s s of g a l l  This  i t h a s on r e p r o d u c t i v e s u c c e s s .  mating males  of and  do n o t  (pers. obs.;  of the males  isa  directed  to obtaining  than defending p a r t i c u l a r  oviposition  possible  territorial  sites. There  are  behaviour. order  Males  may be c r e a t i n g  reasons f o r t h i s space  around  to ensure access t o females a t t r a c t e d  (Smith  and  Scatophaga  Prokopy,  stercoraria  The  males  tend  t o be l a r g e r  of that  move t o w a r d s common. has  several  been  Dragonflies  species  males  selection observed  may  also  Borgia's  L. ( D i p t e r a ) that  and a r e chosen  large  Mate  1980).  by f e m a l e s  bullfrogs  display  another  successfully  release  defend  possibility. territories  i n two ways:  females  a r e a s where l a r g e m a l e s a r e  b a s e d on c o n t r o l in  by pheromone  in  (1981) o b s e r v a t i o n s o f  raise  and towards  themselves  of  oviposition  (Howard,  territoriality  1978a, at  the  sites 1978b). optimum  52  mating p e r i o d If  (Campanella,  males  mating  p r e c e d e n c e , as (Schlager,  found  1975).  after  in  another  water  bugs  male (Smith,  1960), and  Drosophila  1978), m u l t i p l e m a t i n g  is likely.  As  continuing  for females  (Parker,  competition  territorial  behaviour  by  Urophora  have  1979),  melanogaster a  a high  sperm  Tribolium  (Gromko and  result,  there  1970)  and  Pyle,  would  be  continuing  males.  SUMMARY  Both  plants  the U.  flies.  and  buds v a r i e d i n t h e  The  two  quadrifasciata,  species  made  of  choices  with  the  preferred higher level the  f o r both  in the  quality of  two  gall  reduced choices plants.  and  i n the  level  Within  were l e s s  affinis choices  p l a n t s , and  plant  branching  U.  provided  were  likely  d i f f e r e n c e i n bud  to abort  and among  among  buds.  correlated  p l a n t s , both  category.  to  species  These  were  at a  given  size  preference  of  i n the  laboratory  was  abortion,  and  field.  led  to  gall  production.  these  Gall  The  fly,  f l y s p e c i e s p r e v i o u s l y noted  choices seed  and  the  they  different  buds on  plant.  primary  buds  f l y attack.  a l s o observed The  species at  number of buds p e r buds  gall  significantly  knapweed p l a n t s , among g r o u p s of The  resources  three  production  The  outcomes was  formation,  bud  relationship held  reduced  by  both bud  between  among abortion.  and  insect within  53  II.  THE  E F F E C T OF  TIMING OF OF  Gather  ye  TWO  Time  is s t i l l  And  this  same f l o w e r  To-morrow w i l l  ye  and  be  insect-plant Palmblad,  that  1984; yet  smiles  only  Roland,  eggs  and  been  immature  allocation  i n the  1976;  1984;  ( e . g . van  der  Price,  with  Meijden,  and  Parker,  empirically  temporal processes  many  Green  1981;  Thompson and  growth  of  1970;  Myers,  to  plant  dynamics  Feeny,  1982;  possible  introduced  flower  (Asteraceae). the  sites  flies  mortality  the  two  from  dictate of  of  1977), link  their  a  impact  1971.; M o r r i s ,  The  young  ovipositing  overwintering  plant  insect  affinis  flies  galls  Centaurea  stimulate  seed  summer.  density.  resources  knapweed,  larvae  reducing  the  Urophora  (Diptera: T e p h r i t i d a e ) , lay  buds of d i f f u s e  change d u r i n g  the  insects,  (Meig.)  buds, thereby  densities  oviposition adult  the  within  The  Dingle,  quadr i f a s c i a t a  Lam.  formation  role  to host  1986).  U.  i n the  diffusa  it  relative  Dixon,  Sutton,  dynamics  F e m a l e s of Frfld.  and  d e s c r i p t i o n of  population  1963;  (e.g.  1981; has  attack  a critical  Miller  rarely  to-day,  Herrick  insect  plays  Solomon,  detailed on  of  systems  1975;  may,  dying.  timing  development  POPULATION DYNAMICS  a-flying;  - Robert The  THE  INTRODUCED INSECTS  rosebuds while  Old  ATTACK ON  production.  and The  of  suitable  emergence  and  their  The  mobilization  determine  the  gall  of  subsequent  number of  and buds  54  suitable bud and  for oviposition.  s h o u l d be hence  and  that  i n the The  mobilization  independent that  of  buds  attack:  s u p p r e s s bud  slower  bud  relative Many  attack.  bud  growth  of  initiated  buds  (Stephenson,  sites  by U.  initiated  plants  are  can  of  not  Columbia,  (Mean±S.E.) of affinis  galls  or  reduces  galls  resources  not  c o n s i d e r s t h r e e ways change as a r e s u l t proportion  f o r a t t a c k e d buds. 1980).  is  Berube  quadri fasc i a t a  of of  F l y attack  suggests gall  that  densities  1980).  cause  more  resources  Udovic  and  a r e more l i k e l y  initiated  buds on  developed. Roze  abortion  buds  (1981)  be  unattacked  (1981) e s t i m a t e d an  of  diffuse several  average  buds were n o t d e v e l o p e d . initiated  (Chapter I ; Roze,  argue  developed.  From a s u r v e y  of e a r l y  are  t o a s u b s e t of  Aker to  than  1981).  of  Attack  buds  that  This  plant  t h e number o f buds c a p a b l e o f p r o d u c i n g  either  growth  plants  seeds.  Compensatory subject  of  affect population  a lower  initiate  initiated  would n o r m a l l y be d e v e l o p e d response  Chapter  allocate  fruits  proportion  in B r i t i s h  14±3%  U.  plants  selectively  knapweed  of p l a n t  growth r a t e s ,  reduces  and  A significant  among buds  numbers  will  per  affinis.  species  earlier  insects  of g a l l s  The  r e s o u r c e s may  (Berube,  developed  that  This  compensation  growth  t o U.  seeds.  allocation  of p l a n t  and  of  of  years.  reduced  developed,  density  i n a given year  and  fly  the a l l o c a t i o n  insect  may  result  following  relative  i n the d i s t r i b u t i o n  i n the d i s t r i b u t i o n  seeds  sizes  reflected  The  to  grazing  i s a widespread  or d e f o l i a t i o n  (e.g.  phenomenon Bardner  and  in  Fletcher,  55  1974;  Chapin  Pinthus shift  and  Slack,  and M i l l e t ,  of p l a n t  fruits  1978;  resources  (Stephenson,  knapweed  compensates  initiation  should  buds,  p r o b a b i l i t y of  e.g.  for  insect  1981).  following  1972;  Compensation i s a leaves,  Hendrix, attack,  Harris,  buds,  1979). the  If  rate  of  insect attack.  the  in f a s t e r  or  diffuse bud  Knapweed  for aborted buds by i n c r e a s i n g resources  resulting  of  1977;  into l a t e r - i n i t i a t e d  1980;  flowering  The e f f e c t  Harper,  Stephenson,  increase  may a l s o compensate unaborted  1979;  bud growth or an  to  increased  for unaborted buds.  timing of  confounded  by  i n s e c t a t t a c k on g a l l and  production  is  the  effect  responses.  E x p e r i m e n t a l manipulation of  i s o l a t e the  two e f f e c t s .  Increased  of  seed  possible  plant  insect densities  helps  f l y density  should give more  galls  per bud, i n c r e a s e d p r o p o r t i o n s of buds a b o r t e d , and fewer  seeds  per  bud.  If  U. a f f i n i s  a  on  then  increased  density  s p e c i e s should lead to a r e l a t i v e  reduction  U . quadr i fasc i a t a  for  insect attack,  irrespective  of  (2)  flies  describes  development, density attack (4)  (1)  examines  describes  the  insect  plant  experimental m a n i p u l a t i o n s of  insect  of the  attack  relative  of a l t e r e d plant  effect  of t h e i r host p l a n t , change  the e f f e c t  from the e f f e c t  constant  the timing of a t t a c k by two g a l l -  to the development  three ways that  to separate  evaluates  completely  density.  relative  (3)  If p l a n t s compensate  seed production per p l a n t should be  insect  T h i s Chapter forming  density.  argues,  effect  as  in  (1980)  negative  U. q u a d r i f a s c i a t a , of both f l y  Berube  has  of  may  t i m i n g of  insect  resource a l l o c a t i o n ,  relative  t i m i n g on the  and  insects'  population  dynamics.  57  MATERIALS AND METHODS  OBSERVATION METHODS  An  R o b e r t s o n ' s on June 1,  observation  1980.  plot  was  established  A r e c t a n g u l a r g r i d of  fifty  at  (5x10)  p o i n t s was p l a c e d over a 3 m x 6.5 m p o r t i o n of the f i e l d with a visually had  uniform  d e n s i t y of d i f f u s e  begun to b o l t nearest  The  points  on  the  The  staked  observations two d a y s ,  of  each  plants the f l i e s  grid  provided  a  basis  and t h e i r h o s t s .  The l o c a t i o n ,  adult  fly  2.1), all  species,  was  Approximately every  Bud  of the  fly  state,  The date on which a it  Berube and H a r r i s practice  it  possible  the  and evidence  in an i n i t i a t i o n category  (Table  set  bud  of  first  with  (1978) to the nearest  became  all  was  sample for s t a t i s t i c a l measured  s t a t u s of  times d u r i n g  of measurements  Some of the e a r l y sets of measurements  were  each  survey.)  and developmental  developmental  used to place  sizes  of  observation.  height,  to o b t a i n a reasonable  detailed  was recorded at the moment of  size,  sex,  roughly corresponding to a complete  buds.  for  and a c t i v i t y  h e r b i v o r y were a l s o noted. observed  staked  posture,  number, l o c a t i o n ,  Plant  staked.  neighbours.  the buds on a l l the p l a n t s were recorded 19-21 summer.  was  were far enough apart so that  (See Chapter I for a d d i t i o n a l d e t a i l s The  the  The p l a n t which  I conducted a branch by branch v i s u a l survey  staked p l a n t . of  each p o i n t on  grid  p l a n t s were r a r e l y nearest  knapweed.  are  of  combined  comparisons.  calipers  as d e s c r i b e d by  millimeter.  With  some  to v i s u a l l y estimate s i z e s .  Spot  checks w i t h c a l i p e r s confirmed the accuracy of these e s t i m a t e s .  58  Table 2.1  - Dates on which buds were f i r s t observed and corresponding bud i n i t i a t i o n c a t e g o r i e s , Robertson's 1980 Category  Date  1 2 3 4 5 6 7 8 9 10 1 1 12 13 14  June June June June June June June July July July July August August August  1- 9 11-13 15 17 19 23-25 27-29 2- 4 8-10 11-13 26 4- 7 11-13 20-24  In a d d i t i o n to the method d e s c r i b e d (above),  aborted  developmental knapweed  assumed  may  h i s t o r y when that  plants  undeveloped  buds  typically  buds that are  that  also is  be  known.  initiated  late  for a p e r i o d of  by c l i p p i n g them o f f  stored  in folded and s t a p l e d  until  dissection.  plant  was measured  location  of  Methods by  their  Range p o p u l a t i o n s  in  the  season.  each  individually  bags  at  When they were d i s s e c t e d , and  the  bud  were  size,  if  it  on  August  They were then  room  temperature  the height of  developmental  recorded.  I  t h i r t y or more days.  at ground l e v e l .  paper  of  p r o p o r t i o n of  any given bud had been aborted by the plant  PLANT COLLECTIONS P l a n t s were c o l l e c t e d 1980  identified  contain a significant  remained at a constant s i z e  23,  in the General  Buds  each  status,  large enough  and to  59  c o n t a i n e i t h e r g a l l s or seeds were i n d i v i d u a l l y d i s s e c t e d . these,  the  were n o t e d .  number  of  seeds and contents  The g a l l s of the  distinguished;  U. a f f i n i s  two  of any g a l l s  insect  galls  are  species hard  present  are  and  For  easily  woody  and  U. q u a d r i fasc i a t a g a l l s are t h i n and papery. The  collection  of  plants  at  a  single  point  in  time  r e p r e s e n t s a t r a d e o f f between l o s s of seeds from mature buds and an  incomplete  second  generation of  flies.  the c o n c l u s i o n s to the time of c o l l e c t i o n  The s e n s i t i v i t y  was  evaluated  second c o l l e c t i o n of twenty p l a n t s on September 12, plants  were  the  nearest  plants  by  1980.  to randomly s e l e c t e d  of a  These points.  D i f f e r e n c e s between c o l l e c t i o n s are d i s c u s s e d i n Appendix I I A .  INSECT  DENSITY  oviposition  MANIPULATION change  fly  relative  to  summer  a l l o c a t i o n of resources by the p l a n t s .  To  separate  effects  I constructed enclosures  gall  and seed p r o d u c t i o n ,  with d i f f e r e n t d e n s i t i e s enclosures Each 1.5 m  were 3  of  flies  diffuse  stretched  Because e a r l i e r experiments using s i m i l a r  knapweed  completely  the e n c l o s u r e s  plants  of shading on  the  (Berube, p e r s . comm.; p e r s .  open at the t o p .  prevent changes (see  Nine  The bottom edge of the n e t t i n g was b u r i e d i n  the e n c l o s u r e s were l e f t not  two  densities.  fibreglass netting  had demonstrated a s i g n i f i c a n t e f f e c t of  these  at Robertson's in 1980.  enclosure was b u i l t of  ground.  as does the  used, three at each of three i n s e c t  on a wooden frame. the  throughout  densities the  on  sites  The  netting growth obs.),  T h i s arrangement  did  i n p l a n t q u a l i t y as a r e s u l t of  Appendix I I B ) , but  minimized  such  changes  60  while  preserving  enclosures Gall  (see  differences  in  adult  fly  density  among  below).  fly densities  were manipulated  by  moving  dead  stem  p l a n t s from the p r e v i o u s year c o n t a i n i n g d i a p a u s i n g l a r v a e . visible  old  plants  and  density enclosures. received  the  old  were  heads were removed from the low  Each of the three high plants  density enclosures. enclosures  seed  The left  performed on June 1,  and old  in  1980,  All  seed  enclosures  heads from one of the low  plants  in  place. prior  density  the  These  control  density  manipulations  to the emergence  of  were  any  gall  flies. Relative  counts  three d i f f e r e n t days  of  flies  enclosures  (The  counts  among of  10) to ensure  enclosures  gall  suggests that some g a l l  which escaped d e t e c t i o n . ) in  the c e l l s were obtained on  (June 27 and 28 and J u l y  the movement of stem p l a n t s densities.  in  flies flies  in  had  varied  the  low d e n s i t y  I r e c o r d e d the numbers of  flies  timing  of  surveys  among  days  e n c l o s u r e comparisons on the same day. not  be  reliably  seen  Surveys  11:30 a.m. and 2:30 p.m. and took a t o t a l  approximately t h i r t y minutes f o r a l l e n c l o s u r e s . the  fly  emerged from seed heads  each e n c l o s u r e d u r i n g a three minute v i s u a l survey.  were begun between  that  would  Differences  not  Species  affect and  determined through the n e t t i n g ,  was no reason to b e l i e v e  sex  of in  among could  however  that e i t h e r s p e c i e s composition or  there sex  r a t i o d i f f e r e d among e n c l o s u r e s . Plants 1980,  after  were  collected  from  the f i r s t g e n e r a t i o n of  each enclosure on August 16, flies.  Seed p r o d u c t i o n  was  61  incomplete  by  this  date  so seed counts are not comparable to  unenclosed p l a n t s ,  however among treatment comparisons  affected  early  enclosures  by  the  collection  date.  on f l y a t t a c k i s assessed in  were s t o r e d and d i s s e c t e d  The  Appendix  as d e s c r i b e d above.  are  not  effect  of  the  IIB.  Plants  62  RESULTS  INSECT ATTACK AND BUD INITIATION  INSECT  ATTACK  The data from the  suggest that U . a f f i n i s than females, oviposition  Table 2.2  first  generation of g a l l  males emerged two to three days  mating o c c u r r e d as soon as the followed  a  few  days  later  flies  earlier  females emerge, (Table  2.2).  and  These  - Mean day of o b s e r v a t i o n for d i f f e r e n t c a t e g o r i e s of Urophora f l i e s on d i f f u s e knapweed p l a n t s , R o b e r t s o n ' s 1980  Insect  Day  Urophora a f f i n i s Males Females Mating f l i e s Probing f l i e s All flies Urophora q u a d r i f a s c i a t a All flies  of Observation 24. . 9 ± 0 , .3 * 27., 3 ± 0 , .4 27.. 2 ± 0 . .7 30, .0±1 ,. 1 25. , 5 ± 0 . .2  N 689 275 74 32 1046  25., 0 ± 0 , .8  81  - Days from June 1 ( M e a n ± S . E . )  observations  on p l a n t s  observations events, females.  in  the  f i e l d agree with Z w o l f e r ' s  laboratory  in  terms  The  mean  dates for U. a f f i n i s first  generation  (1970)  of the sequence of  though he found that males emerged only one  were s i m i l a r i n the Figure  i n the  day  before  and U. quadr i fasc i a t a  (t=0.827, df=l049,  p=0.408;  2.1).  In the second g e n e r a t i o n ,  U . quadr i fasc i a t a emerged  earlier  63  Figure 2.1. Counts on f i f t y d i f f u s e knapweed p l a n t s of the two s p e c i e s of g a l l f l y at Robertson's in 1980. July 25 d i v i d e s the f i r s t and second generations of g a l l flies.  65  than U. a f f i n i s observed  probings  generation N=11,  (Figure 2.1) of  preceded  and reproduced sooner.  buds  those  p=0.006).  by U. q u a d r i f a s c i a t a i n the by  Seven  U. a f f i n i s out  U. q u a d r i f a s c i a t a matings came (Mann-Whitney, U=13, N=21,  BUD  final  indicate  numbers  diffuse fly  of  before  of  that  the any  knapweed p l a n t s  attack  roughly  linear  generation  INTERACTION  per  The  eight U. a f f i n i s  U. a f f i n i s  Despite  in  bud  timing  outcomes  galls  per  f l y abundance of  the  of  and  (Figure 4.2),  the  varied  in  the  t h e r e was a  during  the  attack  on  buds  first  initiated The  developed bud was g r e a t e r  (Figure  peak of  number  in e a r l i e r  than would be expected  2.3).  The  difference  on the in  f l y abundance and the peak of g a l l s  point  range for o v i p o s i t i o n . oviposition  the  c o n s i d e r a b l y among  sharp changes  numbers  fly  developed bud i s p a r t l y due to the initiation  and  flies.  i n i t i a t e d buds and d e c l i n e d sooner b a s i s of  matings  standard e r r o r s in  throughout the summer are shown i n F i g u r e s 2 . 3 - 2 . 6 . of  U=0,  observed  initiation  varied  and r a i n f a l l  increase  of a d u l t  plant  i n 1980.  ( F i g u r e 2.1)  second  0.002<p<0.02).  the t i m i n g of bud  buds  the  (Mann-Whitney,  INITIATION The r e l a t i v e magnitude of the  F i g u r e 2.2  A l l of  l e n g t h of  bud  at which buds reach a s u i t a b l e  size  throughout  the  summer  suitable  size  (see  below).  for  because bud growth  r a t e s changed with l o c a t i o n of the bud on the p l a n t and with attack  per  between  The time to reach a  time  the  Based on bud growth r a t e s at  the  peak  fly of  F i g u r e 2.2. Average numbers of buds on d i f f u s e knapweed p l a n t s at Robertson's i n 1980. Each p o i n t g i v e s the mean number of buds on f i f t y p l a n t s ± one standard error.  68  Figure 2.3. Mean number of U. a f f i n i s g a l l s per developed bud by bud i n i t i a t i o n category for Robertson's i n 1980. V e r t i c a l l i n e s g i v e ± one standard e r r o r for g a l l s per developed bud. I n t e r p o l a t e d counts of U. a f f i n i s a d u l t s on the same f i f t y p l a n t s in the same i n i t i a t i o n c a t e g o r i e s are a l s o shown. Counts were i n t e r p o l a t e d from the data i n F i g u r e 2 . 1 . Bud i n i t i a t i o n c a t e g o r i e s are d e f i n e d i n Table 2 . 1 .  1.75J  Bud initiation category  70  F i g u r e 2.4. P r o b a b i l i t y of bud a b o r t i o n by bud i n i t i a t i o n category for Robertson's i n 1980. V e r t i c a l l i n e s give ± one standard e r r o r for the p r o p o r t i o n of buds a b o r t e d . I n t e r p o l a t e d counts of U. a f f i n i s a d u l t s on the same f i f t y p l a n t s i n the same i n i t i a t i o n c a t e g o r i e s are a l s o shown. Counts were i n t e r p o l a t e d from the data i n Figure 2.1. Bud i n i t i a t i o n c a t e g o r i e s are d e f i n e d i n Table 2 . 1 . The d o t t e d l i n e between bud i n i t i a t i o n c a t e g o r i e s 10 and 11 i n d i c a t e the assumed change i n the p r o p o r t i o n of buds a b o r t e d . It was not p o s s i b l e to d i s t i n g u i s h between aborted and undeveloped buds i n i n i t i a t i o n category 11.  L.120  Bud initiation category  72  Figure 2.5. Mean number of U. quadr i fasc i a t a g a l l s per developed bud by bud i n i t i a t i o n category for R o b e r t s o n ' s in 1980. V e r t i c a l l i n e s give ± one standard e r r o r for g a l l s per developed bud. I n t e r p o l a t e d counts of U. a f f i n i s a d u l t s on the same f i f t y p l a n t s i n the same i n i t i a t i o n c a t e g o r i e s are a l s o shown. Counts were i n t e r p o l a t e d from the data in Figure 2 . 1 . Bud i n i t i a t i o n c a t e g o r i e s are d e f i n e d in Table 2 . 1 .  Bud initiation category  —i  74  Figure 2.6. Mean number of seeds per developed bud by bud i n i t i a t i o n category f o r R o b e r t s o n ' s in 1980. Vertical l i n e s g i v e ± one standard e r r o r for seeds per developed bud. I n t e r p o l a t e d counts of U . a f f i n i s a d u l t s on the same f i f t y p l a n t s i n the same i n i t i a t i o n c a t e g o r i e s are a l s o shown. Counts were i n t e r p o l a t e d from the data in Figure 2.1, Bud i n i t i a t i o n c a t e g o r i e s are d e f i n e d in Table 2 . 1 .  76  gall  formation and the  suitable  s i z e of probed buds,  the time to reach a  s i z e range for o v i p o s i t i o n probably  difference  of  between  This difference  is  one  corresponds  and two bud i n i t i a t i o n  not enough to e x p l a i n  the  to  a  categories.  contrast  between  the peaks i n f l y abundance and g a l l f o r m a t i o n . A  similar  time  probing does account abortion relative  and timing  abortion changes gall  fly  interval  reach  f o r the d i f f e r e n c e abundance  of  fly  indicate  to  (Figure  abundance,  that  changes  a  in  suitable  the  2.4). gall  size  for  of  bud  timing  These data on the  formation,  and  in bud a b o r t i o n c o i n c i d e d with  i n f l y abundance and suggests that bud a b o r t i o n  formation by U . Despite  reduces  affinis.  the synchronous f i r s t  U. q u a d r i f a s c i a t a a d u l t s production  bud  dropped  (Table  generation of U . a f f i n i s and  2.2),  U. quadr i fasc i a t a  c l o s e to zero d u r i n g the peak of U.  a d u l t abundance ( F i g u r e 2 . 5 ) .  gall  affinis  T h i s drop was n e g a t i v e l y  related  The e a r l i e r second generation of U . quadr i fasc i a t a  relative  to bud a b o r t i o n .  to  U. a f f i n i s  may  U. quadr i fasc i a t a g a l l generation.  The  the o f f s p r i n g  of  number  the  of  peaked  (Figure 2 . 6 ) .  by  the  suppression of  the  early  emerging  successfully seeds  after  per  early  were  ovipositing  produced g a l l s .  developed  U. a f f i n i s the  and  of  first  emerging in the second g e n e r a t i o n  r e l a t e d to the counts of production  explained  formation d u r i n g the peak  flies  U. quadr i fasc i a t a that The  be  on  maximum  bud  staked  was  negatively  plants.  of U. a f f i n i s  There appears to have been a seed refuge  Seed  abundance late  in  77  the  season.  CHANGES IN PLANT ALLOCATION  BUD  GROWTH  Buds  on  primary  branches grew more slowly than buds  on  higher  (Figure  AND DEVELOPMENT  2.7).  knapweed.  The o p p o s i t e  Roze (1981)  REPRODUCTION  days f o r p r o x i m a l  Plants  aborted buds i n three p o s s i b l e increased  after  fly  could  ways:  (1)  attack,  branches diffuse days  buds.  Thus  attack.  have bud  (2)  another bud c o u l d have been developed,  compensated f o r initiation  could  for every bud aborted  or (3) the  to the aborted buds c o u l d have grown f a s t e r to  order  found that d i s t a l buds took 3 2 . 9 ± 0 . 5  growth of developed buds i s slowed by i n s e c t  have  secondary  t r e n d holds f o r unattacked  to flower compared with 4 5 . 6 ± 0 . 6  COMPENSATORY  and  buds  lateral  and been more l i k e l y  develop. The  ruled  first  out,  possibility,  since  corresponding  to  no  increased  change  changes  in  in  the  fly  bud i n i t i a t i o n , may be bud  initiation  a t t a c k was observed  rate (Figure  2.2) . To t e s t the second mechanism, I examined between  the  proportion  of buds a b o r t e d per p l a n t  p r o p o r t i o n of buds developed per p l a n t summer.  Assuming  that  independent of f l y a t t a c k , of  insect  attack  the  (PD) at the  relationship (PA) and the end  of  the  the t o t a l number of buds per p l a n t was then buds which a b o r t e d as  (instead  of  developing)  should  a  result  have been  78  Figure 2 . 7 . D i s t r i b u t i o n of phenology measures a c r o s s branching c a t e g o r i e s . Date i n i t i a t e d and date flowered are i n days from June 1. Time to flower i s the d i f f e r e n c e ( i n days) between i n i t i a t i o n and f l o w e r i n g . Date i n i t i a t e d i s for a l l buds in a given branching category. Date flowered and time to flower are for only those buds which flowered i n a given branching category. V e r t i c a l l i n e s give ± one standard e r r o r .  