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Aspects of the chemical ecology of lygaeid bugs (Oncopeltus fasciatus and Lygaeus kalmii kalmii) feeding… Isman, Murray Bruce 1977

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ASPECTS OF THE CHEMICAL ECOLOGY OF LYGAEID BUGS (ONCOPELTUS FASCIATUS AND LYGAEUS KALMII KALMII) FEEDING ON MILKWEEDS (ASCLEPIAS SPECIES) IN CENTRAL CALIFORNIA by MURRAY BRUCE ISMAN B . S c , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE, in THE FACULTY OF GRADUATE  STUDIES  (Department o f Z o o l o g y )  We a c c e p t t h i s t h e s i s as c o n f o r m i n g to t h e r e q u i r e d s t a n d a r d  THE UNIVERSITY OF  BRITISH'COLUMBIA  A p r i l , 1977 (c) Murray B r u c e Isman, 1977  In p r e s e n t i n g t h i s  thesis  an advanced degree at  further  for  freely  available  Columbia,  I agree  that  r e f e r e n c e and study.  agree t h a t p e r m i s s i o n for e x t e n s i v e copying o f t h i s  this  representatives. thesis for  It  thesis  financial  i s understood that c o p y i n g o r p u b l i c a t i o n g a i n s h a l l not be allowed w i t h o u t my  written permission.  Department The  for  o f the r e q u i r e m e n t s f o r  s c h o l a r l y purposes may be granted by the Head o f my Department o r  by h i s of  fulfilment  the U n i v e r s i t y of B r i t i s h  the L i b r a r y s h a l l make it I  in p a r t i a l  of  ZOOLOGY  U n i v e r s i t y o f B r i t i s h Columbia  2075 Wesbrook P l a c e Vancouver, Canada V6T 1WS  Frontispiece.  A d u l t O n c o p e l t u s f a s c i a t u s and Lygaeus k a l m i i k a l m i i ( c e n t e r ) on a d e h i s c e n t  pod  o f A s c l e p i a s f a s c i c u l a r i s i n Napa C o u n t y , California.  (iii)  (iv) ABSTRACT A p l a n t - i n s e c t a l l o m o n a l s y s t e m was  investigated, involving  seed bugs ( L y g a e i d a e ) on milkweeds ( A s c l e p i a s s p p . ) . the i n s e c t s t o s e q u e s t e r s e c o n d a r y  The a b i l i t y o f  compounds from h o s t p l a n t s  was  studied in detail in central C a l i f o r n i a . A c o l o r i m e t r i c a s s a y was used t o q u a n i t i f y the amount o f c a r d e n o l i d e s ( c a r d i a c g l y c o s i d e s ) i n the l y g a e i d bugs  Oncopeltus  f a s c i a t u s and Lygaeus k a l m i i k a l m i i and n i n e s p e c i e s o f milkweed h o s t plants.  The c a r d e n o l i d e c o n t e n t o f i n d i v i d u a l a d u l t i n s e c t s , d e t e r -  mined i n m i c r o g r a m e q u i v a l e n t s o f d i g i t o x i n , v a r i e d from z e r o to o v e r 300 pg per i n s e c t .  S o u r c e s o f v a r i a t i o n o f c a r d e n o l i d e c o n t e n t i n the  i n s e c t s i n c l u d e d i n t e r s p e c i f i c and i n t r a s p e c i f i c d i f f e r e n c e s i n the c a r d e n o l i d e c o n t e n t o f the h o s t p l a n t s p e c i e s , and a l s o d i f f e r e n c e s i n the c o n t e n t o f p l a n t o r g a n s on w h i c h i n s e c t s were f e e d i n g . When r e a r e d i n the l a b o r a t o r y on a d i e t o f milkweed s e e d s ,  the  u p t a k e o f c a r d e n o l i d e s by the bugs was p r o p o r t i o n a l to the c a r d e n o l i d e c o n t e n t o f the s e e d s .  