80.  80  compensated  for by buds which developed  undeveloped).  (instead  The r e s u l t would be an increase  of  remaining  in PA, no change  in PD, and a decrease  i n the p r o p o r t i o n of undeveloped buds  per  plant  latter  the  (unless  this  proportion  reached z e r o ) .  If  second mechanism was o p e r a t i n g , a p l o t of the p r o p o r t i o n of  buds  aborted  (PA) a g a i n s t  (PD)  should  have a s l o p e  the  proportion  is:  PD = - 0 . 7 0 2 ( ± 0 . 0 8 2 ) P A  + 0.646(±0.025),  df=1,47,  relationship  p<0.00l,  is  buds  developed  not s i g n i f i c a n t l y d i f f e r e n t  observed r e l a t i o n s h i p  F=73.0,  of  r=-0.78.  The  from z e r o .  slope  The  of  significantly  less  than  zero.  r e p r o d u c t i o n does not appear to  have  been  operating  the  Compensatory in  this  case. If  the  third  mechanism  was  acting,  development  and p r o b a b i l i t y of flowering of  have  positively  If  been  affected  resources a v a i l a b l e ,  likely  to a b o r t  if  the  lateral  terminal buds  bud  would  aborted.  affected  by a b o r t i o n of the t e r m i n a l bud s i n c e  on growth.  was  related  to less  Lateral  buds  been the most d i r e c t l y e f f e c t s on  from other  other  influences  I d i v i d e d these l a t e r a l buds i n t o those which had an  not  ( 1 3 . 9 1 ± 0 . 6 9 days 13.07±0.73  have  not have been d i s t i n g u i s h a b l e  a b o r t e d t e r m i n a l bud and those flower  would  then l a t e r a l buds would have been  to  would  buds  negatively  nearest  buds  terminal  the speed of  by a b o r t i o n of the t e r m i n a l bud.  the p r o b a b i l i t y of a bud a b o r t i n g i s  the  then  days  which  did  significantly different  not.  with  time  to  between the two groups  (N=699) with the t e r m i n a l bud not (N=579)  The  aborted  vs.  the t e r m i n a l bud a b o r t e d ) .  The  81  probability  of  significantly  the  bud  aborting  ( x = 2 . 2 3 , df=1,  different  was in the o p p o s i t e 0.33).  lateral  from  also  not  p=0.135) and the trend  2  direction  was  that  predicted  (0.29  vs.  The p r o b a b i l i t y of the l a t e r a l bud f l o w e r i n g behaved as (x =6.47,  predicted  df=1,  2  relatively  small  (0.36  P=0.011),  vs.  T h i s was the only evidence  0.43),  for p l a n t  but  the  effect  a difference  was  of only 16%.  compensation.  INSECT DENSITY MANIPULATION  There were s i g n i f i c a n t treatments  Table 2.3  for  the  differences  in the counts  f l y density manipulations  of  INSECT DENSITY * Control  High  June 27 June 28 J u l y 10  9,11,16 19,21,23 0,2,3  4,8 10,12 0,3  among  (Table 2 . 3 ) .  - Counts of Urophora f l i e s observed i n e n c l o s u r e s , Robertson's 1980  Date  flies  The  density  Low 1,3,6 5,5,9 0,1,1  * Mann-Whitney U - t e s t s were used for p a i r w i s e comparisons of sets of c o u n t s . R e s u l t s of t e s t s for June 27 and June 28 were combined using F i s h e r ' s procedure (Sokal and R o h l f , 1969). Low v s . C o n t r o l , X = 7 . 8 2 , df=4, p=0.098; Control vs. High, ;X. = 9.21, df=4, p=0.056; Low v s . H i g h , =11.92, df=4, p = 0 . 0 l 8 . a  2  difference in  the  between the counts at the end of June and the  middle  plants outside  of  July  agrees  of the e n c l o s u r e s  with the counts (Figure  2.1).  of  counts  i n s e c t s on  82  The  number of buds per p l a n t  among treatments  Table 2.4  did  (F=0.68, df=2,54,  not  vary  p=0.511; Table  significantly 2.4).  - E f f e c t of g a l l f l y d e n s i t y manipulations on d i f f u s e knapweed c h a r a c t e r i s t i c s , g a l l p r o d u c t i o n , seed p r o d u c t i o n , and bud a b o r t i o n  Character  INSECT DENSITY Control  High  Low  Number Buds/Plant Dev./Plant  22 62 . 5 ± 7 . 6 21 . 2 ± 2 . 8  18 67.3±7.3 24.9±2.9  17 77 . 8 ± 1 0 . 1 27.7±4.2  UA/Dev. UQ/Dev. Seeds/Dev.  1 . 10±0.06 0. 0 3 ± 0 . 0 1 0. 5 3 ± 0 . 0 7  0.89±0.06 0.05±0.02 0.79±0.08  0.73±0.05 0.08±0.02 1 . 3 2 ± 0 . 11  Prop A b o r t e d Prop Undev.  0. 1 1 ± 0 . 0 1 0. 2 5 ± 0 . 0 2  0. 1 0 ± 0 . 0 1 0.28±0.02  0 . 13±0.02 0.26±0.03  Seeds/Plant  11 . 4 ± 3 . 3  19.6±4.0  36.6±7.8  Prop UQ * Prop U n a t t . * * * **  0.06  0.10  .0.43  0.51  0.51  P r o p o r t i o n of U . quadr i fasc i a t a g a l l s of a l l g a l l s . P r o p o r t i o n of developed buds unattacked by e i t h e r s p e c i e s of g a l l f l y .  Gall density. the  0.02  by  U. a f f i n i s  The number of U . a f f i n i s  high  control  formation  density  enclosures  (t=2.63, df=9l4,  was  p=0.009)  galls  or  df=905,  developed  bud i n the c o n t r o l e n c l o s u r e s  low  density  enclosures  per  higher  (t=5.00,  the  p<0.00l).  t r a c k e d the change  low  developed than  bud  in e i t h e r  density  The number of U . a f f i n i s  (t=2.!7,  in adult  the  enclosures galls  was a l s o g r e a t e r df=882,  in  per  than i n  p=0.030).  The  83  changes  were  proportionally  smaller  than  the changes  in the  observed a d u l t f l y d e n s i t y .  If male t e r r i t o r i a l i t y and movement  of  had  flies  among  distribution differences  enclosures  of  males  among  resulted enclosures  in g a l l s per developed bud  proportion  different reasons  of  buds  among treatments  for t h i s  include  a  was  enclosure  the  would  densities.  not  significantly  (F=0.96, df=2,54, p=0.389). the  uniform  treatments  in adult  aborted  more  than for females,  among  have been g r e a t e r than the d i f f e r e n c e s The  in  effects  Possible  discussed  in  Appendix I I B . The  attack  by  U . quadr i fasc i a t a  and the seed p r o d u c t i o n  a l s o responded to the change i n t o t a l a d u l t f l y  density.  formation  increased a d u l t  density of  by  U. quadr i fasc i a t a  (high v s .  by  the  galls  change  of  all  in density  galls  were a l s o s i g n i f i c a n t  per  developed  df=898,  in  was  significantly  2  with  the  two  (x >6.88 i n both c a s e s , df=1,  extremes  p<0.0l).  2  the h i g h f l y d e n s i t y e n c l o s u r e s had fewer bud  p=0.0l5)  than or  the  (t=6.25, df=8l9, p<0.00l). bud  The p r o p o r t i o n  (x =27.68, df=2, p<0.00l).  The comparisons of the c o n t r o l d e n s i t y  Plants  with  low; t=2.42, df=723, p=0.U16).  U . quadr i fasc i a t a  affected  dropped  Gall  either  the  plants  p r o d u c t i o n per developed bud  for  plants  i n the low d e n s i t y  The seed  for c o n t r o l p l a n t s was a l s o  control  production  seeds  (t=2.43, enclosures  per  developed  s i g n i f i c a n t l y greater than seed plants  in  the  low  density  enclosures (t=4.06, df=860, p<0.00l). The p r o p o r t i o n of buds unattacked by e i t h e r species of g a l l fly  varied  significantly  with  insect  density  (x =7.33, df=2, 2  84  p=0.026). refuge  T h i s comparison i n d i c a t e s  (Figure  2.6)  that the s i z e of  depends on i n s e c t  density.  the  seed  The change i n  s i z e of the seed refuge was not l i n e a r with the change i n  insect  density. There was no a d d i t i o n a l evidence of compensation for attack.  The t o t a l number of  seeds  related  to  (Table  evidence  that p l a n t s reduced the p r o p o r t i o n of undeveloped  to compensate 2.4).  insect  density  per  plant  2.4).  for attacked buds (F=0.38,  was  There  df=2,54,  insect  negatively was a l s o no  p=0.686;  buds Table  85  DISCUSSION  CHANGES gall  IN  INSECT  DENSITY  fly densities,  galls  As a r e s u l t of manipulation of  r e l a t i v e l y s m a l l changes  per bud were o b s e r v e d .  density  d u r i n g the season  formation. adult  Similarly,  size  the  number  l a r g e changes  had r e l a t i v e l y s l i g h t  The same kind of d i s c r e p a n c y  population  in  in  insect  e f f e c t s on g a l l  between  variation  (1980)  for the c i t r u s  I observed there was no c e i l i n g on g a l l  s i n c e an i n c r e a s e the  number  and  i n the number of  of g a l l s ,  despite  (presumably) s i m i l a r  in f l y density  in  of the season.  l e d to an  density,  increase  in  s i m i l a r numbers of buds per p l a n t  g a l l s per developed bud p r i o r  ( F i g u r e 2.3)  reduced the r e p r o d u c t i v e success of part  flies  the  phenologies.  The drop i n U . a f f i n i s decline  in  swallowtail.  The d e n s i t y m a n i p u l a t i o n experiment a l s o showed that w i t h i n range  of  and v a r i a t i o n i n l a r v a l p o p u l a t i o n s i z e  was observed by H i r o s e et a l .  density  the  suggests  that  the g a l l f l i e s  the  some  factor  in the  latter  The p r e f e r e n c e of probing females  the primary branching c a t e g o r y observed in  to  Chapter  for buds I  could  e x p l a i n the drop,  however the time between  buds  probed and the time of the observed probes d i d  that  were  not change s i g n i f i c a n t l y d u r i n g the days  in  the f i r s t  second h a l f relative  half  preference  season;  of the season  of the season.  the i n i t i a t i o n of  it  was  and 8 . 6 9 ± 1 . 3 7  the  7.94±0.91 days in the  These data suggest that there was  a  for e a r l i e r i n i t i a t e d buds, not an a b s o l u t e  preference. The d e c l i n e  in U. a f f i n i s  gall  production  could  also  be  86  explained  by  summer.  reduced  This  proportion  greater  possibility  of  second halves in  p=0.003).  observed of  the  the  may  because  eggs  size  of  the  egg  of  for  oviposition  sized  buds.  observed drop in g a l l possible  "sink" r e s u l t i n g possible increases (i.e.  in  higher,  or  was  galls.  by U. a f f i n i s  buds w i l l form an i n c r e a s i n g p r o p o r t i o n  first  resulting  the  suitably  unaborted  This  of  cumulative e f f e c t  could" cause  the  that  in egg "wastage" is  search buds).  that time  the for  time  in  two  ways.  aborted buds act as an egg  (Monro,  1967).  The  second  accumulation of a b o r t e d buds suitable  oviposition  sites  of bud a b o r t i o n and r e l a t i v e l y  changes i n g a l l formation with l a r g e changes in i n s e c t alternative  The  Both mechanisms are c o n s i s t e n t with  observed density-dependence  These  aborted  population  is  of  (Chapter I ) , the  formation over  mechanism  mechanism the  i n the  increased  Because aborted buds remain on the p l a n t and remain i n range  late  df=1,  2  despite  mortality  and  actually  (x =8.92,  probes  the  first  was  the  less  to produce  laid  comparing  season  dropped  in  season were  likely  from  by  proportion  proportion  because  later  seen probing i n the  formation  oviposition declined, larvae  tested  The  half  the  oviposition  be  season.  gall  because  and  females  second  Thus  probing,  probing  mechanisms  are e x p l o r e d f u r t h e r  the  small  density.  i n the  next  restrict  the  Chapter. T h i s cumulative e f f e c t reproduction,  not  U. quadr i fasc i a t a .  only  of bud a b o r t i o n of  will  U. a f f i n i s ,  While aborted buds are not,  but in  also general,  of in  87  the s u i t a b l e preventing  s i z e range f o r o v i p o s i t i o n by U . q u a d r i f a s c i a t a , by growth to l a r g e r s i z e s ,  a v a i l a b i l i t y of buds for t h i s U. quadr i fasc i a t a years  i n which  (1981); pers.  1978,  obs.;  have  these  Because  have  been  observed  Berube, p e r s .  comm.; 1979,  1980,  obs.),  abortion  pers.  and  U. a f f i n i s  will  population  density  for  species.  by  be  interspecific  a  consistent  of  five  1977,  suppression  g e n e r a t i o n of of  and  in the  (1976,  the  Roze  Berube, p e r s . comm. and  the  preemption  reduce  U. a f f i n i s  had synchronous phenologies  p r o d u c t i o n d u r i n g the f i r s t bud  bud a b o r t i o n w i l l  of  gall  U. q u a d r i f a s c i a t a oviposition  limiting  U . q u a d r i fasc i a t a .  sites  by  on  the  factor Additional  c o m p e t i t i o n between the two g a l l  by  evidence  fly  species  i s given i n Chapter V .  SEED  REFUGE  flies  and bud i n i t i a t i o n and development  by t h e i r  Roze  (1981)  and  patterns bud  observed  initiation  bud  in  1977  synchrony e x i s t s between the  initiation  initiation  and  and Chase  fly  between the two y e a r s . in  the development  (spotted  emergence Finally,  the peak of U . a f f i n i s of  gall fly  gall  plants. emergence  The  later  was p a r a l l e l e d by a l a t e r peak i n  Berube suggests that  knapweed)  host  the two r e l e a s e s i t e s .  was about two weeks i n advance of  (diffuse  days  of  i n 1976 and 1977 at  emergence. 1979  A h i g h degree  shifted despite  of  plants  fly in  1978 at both Ned's Creek knapweed). in  Again,  bud  the same d i r e c t i o n  a difference  of  twelve  abundance between 1974 and 1975  in Montana,  the degree  synchrony between g a l l  fly  emergence  and spotted  knapweed bud i n i t i a t i o n remained the same (Story and  88  Anderson,  1978).  T h i s synchrony i m p l i e s that refuge of  may  be r e l a t i v e l y c o n s t a n t .  the t o t a l  attack)  potential  will  be  from  seed  available  Chapter V d e s c r i b e s refuges  the s i z e and t i m i n g of the  a technique  (prior  to estimate  the  and a p p l i e s  data at the o r i g i n a l r e l e a s e s i t e s  for the g a l l  parallel  for knapweed seed  systems.  Story  d e n s i t y of U. a f f i n i s buds were a t t a c k e d . of  production  (pers.  i n Montana only 62%  Rhine  constituted  than 70% of a l l  the  one of the sources  Varley by  different more U.  L.  than  48%  43%)  and  the  highly  in Europe (Zwolfer,  and  of  Frazer  spotted  several  knapweed  i n the  i n Europe the  population insect  for  census  flower  samples  percentage  where  U.  This  affinis  l a r v a e , and which was populations.  C . nemoralis work  in  attacked  over  thirty  heads  containing of  with  galls."  attacked  buds  clumped d i s t r i b u t i o n in Carduus nutans  1979).  COMPENSATORY REPRODUCTION Based on Roze  in  in England and Wales showed no sample of  seed  flies.  exists  F . a l s o has a low p r o p o r t i o n a  of  to h i s t o r i c a l  f o r the Canadian U. a f f i n i s  "Preliminary  localities  solstitialis  (c.  Valley  (1947) observed such a refuge  U . jaceana.  it  fly  plants.  l a r v a e d i d not exceed 48%.  i n c l u d e s the Upper greater  size  Zwolfer (1978) observed that  buds a t t a c k e d by any i n s e c t  gall  comm.) found that at the peak  C . maculosa flower buds he c o l l e c t e d  of  to  the next g e n e r a t i o n of  distributions  A refuge  gall  Hence a c e r t a i n p r o p o r t i o n  production to  seed  a  comparison  (1978) argue that d i f f u s e  among  knapweed  years,  compensates  89  for  fly attack.  They suggest that proximal undeveloped buds are  developed when d i s t a l buds support  their claim.  If  are  then  (including  aborted  should remain c o n s t a n t . to  1977, My  abortion  Their  data  do  not  for each d i s t a l bud aborted a proximal  bud was d e v e l o p e d , distal  aborted.  the  proportion  of  undeveloped  buds  buds and proximal undeveloped buds)  As the a t t a c k rate i n c r e a s e d from  1975  the p r o p o r t i o n of buds undeveloped i n c r e a s e d . data  show  i n the  f l o w e r i n g of  that  there  some  compensation for bud  form of a small d i f f e r e n c e  in the p r o b a b i l i t y of  l a t e r a l buds.  is  Despite heavy f r u i t  l o s s e s to  insect  a t t a c k by Haplopappus squarrosus H . and A . , no compensation observed in that for  insect  compensate not  shrub (Louda,  attack  may  be  for aphid a t t a c k  (Dixon,  1982).  The a b i l i t y to  species-specific; (Dixon,  sycamore leaves  1971b).  The  timing  relative  bud  initiation  to  knapweed  evolutionary  change.  m i c r o e v o l u t i o n a r y change, variation,  a genetic  reproduction  or  in  emergence  fly  may  be  the  three  f a c t o r s are r e q u i r e d :  emergence subject  to  view  of  traditional  phenotypic  for t h i s v a r i a t i o n , and d i f f e r e n t i a l of  the  variants.  time and developmental rate of  heritable  ( R i c h a r d s and Myers,  The  There i s  time of the g a l l f l i e s  emergence  third  gall  In  basis  survival  of  i n g r e d i e n t s are almost c e r t a i n l y p r e s e n t .  The  compensate  1971a), while lime l e a v e s do  EVOLUTIONARY CONSEQUENCES  variation  was  two  considerable  ( F i g u r e 2.1)  insects  1980; T a y l o r ,  first  are  and  probably  1981).  f a c t o r , d i f f e r e n t i a l r e p r o d u c t i o n , has at  least  90  three components. (e.g. are  i s the  Mooney et_ a l . , 1981). higher  quality  initiated later degree two  The f i r s t  and  generations  population  This  reproduction that a  mosquito,  can  support  will  to g a l l  increase in  reproductive variable.  possibilities  frequency-dependent  one.  will  dilute  Disruptive selection emergence  in  was  for  later  in  in  the  gall  would r e s u l t  selection  considerably  in  a  generation for  concluded  pitcher  plant  This  mixed  flies  because  reproduction is a  suitable  i n an  may  in  the  their  a l s o act  aborted  buds  unaborted buds.  increased  variance  to  on the t i m i n g of  I have shown that  of  individual  The p l a n t s may be  This  plants  considered  environment to determine when to  347.  resource  t i m i n g of bud i n i t i a t i o n and in the  The number of seeds produced by the two  with  summer may be q u i t e  in d i f f e r e n t i a l  p o p u l a t i o n of  number of buds i n i t i a t e d .  from  fly  A d u l t s which emerge d u r i n g the peak of  a l l o c a t i o n by the p l a n t s .  sampling  the  conditions  optimal.  the  is  frequency  the  the  buds  time.  Natural  vary  than  a gall  f l y abundance w i l l be faced with l a r g e numbers of which  season  K i n g s o l v e r (1979)  Coq.,  The t h i r d component  i n the  component  suitable  voltinism  may a l s o be a p p r o p r i a t e  plants  with only a s i n g l e  requires  smithi i  food  galls  being e q u a l ,  increase  flies  for  more  second  the season.  strategy  Wyeomyia  The  Other t h i n g s year  late  mixed  strategy  a  relative  every y e a r .  Buds i n i t i a t e d e a r l y  i n the season.  of v o l t i n i s m .  synchrony with  variation  plants in  c o r r e l a t e d with the v a r i a t i o n in the t i m i n g  I  initiate  followed  reproduction of  to  bud  be  buds. varied  w i l l be  initiation  91  when  the p l a n t s  early  i n the  produce  summer,  more  display  Stapanian,  plants  seeds  availability). to  are attacked by the  flies.  which  per  initiate  bud  flowers  buds  in  order  to  maximize  other  on  is  most  Udovic,  coevolving  1977; and  twice  a  selection  (cf.  the  Rosenzweig  prey  This  Rather, selective  process  year  (1978)  predicted  could  approach  system turned  However,  under  pressures  of  authors  (e.g.  over  more  that  quickly  very  a year and the  because the  different  may counteract  a  ecological than  T h i s c o n d i t i o n c l e a r l y does not h o l d i n t h i s  biennial.  the  reviewed by S l a t k i n and Maynard Smith,  predator-prey if  coevolve.  where f l i e s may have two generations least  time  either  important  Levin  Schaffer  will  the  has been explored in models by s e v e r a l  at  resource  in d i r e c t i o n or magnitude.  organism  system  selection  coevolution  predators.  will  pollination  the  stability  later  equal  influence,  1979).  attack  1982).  the  and  flies  Knapweed may a l s o be s e l e c t e d for the best  or p l a n t s are constant  because  the  (assuming  T h i s system i s not one in which flies  If  the  system  plants  are  f l i e s may reproduce  conditions,  conflicting  t h e i r more r a p i d t u r n o v e r .  SUMMARY  The  variation  in r e l a t i v e density  the summer s i g n i f i c a n t l y increased U. a f f i n i s per  developed  of g a l l  changed the outcome of  d e n s i t i e s l e d to  bud,  f l i e s per bud d u r i n g  increased  the  interaction;  increased U. a f f i n i s bud  abortion,  galls  decreased  92 #  U. q u a d r i f a s c i a t a production. was lower first  half.  to  developed bud, and decreased  second h a l f of  The  timing  l e d to a refuge  Two e f f e c t s observed  per  The number of U . a f f i n i s  i n the  initiation  galls  of  first  fly  of changing a l l o c a t i o n  This  Chapter  in  bud  than in the  r e l a t i o n to bud  of p l a n t resources  were  Times from bud i n i t i a t i o n  reduced by i n s e c t a t t a c k .  i n the p r o b a b i l i t y of  to aborted buds was  developed  generation  attack  in a d d i t i o n to bud a b o r t i o n .  change  per  i n time for seed p r o d u c t i o n .  f l o w e r i n g were s i g n i f i c a n t l y  a slight  the  galls  seed  f l o w e r i n g of buds  Only  lateral  detected. also  examined  the e f f e c t  of changed  insect  d e n s i t i e s on bud a b o r t i o n , g a l l p r o d u c t i o n , and seed p r o d u c t i o n . Experimental m a n i p u l a t i o n s of s e l e c t i v e attack  by grasshoppers  number of U . a f f i n i s developed  buds  galls  followed  U. quadr i fasc i a t a g a l l s t o t a l adult  fly  f l y d e n s i t i e s were  density.  on e n c l o s e d  confounded  plants,  however  by the  per developed bud and seed numbers in the  expected  per developed  trends.  The number of  bud dropped with  increased  93  APPENDIX U A .  The time  destructive  EFFECT OF COLLECTION  sampling of systems that  creates potentially  system.  The  timing  methodological collections  DATE  of  issue.  are  in  s e r i o u s problems for understanding the the In  sample the  becomes  Urophora-  an  important  Centaurea  at the end of the summer should be  interrupting  changing  timed  system, to  r e p r o d u c t i o n by the second g e n e r a t i o n of  avoid  flies  and  to minimize l o s s of seeds from open seed heads. The from  second c o l l e c t i o n of  the  earlier  collection  number of buds per p l a n t number  of  U. a f f i n i s  second c o l l e c t i o n , of  buds.  diffuse  knapweed  (Table  (though  not  2.5).  was  different  It had a g r e a t e r  significantly  so).  g a l l s per developed bud was lower  p o s s i b l y a r e f l e c t i o n of the  in  the second c o l l e c t i o n  of  U . quadr i fasc i a t a  (X =12.52, df=1, 2  galls  per  p<0.00l).  developed  i n the  greater  The p r o p o r t i o n of buds a t t a c k e d by U . a f f i n i s  bud  The  number is  lower  The number  was  higher,  p r i m a r i l y as a r e s u l t of an increased number of buds a t t a c k e d by U.  quadrifasciata  (x =32.64, df=1, 2  g a l l counts  i n attacked buds.  number  galls  of  per  collections,  if  just  considered.  Taken  p < 0 . 0 0 l ) , r a t h e r than higher  For  both  q u a d r i fasc i a t a  buds  attacked  together,  r a t e as  i n the  after  first  species,  bud d i d not d i f f e r s i g n i f i c a n t l y  these  by  that  second  the f i r s t c o l l e c t i o n ,  generation.  the  between  species  observations  some developed buds were attacked by the U.  insect  suggest  generation  at about the  were that of same  Table 2.5  - E f f e c t of p l a n t c o l l e c t i o n date on d i f f u s e knapweed c h a r a c t e r i s t i c s and g a l l f l y a t t a c k , Robertson's 1980  Character *  First Collection (August 23)  Second C o l l e c t i o n (September 12)  Number of P l a n t s Buds/Plant Dev./Plant Dev./Buds  50 71.7±6.0 30.7±2.4 0.44±0.02  20 74.9±13.6 35.2±7.1 0.46±0.03  UA/Plant UA B u d s / P l a n t UA/Dev. UA/Attacked Prop A t t UA  36.9±4.0 16.9+1.5 1.20±0.04 2.18±0.05 0.55±0.01  36.0±9.8 16.4±4.2 1.02±0.06 2.20±0.08 0.47±0.02  UQ/Plant UQ B u d s / P l a n t UQ/Dev. UQ/Attacked Prop A t t UQ  8 . 3 ± 1 .3 4.5±2.1 0.27±0.02 1.84±0.07 0.15±0.01  17.1+3.7 8.7±2.9 0.49±0.04 1.96±0.11 0.25±0.02  Seeds/Plant Seed Heads/Plant Seeds/Dev. Seeds/Produc ing  106±11 1 7 . 6 ± 1 .6 3.47±0.10 6 . 0 3 ± 0 . 12  138±22 22.5±4.3 3.93±0.16 6 . 1 4 ± 0 . 18  * T h i s Chapter and the f o l l o w i n g Chapters c o n t a i n s e v e r a l t a b l e s with t h i s format. The p l a n t c h a r a c t e r s i n c l u d e : Chewed/Plant (=number of buds damaged by chewing per p l a n t ) , Chewed/Buds (=buds damaged by chewing as a p r o p o r t i o n of a l l buds), D e v . / P l a n t (=number of developed buds per p l a n t ) , UA/Plant (=number of U . a f f i n i s g a l l s per p l a n t ) , UA/Dev. (=number of U . a f f i n i s g a l l s per developed bud), UA/Attacked (=density of U. a f f i n i s g a l l s i n a l l buds c o n t a i n i n g U . a f f i n i s g a l l s ) , Prop Att UA (=proportion of developed buds c o n t a i n i n g U. a f f i n i s g a l l s ) , Seeds/Producing (=density of seeds in a l l buds c o n t a i n i n g s e e d s ) , and Prop. A b o r t e d (=aborted buds as a p r o p o r t i o n of a l l b u d s ) .  95  APPENDIX I IB.  EFFECT OF DENSITY ENCLOSURES  Comparison of the p l a n t s  in the c o n t r o l d e n s i t y  w i t h adjacent unenclosed p l a n t s demonstrates had  no  (Table  significant  effect  on  enclosures  that the  p l a n t height  enclosures  or number of  buds  2.6).  Table 2.6  - E f f e c t of Urophora e n c l o s u r e s on d i f f u s e knapweed c h a r a c t e r i s t i c s and g a l l f l y a t t a c k  Character *  Unenclosed Plants  Enclosed P l a n t s (Control Density)  Number Height Buds/Plant Chewed/Plant Chewed/Buds Dev./Plant Dev./Buds  50 30.0±0.7 71.7±6.0 6 . 6 ± 1 .2 0.09±0.01 30.7±2.4 0.44±0.02  18 30.0±1.9 67.3±7.3 15.3±2.5 0.21±0.02 24.9±2.9 0.39±0.03  UA/Plant UA/Dev.  36.9±4.0 1.20±0.04  22.1±5.6 0.89±0.06  UQ/Plant UQ/Dev.  8 . 3 ± 1 .3 0.27±0.02  1 . 3±0.9 0.05±0.02  Seeds/Plant Seeds/Dev.  106±11 3.47±0.10  19.6±4.0 0.79±0.08  Prop Aborted  0.20±0.01  0.10±0.01  * D e t a i l e d d e s c r i p t i o n s of these c h a r a c t e r s are given Table 2 . 5 .  The most s i g n i f i c a n t selectively  attacked  the  enclosure e f f e c t knapweed  in  was that the  in  grasshoppers  enclosures.  p r o p o r t i o n of buds chewed on enclosed p l a n t s was over double  The the  96  proportion  for  unenclosed  plants.  The  greater  damage  to  quality  of  The n e t t i n g p r o b a b l y reduced moisture s t r e s s ;  the  enclosed p l a n t s may be accounted for by the those p l a n t s . enclosed  plants  were  v i s i b l y greener.  observed on the o u t s i d e response  of  of the  higher  Many grasshoppers were  enclosure  netting.  A  similar  grasshoppers to h i g h e r q u a l i t y p l a n t s i s d e s c r i b e d  in Chapter IV. Damage by the grasshoppers was c o n c e n t r a t e d on buds i n primary  branching  category.  Since  d i s t r i b u t e d among branching c a t e g o r i e s similar high  way as on unenclosed p l a n t s ,  densities  selectively  of  removed.  should not a f f e c t differences  galls  and  The  gall  attack  on enclosed p l a n t s  was in  a  aborted buds and buds with  low  densities  selectivity  of  the r e l a t i v e d i f f e r e n c e s  among treatments a l s o  fly  the  held  of  seeds  were  grasshopper damage  among treatments;  when  the  results  the are  broken down by b r a n c h i n g c a t e g o r y . The  lower  (even when they unenclosed  bud  is  of buds aborted on enclosed  corrected may  also  for  chewing  t e s t e d i n Chapter IV.  between d e n s i t y  damage)  The o v e r a l l  for the lack of  treatments  plants  than  be due to a p l a n t q u a l i t y  a b o r t i o n may be r e s p o n s i b l e  differences aborted.  are  plants  This hypothesis in  proportions  on  effect.  reduction significant  i n the p r o p o r t i o n of buds  97  III.  BUD ABORTION AND POPULATION LIMITATION OF UROPHORA AFFINIS (DIPTERA: TEPHRITIDAE) IN BRITISH COLUMBIA  In the Bailey's  first  (1935)  he  experiments  models  c l a i m e d to have which  field  of  identified  mortality.  three  attack  density-dependent  by  two  assumption of  1954;  (1981)  argues  populations  m o r t a l i t y regulates conclusions  were  that  directly  of  mortality,  third  (C. maculosa Lam.),  stage.  i n a s i m i l a r system,  She assumed that to  parasites the  in  the  Varley  British  Varley's  North American observed  density-dependent  process V a r l e y  on the assumption that the bud  buds  1955)  to  be  processes  in  Columbia.  Hence  identified,  must  larval regulate  Her argument r e g a r d i n g l a r v a l m o r t a l i t y  knapweed  his  1954).  applicable  the  present  aborted  problems with  the a p p l i c a b i l i t y of N i c h o l s o n and  population s i z e .  England are not  in  Varley's  larval  two  diffuse  and  in B r i t i s h Columbia, density-dependent  responsible  population s i z e .  wasps  affinis  that  the  Urophora  U.  system and noted for  (1947)  Finney and V a r l e y ,  B a i l e y ' s model (Andrewartha and B i r c h , Roze  of  invalidated  ranging from s t a t i s t i c a l  and  processes  parasitic  criticisms  (Andrewartha and B i r c h ,  to h i s a p r i o r i  Frfld.  Nicholson  p o p u l a t i o n dynamics, V a r l e y  Several  o r i g i n a l conclusions, analysis  on  assumed c o n t r o l l e d the p o p u l a t i o n d e n s i t y  jaceana Her. in England: larval  based  abortion  by  the  relies  host  plants,  (Centaurea d i f f u s a Lam.) and spotted  knapweed  i s caused by supernumerary are  unable to form g a l l s  larvae.  Larvae  and d i e at an e a r l y  98  An a l t e r n a t i v e assumes that  is  the  mechanism  for  bud  abortion  Roze  suggested by Z w o l f e r ' s (1970) l a b o r a t o r y o b s e r v a t i o n  females  eggs.  to  may probe  extensively  into  buds  without  laying  The mechanical damage caused by t h i s a c t i v i t y might  also  l e a d to bud a b o r t i o n as Berube (1978b) found in Sonchus  arvensis  L.  possible  buds  pricked  mechanisms  may  with be  an  insect  pin.  distinguished  These  two  s i n c e they p r e d i c t  different  numbers of eggs in a b o r t e d buds. Roze (1981) and Chapters I and I I . the  probability  insect  of  bud  a t t a c k and that  abortion  populations,  demonstrated  depends on the  bud a b o r t i o n reduces the  formation i n a t t a c k e d p l a n t s . fly  have  in  the  intensity  potential  Thus bud a b o r t i o n l i m i t s the  sense  that,  if  it  that of  gall gall  d i d not o c c u r ,  p o p u l a t i o n d e n s i t i e s would be h i g h e r . How great basis  of  a  is  the  simple  reduction in population density? analysis  of  On  the  the d i s t r i b u t i o n s of g a l l s and  aborted buds at the end of the summer, I concluded i n Chapter that if  gall  p r o d u c t i o n by U . a f f i n i s  buds had not a b o r t e d .  single  point  in time.  the accumulation attack  of  suggested:  the (1)  aborted  buds  sites.  The  Yet i n s e c t  aborted  gall  flies  a b o r t e d buds increase counts  would have been 72% g r e a t e r attack does not occur at  Chapter II advanced the hypothesis  of  of  the  buds over act  significantly time.  as  an  Two egg  in  aborted  a  that  altered  the  mechanisms  were  "sink",  search time for s u i t a b l e  eggs  I  buds  and  (2)  oviposition will  also  d i s c r i m i n a t e between these two mechanisms. U. quadr i fasc i a t a  ( M e i g . ) , the congeneric g a l l - f o r m e r  that  99  was introduced to North America at also  suffers  U. a f f i n i s and  prefers  Harris,  smaller  from  the  smaller  1978)  and  the  effects  same time as  of  buds than  bud  abortion.  U. quadr i fasc i a t a  affinis, Because (Berube  because probed buds which a b o r t e d were  than those that d i d not  (Chapter I ) ,  U. quadr i fasc i a t a c o n t r i b u t e s  significantly  U. quadr i fasc i a t a  be  will  U.  not  considered  it  is  to  unlikely bud  further  that  abortion. in  this  Chapter. T h i s Chapter (1) aborts  buds because  evaluates of U.  the  affinis.  t e s t s the h y p o t h e s i s that d i f f u s e they  contain  too  many  larvae,  impact of bud a b o r t i o n on the p o p u l a t i o n  knapweed and  (2)  dynamics  100  MATERIALS AND METHODS  BUD COLLECTION  AND  DISSECTION  the number of eggs in aborted and unaborted buds.  on each of  the  first  were made on August 1,  16,  latter  larvae,  8,  or g a l l s  collections  flies  four dates shown i n Table  consisting  eggs,  the  22,  of a  total  and September  of  82  12.  to In  randomly s e l e c t e d p l a n t s were c o l l e c t e d  The remaining c o l l e c t i o n s  of  of  were  determine  Robertson's  period  plants  throughout  nine to s i x t e e n  oviposition  knapweed  obtained  1980,  the  Diffuse  at 3.1.  plants  The numbers  and the p r o p o r t i o n s aborted from these  were not s i g n i f i c a n t l y  different  (a=0.05) and  so they were combined. I dissected  the a p i c a l bud and the t e r m i n a l buds on the  four branches of each p l a n t . had  suggested that  probing, the  I noted the presence  brown  discoloration  oviposition,  immature forms of  response sectioning  to of  larval  or l a r v a l the  eggs  insect.  0.20.  of eggs or the  facilitated  Varley  A  caused  by  location  of  (1947) noted a s i m i l a r Since  serial  the buds was not done, a c e r t a i n p r o p o r t i o n of  i n the  immature f l o r e t s  make i t  The r e l a t i v e  gall  prominence  the of  and t h e i r l a r g e s i z e combined  with l a r v a l  h i g h l y u n l i k e l y that  Eggs l a i d a f t e r  the  larvae.  florets  damage i n C . nemoralis J o r d .  with the c l e a r damage a s s o c i a t e d formation  of  feeding  eggs might have escaped d e t e c t i o n . the  comm.)  these buds were among the buds r e c e i v i n g  h i g h e s t egg l o a d s . distinctive  E a r l i e r work (Berube, p e r s .  top  feeding  and  t h i s p r o p o r t i o n exceeded  formation was w e l l underway or  which f a i l e d to hatch and subsequently  gall  eggs  d i e d would be more l i k e l y  101  to U.  be  overlooked.  jaceana eggs  For  suffered  comparison, relatively  Varley low  h a t c h i n g : 8.9% i n 1935 and 15.3% i n 1936. to  be  associated  receptacle, connections.  with the presence  possibly  caused  by  (1947) found that  mortality  prior  to  Bud a b o r t i o n appeared  of a dark brown band in the  the  blockage  of  vascular  1 02  RESULTS  Oviposition with  fly  in the  abundance.  accumulation  Table 3.1  of  first Table  eggs  and  t e r m i n a l buds was  3.1  demonstrates  larvae  correlated  the  in these buds.  gradual  The biggest  - Urophora eggs and larvae and p r o p o r t i o n of buds a b o r t e d for t e r m i n a l buds of d i f f u s e knapweed, R o b e r t s o n ' s 1980  Date  N  Eggs and Larvae per Bud  June June June July Final  five  17 21 28 10 *  0.14±0.10 0.88±0.16 1.40±0.24 2.53±0.31 3.37±0.16  a b c d  Proportion Aborted  41 55 52 31 185  0.02±0.02 0.03±0.02 0.29±0.05 0.59±0.06 0.5510.02  N 43 58 75 78 410  e f g h  * August 1, 8, 16, 22, and September 12. L e t t e r s i n d i c a t e s t a t i s t i c a l comparison with p r e c e d i n g d a t e : a . t=3.90, df=88, p<0.001; b. t=1.81, df=9l, p=0.074; c . t=2.89, df=83, p=0.005; d . t=2.11, df=214, p=0.036; e. F i s h e r ' s exact t e s t , p=1.000; f. X*=13.12, df=1, p<0.001; g. X - 6 0 , df=1, p<0.00l; h . y^=0.i5 df=1, p=0.505. 2 = l 3  r  increase days  i n eggs and l a r v a e per bud, d i v i d e d by  between  collection  17 to June 21, of  flies  buds  also  thirteen  (18%)  collections buds was  Figure 2.1).  increased,  1.2.  of  contained  The  first  aborted eggs.  buds  significant  proportion  but c a r e f u l d i s s e c t i o n  the  number  of  d a t e s , occurred d u r i n g the p e r i o d June  which c o i n c i d e d with the  (Chapter I I ;  the  from  of  number aborted  r e v e a l e d that the  first  only four  The mean number of eggs in these  These eggs c o u l d be a t t r i b u t e d  to  bud  abortion  1 03  after flies  oviposition  or mistakes  by the o v i p o s i t i n g  female,  since  may not be able to d i s t i n g u i s h a b o r t e d buds from developed  buds on the b a s i s  of e x t e r n a l appearance.  There was no evidence  that buds which aborted were overloaded with eggs or l a r v a e .  1  04  DISCUSSION  OVIPOSITION  BEHAVIOUR  developmental)  difference  those which d i d not just  The  entering  that  size  suggests  that  the s i z e range of s u i t a b l e  aborted  buds  do  it.  This  immature f l o r e t s cue,  such as  detection  in  not subsequently  (Zwolfer,  may  1970)  Zwolfer's  (1970)  buds  s i t e s may  aborted  buds  receive  eggs.  s i z e range of  suitable  least  after  be based on the s i z e of  or  i n t r a c e l l u l a r protein  small  oviposition  females can d e t e c t that a bud i s a b o r t e d , at  probing  presumably  the  The low egg d e n s i t y  Since a b o r t e d buds do not move out of the buds,  (and  between probed buds which aborted and  (Chapter I)  be more l i k e l y to a b o r t . implies  significant  some  other  physiological  concentration.  laboratory studies indicate  that  females  do not n e c e s s a r i l y  d i s c r i m i n a t e between buds on the b a s i s of  presence  of eggs.  The observed contagion of g a l l  in  field  idea is will  the (cf. also  (Myers and H a r r i s ,  with  Rausher's  d i s c r i m i n a t e when the s i z e of  l a r v a l demands. much lower  the host  this  contagion insects  i s small r e l a t i v e that egg loads  are  E p i d e i c t i c pheromones are widely used by t e p h r i t i d f l i e s  to  their  exceptions marking by  i n the  laboratory (Zwolfer,  oviposition (e.g. either  f l i e s are c o n f i n e d  to  a  plant  f i e l d than when g a l l  The  (1979a) c l a i m that  The data I obtained i n d i c a t e  i n the  distributions  Chapter V) supports 1967).  the  to  single  mark  1980;  Dacus t r y o n i on l o q u a t ; Monro, consistent  the  Berube,  sites  (Prokopy,  1978a).  U. a f f i n i s  1970).  or  There i s  1981), but there no evidence  U. quadr i fasc i a t a  for in  are such  North  1 05  America  (Berube, p e r s .  In  a s i m p l i f i e d view of  number  of  eggs  eventually be i f  comm.; p e r s . the  to o v i p o s i t ,  abort,  their  bud  they  females have a f i x e d l a y some i n buds that  be lower than i t would  a b o r t e d buds.  of  e x p l a i n the  reduction in  eggs.  An  then  alternative  gall  oviposition  females  a  successful  locate  (e.g.  oviposition  its  probability symbolically,  suitability  data  be  for l a r v a l  do  their  r e q u i r e d to with  bud  in the search  time  Jones et a l . ,  s i z e and the  of o v i p o s i t i o n this  will  retain  associated  i s an i n c r e a s e  site  a bud of a s u i t a b l e  determine  as the  mechanism i s  formation  Such an a l t e r n a t i v e  a suitable  the  SEARCH TIME BETWEEN OVIPOSITIONS The average to  If,  a b o r t i o n i s caused by p r o b i n g damage and f l i e s  complement  for  if  reproduction w i l l  not l a y eggs i n aborted buds,  abortion.  system,  and i f  they d i s c r i m i n a t e d a g a i n s t  suggest,  obs.).  1980).  search time  leading  the sum of the time  to  time to probe the bud to  development  d i v i d e d by  given a bud of a s u i t a b l e  the  size.  Put  becomes:  AST = (LT + P T ) / p where AST i s PT  is  SSB  search t i m e ,  the probing time,  oviposition. good  the average  buds, (assuming  and p i s  GB, in the t o t a l that g a l l  the  location  the p r o b a b i l i t y of  T h i s p r o b a b i l i t y i s equal  from a b o r t e d buds, A B ) .  to  p o p u l a t i o n of  flies perfectly  the  time,  successful  proportion  of  suitably  sized  buds,  distinguish  good  buds  Thus p = GB/SSB = GB/(GB + A B ) .  A p l a u s i b l e expression density  LT i s  for LT i s an i n v e r s e  of buds of a s u i t a b l e  size  (SSB),  i.e.  f u n c t i o n of  the  106  LT = k/SSB, where  k  is  a  constant  of  proportionality.  r e l a t i o n s h i p between LT and SSB has 0)  on  (0,  The t h e o r e t i c a l  infinity)  and  (infinity,  it. Table  probing  3.2  summarizes  times  buds i n the  Table 3.2  Zwolfer's  for U. a f f i n i s  laboratory.  (1970)  i n spotted  These data suggest that  Duration of Probe  N  probing  is  a  knapweed buds  T o t a l D u r a t i o n of Probing Bout  N  35 ±10 27. 1±5.8 30.0±5.2  7 12 19  1 0 . 4 ± 2 . 1 ** 23 12.5+1.9 26 11.5±1 . 4 49  on  knapweed ( C . maculosa)  - Duration of probing i n t o spotted by female U. a f f i n i s *  Eggs d e p o s i t e d No eggs d e p o s i t e d Combined obs.  observations  * - Data from Zwolfer (1970). ** - Minutes ( M e a n ± S . E . ) .  relatively not  time  significantly  consuming different  Substituting p (= GB/SSB), and  the  and  simplifying,  a c t i v i t y and that p r o b i n g times are whether eggs are d e p o s i t e d expressions  for  or  LT (= k / S S B ) ,  SSB (= GB + A B ) , i n t o the e x p r e s s i o n  the expression  not.  for AST  for AST becomes:  k AB AST = - - + PT(1 + --) . GB GB Assuming constant  bud i n i t i a t i o n and growth,  constant,  average  ovipositions  the  search  time  w i l l be a l i n e a r f u n c t i o n of  such  that  between the d e n s i t y  GB  is  successful of  aborted  1 07  buds with the p r o b i n g time as the constant The  presence  ability  aborted  of the g a l l  constant effect  of  rate may  (Hassell,  viewed  analysis  as a key constant  in  either The  a  form  because  size.  a  This  interference"  MODEL  FORMULATION  importance to the  i s one of  The  p r o d u c t i o n of g a l l s numerical  that  the time spent p r o b i n g  possible  flies  flies  of the a b i l i t y  time buds that are they  to  unsuitable,  are  aborted.  of a b o r t e d buds, which i s a cumulative f u n c t i o n of  attack,  model.  about the system.  the  key s t a t e v a r i a b l e s .  impact  of  by U. a f f i n i s A number of  bud  abortion  on  the  net  was examined by using a simple  s i m p l i f y i n g assumptions were made  I assumed that  the  density  of  ovipositing  was normally d i s t r i b u t e d i n time around a time i n t e r v a l i n  the middle of a season of eleven i n t e r v a l 6; the  s.d.  d i s t r i b u t i o n of  per  interval.  was  flies  even  changed.  assumed to be constant  outside  time i n t e r v a l s  the if The  throughout  tails  of the defined season was  total  number of  number flies  the standard d e v i a t i o n number the  (mean -  The area i n the  season i n p r o p o r t i o n to the Thus  season remained constant distribution  discrete  - 2 i n t e r v a l s ; N=3300).  r e d i s t r i b u t e d w i t h i n the flies  "mutual  they are too s m a l l or because  insect  of  of  the  despite  i n the p o p u l a t i o n l i m i t a t i o n of the g a l l  the s h o r t e s t  density  flies  as  reduce  oviposit,  with buds of a s u i t a b l e  has h y p o t h e s i z e d  has i n d i c a t e d the  detect  significantly  to s u c c e s s f u l l y  of encounter  be  will  proportionality.  1978).  This  and  flies  buds  of  in the of  of probes per f l y  season,  of  independent  the was of  1 08  whether probes r e s u l t e d I  assumed that  in o v i p o s i t i o n or  not.  buds were i n i t i a t e d at a constant  rate  (300  buds per time i n t e r v a l ; Chapter I I ) ,  but were only a v a i l a b l e and  suitable  time  for  oviposition  the  change  interval  they  initiated.  Since  assumed that  the p r o b a b i l i t y of not maturing (independent  attack)  buds  in  increased with time from 2.7% in the  to 29.7% in the eleventh to  i n q u a l i t y d u r i n g the  probe • undeveloped  interval. buds.  Gall  production.  I  omitted the e f f e c t  r a t e s d u r i n g the The t o t a l  flies  T h i s way of  buds w i l l tend to reduce the e f f e c t  of  first  bud  Poisson  summer, I of  interval  undeveloped  abortion  of d i f f e r e n c e s  on  number of probes  i n that  from p r e v i o u s time  i n a given i n t e r v a l was  The mean of  abortion  interval  and  assumed  size according  that  (six  the Poisson d i s t r i b u t i o n  aborted  buds  the  accumulated  was modelled by using an a b o r t i o n t h r e s h o l d ,  probes  in  the  for  which  50%  runs d e s c r i b e d below).  of  buds  I assumed  the p r o b a b i l i t y of a bud a b o r t i n g was d i r e c t l y p r o p o r t i o n a l  to the number of probes per bud. eleven 1.0.  to  intervals.  corresponding to the number of probes aborted  gall  i n bud growth  was c a l c u l a t e d as the number of probes d i v i d e d by the sum of  Bud  not  season.  distribution.  buds i n i t i a t e d  fly  were assumed  treating  to be d i s t r i b u t e d among a l l buds of a s u i t a b l e a  time  were  probes  per  bud  Buds aborted i n each  Buds which r e c e i v e d more  than  were assumed to abort with p r o b a b i l i t y time  interval  were  added  to  the  cumulative number of aborted buds. A complete  l i s t i n g of  the model i s given  i n Appendix I I I A .  1 09  MODEL  RESULTS  The r e s u l t  in F i g u r e 3 . 1 . abortion flies the  A temporal p a t t e r n of g a l l  similar  to  was produced. fly  exactly  observed  in the  suitable  size  Similarly, peak  did  as observed and  in  that  production  per developed bud  field.  per  The  developed  shift bud  between  oviposition  was  the maximum p r o p o r t i o n galls  per  developed  omitted  aborted bud  in  r i g h t of  because  the peak number of g a l l s  aborted  produce  are  with  the  model output;  the  shifted  to  per developed bud, i n p a r t smaller  than  buds which  is  of v a r y i n g the number of probes per bud i n  shown i n F i g u r e 3 . 2 .  developed  bud  increased  abortion,  the  total  and then d e c l i n e d . parameter bud.  slightly  a  galls.  The e f f e c t model  buds  into  as  the model.  coincided the  fly  not as great  from  of  rose,  the  f i e l d because the time for buds to grow for  bud  before  than i t  observed p a t t e r n had the maximum p r o p o r t i o n aborted the  and  peaked  was  shown  generation  and d e c l i n e d more slowly  in the  galls  the model i s  observed for the f i r s t  The g a l l s  abundance  abundance  of a sample run of  If  values  The average number of g a l l s  monotonically,  number of g a l l s  but  because  to  of  The peak number of g a l l s  produced  bud  for  the  used o c c u r r e d at approximately ten probes per  the  values  in  F i g u r e 3.2  of  f u n c t i o n of  the probes per bud with a slope of 2765  total  number  developed  buds  in the model).  probe per bud, bud a b o r t i o n reduced the t o t a l 81%; for ten probes per bud the  reduction is  galls  would have been a  linear  of  per  produced reached a maximum  bud a b o r t i o n d i d not o c c u r , the t o t a l number  corresponding  this  Thus for  number of g a l l s 96%.  (the one by  1 10  Figure 3.1. Sample output from the model of the i n t e r a c t i o n of the g a l l f l i e s with t h e i r host p l a n t over the summer. The p a t t e r n should be compared with F i g u r e s 2.3 and 2.4.  1 12  Figure 3.2. E f f e c t of v a r y i n g probes per bud in the numerical model. G a l l s per bud (xlOOO) i s the s o l i d line. T o t a l g a l l s produced i s the dotted l i n e . Only the number of probes per bud was v a r i e d ; a l l other parameters were unchanged.  1 14  If  the g a l l  flies  could  aborted p r i o r to o v i p o s i t i o n , in  all  time  not  detect  then a t t a c k  i n t e r v a l s except the  the number of g a l l s  whether  buds  l e v e l s would be higher  first;  both bud a b o r t i o n and  per developed bud would be g r e a t e r .  p r o p o r t i o n of buds aborted i n c r e a s e d with the average bud,  this  would  translate  into  lower  total  compared with the case where bud a b o r t i o n i s The model r e s u l t s between  ovipositions  observed temporal formation. buds  demonstrate to  patterns  The e f f e c t  would  describes  due  carry  may  the  probes per  g a l l production  increased  search  bud a b o r t i o n may account  and  drastically  r a t e with  to manipulate the  time  for  reduce  i n t o the second g e n e r a t i o n .  designed  As  detected.  of a reduced encounter  over  experiments  that  were  the gall  suitable  Chapter IV  propensity  of  p l a n t s to abort buds.  SUMMARY  Two  mechanisms  for  insect-caused  knapweed were compared. Roze  (1981)  suggested,  bud  abortion  There was no evidence larval  feeding.  mechanical damage caused by probing females,  in  for the The  diffuse mechanism  alternative,  was c o n s i s t e n t  with  the observed d i s t r i b u t i o n of eggs and l a r v a e among buds. Bud  abortion  may reduce g a l l p r o d u c t i o n by i n c r e a s i n g  search time between s u c c e s s f u l based  on  A numerical  t h i s premise produced a p a t t e r n of g a l l  bud a b o r t i o n s i m i l a r to that implies  ovipositions.  that  even  observed  relatively  low  the  model  formation and  i n Chapter I I .  The  model  l e v e l s of bud a b o r t i o n may  1 15  dramatically  reduce  the  total  number of g a l l s  formed.  1 1 6  APPENDIX I I I A .  A listing effect  of the  LISTING OF THE NUMERICAL MODEL  numerical  of bud a b o r t i o n i s  given  model  used  to  in t h i s Appendix.  evaluate  the  PROGRAM FLYMOD C C C C C C C  FORTRAN 77 PROGRAM TO EXPLORE THE PROPOSED MECHANISM FOR THE EFFECT OF BUD ABORTION ON THE PATTERN OF GALL FORMATION FOR UROPHORA AFFINIS AND ITS LONG TERM EFFECT ON POPULATION LIMITATION. P E T E R  MORRISON, INST I TUTE OF ANIMAL R  1984  INTEGER ABTHR REAL MNFLY '," SDFLV . PRBBUD. PRPABT, PABf REAL F L Y I N T ( I I ) , UNOEV(II). POISSN(12), CUMPSN(IS), TOTGAL(11) REAL A B T B D S ( I I ) , A V A I L ( H ) , U N A T T ( I I ) , ATTBDS(II).  