However, f i e l d c o l l e c t e d l y g a e i d s c o n t a i n e d  fewer c a r d e n o l i d e s than were a v a i l a b l e i n the p l a n t s on w h i c h t h e y were f e e d i n g .  This suggests t h a t several e c o l o g i c a l parameters,  as d i f f e r e n t r e p r o d u c t i v e p h e n o l o g i e s h o s t s p e c i e s , may  and m o r p h o l o g i e s  such  o f the d i f f e r e n t  i n t e r f e r e w i t h the bugs' a c q u i s i t i o n o f c a r d e n o l i d e s .  fj. f a s c i a t u s and L. k. k a l m i i d i f f e r i n t h e i r f e e d i n g r e q u i r e ments, h o s t p l a n t u t i l i z a t i o n , and a b i l i t y to s e q u e s t e r from t h e i r h o s t s .  cardenolides  However, the l a r v a l growth and d e v e l o p m e n t o f  (v) CJ. f a s c i a t u s and L_. k_. k a l m i i i n the l a b o r a t o r y on seeds o f d i f f e r e n t milkweed s p e c i e s d i d n o t v a r y w i t h p l a n t s p e c i e s o r c a r d e n o l i d e o f t h e seeds.  content  T h e r e f o r e , seeds o f a l l p l a n t s p e c i e s were e q u a l l y  s u i t a b l e as f o o d s o u r c e s f o r the bugs. The c o l o n i z a t i o n p a t t e r n o f CJ. f a s c i a t u s on s p e c i e s o f A s c l e p i a s i n n o r t h c e n t r a l C a l i f o r n i a s u g g e s t s . t h a t t h i s s p e c i e s does n o t maximize i t s o p p o r t u n i t i e s to sequester l a r g e q u a n t i t i e s of cardenolides potential hosts.  from  Over 50 per c e n t o f f i e l d c o l l e c t e d l y g a e i d s i n t h i s  s t u d y c o n t a i n e d l e s s than 50 yg o f c a r d e n o l i d e .  The e c o l o g i c a l s i g -  n i f i c a n c e o f c a r d e n o l i d e s e q u e s t r a t i o n by l y g a e i d s as a d e f e n s i v e s t r a t e g y may depend on s e v e r a l modes o f p h a r m a c o l o g i c a l  a c t i v i t y in  p o t e n t i a l v e r t e b r a t e p r e d a t o r s , not simply emetic p o t e n t i a l . A l t e r n a t e l y , the p r e s e n c e o f v o l a t i l e s e c r e t i o n s from the s c e n t g l a n d s and h i s t a m i n e - l i k e compounds i n the d o r s o - l a t e r a l s p a c e f l u i d o f (). f a s c i a t u s and I.  k_. k a l m i i c o u l d be more i m p o r t a n t than  sequestered  c a r d e n o l i d e s as a n t i - p r e d a t o r s t r a t e g i e s . The d a t a s u g g e s t t h a t t h e e f f e c t i v e n e s s o f c a r d e n o l i d e s e q u e s t r a t i o n as a c h e m i c a l d e f e n s e s t r a t e g y may v a r y o v e r the  geographical  r a n g e o f t h e s e i n s e c t s p e c i e s , and may v a r y i n the c o u r s e o f a season a p a r t i c u l a r l o c a t i o n . T h e r e f o r e , c a r d e n o l i d e s e q u e s t r a t i o n does n o t a p p e a r to be a c r u c i a l a s p e c t i n the f e e d i n g and p o p u l a t i o n e c o l o g y o f these l y g a e i d species at l e a s t in c e n t r a l C a l i f o r n i a .  at  (vi) TABLE OF CONTENTS Page T i t l e Page  i  Frontispiece  i i i  Abstract  iv  Table o f Contents  vi  L i s t of Tables  vii  List of Figures  ix  Acknowledgements  xi  I II  INTRODUCTION MATERIALS AND METHODS A. B. C. D. E.  