c  DATA PRBBUD /20.0 / DATA MNFLY / 60.0 /  DATA'""sbFilV ' " / 2 o " o " " / ~  C C ABTHR • NUMBER OF PROBES PER BUD THAT CAUSES SOX OF BUDS C TO ABORT  C  DATA ABTHR f 6 / DATA TOTGAL / 1 1 •0i'6"7  C  C DETERMINE DISTRIBUTION OF PROBES OVER INTERVALS - : USING NORMAL OIST.  "c  TOTPRB • 3300.0*PRBBU0 SUMPRB • 0.0 D  c  C  "  0  _  " " 2 Q " j - ^ Y ' " i " " i " ; " " i " i  _ —  " " " ' "  ORO • ICNT'10.0 FLYINT(ICNT) « EXP(-(ORO-MNFLY)*(ORO-MNFLY)/(2.0*SDFLY»SDFLY)) F L Y I N T r i C N t j " i fbfPRB^ SUMPRB • SUMPRB • FLYINT(ICNT) 20 CONTINUE  "  DIFPRB ' TOTPRB - SUMPRB DO 30 ICNT • 1. 11 FLYiNfTi^ 30 CONTINUE .  C STEP'THROUGH '"fl ME:'"iNT ERVAIS' U P ^ f IN6" THE' 'p'ROPORf ION  C  ABORT ED  CUMABT " 0 . 0  C  C CALCULATE PROPORTION UNDEVELOPED AS A FUNCTION OF TIME  !"c  UNOEV(ICNT) • 0.027 • ICNT * 300.0  C  0E'VBUD"''"''3'^  C  C CALCULATE THE MEAN NUMBER OF PROBES PER BUD AND DISTRIBUTE THEM C ACCORD  C  PRBMN • FLYINT(ICNT) / (DEVBUD + CUMABT)  c  c  DO SO OCNT • 2, 12 CUMPSN(JCNT) • 0.0 50  poiSSN(JCNTy - 6:o  CONTINUE  ""  POISSN(I) • EXP(-1.O'PRBMN) CUMPSN(I) • POISSN(I) C  DO 100 KCNT • 2, 12 POISSN(KCNT) • POISSN(KCNT-I) • PRBMN / FLOAT(KCNT) CUMPSN(KCNT) • CUMPSN(KCNT-I) • POISSN(KCNT) CONTINUE  100  C CALCULATE THE PROPORTION OF BUDS ABORTED  c  PRPABT • 0 . 0 DO ISO MCNT • 2, 12 pABT'0"6•(MCNT - " 1 j / FLOATf*BTHRj I F (PABT .GT. 1.0) PABT • 1.0 PRPABT • PRPABT • PABT'POISSNjMCNT) POiSSN(MCNT) • pbiSSN^MCNTWl.6 - PABT) CONTINUE PRPABT • PRPABT • (1.0 - CUMPSN(12)J  150  c  C CALCULATE PROPORTIONS IN VARIOUS CATEGORIES OF ATTACK C  ABT BOSiH' CNT )"' • DEVBUD • PRPABT AVAIL(ICNT) • 300.0 - UNDEV(ICNT) - ABTBDS(ICNT) UNATTUCNT) • POISSN(I) » DEVBUD ATf BDSTiCNT )' "•" AVAIL(ICNT )~-"UNATf (fcWJ™  C  CUMABT • CUMABT + ABTBDS(ICNT)  c  r  DO 200 NCNT - 1, 12 TOTGAL(ICNT) • TOTGALjICNT) • OEVBUO«POISSN(NCNT)«iNCNT-1) 20OCONTINUE  C 1000 CONTINUE  "  c  "  C CALCULATE STATISTICS AND WRITE OUT RESULTS C  WHIITE(G'ri i6oV" MNFLY'r's  "  1100 FORMAT(' MEAN '.F6.2.' SO '.F6.3.6X, • ' PROBES/BUD ',Fe.3,' ABT. THRESH. ',13,, • / / • I U N O E V E ' L " A B O R T E D A T T A C K E D ""' + 'UNATTACK. GALLS/DEV GALLS/ATT. FLIES ') C  "  ~ _  TOTAVL "• 6 "6 TOTATT • 0.0 SUMGAL • 0.0 bb  isbo i C N T " • ~ i i i R1 • UNDEV(ICNT)/3CO.O R2 • ABTBDS(ICNT)/300.0  R3''-''AtfBb's"riTOfy/3o6'.'6 R4 • UNATT(ICNT)/300.0 IF (AVAIL(ICNT) .GT. 0.O01) THEN R5"'•i fbfGALfiCNf V/AVAlL(iCNf ELSE R5 • 0.0 ENDIF IF (ATTBDS(ICNT) .GT. 0.001) THEN R6 • TOTGAH ICNT)/ATTB0S( ICNT) ELSE R6 - 0.0 ENOIF  )  ~  H7 • FLYINT(ICNT)»10.0/T0TPRB TOTAVL • TOTAVL • AVAIL(ICNT) TOTATT - TOTATT • ATTBOS(ICNT) SUMGAL • "sUMWL"T'fofGAL(ICNf j C  WRITE(6,1200)ICNT,R1,R2,R3, R4, R5 ,R6 ,R7 1200 FORMAT(l3.7Fi6.5) 1500 CONTINUE C c WRITE: bin '"suMMARv'"sTATmics C UAOEV • SUMGAL / TOTAVL UAATT • ' SUMGAL / TOT AT f PRPATT • TOTATT / TOTAVL PRPABT > CUMABT / 3300.0 WRITE<6.1900) 190O FORMAT(//' GALLS/OEV. GALLS/ATT. PROP ATT. PROP ABT. WRITE(6.2000) UAOEV. UAATT, PRPATT, PRPABT, TOTAVL 20O0 FORMAT(4F10.5.F10.2) C STOP ;  DEV BUDS')  1 20  IV.  PLANT QUALITY AND THE POPULATION DYNAMICS OF TWO INTRODUCED INSECTS  Plant  quality  may  have  striking effects  on  1940  Wilson,  insect populations  (e.g.  Dodd,  Myers  1981;  Port and Thompson, 1980;  and  Post,  S e v e r a l mechanisms may lead higher  quality  insects  ( K a i r e v a , 1983;  Chapter  I),  plants,  to  Some  literature Mattson, The  (e.g.  two  from  Vince  and  have  1983;  gall-forming (Meig.)  and s p o t t e d  flies,  summarized  gall  are l i m i t e d by two f a c t o r s :  the d e n s i t y  and I I I ) .  should s h i f t considers these and  two  If  plant q u a l i t y  in favour of higher  the e f f e c t  of n i t r o g e n  population limitation  White, this  Southwood,  1978;  1981). Frfld.  lay  eggs  and in  Centaurea d i f f u s a (Asteraceae).  of o v i p o s i t i o n  increases,  1981;  of  f l y d e n s i t i e s on d i f f u s e  bud a b o r t i o n i n response to probing by female II,  much  Urophora a f f i n i s  C. maculosa Lam.  by moving  1981;  (Diptera: T e p h r i t i d a e ) ,  knapweed,  on  and r e p r o d u c t i o n  Valiela,  knapweed,  1976).  Valiela,  S c r i b e r and S l a n s k y ,  buds of d i f f u s e  In B r i t i s h Columbia,  White,  choice  and  and  1960);  populations  host  1985; Vince  reviews  Rhoades,  immature flower  Lam.,  Myers,  insect  Crawley, 1983; M c N e i l l  U. q u a d r i f a s c i a t a the  ranging  1981;  recent  1980;  larger  in  improved s u r v i v a l , development,  ( S c r i b e r and S l a n s k y , 1976).  to  (cited  phytophagous  flies  both of  knapweed s i t e s and  (Chapters these  I,  factors  insect d e n s i t i e s .  T h i s Chapter  fertilization  watering  factors  and  and on l a r v a l  on  survival  development. Both water and n i t r o g e n ,  separately  and  in  combination,  121  should  increase  the  plants  and  individual  to the b o l t i n g knapweed  buds.  Plants  i n c r e a s i n g the number of buds they  initiate  Based  to  resources a v a i l a b l e  on the  flies  relationships  (cf.  respond  Watson,  i n Chapter I ,  The r e s u l t i n g l e v e l s of a t t a c k  t r e a t e d and u n t r e a t e d If  should be  the  attack  (Stephenson,  the  resources  same  level  proportion  (G.F.W. of  between g a l l  this alternative Increased ability  to  (1977) found the opposite  effect  Meyer)  buds  Engler.).  allocated  larval  young  insects  Maimer,  1980).  larvae  are:  development  Some p o s s i b l e  Personal  the  (Chapter  I),  per developed bud.  the r e l a t i v e  larval  and f a s t e r  and  the  data the  rate  of  Schroeder and the  gall  more  fly  successful  development  second  (1980a,b) and Roze (1981) suggest that f l y p o p u l a t i o n s on d i f f u s e  for  their  .Both l e a f  growth  but see  survival,  i n the t i m i n g of observations  1981;  consequences  to pupae and a d u l t s ,  r e s u l t i n g change  Because of  to buds should increase  ( S c r i b e r and S l a n s k y ,  improved  abortion  the o v e r a l l  growth and development.  water and n i t r o g e n l e v e l s i n c r e a s e  gall  Alternatively,  c o u l d be a b o r t e d i f  should g i v e more g a l l s  support  should level  formation and bud  resources  to  given  of a t t a c k on f e r t i l i z e d p l a n t s was h i g h e r .  tradeoff  for  available  1981), then i n c r e a s e d resources  (though Onuf et a l .  on Rhizophora mangle  same  plants.  bud a b o r t i o n i s a f u n c t i o n of  plant  the  1972).  the number of  lead to a drop i n the p r o b a b i l i t y of a b o r t i o n at a of  by  per p l a n t should be p r o p o r t i o n a l to the number of buds per  plant.  the  observed  should  with  a  generation.  presented  by  two f a c t o r s  knapweed, d e n s i t y  of  Harris limiting  oviposition  1 22  s i t e s and bud a b o r t i o n , may a l s o be a c t i n g on f l y p o p u l a t i o n s on s p o t t e d knapweed. This  Chapter  fertilization  (1)  describes  the  changes  in  nitrogen  bud,  and development due to the  bud  (2)  and other h e r b i v o r e s  p l a n t q u a l i t y , and (3) a s s e s s e s changes  number of g a l l s per developed survival  of  and watering on the number of buds per p l a n t ,  documents the response of the g a l l f l i e s the  effects  abortion,  treatments.  and  to  i n the larval  1 23  MATERIALS AND METHODS  WEATHER  The  natural  the c o n t r o l for the obtained  from  p r e c i p i t a t i o n at the study s i t e s provides watering  Environment  A i r p o r t weather  Canada.  recorded  at  Chase,  B . C . , at and  was observed at the study  EXPERIMENTAL  Data  from  TREATMENTS  data  the  IN  also  rainfall  and  (e.g.  Mispagel,  1978).  may  1979  agreed  with  the  Nitrogen  (e.g.  wheatgrass,  crested  the  stress  Williams  et a l . ,  plant  of  of the  Robertson's. possible  water three The  to  nitrogen  the  plant  1979), even to  a set  of  the  interacting  and f e r t i l i z e r was e s t a b l i s h e d study  plants  "burn".  As a r e s u l t of these c o n s i d e r a t i o n s , treatments  and  1971; Decau and P u j o l , -1973)  water  extent of c a u s i n g f e r t i l i z e r  the days  fertilization  Under more a r i d c o n d i t i o n s ,  increase  the  sites.  Buchner and Sturm,  fertilization  sites:  treatments  combinations of three  none) and three watering l e v e l s the  with  i n terms of s u r v i v o r s h i p of young i n s e c t s feeding on  (e.g.  each  patterns  the opposite end of  watering may i n t e r a c t s i g n i f i c a n t l y both i n terms of response  were  Kamloops  The v a l u e s were c o n s i s t e n t  South Thompson R i v e r v a l l e y , rainfall  Weather  s t a t i o n were used for s p e c i f i c  presented in t h i s C h a p t e r . patterns  treatments.  at  Chase, each  Ned's  site  f e r t i l i z e r levels  Creek,  and  c o n s i s t e d of a l l (high,  of  nine treatments was r e p l i c a t e d three times at each s i t e  for  27 p l o t s per s i t e .  low, and none).  low, and Each  a t o t a l of  (high,  in 1979 at  Each p l o t  consisted  of  one  m  2  1 24  surrounded  by  a space of 0.25  m to e l i m i n a t e  and to permit access to the p l a n t s The nine p l o t s  i n each r e p l i c a t e  spillover  for watering and measurement. were  grouped  together  3.5 m by 3.5 m area with a v i s u a l l y uniform d e n s i t y The  central  either  each  central  from  plant  F i v e of  the  to  the p o i n t s  and  the  the center  outside plant  selected  four p o i n t s  bisecting  the  r a r e l y nearest  four of  bisecting  pencil  of  the p l o t .  the  nearest  the s t r a i g h t  tip  In p l o t s  lines  where  were  between the  plot.  If  the  between ten  taken  selected  The tenth p l a n t was  the  plot.  of  lines  the a d d i t i o n a l p o i n t s  the  chosen nearest  was not p r e v i o u s l y s e l e c t e d and was it  was chosen.  treatment  ammonium  in  1979  nitrate  Selected  Ammonium n i t r a t e was chosen  forms of  i o n i c n i t r o g e n and because i t  would have the g r e a t e s t e f f e c t in t h e i r response  to the  depending on t h e i r pH preference  consisted  pellets  bolting.  may d i f f e r  from the  plants  were  neighbours.  The f e r t i l i z e r application  as  the s t r a i g h t  near adjacent p l o t d i a g o n a l s .  to  and ten  in each p l o t were taken as the c e n t e r  w i t h i n the p l o t boundaries,  form  on  treatment,  an a r b i t r a r i l y chosen p o i n t w i t h i n the  by b l i n d l y f l i p p i n g a p e n c i l i n t o plant  for each  replicates  was  and the four c o r n e r s of  the p o i n t s  plants  two  Each  p l a n t s were f o l l o w e d , as  a  knapweed.  from the two r e p l i c a t e s  of twenty p l a n t s were followed  replicate.  bolting  plot  r e p l i c a t e was separated  of  in  s i d e by 0.5 m.  A total five  effects  on  because i t  of May  a  single  28,  during  provides  both  was not known which i o n i c  on knapweed growth. two i o n i c  forms of  (Buchner and Sturm,  Plants nitrogen  1971;  Gigon  125  and  Rorison,  1972), or the c o n c e n t r a t i o n of the opposite  form (Cox and R e i s n a u e r , levels  were  the  respectively, application  1973).  The r a t e s  equivalent  of n i t r o g e n .  of  It  100  rained  ionic  for the high and  low  and  ha,  50  during  kg  the  per  fertilizer  and none of the p e l l e t s were v i s i b l e one hour a f t e r  applicat ion. Watering treatments approximately every m  during  2  8:30  (i.e.  amounted  July  3.45  23.  a.m. to reduce to  watering  liters  levels,  Robertson's  and  respectively).  per  Chase The  knapweed  m  2  at  respectively) (low  timing  natural p r e c i p i t a t i o n is diffuse  per  was  m  applied  2  a p p l i e d between  evaporative 7%  rainfall  for June 1 to August 31. or 6.9  ml  Water  approximately  t h i r t y year average)  Airport  700  four days d u r i n g June and 250 and 500 ml per  until  a.m. and 9:30  levels  of  July  were 350 and  and  loss. 14%  recorded  Watering  of the normal  at  the  Kamloops  Watered p l o t s  received  Ned's  Creek  (low  and 3.2  or 6.4  and  high  totals  and  high  l i t e r s per m  watering  2  at  levels,  and magnitude of watering added to  shown i n F i g u r e 4 . 1 .  Because  s i t e s were watered on d i f f e r e n t  the  days,  two  between  s i t e comparisons must be q u a l i f i e d a c c o r d i n g l y .  NUTRIENT ANALYSIS The nutrients  in  experimental samples for  the  were  to  soil  treatments taken  nutrient analysis.  screen  initial  levels  could and  affect  between  at each of  of  nitrogen the  site  and  results  other of  the  comparisons.  Six  the three s i t e s on May 29,  The samples were screened through  1979 a  #2  remove p l a n t m a t e r i a l and rocks which would not have  1 26  F i g u r e 4.1. Watering and n a t u r a l p r e c i p i t a t i o n in 1979. The r a i n f a l l recorded at Kamloops A i r p o r t d u r i n g the summer i s shown in the upper part of the f i g u r e . Data are from Environment Canada. The lower p a r t of the f i g u r e gives the sequence and amount of a d d i t i o n a l water a p p l i e d to the experimental p l o t s expressed in mm. The h o r i z o n t a l dashes b i s e c t i n g each watering treatment i n d i c a t e the two treatment l e v e l s .  Ned's Creek Robertson's  watering  Chase  4-4-  ro  13  17 22  June  25  29 29  3  7  11  15 i 15 19 July  1  1  23  27  r™  31  T  4  -r 8  -r-  I  12  16  August  I  20  I  24  I  28  1 28  c o n t a i n e d immediately the  accessible nutrients.  analyzed  by  B.C. Ministry  Kelowna.  Values for each of  T a b l e 4.1  - S o i l c h a r a c t e r i s t i c s at the study  of  samples  Agriculture  were  laboratory in  the s i t e s are given i n  Ned's Creek Organic matter (%) pH Conductivity b N i t r a t e s (ppm) Phosphorous (ppm) Potassium (ppm) Calcium (ppm) Magnesium (ppm)  The  Table  4.1.  sites  SITE Robertson's  Chase  5.4±0.2 7.0±0.1 0.25±0.01 1.3±0.2 64±4 950±30 4200±100 740+14  5.2±0. 2 6.4±0. 1 0 . 2 1 ± 0 . 01 1.5±0. 2 129±11 730±30 3780±80 320±10  3.9±0.1 a 6.6±0.1 0.18±0.01 6.2±1.3 21 ±2 640±20 2900±80 535±7  a - MeaniS.E. b - Measured in mS/cm at 25 degrees C .  Soil  c h a r a c t e r i s t i c s for Ned's Creek and Chase are comparable to  Watson's (1972)  EXPERIMENTAL below) .growth of  values.  TREATMENTS  showed that both and  IN  fertilizer  The and  results water  from 1979 affected  (see plant  the treatments were approximately a d d i t i v e i n terms  numbers of buds per p l a n t .  were  1980  applied  at  In  1980,  a s i n g l e higher l e v e l  fertilizer i n an attempt  and  water  to "push"  the system f u r t h e r . Four p l o t s of of of  f i v e p l a n t s each at R o b e r t s o n ' s and s i x  f i v e p l a n t s each at Chase were t r e a t e d with the s i n g l e fertilizer  and  water.  Plot  plots level  dimensions were i d e n t i c a l  to  1 29  those used in 1979. Control  plots  Plants  were  selected  in  the  same  way.  were e s t a b l i s h e d on June 1 at Robertson's and on  June 2 at Chase.  At each s i t e ,  a  rectangular  grid  of  fifty  (5x10) p o i n t s was p l a c e d over a 3 m x 6.5 m p o r t i o n of the with had  a  visually  uniform d e n s i t y of knapweed.  begun to b o l t nearest  The  points  on  the  each p o i n t on  grid  applied  at  Fertilizer  (18.9  grid  was  staked. staked  neighbours.  was a p p l i e d at  150  kg  per  ha  and  water  700 ml per m , u s u a l l y every two days ( F i g u r e 2  was 4.2).  was a p p l i e d on June 3 at Robertson's and on June 6 at  Chase, d u r i n g the e a r l y phase liters  The p l a n t which  were far enough apart so that  p l a n t s were r a r e l y nearest Fertilizer  the  field  per  m  2  of  bolting.  was a p p l i e d at R o b e r t s o n ' s .  A  total  of  23.8  The t o t a l at Chase  l i t e r s per m ) was lower because watering was h a l t e d 2  when  I s t a r t e d c o l l e c t i n g the s p o t t e d knapweed.  OBSERVATION Berube,  OF  1980)  INSECTS  are  subsequent  In 1979,  s t i c k y traps  Results analysis  from t h i s method are not  (as  in  insect  reported  showed that counts on s t i c k y t r a p s  very s e n s i t i v e to temperature (MS in p r e p . ) . Visual  second  to J u l y gall  surveys of  method  Observations  of  1979  were used as the primary means of measuring  abundance over t i m e . because  IN  of  staked p l a n t s were a l s o done i n 1979 as a measuring  relative  insect  abundance.  were made at each s i t e every 4-5 days from June 13  13, between 8:30 f l y are e a s i l y  a.m. and 12:00 noon.  The  two  species  d i s t i n g u i s h e d by the banding p a t t e r n on  the wings and sexes are d i s t i n g u i s h e d by the prominent  oviscape  1 30  gure 4 . 2 . Watering and n a t u r a l p r e c i p i t a t i o n in 1980. The r a i n f a l l .recorded at Kamloops A i r p o r t d u r i n g the summer i s shown in the upper part of the f i g u r e . Data are from Environment Canada. Note the break in the vertical axis. The lower part of the f i g u r e g i v e s the sequence and amount of a d d i t i o n a l water a p p l i e d to the experimental p l o t s expressed in mm.  1 32  of  the  females.  The f l i e s  was not o b v i o u s l y  are q u i t e d o c i l e and t h e i r behaviour  altered  by  an  relatively  small numbers of  180 d i f f u s e  knapweed p l a n t s d u r i n g the e n t i r e  Creek,  the  observed  for a l l p l a n t s  in  a  of  time as the surveys  OBSERVATION  plots.  OF  for g a l l  370 over at  Ned's  I combined and  The  INSECTS  location,  flies  on  a.m. and 11:30  surveys number of  lasted flies  IN  1980  species,  plants  I  conducted  PLANT COLLECTIONS  same  branch  of each a d u l t f l y  The v i s u a l  usually  most  a  by  in c o n t r o l and t r e a t e d  and sex  were  a . m . , with  observed.  the  Approximately every two days  sites,  from one h a l f  the f l y surveys  (Homoptera:  flies.  recorded at the moment of o b s e r v a t i o n .  begun  surveys  conducted at  9:30  was for  between  a.m.  The  hour to one hour, depending on the  (See Chapter I for a d d i t i o n a l  details  in 1980.)  AND DISSECTION  p l a n t s were c o l l e c t e d and  the  fertilization  spittlebugs  branch v i s u a l survey of each staked p l a n t  25  summer  knapweed at Chase were made at  a l t e r n a t i n g between the two  of  (a t o t a l of  given  unidentified  Cercopidae) on spotted  8:30  of  treatment.  Observations  adult  Because  s i t e with the g r e a t e s t number r e c o r d e d ) ,  the observations watering  flies  observer.  1979,  diffuse  knapweed  on August 22 at Ned's Creek, and on August  26 at R o b e r t s o n ' s .  Robertson's were c o l l e c t e d The r a p i d l o s s of  In  In 1980,  diffuse  knapweed p l a n t s  at  on August 23.  seeds from s p o t t e d  knapweed  seed  heads  1 33  (Hubbard, single  1971)  and  the  p o i n t i n time meant that there  losing  seeds  and  collected  at  In  three  1979, day  p l a n t s were c o l l e c t e d variation  a  tradeoff  spotted  intervals  knapweed  at  within  effects  (Table  untransformed  Chase  from each treatment on each d a t e ,  below).  Analysis  result  (a=0.05) e f f e c t  of  variance  on number of  seed head on each p l a n t shed i t s extended  over  matured.  The same procedure  in  the  period  Both  ground l e v e l .  seeds  before  the  This  1980, first  collection  August 1 to August 24 as seed heads was  used will  for  both  treated  and  underestimate t o t a l  seed  i n d i v i d u a l l y by c l i p p i n g them o f f  temperature  status,  until  dissection.  at  measured  When they were  of each p l a n t was measured and and  with  the  size,  l o c a t i o n of each bud were r e c o r d e d .  Damage r e s u l t i n g from grasshopper feeding was a l s o were  In  e r r o r s are probably s m a l l .  the h e i g h t  developmental  sizes  per  They were then s t o r e d i n f o l d e d and s t a p l e d paper  room  dissected,  just  dried f l o r e t s .  methods  P l a n t s were c o l l e c t e d  at  collection  but by i n c l u d i n g seeds that were not f u l l y developed  seed c o u n t s ,  bags  on  h e l d for both a one way ANOVA and a three  knapweed p l a n t s were c o l l e c t e d  production,  the  treatment  4.7  plants.  thus  treatment v a r i a t i o n i n the summary of  way ANOVA ( i n c l u d i n g f e r t i l i z e r and water t r e a t m e n t s ) .  control  Four  included  date has no s i g n i f i c a n t  spotted  was  is  and l o g transformed data i n d i c a t e that  This  between  from August 8 to 20.  in seeds per p l a n t due to c o l l e c t i o n date  the  plant.  was  c o l l e c t i n g p l a n t s before a l l the seeds had a  chance to mature.  in  n e c e s s i t y of c o l l e c t i n g a p l a n t at a  noted.  Bud  c a l i p e r s as d e s c r i b e d by Berube and  1 34  Harris  (1978) to the nearest m i l l i m e t e r .  Buds (i.e.  large  enough  developed  buds)  to  The  contents  contents  distinguished),  larva  adult  (dead/alive),  pupal  galls  galls  or  of  any  galls  seeds  For these,  present  were c a t e g o r i z e d a c c o r d i n g to f l y  (easily  U. a f f i n i s  either  were i n d i v i d u a l l y d i s s e c t e d .  the number of seeds and noted.  contain  are  (dead/alive), case,  hard  or  and  pupa no  species  (dead/alive),  visible  woody  were  and  remains. those  of  U. quadri fasc i a t a are t h i n and papery. . The  effects  mortality contents  and of  of  development galls  p l a n t s in 1980.  in  diffuse  during  1980a).  1981,  period  knapweed c o l l e c t e d  g a l l s were a t t a c k e d It  is  watering  evaluated  by  on  larval  comparing  knapweed buds were d i s s e c t e d  28,  the  were  and  the  developed buds from t r e a t e d and c o n t r o l  Diffuse  p e r i o d March 3 1 - A p r i l dissected  fertilization  by  and s p o t t e d  knapweed  March 2 1 - A p r i l  8,  mite,  Pynotes  sp.  buds  1981.  from R o b e r t s o n ' s i n 1980,  the  during  were In the  4.1% of  (cf.  not known what the other sources of  the  the  Harris, l a r v a l and  pupal m o r t a l i t y were.  ADDITIONAL STATISTICAL METHODS A set  of T a b l e s ( 4 . 2 ,  4.6,  4.13  the main e f f e c t s  of two way  below)  analyses  are  used  of v a r i a n c e  Statistical  t e s t s of  of  to  present  data  from  the  treatments  in  i n t e r a c t i o n terms are not p r e s e n t e d  terms are not s i g n i f i c a n t  at  a=0.05.  4.9-  1979. if  the  1 35  RESULTS  RESPONSE OF PLANTS  DIFFUSE KNAPWEED The r e s u l t s knapweed  characteristics  significantly 4.2-4.4).  Table 4.2  in  of a n a l y s i s of v a r i a n c e on 1979  show  i n c r e a s e d the number of  The  stronger  response  that  buds  both  per  diffuse  treatments  plant  (Tables  of bud numbers per p l a n t  to  - E f f e c t of f e r t i l i z a t i o n and watering on the t o t a l number of d i f f u s e knapweed buds and the number of developed buds, 1 979  Character Buds  Developed Buds  Control  Low  Treatment  Site  High  Water  NC R  27.30 27. 1 3  39.20 36.57  37. 25 a 45. 36 b  Fert.  NC R  23.67 24.43  34.47 37.81  45.62 c 46.71 d  Water  NC R  10.88 10.70  15.10 1 6.83  1 5. 30 e 1 9.24 f  Fert.  NC R  8.90 10.68  1 4.57 1 6.66  1 7.82 g 1 9.39 h  S i t e s : NC - Ned's Creek, R - R o b e r t s o n ' s . L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=5.18, df=2,171, p=0.006; b. F=6.42, d f = 2 , l 6 9 , p=0.002; c . F=15.32, d f = 2 , 1 7 1 , p<0.00l; d . F=9.19, df=2,169, p<0.001; e. F=4.51, df=2,171, p=0.0l2; f. F=6.93, df=2,169, p=0.00l; g. F=11.63, d f = 2 , 1 7 1 , p<0.00l; h. F=5.46, df=2,169, p=0.005.  n i t r o g e n a d d i t i o n compared to the partly  due  to the  b o l t i n g had begun).  effect  of  watering  t i m i n g of the f e r t i l i z e r a p p l i c a t i o n s  may  be  (after  T a b l e 4.3 - E f f e c t o f f e r t i l i z a t i o n Ned's C r e e k 1 9 7 9 Fertilization  Level  Watering Level  a n d w a t e r i n g on d i f f u s e knapweed c h a r a c t e r i s t i c s a n d I n s e c t  None  None  Low High  Low  None  Low  attack,  High  -  High  None  Low  High  Height 19+1 16±2 Buds/Plant C h e w e d / P l a n t 0.2±0 1 Chewed/Buds 0.01+0 01 5.4±0 8 Dev./PI a n t Dev./Buds 0.33+0 03  22+3 0.5±0 2 0.03+0 01 9+1 0.4210 04  2111 32+6 0.4+0.2 0.0110.01 12+2 0.41+0.05  2011 3215 0.610.3 0.0210.01 14±3 0.3710.03  2311 3714 1.410.4 0.0310.01 14±2 0.3610.04  2211 34+4 1.410.5 0.04+0.01 16±2 0.4310.03  2011 3416 0.5+0.3 0.0110.01 14+3 0.3510.04  24+1 5817 3.1+0 9 0.0510 01 22+3 0.3610 03  2111 45+7 0.810 3 0.0210 01 18+3 0.3910 0 3  UA/Plant UA/Dev. UA/Attacked P r o p A t t UA  3.2+0 8 0.62+0 08 1.5±0 1 0.41±0 05  4±1 0.48+0 05 1.26+0 06 0.38+0 04  1113 0.8610.07 1.67+0.08 0.5110.03  712 0.5910.06 1.6310.09 0.3610.03  7+1 0.4910.05 1.4210.08 0.3410.03  1012 0.6810.06 1.7210.07 0.40+0.03  1418 1.0710.09 2.210.1 0.48+0.03  1514 0.7210 0 5 1.6510 07 0.4310 02  9+2 0.55+0 0 5 1 .44+0 06 0.3810 0 3  UO/Plant UQ/Dev. UO/Attacked P r o p A t t UQ  0.7+0 0.13+0 1.9+0 0.07+0  5 05 2 02  2.910.9 0.2310.04 1.610.2 0.1510.02  312 0.2610.06 2.2+0.3 0.1210.02  2.310.7 0.1710.08 1.610.2 0.1110.02  2.710.8 0.1810.03 1.610.1 0.1110.02  312 0.20+0.04 1.710.2 0.1210.02  412 0.19+0 03 1 .7+0 2 0.1110 02  2.810 8 0. 1710 03 1 .410 1 0.12+0 02  54110 6.3+0 3 7.5+0 3  76117 6.110.3 7.710.3  68+14 5.5+0.3 6.7+0.3  80118 6.010.3 8.110.3  89119 5.9+0.3 7.310.3  55120 4.310.3 6.410.3  110120 5. 1+0 3 7.0+0 2  80115 4.810 3 7.0+0 3  0.1210. 02  0.1010.02  0. 1110.02  0.0910.01  0.1010.02  0.0910.02  0.0810 02  0.0810 01  Seeds/Plant Seeds/Oev. Seeds/Prod  3 06 5 03  25±4 4.9±0 4 7.2+0 4  P r o p A b o r t e d 0.07±0 01  20±1  1 .610 0.18+0 1 .7+0 0.1110  T a b l e 4.4  - E f f e c t of f e r t i l i z a t i o n R o b e r t s o n ' s 1979  Fertilization  Level  Watering Level  None  and w a t e r i n g o n d i f f u s e knapweed c h a r a c t e r i s t i c s a n d i n s e c t  None Low  Low High  None  Low  High High  None  Low  High  0.3910..03  2411 62111 2115 0 . 2 8 1 0 . 04 2615 0 . 4 5 1 0 . 03  1714 0.8410.05 1.6210.06 0.51+0.03  612 0.6410..07 1.63+0.. 10 0.3910..04  18+6 0.7610.05 1.7310.06 0.4410.02  24+5 0.90+0. 05 1 . 7 2 1 0 . 06 0 . 5 2 1 0 . 02  1.010.3 0.0510.02 1.4+0.1 0.0410.01  2.510.7 0.1210.03 1.5+0.2 0.0810.02  1.2+0.4 0.1210.,03 1.410. 2 0.0910. 02  412 0.15+0.03 2.010.2 0.0810.01  0.1810. 02 1 . 2 9 1 0 . 08 0 . 1 4 1 0 . 02  4919 4.210.3 5.710.3  65+17 3.510.2 5.610.2  88+22 4.410.2 6.2+0.2  41110 4.5+0.3 6.710.,4  97122 4.210.2 5.610.2  4.210. 2 5.510. 2  0.0910.02  0.0610.01  0.0810.02  0.1010.02  0.0810.02  0.0710.01  18.0+0..8 19±2 1. 1+0 .3 0.06±0..02 9.010,.8 0.4910..03  2212 29+4 2.910,.9 0.1010 .02 12+2 0.4210..02  21 + 1 3215 5+3 0.1210.03 1212 0.3710.03  2111 3719 611 0.17+0.03 18+5 0.52+0.02  2312 46+6 1113 0.20+0.03 2013 0.4810.03  17.810..9 25+3 4.610..7 0.2010..03  UA/Plant UA/Dev. UA/Attacked P r o p A t t UA  0.57±0..06 1.65±0..09 0.35+0..03  711 0.73+0..07 1.5310. . 10 0.4710..04  10+3 0.8010..07 1.6310. .09 0.49+0..03  813 0.6810.07 1.7010.10 0.40+0.03  26114 1.4510.08 2.22+0.08 0.65+0.03  UQ/Plant UQ/Dev. UQ/At t a c k e d P r o p A t t UQ  1.4+0. 5 0.12+0. 03 1.5+0. 2 0.08±0. 02  1.0+0. 3 0 . 1 1 1 0 ..03 1.3+0. 2 0.0810. 02  1.210..6 0.10+0..03 1.5+0..3 0.07+0.,02  0.510.3 0.0410.02 1.4+0.2 0.0310.01  Seeds/Plant Seeds/Dev. Seeds/Prod  51+9 4.6+0. 3 6.2+0. 3  36+4 4.0+0. 3 5.6+0. 3  4117 3.510. 2 5.410. 3  0.08+0.02  0.1010.02  P r o p A b o r t e d 0.0710.02  '  2312 54111 1313 0.2310.03 23+5 0.4710.04  Height 18+1 Buds/Plant 25±5 Chewed/Plant 2.210 .7 Chewed/Buds 0.0810 .02 Dev./Plant . 11+2 Dev./Buds 0.5210..04 6+1  attack,  9+1  5+1  111125  1 38  Based on a comparison of the means for the main e f f e c t s the  two  diffuse  knapweed s i t e s  not appear to be s i g n i f i c a n t treatments  which c o u l d  nutrients  available  be at  differences  in n i t r a t e  concentration,  experimental The differed per 4.5).  attributed two  i n the to  there d i d  responses to  differences  sites.  between s i t e s were  (Table 4 . 2 ) ,  in  the  I conclude that  (Table 4 . 1 ) ,  unimportant  the  the  in p a r t i c u l a r  relative  to  the  treatments.  fertilized  and  significantly  plant  differences  the  significant  in 1979  at  watered  diffuse  knapweed  in  1980  number  of  buds  from the c o n t r o l i n the  ( l o g transformed d a t a ,  t=3.04, df=68,  p=0.003; Table  The p r o p o r t i o n of buds developed per p l a n t was much lower  on the f e r t i l i z e d and watered p l a n t s 4.5).  The d i f f e r e n c e  grasshoppers  than on the c o n t r o l  was p r i m a r i l y due to s e l e c t i v e  on f e r t i l i z e d p l a n t s  (discussed  "burn" was apparent at the higher r a t e of d e s p i t e the higher rate of  little  both t o t a l  buds  expected  (Table  effect and  U. quadr i fasc i a t a g a l l s , fertilization  and  on s p o t t e d  developed  4.6),  however  buds  knapweed. were  total  and t o t a l  and  Fertilizer  fertilization  watering  watering  in  in  in  (Table 4 . 8 ) .  1979  the  1980,  had  not  direction  galls,  total  affected  by  4.7). 1980  produced  knapweed with many more buds and developed buds per control plants  in  The e f f e c t s on  U. a f f i n i s  seeds were  or watering at Chase (Table  Fertilization  feeding by  watering.  SPOTTED KNAPWEED The f e r t i l i z a t i o n relatively  below).  (Table  There was no evidence  spotted  plant of  than  fertilizer  1 39  Table 4.5  - E f f e c t of f e r t i l i z a t i o n and watering on d i f f u s e knapweed c h a r a c t e r i s t i c s and i n s e c t a t t a c k , Robertson's 1980  Character *  Control  Exper imental  Number of P l a n t s Height Buds/Plant Chewed/Plant Chewed/Buds Developed/Plant Developed/Buds  50 30.0±0.7 72±6 6.6±1.2 0.09±0.01 30.7±2.4 0.44±0.02  20 28. 1 ± 1 . 3 124±21 29.3±6.1 0.23±0.03 35.9±8.1 0.28±0.03  UA/Plant UA/Developed UA/Attacked Prop A t t UA  37±4 1 .20±0.04 2 . 18±0.05 0.55±0.01  37±14 1 .02±0.05 2. 1 9 ± 0 . 0 7 0.47±0.02  UQ/Plant UQ/Developed UQ/Attacked Prop A t t UQ  8 . 3 ± 1 .3 0.27±0.02 1.84±0.07 0.15±0.01  5.0±2.8 0.14±0.02 1 .77±0.13 0.08±0.01  Seeds/Plant Seeds/Developed Seeds/Produc ing  106±11 3.47±0.10 6.03±0.12  106±32 2.97±0.16 5.98±0.24  Prop Aborted  0.20±0.01  0.13±0.01  * Detailed descriptions Table 2 . 5 .  of these c h a r a c t e r s are given  "burn" at  this  in  site.  RESPONSE TO PLANTS  GALL  FLIES  observed  DIFFUSE KNAPWEED Only l i m i t e d numbers of  i n 1979.  the nine treatment  If  the numbers of  flies  on p l a n t s  p l o t s are combined, the expected  with  the  one.  T h i s was observed at both d i f f u s e  flies i n each  were of  relationship  number of buds or developed buds i s a p o s i t i v e knapweed s i t e s  for  linear both  1 40  Table 4.6  - E f f e c t of f e r t i l i z a t i o n and watering on the t o t a l number of s p o t t e d knapweed buds and the number of developed buds, 1979  Character Buds  Developed Buds  Treatment  Site  Control  'Low  Water  C  7.42  7.95  8.45  a  Fert.  C  5.78  8.25  9.78  b  Water  C  2.95  2.70  3.13 c  Fert.  C  2.58  2.92  3.28 d  High  S i t e : C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=0.14, df=2,171, p=0.867; b. F=14.38, df=2,171, p<0.00l; c. F=0.35, df=2,171, p=0.704; d . F=1.09, df=2,171, p=0.337.  species  of  flies  (r>0.70, df=7,  U. quadr i fasc i a t a v s . p>0.05).  The  total  counts  of  the r e l a t i v e abundance of Ned's Creek In  (370 v s .  1980,  p<0.05 in a l l cases except  buds at R o b e r t s o n ' s , flies  flies  170 at  on p l a n t s was  in 1979 i n d i c a t e  about  twice  both s p e c i e s of  flies  p<0.0l  for a l l c o m p a r i s o n s ) .  the  range of buds per p l a n t  fertilized  plants,  buds per p l a n t and  in  a positive flies  per  1979.  of  three times as  at  buds  expected,  Within  0.27 great  This trend holds  (Figure 4.3).  opposite d i r e c t i o n of the response  c o n s i d e r i n g the o b s e r v a t i o n s  number  The average of  as the average of 0.098 for f e r t i l i z e d p l a n t s .  in  great  f e r t i l i z e d and watered p l a n t s .  per bud on c o n t r o l p l a n t s was almost  over the e n t i r e  as  that  f l y were observed more f r e q u e n t l y  T h i s was true based on number of p l a n t s and on 2  df = 7,  Robertson's).  on the c o n t r o l p l a n t s than on the  ( x ^ 7 . 3 , df=1,  r = 0.60,  for  This  was  especially  the  group  of  c o r r e l a t i o n was observed between plant.  There  was  no  overall  T a b l e 4.7 - E f f e c t o f f e r t i l i z a t i o n C h a s e 1979 F e r t i l i z a t i o n Level Watering Level  None  a n d w a t e r i n g o n s p o t t e d knapweed c h a r a c t e r i s t i c s a n d I n s e c t  None Low  Low High  Low  High  21 + 1  20+2  6.4+0.9 1 . 4 1 0 .3 0.24+0,.06 2.810,.05 0.4510 .05  1911 4.9+0..5 0.510,. 1 0.1010,.03 1.910.3 0.3710,.04  811 0.910..3 0.12+0..04 3.2+0..6 0.40+0..04  1811 7.4+0,.8 2.310..8 0.2810..07 2.010..5 0.2910,.04  UA/Plant UA/Dev. UA/At t a c k e d P r o p A t t UA  3.0+0..7 1.0±0..2 2.3+0..2 0.44+0..07  3.5+0..8 1.3+0..2 2.1+0..2 0.60+0..07  3.211..0 1.810..3 2.310..4 0.7710..07  612 1.9+0..3 3.0+0.,3 0.6310..06  UO/Plant UQ/Oev. UQ/Attacked P r o p A t t UQ  0.2+0.. 1 0.05±0.,04 1.5±0..5 0.0310.,02  0.0510..05 0.02+0..02 1 .0 0.02+0. 02  0.3+0.. 1 0.1710..09 1.510. 3 0.1110.. 0 5  Seeds/Plant Seeds/Dev. Seeds/Prod  2715 9.010. 4 9.710. 3  30+7 10.8+0. 7 11.810. 6  1313  0.09+0.04  P r o p A b o r t e d 0.0910.03  22+1  High  None  Height 21 + 1 Buds/Plant 6.1±0..7 C h e w e d / P l a n t O.3±0,. 1 Chewed/Buds 0.03±0.. 0 1 3.2+0..4 Dev./Plant Dev./Buds 0.54±0..04  attack.  Low  None  2212  High  1 . 8 1 0 ,.8 0.1310,.04 3.610..7 0.3810 .04  8.3+0..8 2.7+0..8 0.2610..06 2.4+0.3 0.3210..04  0 . 3 1 + 0 . .06  3.410..5 0.3710.. 0 5  2111 1112 3.110,.8 0.2410..05 4.011..0 0.3610..05  311 1.610.,3 3.010..4 0.5610..08  3.7+0..9 1 . 1 1 0 ..2 2.210..2 0.4910..06  1.7+0.4 0.810..2 1.810..2 0.4210..07  5+2 1 . 7 1 0 ..3 3.210..5 0.55+0..06  7+2 1.810. 2 2.810. 2 0.6210. 06  0.610..3 0.1810..07 1.610..3 0.1110.,04  0.110.. 1 0.0610. 06 2.0 0.03+0..03  0.8+0..4 0.210.. 1 2.5+0..6 0.09+0.,03  1.7+0. 3 0.07+0. 04  0.5+0. 3 0.1510. 08 2.310.,5 0.0710. 03  0.1510. 08 0.0410.,02 1 .0 0.04+0.,02  0 8.711. 0  1816 5.810. 4 8.010. 8  9+3 4.810. 8 6.910. 9  30110 8.5+0. 9 12.310. 7  1213 5.2+0. 8 8.110. 8  20+4 6.5+0. 5 9.810. 8  30110 7.6+0. 9 12.410. 9  0.11+0.04  0.0410.01  0.0810.02  0.1310.03  0.07+0.02  0.07+0.02  7.2+1.  10+2  19+1  0.3+0..  1  0 . 1 1 + 0 ..07  10+1  3.5+0..8  0.1010.03  1 42  Figure 4.3. Counts of t o t a l g a l l f l i e s observed per p l a n t for t r e a t e d and c o n t r o l d i f f u s e knapweed p l a n t s at Robertson's in 1980.  70.  o  •  a  o fertilized o  . control  •  I  o  40  °  °o  80  120  160  200  240  Buds per plant  280  320  360  400  1 44  Table 4.8  - E f f e c t of f e r t i l i z a t i o n and watering on s p o t t e d knapweed c h a r a c t e r i s t i c s and i n s e c t a t t a c k , Chase 1980  Character *  Control  Exper imental  Number of P l a n t s Height Buds/Plant Chewed/Plant Chewed/Buds Dev./Plant Dev./Buds  50 26.4±1.1 4.5±0.3 0 . 5 0 ± 0 . 13 0.08±0.02 2.64±0.18 0.58±0.03  30 26.0±1.5 16.9±2.7 5.30±0.74 0.32±0.03 7.50±0.90 0.42±0.03  UA/Plant UA/Developed UA/Attacked Prop A t t UA  3.2±0.5 1.22±0. 1 1 1,87±0. 1 3 0.65±0.04  7.3±1 . 6 1 .03±0.09 1.91±0.10 0.54±0.03  UQ/Plant UQ/Developed UQ/Attacked Prop A t t UQ  0.84±0.26 0.32±0.08 2.10±0.34 0.15±0.03  0.70±0.37 0.10±0.03 2.10±0.35 0.05±0.01  Seeds/Plant Seeds/Dev. Seeds/Prod.  15.4±0.8  17.2±0.7  150±26 21.2±0.6 24.4±0.2  P r o p . Aborted  0.03±0.01  0.05±0.02  40±4  * D e t a i l e d d e s c r i p t i o n of Table 2.5.  these  difference  two  observed plants  the  on f e r t i l i z e d  ( x = 0 . 7 9 , df=1,  diffuse  KNAPWEED knapweed,  knapweed  in  control  number of  In  plants  to  contrast  gall  flies  1980 as expected. plants  fly  s p e c i e s in the flies  in  r a t i o of  observed  on  flies  control  p=0.374).  2  SPOTTED  and  between  c h a r a c t e r s are given  to  the  responded U. a f f i n i s  in approximately  buds and developed  buds  the  per  response on to  fertilized  fertilized  o c c u r r e d on  spotted fertilized  same p r o p o r t i o n as plant.  Of  the  the  total  1 45  number  of  U. affinis  adults,  p l a n t s compared with 69% p=0.632) The on  of  67% were observed on f e r t i l i z e d  the  total  and 63% of the developed  OTHER  2  that  significant the  plants  ways.  had  been  Different  different  Robertson's was  the t o t a l  ( F i s h e r ' s exact t e s t ,  sites.  df=1,  p=0.066).  flies  was  lower  p<0.05).  on  the  visible.  At  effect  because Ned's  2 . 4 ± 0 . 3 % of of  at  the  Creek,  Robertson's,  Creek  and  biologically  in  the  end  of  the  branches  damage  4.9) were  with watering and f e r t i l i z a t i o n .  At chewed  was evident Chase  by  was  watering,  the  are  slight  no  longer  was r e l a t i v e l y  light;  There was no  linear  greater  increased effect  (overall  with  At mean  significantly  i n 1980 (Table  i n 1979, the p r o p o r t i o n of spotted  though  The  The same increased a t t a c k  for R o b e r t s o n ' s  grasshoppers  knapweed  on the p r o p o r t i o n of buds chewed.  the grasshopper a t t a c k  at  damage  summer.  16±1%) and the p r o p o r t i o n of buds chewed increased  treatment  and  chewing  the  (Tables 4 . 3 - 4 . 5 ,  chewed  1979  watered d i f f u s e  the buds were chewed.  the treatments  in  grasshopper  fertilized  of the damage caused  underestimates,  overall,  Ned's  i n both 1979 and 1980,  evident  estimates  altered  also  h e r b i v o r e s responded to the changes At  p l a n t s which were c o l l e c t e d  4.9).  df=1,  2  HERBIVORES The responses of v a r i o u s other h e r b i v o r e s  indicate  at  (x =0.23,  buds ( x = 3 . 3 7 ,  p r o p o r t i o n of U . quadr i fasc i a t a of f e r t i l i z e d plants  buds  with  4.5).  knapweed buds  fertilization  of watering was not l i n e a r  and (Table  In 1980, the p r o p o r t i o n of buds or branches chewed on the  f e r t i l i z e d p l a n t s was much higher than the c o n t r o l  (Table 4 . 8 ) .  1 46  Table  4.9 - E f f e c t of f e r t i l i z a t i o n and water ing on the p r o p o r t i o n of knapweed buds chewed, 1 979  Spec ies  Treatment  Site  Control  Low  Water  NC R  0.013 0.131  0.035 0. 155  0.024 a 0. 196 b  Fert.  NC R  0.016 0.081  0.030 0. 163  0.026 c 0.237 d  Water  C  0. 1 37  0.275  0. 1 57 e  Fert.  C  0. 1 25  0. 175  0.269 f  Di f fuse Knapweed  Spotted Knapweed  High  S i t e s : NC - Ned's Creek, R - R o b e r t s o n ' s , C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=4.98, df=2,171, p=0.008; b. F=3.82, df=2,170, p=0.024; c . F=2.10, df=2,171, p=0.126; d . F=22.01, d f = 2 , l 7 0 , p < 0 . 0 0 l ; e. F=6.92, df=2,171, p=0.00l; f. F=6.66, df=2,171, p=0.002.  Unidentified  spittlebugs  (Homoptera:  Cercopidae)  responded to the changes caused by the added n i t r o g e n i n knapweed  in 1979.  Only 8.9% of the t o t a l number of  (N=45) were observed on expected one t h i r d attacked  unfertilized  (x = 12.1, 2  fertilized  df =1,  plants  p<0.001).  2  spotted  spittlebugs  compared  to  the  The c e r c o p i d s  also  p l a n t s more h e a v i l y than would be  on the b a s i s of bud numbers ( x = 5 . 6 5 , df=1,  also  expected  p=0.0l7).  CHANGE IN INTERACTION  ATTACK LEVELS 1979 aborted  was  not  DIFFUSE  KNAPWEED  significantly  The  proportion  affected  by  resources a v a i l a b l e to the p l a n t s at e i t h e r of the knapweed s i t e s in 1979 The  the two  of  buds  increased diffuse  (Table 4 . 1 0 ) .  outcome of g a l l f l y a t t a c k c o u l d a l s o  reflect  increased  1 47  Table  4.10 -  Species Di f fuse Knapweed  Spotted Knapweed  E f f e c t of f e r t i l i z a t i o n and watering on the p r o p o r t i o n of knapweed buds a b o r t e d , 1 979  Treatment  Site  Control  Low  Water  NC R  0.091 0.086  0.097 0.072  0.093 a 0.083 b  Fert.  NC R  0.096 0.084  0. 100 0.076  0.085 c 0.080 d  Water  C  0. 065  0.079  0.113  Fert.  C  0.095  0.083  0.080 f  High  e  S i t e s : NC - Ned's Creek, R - R o b e r t s o n ' s , C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=0.09, d f = 2 , 1 7 1 , p=0.9l8; b. F=0.58, df=2,170, p=0.561; c . F=0.60, d f = 2 , 1 7 1 , p=0.548; d . F=0.21, df=2,170, p=0.8l4; e. F=2.44, d f = 2 , 1 7 1 , p=0.090; f. F=0.26, d f = 2 , 1 7 1 , p=0.770.  plant  resources  if  the p r o p o r t i o n of buds aborted was unchanged  and the number of g a l l s Creek,  the  number  per developed bud i n c r e a s e d .  of  U. a f f i n i s  galls  all  treated  plants  combined  (t=1.03,  however the e f f e c t s  of  no  the number of U . a f f i n i s  fertilization,  the treatments  bud i n c r e a s e d with w a t e r i n g . the  number  of  U. a f f i n i s  i n c r e a s e d watering  (hence the  term in the ANOVA; Table The changes bud  with  the  knapweed s i t e s . per  developed  the  df=120,  number  p=0.305),  galls  per  With  developed  fertilization  level,  per developed bud dropped with  significance  of  the  interaction  4.11).  i n the number of U . a f f i n i s treatments  were  At R o b e r t s o n ' s , bud  from  were q u i t e complex.  At the high galls  Ned's  per developed bud i n  c o n t r o l p l a n t s was not s i g n i f i c a n t l y d i f f e r e n t in  At  in  all  galls  not c o n s i s t e n t  per  developed  between  diffuse  the number of U. a f f i n i s treated  plants  combined  galls was  1 48  Table 4.11  - E f f e c t of f e r t i l i z a t i o n and watering on the number of U . a f f i n i s g a l l s per developed bud, 1 979  Species  Treatment  Site  Control  Low  Water  NC R  0.789 0.632  0. 598 0. 703  0.677 a 0.861 b  Fert.  NC R  0.678 0.697  0.590 0.784  0.747 c 0.778 d  Water  C  1 .26  1 . 54  1 . 52 e  Fert.  C  1 .27  1 .50  1.51  Di f fuse Knapweed  Spotted Knapweed  High  f  S i t e s : NC - Ned's Creek, R - R o b e r t s o n ' s , C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=7.63, df=2,2350, p<0.00l; b. F=9.99, df=2,2369, p < 0 . 0 0 l ; c . F=5.62, df=2,2350, p=0.004; d . F=1.46, df=2,2369, p=0.232; e. F=1.11, df=2,490, p=0.330; f. F=0.84, df=2,490, p=0.431. The i n t e r a c t i o n s of the main e f f e c t s at Ned's Creek and Chase were s t a t i s t i c a l l y s i g n i f i c a n t (F=11.98, df=4,2350, p<0.001; F=4.68, df=4,490, p<0.00l, r e s p e c t i v e l y ) , but i n n e i t h e r case was the i n t e r a c t i o n c o n s i s t e n t among r e p l i c a t e s .  significantly P<0.001).  higher than i n  There  was  an  control increase  developed bud with watering consistent  among  (Table  replicates  and  plants in  T h i s was a l s o the only t r e a t m e n t - s i t e - y e a r a significant (Table  increase  the  The  df=275,  galls  per  increase  was  fertilization  levels.  combination which had  proportion  of  buds  effect  on  the  per developed bud  that  was  developed  4.12).  There  was  no  U. q u a d r i f a s c i a t a g a l l s among  in  U. a f f i n i s  4.11). among  (t=3.34,  replicates  (The e f f e c t replicates.)  treatment  at e i t h e r d i f f u s e  knapweed s i t e  number  of  consistent  (Table 4 . 1 3 ) .  of n i t r o g e n at Robertson's was not c o n s i s t e n t  among  1 49  4.12 - E f f e c t of f e r t i l i z a t i o n and watering oni the p r o p o r t i o n of knapweed buds developed, 1979 *  Table  Species  Treatment  Site  Control  Low  Water  NC R  0.379 0.476  0.403 0.557  0.436 a 0.552 b  Fert.  NC R  0.396 0.517  0.421 0.517  0.401 c 0.549 d  Water  C  0.486  0.530  0.447 e  Fert.  C  0. 520  0.450  0.493 f  Diffuse Knapweed  Spotted Knapweed  High  * - P r o p o r t i o n s are a d j u s t e d by s u b t r a c t i n g chewed buds from the t o t a l number of buds per p l a n t . S i t e s : NC - Ned's C r e e k , R - R o b e r t s o n ' s , C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=1.81, df=2,171, p=0.167; b. F=5.04, df=2,170, p=0.008; c . F=0.38, df=2,171, p=0.684; d . F=0.84, df=2,170, p=0.433; e. F=1.57, d f = 2 , l 7 l , p=0.211; f. F=2.11, df=2,171, p = 0 . l 2 4 . The i n t e r a c t i o n of the main e f f e c t s at Robertson's was s t a t i s t i c a l l y s i g n i f i c a n t (F=4.80, d f = 4 , l 7 0 , p < 0 . 0 0 l ) , but was not c o n s i s t e n t among r e p l i c a t e s . The main e f f e c t of watering was c o n s i s t e n t among r e p l i c a t e s .  The  number  by any of  of g a l l s  the treatments  per bud was not s i g n i f i c a n t l y  i n 1979,  despite  large  reduced  increases  in the  number of buds per p l a n t .  SPOTTED KNAPWEED N e i t h e r insect  attack  treatments 4.10;  to  knapweed galls  U. q u a d r i f a s c i a t a g a l l s  ATTACK LEVELS  1980  the  two  predicted  responses  improved p l a n t q u a l i t y were d e t e c t e d  of s p o t t e d  U. a f f i n i s  of  per  in  1979  (bud  developed  per developed bud, Table  DIFFUSE  aborted was s i g n i f i c a n t l y  KNAPWEED  The  with the  abortion, bud,  of  Table  Table 4.11;  4.13).  proportion  of  lower on f e r t i l i z e d and watered  buds plants  1 50  Table 4.13  - E f f e c t of f e r t i l i z a t i o n and watering on the number of U . quadr i fasc i a t a g a l l s per developed bud, 1979  Spec i e s  Treatment  Site  Control  Low  Water  NC R  0.214 0.094  0.181 0. 139  0. 188 a 0. 1 46 b  Fert.  NC R  0. 193 0.110  0.200 0.087  0. 185 c 0. 172 d  Water  C  0.113  0.079  0. 1 33 e  Fert.  C  0.067  0. 168  0.093 f  Diffuse Knapweed  Spotted Knapweed  High  S i t e s : NC - Ned's Creek, R - R o b e r t s o n ' s , C - Chase. L e t t e r s i n d i c a t e s t a t i s t i c a l t e s t s of main e f f e c t s : a . F=0.49, df=2,2350, p=0.614; b. F=1.43, df=2,2369, p=0.239; c . F=0.11, df=2,2350, p=0.892; d . F=6.87, df=2,2369, p=0.00l; e. F=0.27, df=2,490, p=0.763; f. F=1.87, df=2,490, p=0.!56.  than  on  control  p r e d i c t i o n of the  plants  (Table 4.5)  reduced bud a b o r t i o n in  reduction  is  chewed buds i s  a p p a r e n t l y s u p p o r t i n g the treated  plants,  only m a r g i n a l l y s i g n i f i c a n t  removed (t=1.70 , df = 68,  There was no i n c r e a s e  in U . a f f i n i s  if  however  the e f f e c t  p=0.094). galls  per developed bud  c o r r e s p o n d i n g to the  lower p r o p o r t i o n of buds a b o r t e d ;  the  per developed bud dropped s i g n i f i c a n t l y  number of g a l l s  both s p e c i e s . lower  for  The p r o p o r t i o n of both  U . quadr i fasc i a t a  U . aff i n i s ( x = 22 .88,  galls  in  attacked  either  fly  species  aborted  and  lower counts  2  buds  developed ( x = 12.72, 2  df=1,  were  (Table 4 . 5 ) .  flies  per  plant  instead,  attacked  was  df=1,  p<0.00l)  and  p<0.001) and the  numbers  not s i g n i f i c a n t l y d i f f e r e n t The lower p r o p o r t i o n s  relative  for  buds  a t t a c k e d on t r e a t e d p l a n t s are c o n s i s t e n t of  of  to  of with  controls.  of for  buds the The  151  proportional  reduction  in g a l l s  per bud was much l e s s than the  r e d u c t i o n in the number of a d u l t  flies.  A f t e r a d j u s t i n g for the e f f e c t proportion diffuse  of grasshopper  of buds developed was s i g n i f i c a n t l y  knapweed.  proportion  of  This  buds  drop  parallels  attacked.  v a r i a b l e s was observed with the  An  the  lower on t r e a t e d  the  drop  increase  treatments  damage,  in  the  i n both of  these  at  Robertson's  in  1979.  SPOTTED  KNAPWEED  Bud a b o r t i o n was not s i g n i f i c a n t l y  the f e r t i l i z e d and (Table  4.8)  increase.  nor  watered did  the  spotted  knapweed  number  of  galls  than on the c o n t r o l s  df=1,  The  p=0.035).  U. q u a d r i f a s c i a t a (Table number  plants  of  galls  same 4.8;  2  1980  plants  (Table 4.8;  relationship  x =11.5,  in  per developed bud  A lower p r o p o r t i o n of buds on f e r t i l i z e d  a t t a c k e d by U . a f f i n i s  reduced on  df=1,  was  x =4.47, 2  holds  for  p=0.00l).  The  i n a t t a c k e d buds d i d not d i f f e r  significantly  between t r e a t e d and untreated p l a n t s .  The  proportion  i n f e r t i l i z e d p l a n t s was  of  U. q u a d r i f a s c i a t a g a l l s  c o n s i s t e n t with the r e l a t i v e l y observed a  on these p l a n t s .  slight  decline  approximately  in  equal  fewer  which  suggests  bud growth may be  adults  of  this  smaller  species  At Chase i n the same y e a r , there was  galls  per  developed  bud  despite  numbers of a d u l t s per developed bud.  r e d u c t i o n was due to a drop i n the 4.8)  relatively  proportion  that a f e r t i l i z e r e f f e c t  responsible.  attacked  This (Table  on the timing of  1 52  LARVAL SURVIVAL AND DEVELOPMENT DIFFUSE and  watering of d i f f u s e  the  rate  of  Table 4.14  KNAPWEED  Fertilization  knapweed in 1980 i n c r e a s e d m o r t a l i t y and  development  for  U. a f f i n i s  larvae  (Table 4 . 1 4 ) .  - Contents of Urophora g a l l s from c o n t r o l and t r e a t e d d i f f u s e knapweed p l a n t s , Robertson's 1980 PERCENT IN CATEGORY * affinis U. q u a d r i f a s c i a t a Control Treated Control Treated  Gall Contents L i v e Larvae Dead Larvae Proceeding in Development (Successful)  51 .9 18.2  44.0 22.9  29.9  33.0  89.0  71.7  (67.5)  (57.5)  (62.0)  82  99  ** (71.5)  N  715  1 .2 9.8  698  0.0 28.3  Columns may not add to 100% because of r o u n d i n g . P r o p o r t i o n of l a r v a e proceeding in development that s u r v i v e d to time of d i s s e c t i o n .  