III  1  F i e l d Study o f Milkweeds and L y g a e i d s E x t r a c t i o n o f C a r d e n o l i d e s from P l a n t M a t e r i a l C o l o r i m e t r i c Assay o f C a r d e n o l i d e s E x t r a c t i o n o f C a r d e n o l i d e s from L y g a e i d s Laboratory Rearing o f Lygaeids  6 9 11 12 15  RESULTS A. B. C. D. E.  M i l k w e e d F l o r a and L y g a e i d Fauna Cardenolide Content o f P l a n t M a t e r i a l Cardenolide Content o f F i e l d C o l l e c t e d Lygaeids Cardenolide Content o f Laboratory-Reared Lygaeids L a r v a l Growth and Development o f L y g a e i d s on  20 25 32 47 47  D i f f e r e n t Species o f Milkweed i n the Laboratory IV  Discussion  References  73 97  (vii) LIST OF TABLES Table  Page O c c u r r e n c e o f CL f a s c i a t u s and L^. k. k a l m i i on d i f f e r e n t S D e c i e s o f A s c l e p i a s i n two a r e a s o f C a l i f o r n i a , summer 1976  12  II  Gross c a r d e n o l i d e c o n t e n t o f seed o f A s c l e p i a s s p e c i e s from C a l i f o r n i a  27  III  Gross c a r d e n o l i d e c o n t e n t o f p l a n t samples o f A s c l e p i a s from C a l i f o r n i a  29  IV  Gross c a r d e n o l i d e c o n t e n t o f CJ_. f a s c i a t u s and L^. k_. k a l m i i c o l l e c t e d on A s c l e p i a s i n c e n t r a l C a l i f o r n i a i n 1976  36  V  Temporal v a r i a t i o n i n g r o s s c a r d e n o l i d e c o n t e n t o f f i e l d c o l l e c t e d CL f a s c i a t u s from c e n t r a l C a l i f o r n i a  44  VI  Gross c a r d e n o l i d e c o n t e n t o f (3. f a s c i a t u s and L. k. k a l m i i r e a r e d i n the l a b o r a t o r y a t 25°C on milkweed seed  48  VII  Gross c a r d e n o l i d e c o n t e n t o f CJ. f a s c i a t u s r e a r e d i n the the l a b o r a t o r y a t 21oC on milkweed seed  51  VIII  D u r a t i o n o f l a r v a l d e v e l o p m e n t and t e n e r a l a d u l t wet w e i g h t o f 0_. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 25°C on t h e seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and Helianthus  57  D u r a t i o n o f l a r v a l d e v e l o p m e n t and t e n e r a l a d u l t wet w e i g h t o f I. k. k a l m i i r e a r e d i n the l a b o r a t o r y a t 25°C on the seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and H e l i a n t h u s  58  I n f l u e n c e o f s e q u e s t e r e d c a r d e n o l i d e s on l a r v a l d e v e l o p m e n t o f 0_. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 21°C on the seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s  59  A d u l t body w e i g h t o f CJ. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 21°C on the seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s  65  P r o n o t a l w i d t h o f a d u l t CJ. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 21°C on the seeds o f d i f f e r e n t s p e c i e s o f Asclepias  69  I  IX  X  XI XII  Comparison o f f e m a l e t o male r a t i o s f o r t e n e r a l wet w e i g h t and c a r d e n o l i d e c o n t e n t o f 0_. f a s c i a t u s r e a r e d on d i f f e r e n t seed d i e t s C o r r e l a t i o n s between mean c a r d e n o l i d e c o n t e n t and means o f body w e i g h t , body s i z e and l a r v a l d u r a t i o n i n fj. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on t h e seeds o f d i f f e r e n t species of Asclepias  (ix) L I S T OF FIGURES Frontispiece  A d u l t O n c o p e l t u s f a s c i a t u s and Lygaeus k a l m i i k a l m i i ( c e n t e r ) on a d e h i s c e n t pod o f A s c l e p i a s f a s i c u l a r i s i n Napa County Cal i form'a  Page 111  Figure 1  S t r u c t u r e s o f some c a r d e n o l i d e s  3  2  Map o f C a l i f o r n i a showing l o c a l i t i e s where m i l k w e e d p l a n t s were examined and p l a n t m a t e r i a l collected  7  F r u i t i n g season i n n a t i v e C a l i f o r n i a n A s c l e p i a s s p e c i e s , and the p o p u l a t i o n t r e n d o f fJ. f a s c i a t u s a t one milkweed s t a n d  24  4  Gross c a r d e n o l i d e c o n t e n t o f seed o f A s c l e p i a s s p e c i e s from C a l i f o r n i a  31  5  Gross c a r d e n o l i d e c o n t e n t o f p l a n t samples o f A s c l e p i a s from C a l i f o r n i a  34  6  Gross c a r d e n o l i d e c o n t e n t o f f i e l d c o l l e c t e d CJ. f a s c i a t u s  38  7  Gross c a r d e n o l i d e c o n t e n t o f f i e l d c o l l e c t e d L. k_. kalmi i  40  8  Comparison o f g r o s s c a r d e n o l i d e c o n t e n t s o f f i e l d c o l l e c t e d 0. f a s c i a t u s and L. k. k a l m i i  42  9  Gross c a r d e n o l i d e c o n t e n t o f f i e l d c o l l e c t e d l y g a e i d s : d i s t r i b u t i o n o f c l a s s e s based on cardenolide content  46  10  R e l a t i o n s h i p between c a r d e n o l i d e c o n c e n t r a t i o n i n t h e d i e t (milkweed s e e d s ) and the c a r d e n o l i d e c o n t e n t o f a d u l t (J. f a s c i a t u s and L_. k_. k a l m i i  50  11  R e l a t i o n s h i p between c a r d e n o l i d e c o n c e n t r a t i o n i n the d i e t (milkweed s e e d s ) and the c a r d e n o l i d e c o n t e n t o f a d u l t male and f e m a l e fJ. f a s c i a t u s r e a r e d a t 21°C  53  R e l a t i o n s h i p between d u r a t i o n o f l a r v a l d e v e l o p m e n t and t e n e r a l w e t w e i g h t o f 0. f a s c i a t u s and _L. J<. k a l m i i r e a r e d i n t h e l a b o r a t o r y a t 25°C on s e e d s o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and He!ianthus Weight g a i n i n fJ. f a s c i a t u s and L k. k a l m i i during l a r v a l development, reared i n the l a b o r a t o r y a t 25°C on t h e s e e d s o f A. f a s c i c u l a r i s R e l a t i o n s h i p between g r o s s c a r d e n o l i d e c o n t e n t and d u r a t i o n o f l a r v a l d e v e l o p m e n t o f fJ. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on t h e s e e d s o f d i f f e r e n t species o f Asclepias R e l a t i o n s h i p between g r o s s c a r d e n o l i d e c o n t e n t and a d u l t body w e i g h t o f Cj. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on t h e s e e d s o f d i f f e r e n t species o f Asclepias  (xi) ACKNOWLEDGEMENTS I would l i k e t o e x p r e s s my s i n c e r e s t t h a n k s t o P r o f . G.G.E. S c u d d e r , who, as my r e s e a r c h s u p e r v i s o r , p r o v i d e d  invaluable  encouragement, c r i t i c i s m , and g u i d a n c e t h r o u g h o u t t h e c o u r s e o f t h i s study.  