Larvae of t h i s  s p e c i e s in t r e a t e d p l a n t s were more l i k e l y to  than l a r v a e in higher  control  proportion  of  proceeded i n development  (x =7.96,  df=1,  2  U. a f f i n i s to the next  larvae  in  p=0.005). treated  generation  (i.e.  d i a p a u s e ; e x c l u d i n g dead l a r v a e , x = 4 . 5 7 , df=1,  enter I  plants  2  detected  U. a f f i n i s  no  obtain  difference  in  the  A  plants did  not  p=0.033).  mortality  of  l a r v a e proceeding in development between t r e a t e d and  untreated plants The  significant  die  (x =1.04, df=1, 2  p=0.308).  counts of l i v e U. quadr i fasc i a t a l a r v a e were too low to reliable  estimates  of  larval  mortality  or  of  the  1 53  proportion  proceeding  higher m o r t a l i t y of  larvae  affected  proceeding  KNAPWEED  affected  in  and  the c o n t r o l ) , 16.5%) (from  control  of  was  live  plants  larvae  not  increased  4.4%  to  21.1%).  are  compared with 21%  excluded, in  the  35% of  knapweed  in  in a l l g a l l s was s i m i l a r  proportion the  significantly  spotted  (62.8%, N=218 v s .  If  significantly  were  but l a r v a l m o r t a l i t y was reduced an  The success  p=0.584).  U . af f i n i s  and watering of  and  development  (Table 4 . 1 4 ) .  df=1,  2  Larvae  The p r o p o r t i o n of  though the data suggest  development (x =0.30,  by f e r t i l i z a t i o n  treated  development,  in f e r t i l i z e d p l a n t s  by f e r t i l i z a t i o n  SPOTTED  1980.  in  62.1%, N=161 (from  proceeded  larvae  in  which  33.5%  plants  on to  development  proceeded  l a r v a e d i e d in c o n t r o l  fertilized  in  (x =8.12, 2  in  plants df=1,  p=0.004). U. quadr i fasc i a t a spotted only  emerged  from a l l  knapweed p l a n t s as compared with  71%  p<0.005).  of  42  galls  in c o n t r o l p l a n t s  21 g a l l s adults  in  fertilized  emerging  (Fisher's  exact  from test,  1 54  DISCUSSION  RESPONSE OF PLANTS  Both treatments exception  of  Similarly,  increased the number of buds per p l a n t , the  watering  treatment  at  Chase  with  in  the  1979.  Schirman (1981) observed both s o i l moisture and s i t e  p r o d u c t i v i t y e f f e c t s on bud p r o d u c t i o n . The weaker response in  1980 was the opposite  application rates. were in  of d i f f u s e  deleterious  This observation  suggests  of  which  given the that  the a d d i t i o n of more f e r t i l i z e r  effect  on  plant  treatments  growth.  This  plants  absorption  a c t u a l l y had effect  higher  would have tended to a l l e v i a t e  higher  the  l i m i t for n i t r o g e n  d e s p i t e the higher watering l e v e l s and the 1980,  the  of what was expected,  c l o s e to t h e i r p h y s i o l o g i c a l  1979 and that  knapweed to  a  occurred  rainfall  the n e g a t i v e  in  effect  a too heavy f e r t i l i z e r a p p l i c a t i o n . The c o n t r a s t  expected observed  between 1979 and 1980 was much c l o s e r  difference  on spotted  i n both years and  developed  buds  suggests that  to  the  spotted  knapweed.  the  response  treatment  knapweed  a p p l i e d n i t r o g e n than d i f f u s e  can  to  the  The same e f f e c t s  were  of  bud  was stronger utilize  numbers in 1980.  higher  and This  levels  of  knapweed.  RESPONSE TO PLANTS  GALL  FLIES  The  data  for  1979  indicate  that  there  was no  1 55  important d e v i a t i o n from the d i s t r i b u t i o n of the  basis  of bud numbers at any of  the response  of the  flies  to  knapweed in 1980 matched the change  pattern.  The g a l l  flies  despite  This  density  fly  containing galls of  fly density  if  on  OTHER  flies  invertebrate  led  to  to  this  buds  per  plant.  a lower p r o p o r t i o n of The higher r e l a t i v e  This explanation  Vince  response  buds  density lower  crop  insect the  is  consistent  left  with  the  s i t e s and y e a r s .  and to  marsh p l o t s .  grasshoppers,  expected.  were d i s t u r b e d by the grasshoppers and  fertilized of  spotted  i n 1980 were an exception  h i g h e r numbers of  from a l l other  HERBIVORES  watered  t r e a t e d p l a n t s c o u l d have caused the  the knapweed p l a n t s . observations  Similarly,  i n bud numbers as  for both s p e c i e s .  grasshoppers  and  on  were observed r e l a t i v e l y l e s s often on  the t r e a t e d p l a n t s , reduced  expected  the three s i t e s .  fertilized  The data from R o b e r t s o n ' s  flies  Valiela  the  (1981) observed a s i m i l a r  ones  I  T h e i r treatment  obtained  increased the  herbivores,  primarily  same  that  groups  when  they  standing  homopterans  responded  to  and  improved  knapweed q u a l i t y . The  response  suggests  that  grasshoppers may McNeill  levels  one be  grasshoppers  of  the  the  to  factors  low  Popova  (1961; c i t e d in  knapweed.  (1964;  nitrogen  in Watson, Bolting  cited 1972) plants  fertilized  limiting  and Southwood (1978) argue that  a p l a n t defence. Fletcher  of  content  the of  knapweed attack  knapweed.  low n i t r o g e n may act in  Watson,  by  1972)  as and  both observed low p r o t e i n had l e s s than 8.3% true  1 56  protein  (by dry weight) at the beginning of  declined values  to  (cf.  content  close  zero  Strong et a_l. ,  of knapweed may  defoliators. tissues  to  in  The  concentrations Because  1984)  indeed  gall  bolting  by  fly  plants  result,  be  system  These  a  the low n i t r o g e n  barrier  to  and  Onuf e_t a l .  which  have  the  highest  control  plants  (cf.  feeding  Parker,  of  buds 1984).  biomass  than on u n f e r t i l i z e d t r e e s .  f r u i t and observed p r o d u c t i o n  of  the  "leakiness"  of  o u t s i d e of the system which i n f l u e n c e  As a  system. that  system  of organisms and i n t e r a c t i o n s ,  The the  experiments response  of  the  described other  there  variables in  this  herbivores  v a r i a t i o n i n knapweed p l a n t q u a l i t y may s u b s t a n t i a l l y a l t e r fly-knapweed  to  leaves  ecological  are  gall  in  between groups.  For every set  indicate  the  the number of developed  boundaries.  Chapter  nitrogen  of other h e r b i v o r e s i n the Urophora- Centaurea  illustrates  i n c l u d e d i n the  on the  (1977) observed that a marked i n c r e a s e  four times g r e a t e r  response  by  1978).  of mangroves l e d to a l o s s  the biomass of  forces  feeding  l a r v a e are probably feeding  were not s i g n i f i c a n t l y d i f f e r e n t The  the end of the summer.  i t was c o n c e n t r a t e d on t r e a t e d p l a n t s ,  the n i t r o g e n content herbivores  This  ( M c N e i l l and Southwood,  treated  Similarly,  summer.  i n d i c a t e that  by grasshoppers tended to e q u a l i z e between  the  to the  system.  CHANGE IN INTERACTION  EFFECT  OF  BUD ABORTION  The  improved  resource s t a t u s of  the  1 57  plants did aborted,  not  significantly  except  to  These o b s e r v a t i o n s  alter  reduce i t  suggest that  the  proportion  s l i g h t l y at Robertson's  of  buds  in  1980.  the experimental treatments  not a l t e r  knapweed's p r o p e n s i t y to abort buds under heavy  attack.  Much  this  larger  increases  did insect  i n s o i l moisture than used i n  Chapter might reduce the p r o p e n s i t y for knapweed  to  abort  buds (Chapter V ) . A reduced p r o p e n s i t y to abort buds c o u l d be c o n s i s t e n t the r e s u l t s more  obtained i f  intense.  This  the o v e r a l l attack on t r e a t e d p l a n t s would  developed  bud.  developed  bud  treatments  at R o b e r t s o n ' s  with an i n c r e a s e decline  be  Consistently were  in  with  only  reflected higher  observed i n 1979.  the  in  numbers in  more of  was  galls  per  galls  one i n s t a n c e :  per  watering  T h i s increase was c o r r e l a t e d  proportion  of  buds  developed.  (A  in the p r o p o r t i o n of buds developed was c o r r e l a t e d with  a drop i n the p r o p o r t i o n of  buds  attacked  at  Robertson's  in  1980). The  proportion  of buds developed may be an i n d i c a t o r to a  q u a l i t a t i v e l y higher " c a r r y i n g c a p a c i t y " of buds. changes  in  the  number  p r i m a r i l y to changes simpler  mechanism  discussed buds  in  of  galls  the  proportion  consistent  i n Chapter III  per  with  is possible:  developed of  buds  the e f f e c t the higher  developed may l e a d to an e l e v a t e d encounter  suitable If aborted  Because  the  bud are due attacked,  a  of bud a b o r t i o n proportion  of  rate with buds  for o v i p o s i t i o n . knapweed p l a n t s do not change because  of  insect  attack,  the  proportion  of  the p r o p o r t i o n of buds  buds left  1 58  undeveloped in the normal sequence of development constant.  Roze  (1981) concluded that weather  the p r o p o r t i o n of undeveloped buds per p l a n t . (1982)  suggests  changes  by  that Yucca w h i p p l e i T o r r .  adjusting  inflorescence  may  also  d i d not  regulate  Similarly,  responds to  size  rather  be  Aker  moisture  than  the  p r o p o r t i o n of buds developed.  LARVAL  SURVIVAL  U. a f f i n i s knapweed  AND DEVELOPMENT  greater  and U. quadr i fasc i a t a l a r v a e in  1980  may  be  due  to  grasshopper feeding on the p l a n t s ' effect  The  of  fertilizer  "burn".  in  the  mortality  fertilized destructive  v a s c u l a r systems In  either  case,  diffuse effect  of  to  the  or the  increased  m o r t a l i t y in t r e a t e d p l a n t s would be due to a r e d u c t i o n  in  q u a n t i t y or q u a l i t y of p l a n t resources a v a i l a b l e to the Two  other  mortality:  heavier  intraspecific likely.  explanations  The g a l l f l i e s  treated  for  would  to  the  knapweed.  The d i f f e r e n c e  i n d i v i d u a l buds.  knapweed  increased  or  increased  space.  Neither explanation  (Table effect  larval mortality  spotted  the  was  is  i n North America  competition  for  space  be lower than i n c o n t r o l p l a n t s ;  U. a f f i n i s  that  larvae.  enemies  per developed bud was lower  contrast  for  the  natural  Intraspecific  both s p e c i e s of g a l l f l y In  possible  have no known p a r a s i t e s  1980).  plants  number of g a l l s for  by  competition  (Myers and H a r r i s , in  attack  are  of  in  treated  the  plants  4.5). of~treating diffuse  lower  fertilized  spotted  between the two p l a n t s p e c i e s  suggests  allocates  This is consistent  in  knapweed,  increased with the  resources  increased  to  number  1  of  seeds  per  bud  F e r t i l i z e d diffuse fewer g a l l s  knapweed had fewer  development  faster  knapweed.  in t r e a t e d  U. quadr i fasc i a t a suggests that  bud,  despite  s p e c i e s responded  f e r t i l i z e r and a d d i t i o n a l water  U. a f f i n i s  diffuse  larval  the  significantly faster  per  r a t e s of both i n s e c t  to the combination of  s u p p l i e d to s p o t t e d also  seeds  l a r v a l development  knapweed.  development  flow  of  nutrients  altered  by  the  to  (No was  difference detected.)  individual  treatments.  The r e s u l t of  g e n e r a t i o n r e l a t i v e to the f i r s t g e n e r a t i o n .  suggest that the p h y s i o l o g i c a l c o n d i t i o n of the effect  on l a r v a l  initiation  (cf.  availability  during  et  al.,  larval  1979).  development  of  plant  and  i n i t i a t i o n may be s e l e c t e d for  its  resource  is  c o r r e l a t e d with a  season,  this  the  greater  latter  the  the  If  finding suitable oviposition sites  of  was  diapause  g r e a t e r p r o b a b i l i t y of part  in  These data  development may modify the process of Brown  was  This  buds  l a r v a l development would be to increase the s i z e  second  4.8).  per developed bud than c o n t r o l p l a n t s .  Larval positively  i n f e r t i l i z e d spotted knapweed (Table  59  flexibility  (Tauber et a l . ,  in  i n the  diapause  1986).  EFFECT OF PLANT QUALITY ON POPULATION DYNAMICS  The  impact  of a s h i f t  availability) how  the  The  first  resources.  in plant quality (e.g.  on the p o p u l a t i o n dynamics of  shift  alters  process Bigger  n i t r o g e n or water  insects  the net outcome of a s e r i e s of  is and  the  plant's  allocation  of  depends  on  processes. additional  more vigorous p l a n t s may not be  better  160  food.  Such p l a n t s may have improved defences a g a i n s t  attack the  (Fraenkel,  1 9 5 9 ; Rhoades,  insect's detection  (e.g.  Van  Emden,  exploitation  of  depends  the  on  (Solomon,  of  the q u a l i t a t i v e  1972).  The  the a d d i t i o n a l  1949)  insect's  may  be  altered  Southwood, of  by  1978;  any change  functional  and  insect's  plant  but see  quality  natural  an  in  In  plant  plant  the  insect's  This  process  Finally,  population  there  dynamics,  each of which  (e.g.  M c N e i l l and  1981).  The nature  general,  such  of h e r b i v o r e s ,  regulation  productivity  of  primary  Cases where food q u a l i t y 1971; White,  is  1976)  biomass on which one or high net  r a t e s of  processes. outbreak  will  occur  increases  are  probably  g i v i n g the appearance of (Mattson and Addy,  1975).  i m p l i c a t e d i n i n s e c t outbreaks seem to r e q u i r e a r e s e r v o i r  more  in  q u a l i t y are p r o b a b l y rare in  absorbed by a c o l l e c t i o n  sustain  lags.  changes  under which an i n s e c t  is  n u m e r i c a l responses  Auerbach and S t r o n g ,  increase  systems.  Kimmins,  the  in the p o p u l a t i o n dynamics r e l i e s on the change  conditions  following  in  r e p r o d u c t i o n and d i s p e r s a l ,  the magnitude and t i m i n g of the preceeding The  change  resources.  with t h e i r a s s o c i a t e d time  development,  The second process  t h i r d process i s  food  are the processes u n d e r l y i n g the survival,  1983).  herbivore  generations  of  the  of  (e.g. plant  insect  can  reproduction.  FERTILIZATION AS A MANAGEMENT TOOL  It  is  forage  unlikely plants  that  to r e s i s t  fertilization  will  knapweed i n v a s i o n .  improve the a b i l i t y of In  the  absence  of  161  grazing,  Popova  (i960; c i t e d  manure a d d i t i o n s 56.4±2.3%  to  in Watson,  1972)  i n c r e a s e d the percent cover  74.1±4.4%  at  found that  horse  knapweed  from  by  the expenses of grasses and f o r b s .  Myers and Berube (1983) f e r t i l i z e d a l i g h t l y grazed ammonium  nitrate  biomass, on  and  found  no  effect  i n p a r t because c a t t l e on that  treated  with  knapweed or  grass  range fed  preferentially  plots.  F e r t i l i z a t i o n may prove u s e f u l  through a s y n e r g i s t i c  with h e r b i c i d e .  Sheley et JELL. (1984)  application  of  picloram  grass y i e l d s  and the best  mechanism  on  range  they  grasses a f t e r  with  the  was  that  a  f e r t i l i z e r produced the  control  proposed  discovered  of  spotted  increased  residual effect  effect fall  highest  knapweed.  competition  The  from the  of the h e r b i c i d e had worn  off.  SUMMARY  T h i s Chapter d e s c r i b e s treatments  on  knapweed,  treated plants, plants.  differed  and  Knapweed  fertilization  the e f f e c t the  the  f e r t i l i z a t i o n and  response  consequences  plants  were  and w a t e r i n g ,  between  of  between  sites,  The most c o n s i s t e n t response  increase  in  fertilization to  greater  buds  response  "burn"; in  1980.  the  and  flies  attack  on  per p l a n t .  the  by both  of  changes  the between  plant was  The higher l e v e l  i n 1980 over  same increase  to  affected  to the treatments  and watering at Robertson's  fertilizer  fly  significantly  species.  of  of  the a d u l t  though the d e t a i l s  years,  numbers  of  watering  1979  an of led  at Chase gave a much  162  In g e n e r a l , a d u l t f l i e s direct  proportion  plant.  The one exception  recorded  on  to  treated  r e d u c t i o n appeared grasshoppers  the  to  the  due  The  gall  led  In g e n e r a l ,  plants  galls of  the  to  the  t r e a t e d spotted  The  and  which  limited  limit  did  not  gall  increases  in  developed  in g a l l s  per  alter  the  significantly  In the two cases the numbers of  i n the same d i r e c t i o n . knapweed  Survival  of  plants  was  U. a f f i n i s  knapweed p l a n t s was improved  fly  by the d e n s i t y of  proportional increase  diffuse  control.  1980.  Grasshoppers, s p i t t l e b u g s ,  p r o p o r t i o n of buds developed changed,  l a r v a e in f e r t i l i z e d  adults  of  are  per developed bud s h i f t e d  relative  in  increased  p r o p o r t i o n of a t t a c k e d buds that were a b o r t e d . where  of  density  the experimental a  plants  the  factors  flies  to  number  improved p l a n t q u a l i t y .  to three  o v i p o s i t i o n s i t e s since plant  to  reduced  to  in  i n the number of buds per  knapweed  on t r e a t e d p l a n t s .  populations.  plant.  was  be  I examined changes  per  increase  diffuse  cows responded p o s i t i v e l y  buds  were observed on t r e a t e d p l a n t s  over  the  Survival reduced larvae in control  plants. There flies will  was  in response be of  problem.  no  evidence  of p o s s i b l e  outbreaks by the  to the experimental t r e a t m e n t s .  limited  use  in  the  management  of  gall  Fertilization the  knapweed  1 63  V.  POPULATION LIMITATION OF TWO INTRODUCED INSECTS:  PROCESSES  WITHIN AND BETWEEN YEARS  The  choice  population  of  spatial  dynamics  behaviour  of  may  and  temporal s c a l e in s t u d i e s of  dramatically  the system.  alter  Large f l u c t u a t i o n s  the and  at a l o c a l l e v e l may appear smoothly continuous aggregated  (e.g.  This scale  The  the e f f e c t  limiting  gall-forming  U. q u a d r i f a s c i a t a the  examines  population  insects.  and  (Meig.)  spotted  Previous  flies,  evaluates seasons.  focussed  same  with  f i e l d observations  earlier  workers  i n t r o d u c t i o n of  this  the g a l l  Chapters important  I  of  the  plant  Frfld. eggs  This  in  fly  Chapter  rest  of  this  thesis  of comparisons among y e a r s .  are Three  are combined with data c o l l e c t e d  (e.g.  1980; IV  and  (Asteraceae).  season.  Roze,  Berube,  1980;  Harris,  1981).  concluded  sites,  by  back to the o r i g i n a l  that  i n l i m i t i n g the p o p u l a t i o n s of g a l l  a v a i l a b i l i t y of o v i p o s i t i o n status  the  flies  through  introduced  lay  Lam.  system extending  1980a,b; Myers and H a r r i s ,  temporal  as they act between one or more  from  years of  1935).  on processes l i m i t i n g the g a l l  the r e s u l t s  on  two  are  knapweed, Centaurea d i f f u s a  C . maculosa  processes  The c o n c l u s i o n s  contrasted  they  Urophora a f f i n i s  which acted w i t h i n a s i n g l e the  for  (Diptera: Tephritidae),  knapweed,  Chapters  populations  when  of a change of  processes  immature flower buds of d i f f u s e  Lam.,  "extinctions"  H u f f a k e r , 1958; N i c h o l s o n and B a i l e y ,  Chapter  on  observed  two f a c t o r s flies.  was a f f e c t e d  by the  The  were  first,  resource  (Chapter I V ) , and by non-random a t t a c k by  1 64  the  flies  these  i n space and time  components  evident  in  of  the  precipitation changes in distribution  oviposition  comparisons  from  the  (Chapters I ,  year  number  of g a l l s  to of  site  year buds  should r e f l e c t  be  plant.  plants  analysis  of processes w i t h i n a s i n g l e availability  Both  Changes  will  is  related  will  was  The  historical  constant  season; t h i s vary  among  to mature p l a n t d e n s i t y ,  l i m i t the a v a i l a b i l i t y of o v i p o s i t i o n  years  sites  for  years.  second f a c t o r  II,  and I I I ) .  vary  l i m i t i n g the g a l l  While the p r o p e n s i t y  from  year  developed  reduced the  bud.  to  year,  Among  Bud  availability  U. quadr i fasc i a t a  If  two  seed flies  or  more  f l y populations  year  (Chapter  there  should be a c o r r e l a t i o n  suitable  oviposition  comparisons  like  these  particular  process.  system.  They  can,  processes  as  they  are  galls affinis  .sites  not  for  controlled  demonstrations  however,  and do give an a p p r e c i a t i o n of  different  of  II).  and thus cannot be c o n c l u s i v e  evidence  the  (Chapters  a b o r t i o n was one way that U . of  is  f o r a p l a n t to abort buds  experiments  of  Gall  the g a l l  between the p r o p o r t i o n of buds a b o r t e d and the number per  the  component of  a b o r t i o n of buds that are h e a v i l y a t t a c k e d by i n s e c t s  may  In  later. The  I,  in  c o r r e l a t e d with  formation decreases seed p r o d u c t i o n by knapweed p l a n t s . production  of  non-random f l y a t t a c k .  the d e n s i t y  site  of mature  years.  should per  and I I I ) .  a v a i l a b i l i t y should be  among  addition,  oviposition  II,  the  interact  act  of  a  as  supporting  relative  importance  i n the undisturbed  1 65  This  Chapter  populations  of  (1)  evaluates  differences  availability,  in p a r t i c u l a r  attack,  changes  and  limitation as gall  of  a result fly  the  among due  to  effect  years  in  on  oviposition  precipitation,  in seed p r o d u c t i o n ,  species.  interaction  fly site  non-random  and (2) d i s c u s s e s  the number of g a l l s per developed bud, of bud a b o r t i o n and the  gall  the  especially  between the  two  1 66  MATERIALS AND METHODS  WEATHER To t e s t whether the r e s o u r c e s t a t u s of p l a n t s i s changed by p r e c i p i t a t i o n , weather data were Canada.  The  weather  station  patterns  rainfall  measurements  PLANT  recorded  at  Chase,  and  also  was recorded at the study  COLLECTIONS  IN  1979  effect  of  changes  the c o n t r o l p l o t s m  2  Kamloops A i r p o r t  consistent  agreed  with  the  end of  the  with  the  days  experimental  plots  were  study s i t e s in 1979 to  plant  p o p u l a t i o n dynamics (Chapter I V ) .  one  the  Environment  sites.  Similar  in  from  B . C . , at the opposite  e s t a b l i s h e d at each of the three the  at  used i n t h i s Chapter were  South Thompson R i v e r v a l l e y , rainfall  obtained  quality  on  the  examine gall  fly  The p l o t s d e s c r i b e d here were  for these experiments.  p l o t s were l o c a t e d in a s t r a i g h t  At  each  line,  site,  three  separated by 3 m  in an area with a v i s u a l l y uniform d e n s i t y of knapweed. A t o t a l of twenty p l a n t s were followed at each  site,  five  each from the two end p l o t s and ten from the c e n t r a l p l o t .  Each  plant  was  selected  as  the  nearest  a r b i t r a r i l y chosen p o i n t w i t h i n the p l o t . each p l o t were taken as the c e n t e r points  bisecting  the s t r a i g h t  four c o r n e r s of the p l o t . additional straight  points  were  l i n e s between  diagonals.  The  tenth  lines  In the taken  the  as  plant  to  an  F i v e of the p o i n t s plot  and  the  in  four  between the center and the  central  the s e l e c t e d plant  of  bolting  the plants  plot, points near  four  of  the  bisecting  the  adjacent  was chosen by b l i n d l y  plot  flipping a  1 67  pencil was it  i n t o the p l o t .  If the nearest  p l a n t to  the  pencil  tip  not p r e v i o u s l y s e l e c t e d and was w i t h i n the p l o t b o u n d a r i e s , was chosen. Plots  Diffuse  at  S e l e c t e d p l a n t s were r a r e l y nearest all  knapweed  sites plants  were  established  were  on  May 28,  1979.  c o l l e c t e d on August 22 at  Ned's  Creek and on August 25 and 26 at R o b e r t s o n ' s . at  Chase  neighbours.  Spotted  knapweed  was c o l l e c t e d at three day i n t e r v a l s from August 8 to  August 20.  Four p l a n t s were c o l l e c t e d on each day.  PLANT COLLECTIONS IN 1980 In 1980,  similar  were  Robertson's and on June 2 at  established  Chase. was  on  June  At each s i t e ,  placed  over  a  1  at  a r e c t a n g u l a r g r i d of  fifty  3 m x 6.5 m  of  portion  v i s u a l l y uniform d e n s i t y of knapweed. to b o l t nearest on  the  grid  were  All  collected  on  August  1980.  collected  just  before  23, the  diffuse  first  plots  points  the f i e l d with a  The p l a n t which had begun  far enough apart so that  neighbours.  This  (5x10)  each point on the g r i d was s t a k e d .  r a r e l y nearest  florets.  experimental  The  points  staked p l a n t s  knapweed  plants  Spotted knapweed p l a n t s seed  head  shed  its  were were were dried  c o l l e c t i o n extended over the p e r i o d August 1 to  August 24 as seed heads matured. E a r l y in the summer of Creek  site  with  1980,  the owner  the  herbicide  trichloropicolinic acid).  Forty five  h e r b i c i d e treatment were c o l l e c t e d 12.  sprayed  picloram  the  Ned's  (4-amino-3,5,6-  p l a n t s which s u r v i v e d  the  from Ned's Creek on September  1 68  PLANT  COLLECTIONS  IN 1981 On October 9,  p l a n t s were c o l l e c t e d plants  at  Chase  (N=50)  and  plants  collection spotted  date  to  randomly  means  that  selected  spotted knapweed diffuse  were c o l l e c t e d at R o b e r t s o n ' s (N=20).  the nearest  knapweed  These p l a n t s were The  late  some seed may have been l o s t  from  points.  knapweed heads.  PLANT DISSECTIONS P l a n t s were c o l l e c t e d them o f f  at ground l e v e l .  stapled  paper  bags at  they were d i s s e c t e d , the  1981,  size,  i n d i v i d u a l l y by c l i p p i n g  They were then stored in  folded  room temperature u n t i l d i s s e c t i o n .  the h e i g h t  developmental  of each p l a n t was  status,  measured  and When and  and l o c a t i o n of each bud were  recorded. Buds l a r g e enough to c o n t a i n e i t h e r individually contents hard  and  papery.  dissected.  For  of any g a l l s present woody  and  those  these,  galls the  were noted. of  or  seeds  were  number of seeds and U. a f f i n i s  galls  are  U. quadri fasc i a t a are t h i n and  169  RESULTS  AMONG YEAR DIFFERENCES NED'S CREEK The number of buds on knapweed p l a n t s at Ned's (Table 5 . 1 ) .  Table 5.1  -  Creek  increased  from  1979  diffuse to  The p r o p o r t i o n of buds that matured i n c r e a s e d from  D i f f u s e knapweed c h a r a c t e r i s t i c s and Urophora attack l e v e l s , Ned's Creek 1979- 1980  Character *  1 979  1 980  Number of P l a n t s Buds/Plant Chewed/Plant Chewed/Buds Dev./Plant Dev./Buds  20 16.2±1.9 0.55±0.20 0.03±0.01 5 . 1±0.8 0.33±0.03  45 50.6±5.8 1 . 0 8 ± 0 . 30 0.02±0.01 26.4±2.5 0.5710.02  UA/Plant UA/Dev. UA/Attacked Prop A t t UA  3.2±0.8 0.62±0.08 1 . 5 0 ± 0 . 10 0.41±0.05  15.9±3.4 0 . 61±0.03 1 .84±0.07 0.33±0.02.  UQ/Plant UQ/Dev. UQ/Attacked Prop A t t UQ  0.7±0.3 0.13±0.06 1.86±0.46 0.07±0.03  3.3±1.5 0.13±0.01 1.47±0.08 0.09±0.01  Seeds/Plant Seeds/Dev. Seeds/Produc ing  25±4 4.88±0.41 7.22±0.35  161+26 6.25±0.13 7.23±0.13  Prop. Aborted  0.07±0.02  0.21±0.02  * Detailed descriptions Table 2 . 5 .  1979  to  1980.  The  of  these c h a r a c t e r s are given  number of g a l l s per developed  significantly  different  however  proportion  the  1980  between years of  buds  in  bud was not  for both s p e c i e s  aborted i n c r e a s e d  of  fly,  threefold.  1 70  More of  the developed buds produced seeds in 1980 than i n  the number of  seeds i n buds which contained seeds d i d not change  significantly increased.  1979;  while  the  number of seeds in a l l developed buds  T h i s was not c o n s i s t e n t  numbers of g a l l s  with the r e l a t i v e l y  per developed bud, however  it  i s not  constant known  to  what extent the h e r b i c i d e and the r e s u l t i n g d r a s t i c r e d u c t i o n in p l a n t d e n s i t y a l t e r e d f l y a t t a c k or seed p r o d u c t i o n .  ROBERTSON'S  The  Robertson's 1981  number  1979  change  to  The p r o p o r t i o n of buds that 1980  (t=2.10,  significantly  U. a f f i n i s galls  buds per d i f f u s e  knapweed p l a n t at  i n c r e a s e d between 1979 and 1980 and between 1980 and  (Table 5 . 2 ) .  from  of  increased  df=28, p=0.045) and then d i d not  between over  matured -dropped  1980  the  and  three  1981. years,  Attack  both i n terms of  per a t t a c k e d bud and the p r o p o r t i o n of buds a t t a c k e d .  p r o p o r t i o n of buds a b o r t e d complemented the p r o p o r t i o n developed; change  it  increased  significantly  between  between  1980  1979 and  U. q u a d r i fasc i a t a i n c r e a s e d from 1979 to 1980  to  1981.  negatively  CHASE  The  and  1981. 1980,  buds  but d i d not Attack  by  but d e c l i n e d from  attack,  yet  i t was only between  the number of seeds i n buds c o n t a i n i n g  seeds  significantly.  height  from 1979 to 1980  that  1980,  of  The  number of seeds in a l l developed buds was  r e l a t e d to U . a f f i n i s  1980 and 1981 declined  The  and  by  1981,  1981  of s p o t t e d  knapweed p l a n t s at Chase i n c r e a s e d  but the number of buds only i n c r e a s e d between  (Table  5.3).  The  proportion  of  buds  that  171  Table 5.2  - D i f f u s e knapweed c h a r a c t e r i s t i c s and Urophora a t t a c k l e v e l s , Robertson's 1979-1981  Character *  1979  1980  1981  Number of P l a n t s Height (cm) Buds/Plant Chewed/Plant Chewed/Buds Dev./Plant Dev./Buds  20 1 8±1 25±5 1 . 8 ± 0.7 0 . 0 6 ± 0 .02 1 1 . 1 ± 1 .5 0 . 5 2 ± 0 .04  50 30±1 72±6 6.6±1.2 0.09±0.01 30.7±2.4 0.44±0.02  20 39±2 132±20 13.3±2.6 0.09±0.01 55.6±7.2 0.45±0.03  UA/Plant UA/Dev. UA/Attacked Prop A t t UA  6.4±1 0.57±0 1.65±0 0.35±0  .0 .06 .09 .03  36.9±4.0 1 .20±0.04 2. 1 8 ± 0 . 0 5 0.55±0.01  116+17 2.10±0.05 2.73±0.05 0.77±0.01  UQ/Plant UQ/Dev. UQ/Attacked Prop A t t UQ  1 . 4 ± 0.5 0 . 1 2 ± 0 .03 1 . 5 0 ± 0 .17 0 . 0 8 ± 0 .02  8.3±1.3 0.27±0.02 1 .84±0.07 0. 1 5 ± 0 . 0 1  11.6±2.7 0.21±0.02 1.63±0.08 0.13±0.01  Seeds/Plant Seeds/Dev. Seeds/Produc ing  51 ±9 4 . 5 5 ± 0 .27 6 . 2 0 ± 0 .26  106±11 3 . 4 7 ± 0 . 10 6.03±0.12  93±22 1 .68±0.08 4.26±0.13  Prop.  0 . 0 7 ± 0 .01  0.20±0.01  0.20±0.02  Aborted  * D e t a i l e d d e s c r i p t i o n s of Table 2 . 5 .  developed  did  not  these c h a r a c t e r s are g i v e n  change s i g n i f i c a n t l y .  A t t a c k by U .  did  not change s i g n i f i c a n t l y between 1979 and 1980,  an  increase  1980 to  in  affinis  except  in the p r o p o r t i o n of developed buds a t t a c k e d .  1981,  dramatically;  all  measures  of  U. a f f i n i s  attack  From  increased  almost a l l of the developed buds c o n t a i n e d  galls.  The p r o p o r t i o n of buds aborted d i d not behave as p r e d i c t e d ; proportion changes aborted  declined  in U. a f f i n i s in  1981  was  from  1979 to  1980,  gall densities. approximately  despite  for  the  nonsignificant  The  proportion  the  same as  of  i n 1979  buds even  1 72  Table 5.3  - S p o t t e d knapweed c h a r a c t e r i s t i c s and Urophora a t t a c k l e v e l s , Chase 1979-1981  Character *  1 979  1980  1981  Number P l a n t s Height (cm) Buds/Plant Chewed/Plant Chewed/Buds Dev./Plant Dev./Buds  20 21.4±1 6.10±0 0.25±0 0.03±0 3.15±0 0.54±0  .2 .73 .10 .01 .36 .04  50 26.4±1. 5.02±0. 0.50±0. 0.08±0. 2.64±0. 0.58±0.  1 30 13 02 18 03  50 32.5±0. 9 8 . 2 2 ± 0 . 58 1 . 6 0 ± 0 . 26 0 . 1 7 ± 0 . 02 4 . 2 6 ± 0 . 27 0 . 5 5 ± 0 . 03  UA/Plant UA/Dev. UA/Attacked Prop A t t UA  3 . 0 ± 0 .7 1 . 0 0 ± 0 .18 2 . 2 7 ± 0 .23 0 . 4 4 ± 0 .07  3.2±0. 1.22±0. 1.87±0. 0.65±0.  5 1 1 13 04  16.7±1. 3.96±0. 4.26±0. 0.93±0.  5 17 16 02  UQ/Plant UQ/Dev. UQ/Attacked Prop A t t UQ  0.15±0 0.05±0 1.50±0 0.03±0  0.84±0. 0.32±0. 2.10±0. 0.15±0.  26 08 34 03  1.10±0. 0.26±0. 1.90±0. 0.14±0.  30 06 26 02  Seeds/Plant Seeds/Dev. Seeds/Produc ing  2 6 . 6 ± 4 .6 9 . 0 ± 0 .4 9 . 7 ± 0 .3  39.9±3. 5 15.4±0. 8 17.2±0. 7  19.7±2. 6 4.7±0. 3 5.7±0. 3  Prop.  0 . 0 9 ± 0 .03  0 . 0 3 ± 0 . 01  0 . 0 8 ± 0 . 02  Aborted  . 1 1 .04 .50 .02  * D e t a i l e d d e s c r i p t i o n s of Table 2 . 5 .  though a t t a c k by both  these c h a r a c t e r s are given  gall  flies  was  much  higher  in  in  19  A t t a c k by U . quadr i fasc i a t a increased s h a r p l y from 1979 to primarily  through an i n c r e a s e d number of buds a t t a c k e d ,  not s i g n i f i c a n t l y changed between 1980 and 1981. seeds  per  but  i n 1981  in  seeds  developed  bud a l s o  dropped to 30% of  but was  The number  increased between 1979 and  its  value i n 1980.  1980,  The  of  1980,  contrast  per developed bud between 1980 and 1981 may be p a r t l y  due to a l a t e r c o l l e c t i o n date  in  1981.  1 73  EFFECT OF RAINFALL Based on a simple e x t r a p o l a t i o n of numbers of buds at R o b e r t s o n ' s rainfall total  significantly  indicates  lower  for  1981  the  plant.  difference that  is  76.2  buds per p l a n t .  between the observed  and  t o t a l p r e c i p i t a t i o n over the  flower  total  is considered is  the r a i n f a l l  transformed d a t a ,  number  observed  (i.e.  F=66.0,  of  is 1981  predicted  df=1,88,  precipitation  for those three years the r e l a t i o n s h i p  three months i s  not  buds  per  produced  the  number  of  buds  reserves and the d e n s i t y  (Figure 5.1).  buds  increased  same response per  plant  rainfall  bud and  a  direct  Using  log  (mm) + 2 . 8 3 ( ± 0 . 1 3 ) , The number of buds per plant 1980  Other p o s s i b l e per p l a n t  of b o l t i n g  Bud p r o d u c t i o n by spotted the  first  is:  r=0.65, p < 0 . 0 0 l .  (Figure 5.1).  values  between the number of buds per plant  at Ned's Creek a l s o i n c r e a s e d from 1979 to  of  This  June 10 to J u l y 27),  ln(BUDS+l) = 0 . 0 2 5 6 ( ± 0 . 0 0 3 2 ) R A I N  have  total  1 3 2 ± 2 0 for  If only p r e c i p i t a t i o n between the time of  relationship  in  observed  than the observed v a l u e of  an adequate p r e d i c t o r of  and  and  5.2).  The  first  1980  for the three months June to August, the p r e d i c t i o n of  buds per p l a n t  (Table  in 1979 and  with  sources  i n c l u d e the  increased  of v a r i a t i o n  s i z e of  rosette  plants.  knapweed p l a n t s appeared  not  to  to changes i n p r e c i p i t a t i o n ; the number  dropped (Table  between 5.3).  In  1979  and  contrast,  1980 plant  changes were c o n s i s t e n t with changes i n p r e c i p i t a t i o n .  despite height  1 74  Figure 5.1. E f f e c t of t o t a l r a i n f a l l d u r i n g the p e r i o d June 10 - J u l y 27 on the f i n a l number of buds per d i f f u s e knapweed p l a n t . The p r e d i c t e d value for R o b e r t s o n ' s for 1981 i s based on s t r a i g h t l i n e e x t r a p o l a t i o n from the v a l u e s for 1979 and 1980. The r e g r e s s i o n l i n e shown i s based on the observed values for R o b e r t s o n ' s 1979 to 1981. D e t a i l s of the r e g r e s s i o n are given in the t e x t .  1 76  DISCUSSION  BUD DENSITY In the the  gall  and by  flies  the  rainfall  short term, the d e n s i t y  i s a l t e r e d by the  timing with  of  buds  bud per  of buds a v a i l a b l e  resource  s t a t u s of the  initiation. plant  The  (Figure  densities  will  to the b o l t i n g p l a n t .  5.1)  of  supports  the  affected  by  T h i s i m p l i e s that bud  vary among years depending on the  in those y e a r s .  plants  correlation  c o n c l u s i o n of Chapter IV: bud numbers are d i r e c t l y the water a v a i l a b l e  to  Schirman's (1981 ) data a l s o  precipitation  support  the  same  conclusion. A  substantial  f r a c t i o n of s u i t a b l e  any given year because of the t i m i n g of bud  initiation  (Chapter  (Chapters II and I I I ) , aborted  buds  describes  on  proportion  of  ovipositing  gall  available  at  buds  of  low  production  proportion  extended  p e r i o d of  that  flies.  were The  actually  proportion  the estimated on  diffuse  of  effect  bud i n i t i a t i o n  depends on the d e n s i t y  of  mature  s u r v i v a l of  i n that  to  of  0.96.  the the buds  to be 0.72.  may r e f l e c t  At The  the more  species.  of s u i t a b l e plants  to  Appendix VA  developed  was  in  densities  available  proportion  knapweed  long term, the d e n s i t y  and the  fly  (Chapter I I I ) .  Ned's Creek in 1980 was estimated  smaller  production  because  relative  of the g a l l d i s t r i b u t i o n s to estimate  Chase one year l a t e r ,  In the  f l y attack  and because of the cumulative  gall  an a n a l y s i s  II),  buds are unattacked  oviposition  and  immature p l a n t s .  have a major impact on seed p r o d u c t i o n w i t h i n and  hence  sites  on  seed  The g a l l  flies  among  plants  1 77  (Chapter  I).  The  data  from  Robertson's and Chase i n d i c a t e negatively is  not  the  to  year comparisons  that U . a f f i n i s  r e l a t e d to the number of  possible  among  evaluate  density  is  seeds per developed bud.  It  the  gall  reduction  in  seed output  d i r e c t l y using a l l the h i s t o r i c a l data s i n c e  only bud  were  production  recorded  from  1973  to  at  1978;  seed  densities was not  measured. At the two s i t e s where the best time s e r i e s (Ned's Creek and Chase), unit  area  rapidly,  are s i m i l a r  peaked,  in  1979  available  the changes i n g a l l and bud d e n s i t y ( F i g u r e s 5.2,  and d e c l i n e d .  the peak i n f l y d e n s i t i e s . densities  are  The f l i e s  increased  Bud d e n s i t i e s d e c l i n e d  following  Bud  5.3).  densities  have  remained  of buds i n 1985 were v i r t u a l l y i d e n t i c a l to  (Myers, p e r s .  the  per bud w i l l a l s o d e c l i n e Assuming that  seeds  per  developed  produces 26.6 estimated result in  1981  of  seeds  formation w i t h i n  unattacked d i f f u s e bud  and that  per  knapweed  extreme  developed  bud  and 84% for s p o t t e d  including:  remain How  prior  seeds  developed  produces  unattacked spotted (Watson,  12.5  knapweed  1972),  the  seeds produced per p l a n t as a  f l y a t t a c k was 89% f o r d i f f u s e  c o m p e t i t i o n among p l a n t s ? density  due to g a l l  r e d u c t i o n i n numbers of  Many q u e s t i o n s density  densities  drop i n d e n s i t i e s of buds because the number of  buds.  low;  comm.).  The r e d u c t i o n i n seed p r o d u c t i o n w i l l be even more than  per  knapweed at  Robertson's  knapweed at Chase in the same y e a r . regarding  important How  annual  is  important  to b o l t i n g r e l a t i v e  seed are  changes  in  input r e l a t i v e plant  size  bud to and  to s o i l moisture l e v e l s d u r i n g  1 78  F i g u r e 5.2. D e n s i t i e s of d i f f u s e knapweed buds and t o t a l Urophora g a l l s per m at Ned's Creek 1972-1979. Density data are from H a r r i s (1980a). A l s o shown i s the r e l a t i v e d e n s i t y of g a l l s per developed bud (19721980). R e l a t i v e d e n s i t y data are from H a r r i s (unpublished data) and data i n t h i s t h e s i s . Vertical l i n e s give ± one standard e r r o r . No standard e r r o r s were given for a b s o l u t e d e n s i t i e s of g a l l s 1972-1974 in the o r i g i n a l r e f e r e n c e . Standard e r r o r s f o r the r e l a t i v e d e n s i t i e s of g a l l s are c l o s e to the s i z e of the symbol for 1972-1974. 2  180  Figure 5.3. D e n s i t i e s of spotted knapweed buds and t o t a l Urophora g a l l s per m at Chase 1971-1979. D e n s i t y data are from H a r r i s (1980a). A l s o shown i s the r e l a t i v e d e n s i t y of g a l l s per developed bud (1971-1981). R e l a t i v e d e n s i t y data are from H a r r i s (unpublished data) and data i n t h i s t h e s i s . V e r t i c a l l i n e s give ± one standard e r r o r . No standard e r r o r s were given for a b s o l u t e d e n s i t i e s of g a l l s 1971-1974 i n the o r i g i n a l reference. 2  Density (per m ) x 100 2  Galls / developed bud  T8T  182  bud  initiation?  and  Is  there a d i f f e r e n c e  i n the d e n s i t y  of  galls  seeds produced from small densely-packed p l a n t s compared  larger have  and  more  immediate  provided  widely-spaced p l a n t s ? management  preliminary  A l l of  implications.  evidence  on some of  these  Roze  to  questions  (1981)  these i s s u e s ,  has  but her  work must be extended and r e f i n e d .  EFFECT OF BUD DENSITY ON GALL DENSITY The r e p r o d u c t i v e  potential  of  of  the Urophora a d u l t s  increases  in  is  sufficient  bud d e n s i t i e s .  there was a t h r e e f o l d  increase  and  galls  the  number  From 1979 to in  the  galls and  of  of  1980,  i n the number of buds  plant  per developed bud remained  buds per p l a n t almost per  bud  constant.  there was a f i v e f o l d  per developed bud increased over 260%.  galls  per  increase  buds per p l a n t and the number of U.  watering treatment  large  At Ned's Creek from 1979 to  1981 at R o b e r t s o n ' s ,  number  to take advantage  at Chase in 1980  f o u r f o l d and  o b s e r v a t i o n may include an e f f e c t  of  fertilization  i n c r e a s e d the number of  the  dropped only s l i g h t l y  The  affinis  density  of  U.  affinis  (Chapter I V ) , though  f l i e s moving  onto  this  treated  plants.  are  Despite  their  limited  by  (Chapters  large r e p r o d u c t i v e p o t e n t i a l ,  the  density  I and I V ) .  i s c l e a r l y seen  in  of  The e f f e c t Figures  suitable of t h i s  5.2  and  d e c l i n e d at Ned's Creek and Chase a f t e r u n i t area a l s o dropped. will  be  a  function  Thus the of  oviposition  bud  flies sites  r e l a t i o n s h i p over  time  5.3;  as  1976,  g a l l d e n s i t i e s per  fluctuations  resource  the g a l l  densities  in i n s e c t  availability.  density  Dempster and  1 83  Pollard  (1981) argue that  this  i s a widespread c a u s a l  link  for  insects.  GALL  DISTRIBUTIONS  galls  per developed bud d i d not  two  sites  where  Table  the  best  l i m i t a t i o n o c c u r r e d while a buds  did  5.4  demonstrates increase  time  factors aside  monotonically  series  significant  not c o n t a i n any g a l l s from the a b s o l u t e  that the number of the  are a v a i l a b l e . fraction  (Appendix V A ) . number  at  of  of  This  suitable  Obviously other  suitable  buds  are  limiting g a l l fly populations. Among  site differences  developed bud.  affect  the mean number of g a l l s per  The number of U . a f f i n i s  at Robertson's i n 1981 was h i g h e r than Creek  (Table  5.4).  The  turn  a  c a p a c i t y " of Story  function individual and  U. a f f i n i s  at  years.  the  At  developed  of  9.3.  Again,  the outcome of  (1984)  followed  of  their  Ned's  suitable  the  buds  "carrying  increase  study,  fly  among s i t e d i f f e r e n c e s  of  in Montana over four the  percent  per developed bud ranged  sites  from  significantly  of  2.1  affected  attack. i n the number  can support (Myers and H a r r i s ,  c a p a c i t y " of  r a t e with  buds per p l a n t ) and of the  The two p l a n t s p e c i e s d i f f e r bud  at  a t t a c k e d ranged from 63-99% over the f i v e  and the mean number of g a l l s to  year  between these s i t e s are  s p o t t e d knapweed s i t e s  conclusion  buds  any  buds (Chapter I V ) .  Nowierski five  in  differences  presumably a f u n c t i o n of the encounter (in  g a l l s per developed bud  1980).  spotted knapweed buds i s  of  galls  The higher  reflected  in  each  "carrying  the  higher  184  Table 5.4 - Urophora g a l l s per developed bud at the three study s i t e s , 1973-1981 * Year  Ned's Creek  Urophora af f i n i s 1 973 0 . 1 4 ± 0 . 0 1 ** 1 974 0.23±0.01 1975 0.79±0.04 1 976 1.24±0.03 1 977 0.84±0.04 1 978 1.10±0.04 1 979 0.62±0.08 1980 * * * 0 . 6 1 ± 0 . 0 3 1 981  Robertson's  Chase  0 . 1 0 ± 0 . 01  0.4310.01 0.3010.01 1.3410.05 3.1810.09 4.8910. 14 2.5210.05 1 .83 + 0. 10 1.2210.12 3.96 + 0. 17  0.5710. 06 1.2010. 04 2.10+0. 05  Urophora quadr i fasc i a t a 1 973 0.06±0.01 1 974 0.29±0.01 1 975 0.78±0.05 1976 0.4210.03 1 977 0.40±0.03 1 978 0.05±0.01 1 979 0.13±0.02 1 980 0.13±0.01 1 981  0.2410. 01 0.1210. 03 0.2710. 02 0.2110. 02  Both Urophora s p e c i e s combined 1 973 0.20±0.01 1 974 0.52±0.02 1 975 1.58±0.06 1 976 1.65±0.04 1 977 0.3410. 1.24±0.04 1 978 1.15±0.04 1 979 0.75±0.06 0.6910. 0.7410.04 1.47+0. 1 980 1 981 2.3010.  02 07 04 05  0.1710.03 0.1110.02 0.8110.03 0.1210.03 0.3210.08 0.2610.06 0.4310.01 0.3010.01 1.3410.05 3.3510.09 4.9910.13 3.3310.06 1.9510.10 1.55 + 0. 14 4.2210.17  * Data for 1973-1978 from H a r r i s (unpublished d a t a ) . ** MeaniS.E. * * * Ned's Creek was sprayed with h e r b i c i d e in t h i s y e a r .  average (Table  5.4).  between their  number of g a l l s per bud observed at the p o p u l a t i o n peak Harris  (1980a)  the two knapweeds  flower  receptacles,  suggests  that  i s due to a d i f f e r e n c e  the  difference  in the area of  the s i t e s of g a l l f o r m a t i o n .  185  The two observed  contrasts  range  in  just  discussed  for e i t h e r  developed bud or the d e c l i n e s observed  at  i n d i c a t e that the  numbers  prevented  continuing  establishment  the l i m i t a t i o n of  of  the  of  of the g a l l  galls  per  f o l l o w i n g peak g a l l s per developed  Ned's Creek and Chase.  from  part  the mean number of g a l l s per developed bud,  but they do not account  bud  explain  galls  per  the  flies  The temporal p a t t e r n s developed  increase  and  that  bud  observed  there  were during  are  factors  a c t i n g over a longer time span to reduce the g a l l s per developed bud. Chapters  I,  II,  and  a t t a c k by the g a l l f l i e s or  time.  One  of  III  was not randomly d i s t r i b u t e d  the  outcomes  a b o r t i o n , may have prevented the bud  during  1975  to  "superparasitized"  1978.  time.  of  non-random  increase  While  space  attack,  bud  i n g a l l s per developed  Roze's  in t h i s  thesis,  (1981)  data  her data can  i n d i c a t e the q u a l i t a t i v e changes  She  in  on  buds are not d i r e c t l y comparable to the data  on aborted buds presented be used to  showed that the d i s t r i b u t i o n of  reported  that  probably  in bud a b o r t i o n over  the p r o p o r t i o n of " s u p e r p a r a s i t i z e d "  buds at Ned's Creek was c l o s e to 0% in 1975 and then jumped to a value of about  10% i n 1976 which then d i d not change  from  to  1976  "superparasitized" developed  bud  from  1978.  At  buds  tracked  1975  to  t o t a l number of buds i n 1977. hypothesis of  galls  Chase, the  1978,  the numbers  noticeably  proportion of  galls  peaking at about  Her data are c o n s i s t e n t  of per  10% of  the  with  the  that bud a b o r t i o n prevented an increase i n the number  per developed bud.  186  The  p a t t e r n of the p r o p o r t i o n of buds aborted from 1979  1981 at Robertson's  (Table 5.2)  and Chase  (Table  5.3)  may  e x p l a i n e d by a d e c l i n i n g p r o p e n s i t y to abort buds over the years  combined  with  the  d e c l i n i n g propensity improved buds)  plant  which  abort  quality  in  precipitation  to  observed  turn  is  consistent  1981.  between  watering  at  Many decline only  not  with  to  for  altered  the  by  (Figures 5.2  could  act  there and 5 . 3 ) .  a reduced encounter  changes  relative  in  differences  to the treatments results.  The  difference  of  over  in  high  Ned's Creek in 1979 added 6.9 mm to  (Figure  which  heavier the  The magnitude of the  years  in the number of g a l l s  one  density  factors  the  Chapter IV concluded that  n a t u r a l p r e c i p i t a t i o n compared to a between 1979 and 1981  with  A  the  correlated  Chapter IV may account f o r the c o n t r a s t i n g of  in f l y a t t a c k .  was  resource s t a t u s of the p l a n t s .  level'  three  and number of  from 1979 to  precipitation  buds  be  (measured by p l a n t h e i g h t  p r o p e n s i t y to abort buds was  in  changes  to  the  60 mm  5.1). over  s e v e r a l years to cause  per developed i s any evidence If  the  bud, is  the  the drop i n bud  reduced bud  r a t e with s u i t a b l e  however  the  buds,  density  fewer  galls  led per  bud would r e s u l t . T h i s hypothesis of bud.  suitable The  p r e d i c t s that  buds w i l l  evidence  affect  from  hypothesis,  however  undeveloped)  buds was a l s o  two exceptions  l a r g e changes  i n the  the number of g a l l s  Chapter  the d e n s i t y  IV  does  not  of u n s u i t a b l e  density  per developed support  (i.e.  a b o r t e d or  i n c r e a s e d i n these experiments.  to the g e n e r a l p a t t e r n ,  this  The  the data from R o b e r t s o n ' s  187  in  1979  critical  and  1980,  factor  is  u n s u i t a b l e buds. may  are c o n s i s t e n t  the  with the hypothesis  The context  of o v i p o s i t i o n and on the a b i l i t y of  them (reviewed by K a i r e v a ,  1983).  experimental  plant density  changes  this  in  BETWEEN  comparisons,  the  GALL  number  number of buds per p l a n t . I  for  adult  f e r t i l i z e d and watered  of  a  quite  differences  i n s e c t s to  locate  natural  and  (MS in p r e p . ) w i l l  help  In  U. a f f i n i s  the  among  flies  and U . q u a d r i f a s c i a t a  both are c o r r e l a t e d  and  in  Chapter  of the two  pattern.  i n the number of g a l l s  species  1974 at Ned's Creek and 1977 at  the  number  of  galls  per  Urophora  U . quadr i fasc i a t a may r e f l e c t  In  every  evident  site-year  Robertson's,  developed  bud  (2)  has a negative  galls  a negative  s p e c i e s i n two ways:  developed bud with the other or  5.4).  (1980) argues that U. a f f i n i s  d i s t r i b u t i o n of g a l l s the  buds  than  affinis. Berube  on  (Table  fewer  within  per developed bud are  combination  U.  in  C o n s i s t e n t and s i g n i f i c a n t  species  had  the  IV for g a l l s  between the two f l y  U. quadr i fasc i a t a  with  plants.  