H i s t i m e consuming a s s i s t a n c e i n t h e p r e p a r a t i o n o f m a n u s c r i p t s  d e r i v e d from t h i s t h e s i s f o r p u b l i c a t i o n i s most a p p r e c i a t e d . Although  n o t o f f i c i a l l y r e c o g n i z e d as a c o - s u p e r v i s o r ,  Dr. S.S. D u f f e y g e n e r o u s l y  p r o v i d e d w o r k i n g s p a c e and s u p p l i e s d u r i n g  a f i v e month s t a y i n h i s l a b o r a t o r y i n t h e Department o f Entomology, U n i v e r s i t y o f C a l i f o r n i a a t Davis.  His combination  o f p a t i e n c e and  p r e s s u r e h e l p e d me t o overcome my i n e r t i a i n d e a l i n g w i t h t h e phytochemical  techniques  r e q u i r e d t o do t h i s s t u d y .  I would a l s o l i k e  to e x p r e s s my thanks t o Dr. C. Juddson and t h e Department o f Entomology f o r a l l o w i n g me t h e use o f t h e  spectrophotometer.  Ken E. Evans r e c e i v e s s p e c i a l t h a n k s f o r s e n d i n g  several  packages o f milkweed s e e d s , w h i c h e s t a b l i s h e d t h e f o u n d a t i o n f o r t h i s study.  I a l s o thank Ken f o r p e r m i s s i o n t o r e p r o d u c e h i s p h o t o g r a p h  which a p p e a r s as t h e f r o n t i s p i e c e o f t h i s t h e s i s .  I w i l l remember Ken  not o n l y f o r p r o v i d i n g p l a n t m a t e r i a l and some i n s e c t s , b u t a l s o f o r our s t i m u l a t i n g d i s c u s s i o n s i n r e g a r d t o o u r r e s p e c t i v e s t u d i e s o f lygaeids.  F i n a l l y , Ken's e n t h u s i a s m on o u r j o i n t c o l l e c t i n g t r i p s made  the f i e l d work a p l e a s u r e . I would a l s o l i k e t o thank S t e v e n P. L y n c h , who I c o n s i d e r t o be an e x p e r t on t h e A s c l e p i a s f l o r a o f w e s t e r n North A m e r i c a .  Steve  (xii) p r o v i d e d p l a n t and i n s e c t samples,  and s p e n t much o f h i s v a l u a b l e time  t o a i d me i n l o c a t i n g milkweed s t a n d s . Drs. C.N. Roeske and J.N. S e i b e r a r e thanked f o r t h e i r h e l p with t e c h n i c a l problems,  and f o r g e n e r o u s l y p r o v i d i n g me w i t h a copy  of t h e i r manuscript dealing with cardenolides i n A s c l e p i a s , before i t was p u b l i s h e d .  The i n f o r m a t i o n i n t h a t m a n u s c r i p t g r e a t l y a i d e d me i n  s h a p i n g my s t u d y .  Dr. S e i b e r a l s o p r o v i d e d samples o f p u r i f i e d  A s c l e p i a s c a r d e n o l i d e s w h i c h had been i s o l a t e d i n h i s l a b o r a t o r y . Drs. J . Myers and B.A. Bohm k i n d l y r e a d an e a r l y d r a f t o f t h i s t h e s i s , and a l s o p r o v i d e d comments and c r i t i c i s m o f a m a n u s c r i p t prepared f o r p u b l i c a t i o n . F i n a l l y , my f e l l o w s t u d e n t s i n t h e e n t o m o l o g y 'department' d e s e r v e s p e c i a l thanks f o r t h e i r c o n s t a n t encouragement and moral support.  In p a r t i c u l a r , John Spence r a i s e d many t h o u g h t  p o i n t s , and Syd Cannings  provoking  p r o v i d e d c h e e r f u l encouragement both on and  o f f the i c e . The r e s e a r c h was s u p p o r t e d by a N a t i o n a l R e s e a r c h C o u n c i l o f Canada g r a n t t o P r o f . G.G.E.  