different  except  year  S i m i l a r c o r r e l a t i o n s were observed i n  The d i s t r i b u t i o n of g a l l s shows  sites  A comparison of  FLY SPECIES  per p l a n t changed t o g e t h e r ;  Chapter  feeding  issue.  INTERACTION  galls  the  r a t i o between the numbers of s u i t a b l e and  have a s t r o n g i n f l u e n c e  resolve  that  (1)  per  effect  bud.  The  i n t e r a c t i o n between  the numbers of g a l l s  s p e c i e s may be lower than  the p r o p o r t i o n of buds c o n t a i n i n g g a l l s  per  without,  of both s p e c i e s  188  may  be smaller than that p r e d i c t e d from  the  two  first  species.  Myers  and H a r r i s  c r i t e r i o n and demonstrated that  developed bud do behave as i f The  observed  buds  predicted  zero c l a s s .  from the three  by e i t h e r  class,  direction  the  interaction  (1980) have addressed  the  the numbers of  is a negative  number  expected test,  the d i f f e r e n c e  the  comparison  was  significant from  independent  galls  per  interaction.  (x  the  zero  seventeen out of  of  For  was s i g n i f i c a n t  If  a=0.05).  (x  ten  of  test,  2  the  presence  of  fly  another.  The e f f e c t  these  a=0.05).  for  which  difference  zero  by  classes  independent  (signs t e s t , are not  independent  There a r e , of c o u r s e , this  lack  of  in the  p<0.00l).  i n the d i r e c t i o n p r e d i c t e d i f  i n t e r a c t i o n were o c c u r r i n g .  zero  b i n o m i a l (Appendix VA)  predicted  species  be  negative  seventeen d i s t r i b u t i o n s d e v i a t e  interaction  for  to  a  i n t e r a c t i o n , the  classes  the  than the observed  p=0.00l).  d i r e c t i o n of a negative  is  predicted  basis  truncated negative  two  with  d i s t r i b u t i o n (Chase i n 1978)  test,  2  explanations  buds  the  suggests a p o s i t i v e  are compared with the  the  of  on  attack  seventeen d i s t r i b u t i o n s  s p e c i e s was g r e a t e r  the one e x c e p t i o n a l  calculated  by  the  (signs  distributions,  possible  by  In s i x t e e n out of  sites,  unattacked  attack,  attack  second c r i t e r i o n was t e s t e d by comparing the number of  unattacked  For  there  independent  a  The of  negative  several  independence  one  other  besides  competition. In U.  affinis  a  similar  analysis,  McEvoy  and U . quadr i fasc i a t a g a l l s  randomly d i s t r i b u t e d i n a spotted  (1984) were  concluded  independently  that and  knapweed p o p u l a t i o n i n Oregon.  189  H i s a b i l i t y to d e t e c t a non-random p a t t e r n was l i m i t e d , however, because  in  U. a f f i n i s  the sample he c o l l e c t e d only two buds c o n t a i n e d two galls  and only 11  U. quadr i fasc i a t a of  either  galls.  out  of  869  No buds contained more than two  evidence  for a negative  galls.  The  proportion  of  i n c r e a s e d over time  r=0.7l,  0.05<p<0.1)  df=5,  Combined with the evidence claim for a negative the  face  galls  and from  at  why  release  are kept below the  effects,  or (2)  refuges  Chapter  and  preferences  for  Creek  II,  Hassell,  (Berube and  (Spearman  (Figure  5.4).  Berube's  Figure  (1980)  that  approximately 5-20% of the  total  even a f t e r  5.4  the  Birch  two  species  (1979) g i v e s two  level  necessary  in time or space. for  for  species  competitive  The d e n s i t i e s  competitive  at  the  to  be  effects  though the c o m p e t i t i o n i s not symmetrical 1981).  The  Harris,  1978)  difference will  There i s a set  of  unattacked  in  only if  U. quadrifasciata oviposition prior  by U . a f f i n i s .  total  i n f l u e n c e from U . a f f i n i s ,  temporal refuge at the beginning of the season enough  i n the  shows  sites,  s i t e s are h i g h enough  observed (Chapter I I ) , (Lawton  galls  c o m p e t i t i v e e x c l u s i o n might not o c c u r : (1)  densities  release  distributions  Robertson's  persist?  constitutes  the  the  Ned's  have been i n t e r a c t i n g for s e v e r a l y e a r s . reasons  galls  i n t e r a c t i o n i s supported.  U . quadr i fasc i a t a  formed at  at  of t h i s d e l e t e r i o u s  U. quadr i fasc i a t a  in  U. a f f i n i s  number of g a l l s  how does  two  i n f l u e n c e of U . a f f i n i s on  U. q u a d r i f a s c i a t a from the annual changes  In  contained  species.  There i s  of  buds  or  bud lead  size to  buds are  a  large  to heavy a t t a c k only  lightly  1 90  F i g u r e 5.4. Changes in the p r o p o r t i o n of U . a f f i n i s g a l l s of a l l Urophora g a l l s over time at the three study s i t e s .  1973  1974  1975  1976  1977 Year  1978  1979  1980  1981  1 92  attacked  buds  that  were  that c o u l d a c t as a refuge l a r g e r second generation Roze,  1981).  i n i t i a t e d after late of  the  first  generation  i n the summer for the  relatively  U. q u a d r i f a s c i a t a  Both of these p o s s i b l e  refuges  (Appendix  UA;  are contingent  on  the year to year v a r i a t i o n i n the numbers of g a l l  flies  relative  The among year  t i m i n g of a t t a c k on t h e i r host p l a n t s .  comparisons show that between some years the per  numbers  developed bud for the two s p e c i e s move together  other years they move i n o p p o s i t e Thus  other  factors  affect  directions  the  and  of  the  galls  and between  (Table  5.2,  U . quadr i fasc i a t a  5.3).  densities  besides the d e n s i t y of U. a f f i n i s . A refuge of  in space  superior  reproductive  U. quadr i fasc i a t a Robertson's insects  much  for U . a f f i n i s ; the  first  may  i n 1980,  was  for U . q u a d r i fasc i a t a may e x i s t by v i r t u e  be  more  than  observed  of than  p<0.00l).  galls  for U . a f f i n i s  (Harris, knapweed  that U . quadr i fasc i a t a was present  U. a f f i n i s  (six  suggesting  (4.99  was  indicated  to one),  to  The r a t e of  establishment  (1981) data from a v a r i e t y of d i f f u s e  abilities.  U. a f f i n i s .  higher for U . quadr i fasc i a t a  2  U. quadr i fasc i a t a  dispersal  fecund  the r a t i o of  x =427, df=1,  years  and  that of  At  observed vs.  1.91  increase  higher 1980a). sites  in for  Roze's in  1977  at more s i t e s than the  two  gall  fly  s p e c i e s U. quadr i fasc i a t a spreads more r a p i d l y . The  relative  evaluated.  importance  In c o m b i n a t i o n , they  of  these appear  factors to  be  has not been sufficient  ensure that U . q u a d r i fasc i a t a remains a s i g n i f i c a n t the  insect  complex that  i s d e v e l o p i n g on the  to  component of  knapweeds  i n North  1 93  Amer i c a .  SUMMARY  T h i s Chapter focusses on an a n a l y s i s of at the r e l e a s e s i t e s . of  field  work  i n t r o d u c t i o n of sites  and  historical  the g a l l  data  flies.  The  extending density  bud was d i f f e r e n t  knapweed s p e c i e s .  of  flies  and  the  buds  may  years  to  the  oviposition  the a v a i l a b i l i t y of  were  reduction  limited  by  The number of g a l l s  the per  among the r e l e a s e s i t e s and between  Bud a b o r t i o n changed with  insect  attack  as  p r o p e n s i t y for p l a n t s to abort buds may have  changed from year to suitable  The  of a v a i l a b l e and s u i t a b l e buds.  developed  expected  back  buds i n time, and, in the longer term, on the  in seeds by the g a l l f l i e s . density  years  I c o n s i d e r e d changes over the three  appears to have depended on r a i n f a l l ,  suitable  year. account  The  decline  There  from g a l l d i s t r i b u t i o n s that U. a f f i n i s JJ. quadr i fasc i a t a ,  though  excluded U . q u a d r i f a s c i a t a .  in  the  for the drop in g a l l s  bud f o l l o w i n g peak g a l l d e n s i t i e s .  on  the changes among  of  per developed  further  evidence  had a negative  influence  U. a f f i n i s  is  density  has  not  completely  194  APPENDIX VA.  There  are  Centaurea -  two  ESTIMATION OF BUD AVAILABILITY  basic  Urophora  elements  system.  of  aggregation  Because of  the  refuge  in  in time  knapweed buds (Chapter I I ) ,  a v a r i a b l e number of buds w i l l  be a v a i l a b l e for  When  computation  of  attack. means,  variances,  m i s l e a d i n g and spurious r e s u l t s would if  indicate  the  attack  independent.  these and  may be  clumping (because of on  available  The  second  buds  buds  are  the  results  METHODS An estimate of the c o n t r i b u t i o n of the two elements  may  be  obtained  1960)  or  Since  by the use of e i t h e r  the  truncated  negative  the t r u n c a t e d Poisson  negative  binomial  accommodate  cases  t r u n c a t e d negative  aggregation  and the  between a v a i l a b l e  of  random  even  is  d i s t r i b u t i o n of g a l l s  element  The  perfectly  in  ratios,  l a r g e zero c l a s s )  was  for  never  included  variance-mean obtained.  the  buds.  the t r u n c a t e d Poisson (Cohen, binomial  (Sampford,  1954).  i s a l i m i t i n g case of the truncated  (when  k=infinity)  and  where  clumping i s due to both elements,  b i n o m i a l seems to be  the  better  latter  suited  can  to  the the  e s t i m a t i o n problem. A FORTRAN program which computed both the t r u n c a t e d Poisson and  truncated  negative  binomial  d i s t r i b u t i o n s was w r i t t e n .  parameters for the  The t r u n c a t e d  Poisson  based on Cohen (1960) and the t r u n c a t e d n e g a t i v e maximum  likelihood  method  available  fitting  binomial on the  of Sampford (1954) using an  estimate suggested by Brass (1958).  was  An example of  an  initial observed  195  distribution Figure  and  the  two  fitted  distributions  in  5.5.  The number of buds "unseen" i n t h i s a n a l y s i s difference  between  unattacked  as  a  result  d i s t r i b u t i o n of a t t a c k . females  is  the  of  the  truncated  estimated  the  to  be  p r o p e r t i e s of  the  The p r o p o r t i o n "unseen" by  number  of  distribution  negative  are  the s t a t i s t i c a l  ovipositing  buds "unseen" d i v i d e d by the  number of buds in the sample. that  i s simply  the number of buds that are unattacked i n a  given sample and the number of buds that  is  are given  The assumption of  binomial  attack  in  this  total  analysis  i s w e l l d e s c r i b e d by the  distribution  or  the  truncated  Poisson d i s t r i b u t i o n .  RESULTS The e n t r i e s 5.7  indicate  differs of  in the f o u r t h column of Tables 5.5,  that the estimated  significantly  cases  (x  distribution additional negative  of  binomial  within  similar  to the g a l l  the  1973;  is  proportion  useful  available  for  fitting  for  describing  The two d i s t r i b u t i o n s  the  clumped  buds.  Thus the  the the tend  truncated observed to  give  flies.  gall  Table  the  reflects  estimates of the p r o p o r t i o n s of buds u n a v a i l a b l e  At Ned's Creek, by  This  available  distributions accurately. quite  t r u n c a t e d Poisson d i s t r i b u t i o n  a=0.05).  galls  parameter  and  from the observed d i s t r i b u t i o n in a number  test,  2  5.6,  flies 5.5).  dropped.  the estimated p r o p o r t i o n of was very l a r g e at As  relative It  appears  buds  low f l y d e n s i t i e s  fly that  density  "unseen" (0.70  increased,  in the  i t had s t a b i l i z e d at a  1 96  gure 5 . 5 . Observed d i s t r i b u t i o n of U. a f f i n i s g a l l s in developed buds at Ned's Creek i n 1979 and f i t t e d , distributions. The l a r g e p r o p o r t i o n of buds "unseen" is evident. In t h i s case, both t r u n c a t e d d i s t r i b u t i o n s g i v e a good f i t to the observed d i s t r i b u t i o n (see Table 5.5) .  197  400  |  | observed truncated Poisson distribution  300. W i l l i  truncated negative binomial distribution  ••••• •  • • • i  i • • • •  •••• i  11111  >» o c a>  200.  3 _ CT 0)  I * rI ***' r * * s  [r ** *' •**  100. l • •  I**  I • •  r *'  r *  I * * I * * I *  I * *  •  L • I * *  2  3  Galls per bud  4  1 98  Table 5.5 - P r o p o r t i o n of d i f f u s e knapweed buds unattacked and estimated p r o p o r t i o n s of buds u n a v a i l a b l e to o v i p o s i t i n g g a l l f l i e s , Ned's Creek 1973-1980  Year  Truncated Signif. Poisson Diff. Prop. U n a v l . ?  Proportion Unattacked  UROPHORA AFFINIS 1 973 0.88410.004 1 974 0.81410.004 1 975 0.43910.024 1 976 0.36710.012 1 977 0.54810.016 1978 0.48410.016 1 979 0.60110.019 1980 0.66710.014  Truncated Negbinomial Prop. U n a v l .  Suitable Estimate ?  0.57 0.49 -0.09 0.19 0.40 0.38 0.36 0.55  Yes Yes No Yes No Yes No Yes  0.77 0.67 0.16 0.16 0.42 0.37 0.44 0.42  Yes Yes Yes Yes Yes Yes Yes Yes  UROPHORA QUADRIFASCIATA 1 973 0.95210.003 0.90 1974 0.81210.004 0.69 1 975 0.54910.024 0.36 1976 0.79410.010 0.74 1 977 0.81210.012 0.77 1 978 0.95910.006 0.87 0.77 1 979 0.87210.013 1 980 0.91210.008 0.84  No Yes No Yes No No No No  0.92 0.71 0.38 0.69 0.76 0.93 0.81 0.85  Yes Yes Yes Yes Yes Yes Yes Yes  BOTH SPECIES COMBINED 1 973 0.83510.005 1974 0.65110.005 1 975 0.22010.020 1 976 0.22710.01 1 1 977 0.39310.016 1 978 0.46010.016 1 979 0.50910.019 1980 0.58810.014  Yes Yes No Yes No Yes No Yes  0.70 0.45 0.03 -0.04 0.25 0.34 0.33 0.28  Yes Yes Yes. Yes Yes Yes Yes Yes  r e l a t i v e l y constant low  proportions  0.52 0.39 0.03 0.07 0.25 0.35 0.26 0.44  value of about 0 . 3 0 .  unattacked  in  The high  in those y e a r s ,  estimated  to z e r o .  p r o p o r t i o n "unseen" almost samples  proportion  from R o b e r t s o n ' s  unattacked  and  a  and  1975 and 1976, p o s s i b l y due to  delayed p l a n t and i n s e c t development  The  density  gave  a  steadily  corresponding  reduced the  decreasing  decline  in  the  1 99  estimated  p r o p o r t i o n "unseen"  T a b l e 5.6  - P r o p o r t i o n of d i f f u s e knapweed buds unattacked and estimated p r o p o r t i o n of buds u n a v a i l a b l e to o v i p o s i t i n g g a l l f l i e s , Robertson's 1977-1981  Year  Proportion Unattacked  (Table 5 . 6 ) .  Truncated Signif. Poisson Diff. Prop. U n a v l . ?  UROPHORA AFFINIS 1 977 0.906±0.006 0. 50 1978 no data a v a i l a b l e 0.653±0.032 0. 48 1 979 1980 0.447±0.013 0. 34 1981 0.232±0.013 0. 16 UROPHORA QUADRIFASCIATA 1 977 0.851±0.007 0.77 1 978 no data a v a i l a b l e 1 979 0.919±0.018 0.86 0.853±0.009 1980 0.80 1 981 0.872±0.010 0.81  at  Robertson's  four to f i v e The  the  Truncated . S u i t a b l e Negbinomial Estimate Prop. U n a v l . ? 0. 76  No  Nd Yes No  0. 57 0. 29 0. 1 7  No Yes Yes  Yes  0 .76  Yes  NO NO NO  0 .88 0 .81 0 .81  No Yes Yes  Yes  0 .60  Yes  No Yes Yes  0 .52 0. 1 9 0 .12  Yes Yes Yes  o c c u r r e d more slowly  Creek and lagged behind the p o p u l a t i o n i n c r e a s e by  in  Yes  BOTH SPECIES COMBINED 1977 0.770±0.009 0.60 no data a v a i l a b l e 1978 1 979 0.595±0.033 0.42 1 980 0.350±0.012 0.24 1 981 0.1B7±0.012 0. 12  proportions  The changes  at  than at  Ned's  Ned's  Creek  years.  estimated  proportion  of  buds  "unseen"  at  Chase  decreased almost monotonically d u r i n g the sampled years u n t i l reached a r e l a t i v e l y constant The  value of  0.05  p r o p o r t i o n of buds unattacked reached  i n 1976 a  (Table  minimum  in  it  5.7). 1977,  200  Table 5.7  - P r o p o r t i o n of s p o t t e d knapweed buds unattacked and estimated p r o p o r t i o n of buds u n a v a i l a b l e to o v i p o s i t i n g g a l l f l i e s , Chase 1973-1981  Proportion Unattacked  Year  Truncated Signif. Poisson Diff. Prop. U n a v l . ?  UROPHORA AFFINIS 1973 0.685±0.008 0.788±0.005 1974 1 975 0.310±0.019 1 976 0.117±0.01 3 1 977 0.077±0.012 1978 0.180±0.009 1979 0.263±0.025 0.346±0.042 1980 1981 0.071±0.018  Truncated Negbinomial Prop. U n a v l .  Suitable Estimate ?  0.35 0.59 0.12 0.09 0.07 0.13 0.17 0.14 0.06  Yes Yes Yes Yes Yes Yes Yes No Yes  0.49 0.63 0.16 0.07 0.06 0.08 0.10 0.10 0.05  Yes Yes Yes Yes Yes Yes Yes Yes Yes  UROPHORA QUADRIFASCIATA 1976 0.922±0.01 1 0.91 1977 0.945±0.010 0.93 1 978 0.612±0.012 0.52 1979 0.918±0.015 0.85 1980 0.846±0.032 0.81 1981 0.863±0.024 0.82  No No Yes No No No  0.90 0.92 0.50 0.88 0.78 0.73  Yes Yes Yes Yes Yes Yes  BOTH SPECIES COMBINED 0.094±0.012 1976 1 977 0.058±0.010 1978 0.131±0.008 1 979 0.229±0.024 1980 0.290±0.040 1 981 0.057±0.016  Yes Yes Yes Yes No Yes  0.05 0.04 0.07 0.06 0.09 0.04  Yes Yes Yes Yes Yes Yes  increased u n t i l A that  there gall  1980,  comparison  the estimated  inversely  to  0.07 0.05 0.11 0.14 0.16 0.04  and then d e c l i n e d again in  of  Tables  5 . 5 - 5 . 7 with Table 5.4  p r o p o r t i o n of buds "unseen"  the d e n s i t y  1981.  of g a l l s  per bud.  changes  indicates roughly  T h i s suggests  i s no f i x e d p r o p o r t i o n of buds that are u n a v a i l a b l e to flies  between  years,  and  hence  p r o p o r t i o n of buds i n a seed r e f u g e .  there  is  An increase  no in f l y  that the  constant density  201  will  not  lead  proportion differences abortion  to  a  proportional  "unseen", in  however,  the  timing  (Chapter I I I ) .  described difference  in  Chapter  in a d u l t  The II  density  unattacked by only 8%.  of  r e d u c t i o n i n the  because attack  density showed changed  of  the  (Chapter  II)  manipulation  that the  a  roughly proportion  estimated observed and bud experiment threefold of  buds  202  CONCLUDING DISCUSSION  The criteria  I n t r o d u c t i o n to t h i s t h e s i s i d e n t i f i e d for  evolutionary  evolutionary success,  of  how s u c c e s s f u l  has  focussed  the  gall  Morrison, will  flies:  The  bud,  the p l a n t ,  ephemeral  support g a l l  and  bud  about  which  oviposition production.  of  these  variable  i s the b a s i c  As o v i p o s i t i o n resource.  and time of  of (cf.  levels  buds they o v i p o s i t s e l e c t i o n are g a l l  in.  sites,  unit  depending  for  buds  The a b i l i t y of  are  buds  on  to  size,  initiation.  t h i s v a r i a t i o n , the g a l l  flies  are  selective  The d i r e c t consequences of  formation and a r e d u c t i o n in seed  Bud a b o r t i o n r e s u l t s from common s e l e c t i o n c r i t e r i a  among i n s e c t s and h i g h r e l a t i v e outcome  each of  formation v a r i e s c o n s i d e r a b l y  face of  This thesis  and the p o p u l a t i o n  in knapweed p l a n t s  location within plants, In the  future.  indicator  turn.  both g a l l and seed p r o d u c t i o n . an  i s a key  l e v e l s of v a r i a t i o n in the host p l a n t s  The p r o c e s s e s a c t i n g . a t  flower  interlinked  f o u r t h c r i t e r i o n of  response to v a r i a t i o n ,  the  be summarized in  BUDS  The  a s p e c i e s w i l l be in the  on three  1984).  success.  four  f l y attack  d e n s i t i e s of g a l l  eliminates  This  both g a l l and seed p r o d u c t i o n .  F l i e s do not appear to d e t e c t aborted buds without rarely oviposit  flies.  probing  and  i n them.  PLANTS In the absence of v e g e t a t i v e r e p r o d u c t i o n , the i n d i v i d u a l plant  is  the  demographic  unit  for the plant p o p u l a t i o n .  The  203  unique p a t t e r n of resource a l l o c a t i o n for each p l a n t means every  plant  may  also  be  p o p u l a t i o n of buds ( c f . the  form  viewed  White,  as  1979).  that  a d i s c r e t e and changing Increased  of n i t r o g e n f e r t i l i z e r and water  resources  l e d to  in  i n c r e a s e d bud  initiation. Gall buds  on  flies the  responded to the changes plants.  i n the  In g e n e r a l , g a l l f l i e s  p l a n t s in d i r e c t p r o p o r t i o n to the number However, plant.  galls The  "partial  are  Urophora  species  predators"  fly  branching  of  were observed on buds  per  plant.  unevenly d i s t r i b u t e d among buds on a given act  in  (Harvell,  e l i m i n a t i n g seed p r o d u c t i o n . among  of  populations  categories  a  similar  1984),  The  way  fashion  never  plants  to  completely  allocate  buds,  and in time, a l t e r e d the outcome of  attack. P l a n t s aborted buds i n response  there was minimal compensation for  to heavy i n s e c t the  lost  seed  attack,  but  production.  The p r o p o r t i o n of buds aborted was not s i g n i f i c a n t l y a f f e c t e d by fertilization  or  watering  buds maturing appeared to  treatments. increase  the  A h i g h e r p r o p o r t i o n of number  of  galls  per  developed bud.  POPULATIONS changes  Populations  is  between y e a r s ,  and  the g r e a t e s t  in the p l a n t s and are the l e v e l  variation  plant  give  density,  time.  critical.  Both  for example due to shift  changing  at  scope for long-term which  year-to-year  resource a v a i l a b i l i t y  precipitation,  and  the d e n s i t y of o v i p o s i t i o n s i t e s  changing in  space  204  E s t a b l i s h e d p o p u l a t i o n s of g a l l f l i e s bud  density  very  well,  however  i n d i c a t e d that a s i g n i f i c a n t unattacked  because  of  a  the  tracked  results  changes  of  Chapter II  f r a c t i o n of the bud p o p u l a t i o n refuge  in time.  the  gall  searching  flies'  ability.  oviposition  Their  preventing  an  reduced g a l l  increase  changed  ability  a l i m i t a t i o n on t h e i r  to  discover  the  bud a b o r t i o n and  gall  trends  clearly  The  formation,  within  that  population  the two o r i g i n a l r e l e a s e s i t e s .  were w e l l e s t a b l i s h e d ,  only  indicate  a  small  the numbers of g a l l s range.  Further  bud  increase  was  The drop in seed  with a much lower d e n s i t y  This  in turn reduced g a l l d e n s i t i e s to t h e i r present known how the number of g a l l s  Once the per  correlated  production  of o v i p o s i t i o n  per bud  will  sites.  levels.  It  change  with  thesis,  each  density. Several  processes  have been explored in t h i s  with t h e i r own s p a t i a l and temporal s c a l e . broader  spatial  processes disappear effect the  factor  per bud.  was  bud  effects  important  number of g a l l s  prevented i n p a r t by bud a b o r t i o n .  i s not  suitable  formation by U. q u a d r i f a s c i a t a .  population  flies  in  attack,  l i m i t a t i o n o c c u r r e d at gall  is,  Bud a b o r t i o n may be the most  of U . a f f i n i s  The  that  properties  s i t e s was f u r t h e r reduced by the cumulative  of bud a b o r t i o n .  effects  attack,  was  Another a d d i t i o n a l  p r o p o r t i o n was unattacked because of the s t a t i s t i c a l of  in  of  relative  scale and  oviposition  and  In  switching  a  longer  temporal  others  become  more  selection  to  scale,  some  prominent.  The  i s combined with the e f f e c t  t i m i n g of bud i n i t i a t i o n and g a l l  a  f l y emergence  of in  205  generating the  non-random g a l l d i s t r i b u t i o n s .  relative  rates  of d i s p e r s a l of  At the other  the  i n s e c t s and the  w i l l affect  the extent to which the p l a n t p o p u l a t i o n i s  by  a t t a c k over s e v e r a l y e a r s ,  insect  extreme,  yet  reduced  dispersal will  apparent in the d a y - t o - d a y changes o c c u r r i n g on a s i n g l e For p r a c t i c a l reasons, such  as  this  (Because  one  to  than i f  arises  from  knowledge are  be  spatial  importance of  is  regular the  necessary  to  imposed by and  the  desire  informative,  or  but  inconsistent  through  scales.  that  the  The l a t t e r  requirement  reliable  knowledge,  for  description  study  the s c a l e s may  requirement  in  plant.  i m p l i c a t i o n s . ) An  that can be used to make p r e d i c t i o n s .  sporadic  not be  a  temporal  the weeds,  consistent.  scientist's  limit  and  the study had no management  additional constraint processes  is  certain  of the economic  be g r e a t e r  it  plants  Processes which  their  effects  rather  than  may  be  systematic  experimentation. For  every e c o l o g i c a l  system,  there are p r o c e s s e s which are  not a p a r t of the d e f i n e d system,  but which have  its  system  behaviour.  Expanding  the  an  definition,  i n c r e a s i n g the s p a t i a l or temporal s c a l e of a n a l y s i s , avoid  the  problem.  Perhaps  the  process  was the h e r b i c i d e treatment  had  drastic effect  a  r a d i c a l l y change the their  hosts.  on p l a n t d e n s i t y  interaction  that  studying  could  followed  were  perhaps by does  in 1980.  and had the p o t e n t i a l  between  on  not  example of such a  at Ned's Creek  (Remarkably, i t d i d n o t . )  and the a c t i o n and  clearest  impact  the  gall  flies  It to and  Yet the human d e c i s i o n  outside  the  system  not have been p r e d i c t e d from the  I  was  processes  206  o c c u r r i n g w i t h i n and among y e a r s . 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