Scudder.  1 I Many a p o s e m a t i c  INTRODUCTION  i n s e c t s have been h y p o t h e s i z e d t o s e r v e as  models i n m i m i c r y r i n g s o r complexes b e c a u s e t h e y have t h e a b i l i t y t o s e q u e s t e r and s t o r e b i t t e r - t a s t i n g o r t o x i c c h e m i c l a s from t h e i r h o s t plants.  These c h e m i c a l s can a c t as d e t e r r e n t s t o v e r t e b r a t e p r e d a t o r s ,  thus p r o v i d i n g a form o f d e f e n s e which would n o t be a v a i l a b l e t o t h e i n s e c t s had t h e y f e d on a f o o d s o u r c e l a c k i n g t h e s e compounds ( R o t h s c h i l d 1972). One such c l a s s o f c h e m i c a l s i s t h e c a r d e n o l i d e s ( c a r d i a c g l y c o s i d e s and t h e i r g e n i n s ) , ( F i g u r e 1 ) , produced  by s e v e r a l f a m i l i e s  o f a n g i o s p e r m s ( S i n g h and R a s t o g i 1970, P a t t e r s o n e t aj_. 1975).  These  h e a r t p o i s o n s , w h i c h a r e h i g h l y t o x i c t o many v e r t e b r a t e s (Hoch 1961, D e t w e i l e r 1967, T h o r p and Cobbin 1967), a l s o i n d u c e e m e s i s  (Parsons  and Summers 1971, B o r i s o n and Wang 1953), and a r e v e r y b i t t e r ( R e i c h s t e i n ejt aj_. 1968, Brower and G l a z i e r 1975). Temperate and s u b t r o p i c a l milkweeds ( A s c l e p i a d a c e a e ) a r e r i c h s o u r c e s o f c a r d e n o l i d e s (Roeske e t al_. 1976), and s u p p o r t a w e l l d e f i n e d i n s e c t f a u n a ( P r i c e 1975, Weiss and D i c k e r s o n 1921). been  I t has  e s t a b l i s h e d t h a t c e r t a i n b r i g h t l y - c o l o u r e d i n s e c t s w h i c h f e e d on  milkweed a t some s t a g e i n t h e i r l i f e c y c l e a r e a b l e t o s e q u e s t e r and s t o r e c a r d e n o l i d e s d e r i v e d from t h i s group o f p l a n t s .  In some c a s e s ,  the i n s e c t s a r e c a p a b l e o f s t o r i n g l a r g e q u a n t i t i e s o f t h e s e compounds i n t h e i r b o d i e s , w h i c h may have t h e p o t e n t i a l t o s e r v e as a c h e m i c a l d e f e n s e a g a i n s t v e r t e b r a t e p r e d a t o r s (von Euw e t al_. 1967, 1971 , D u f f e y and S c u d d e r 1972, Brower 1969, Abushama and Ahmed 1976).  Well  FIGURE 1:  S t r u c t u r e s o f some c a r d e n o l i d e s . 1.  General s t r u c t u r e (R = one o r more s u g a r m o i e t i e s i n t h e g l y c o s i d e ; R = H i n the genin)  2.  Calotropin - calactin (configurational ( a f t e r Roeske e t al_. 1976)  3.  Digitoxin  isomers)  4 documented examples o f i n s e c t s which s t o r e c a r d e n o l i d e s o b t a i n e d milkweeds a r e the monarch b u t t e r f l y , Danaus p l e x i p p u s L. (Brower and an A f r i c a n g r a s s h o p p e r ,  Poekilocerus bufonius  from 1969)  ( K l u g ) (von Euw e t a l .  1967). Brower et_ al_. (1972) and Brower and M o f f i t t (1974) have shown t h a t t h e r e i s a wide v a r i a t i o n i n the c a r d e n o l i d e c o n t e n t o f f i e l d c o l l e c t e d monarch b u t t e r f l i e s .  The c a r d e n o l i d e c o n t e n t can be r e l a t e d  t o the p l a n t s p e c i e s f e d upon by the l a r v a e o f the b u t t e r f l y (Brower e t al_. 1975,  Roeske e t al_. 1976).  F u r t h e r , Brower (1969) and Roeske ejt aj_.  (1976) have d e m o n s t r a t e d t h a t the e m e t i c p o t e n t i a l o f the monarch b u t t e r f l y t o a v e r t e b r a t e p r e d a t o r , the b l u e j a y ( C y a n o c i t t a c r i s t a t a bromia O b e r h o l s e r ) , i s d e t e r m i n e d by the h o s t p l a n t s p e c i e s upon which the l a r v a e f e d .  The e x i s t e n c e o f a r e l a t i o n s h i p between h o s t p l a n t  s p e c i e s , c a r d e n o l i d e c o n t e n t and e m e t i c p o t e n t i a l o f a m i l k w e e d - f e e d i n g i n s e c t has thus been w e l l e s t a b l i s h e d . As i n the monarch b u t t e r f l y , the a b i l i t y o f the milkweed bugs O n c o p e l t u s f a s c i a t u s D a l l a s and Lygaeus k a l m i i k a l m i i St§1  to  sequester  and s t o r e c a r d e n o l i d e s from milkweed p l a n t s i n the l a b o r a t o r y has been w e l l documented ( D u f f e y and S c u d d e r 1972, IP.  1974).  Laboratory studies of  b u f o n i u s , D_. p l e x i p p u s and the l y g a e i d s fj. f a s c i a t u s and L. k_. k a l m i i  s u g g e s t t h a t none o f t h e s e i n s e c t s a r e c a p a b l e o f s y n t h e s i z i n g c a r d e n o l i d e s , and so must o b t a i n t h e s e c h e m i c a l s Euw e t a l . 1967,  Brower 1969,  from t h e i r h o s t p l a n t s  (von  D u f f e y and S c u d d e r 1972).  Both fJ. f a s c i a t u s and IL. J < . k a l m i i have a c l o s e f e e d i n g a s s o c i a t i o n w i t h members o f A s c l e p i a s L. i n t e m p e r a t e North  America  5  (Ralph 1976, S c u d d e r and D u f f e y 1972, Eggermann and Bongers 1971, Simanton and Andre 1936, Andre 1934).  Over t h i r t y o f t h e 108 d e s c r i b e d  s p e c i e s o f A s c l e p i a s i n North A m e r i c a have been shown t o c o n t a i n c a r d e n o l i d e s ( D u f f e y and S c u d d e r 1972, Roeske e t al_. 1976), and Roeske e t al_. (1976) have documented many examples o f i n t r a s p e c i f i c v a r i a t i o n . in cardenolide content.  I t has been s u g g e s t e d  t h a t such v a r i a t i o n c o u l d  g i v e r i s e t o a p a l a t a b i l i t y s p e c t r u m among l y g a e i d s f e e d i n g on t h e s e p l a n t s ( D u f f e y and S c u d d e r 1972). In t h i s t h e s i s I have i n v e s t i g a t e d t h e g r o s s c a r d e n o l i d e  content  o f fj. f a s c i a t u s and j_. k_. k a l m i i and t h e i r h o s t s ( A s c l e p i a s spp.) i n c e n t r a l C a l i f o r n i a , an a r e a w i t h a d i v e r s e milkweed f l o r a .  The p u r p o s e  o f t h i s s t u d y was 1.) t o e s t a b l i s h a r e l a t i o n s h i p between t h e c a r d e n o l i d e c o n t e n t o f t h e h o s t s p e c i e s and t h a t o f t h e l y g a e i d s f e e d i n g on i t ; 2.) t o i n v e s t i g a t e t h e e f f e c t s o f c a r d e n o l i d e s on t h e growth and  develop-  ment o f l y g a e i d s ; 3.) t o d e t e r m i n e i f c a r d e n o l i d e s p l a y a r o l e i n t h e c o l o n i z a t i o n p a t t e r n o f l y g a e i d s on a milkweed s p e c i e s complex; and 4.) t o a s s e s s t h e r o l e o f c a r d e n o l i d e s i n ' d e f e n s e s t r a t e g i e s o f l y g a e i d s .  6 II MATERIALS AND METHODS A.  F i e l d Study o f Milkweeds and  Lygaeids  T h r o u g h o u t the summer o f 1976, milkweed s t a n d s were examined i n t e n c o u n t i e s i n n o r t h and c e n t r a l C a l i f o r n i a .  Most o b s e r v a t i o n s  and  c o l l e c t i o n s were made i n two a r e a s o f the s t a t e : the n o r t h bay a r e a , r e p r e s e n t e d by Y o l o , S o l a n o , Napa and C o n t r a C o s t a c o u n t i e s , and t h e F r e s n o a r e a , r e p r e s e n t e d by F r e s n o and T u l a r e c o u n t i e s ( F i g u r e 2 ) . Many o f t h e l o c a t i o n s o f milkweed s t a n d s were p r o v i d e d by o t h e r  workers,  however, new l o c a t i o n s were found d u r i n g r o u t i n e c o l l e c t i n g t r i p s . Once a milkweed s t a n d had been l o c a t e d , s e v e r a l c h a r a c t e r i s t i c s were n o t e d , i n c l u d i n g a p p r o x i m a t e  number o f p l a n t s i n the p o p u l a t i o n ,  degree o f f l o w e r i n g o r f r u i t p r o d u c t i o n , and the p r e s e n c e o r a b s e n c e o f lygaeids and/or other i n s e c t h e r b i v o r e s . As the p o p u l a t i o n dynamics o f 0_. f a s c i a t u s on milkweed  was  c u r r e n t l y under i n v e s t i g a t i o n i n n o r t h e r n C a l i f o r n i a (K.E. Evans, u n p u b l i s h e d r e s u l t s ) , no f o r m a l a t t e m p t was made t o f o l l o w the and p o p u l a t i o n dynamics o f m i l k w e e d - f e e d i n g  lygaeids.  phenology  However, s e v e r a l  milkweed s t a n d s i n the v i c i n i t y o f D a v i s ( Y o l o Co.) were v i s i t e d on a w e e k l y b a s i s , and a t one l o c a t i o n (Woodland, Y o l o Co.) the t o t a l numbers o f (D. f a s c i a t u s a d u l t s and l a r v a e were r e c o r d e d by d i r e c t c e n s u s . was a c c o m p l i s h e d  This  by c o u n t i n g a l l the bugs w i t h i n a w e l l d e f i n e d s t a n d ,  a t a s k a i d e d by t h e c o n s p i c u o u s c o l o r a t i o n and b e h a v i o u r o f t h e s e i n s e c t s (Root and C h a p l i n 1976). The f r u i t i n g season o f d i f f e r e n t A s c l e p i a s s p e c i e s was  estimated  FIGURE 2:  Map o f C a l i f o r n i a showing l o c a l i t i e s where m i l k w e e d p l a n t s were examined and p l a n t m a t e r i a l "NORTH BAY AREA" 1 2 3 4  Napa C o u n t y Y o l o County S o l a n o County C o n t r a C o s t a County  "FRESNO 5 6  AREA"  Fresno County T u l a r e County  SF = San F r a n c i s c o  LA = Los A n g e l e s  Milkweed s p e c i e s : O  Asclepias fascicularis  A  A. e r o s a T o r r e y  e  eriocarpa  Dene.  Benth.  ffl A. c a l i f o r n i c a g r e e n e i Woodson •  A_. c o r d i f o l i a ( B e n t h . ) J e p s .  •  /\. v e s t i t a v e s t i t a Hook & A r n .  $  A. s p e c i o s a T o r r e y  s  A. s o l a n o a n a Woodson  c  A. c u r a s s a v i c a L.  collected.  I 100  1  km  Map o f C a l i f o r n i a showing l o c a l i t i e s where milkweed p l a n t s were examined and p l a n t m a t e r i a l c o l l e c t e d  9 by p e r s o n a l o b s e r v a t i o n s , f i e l d notes  ( S . P . L y n c h , p e r s . comm.) and by  e x t r a p o l a t i o n from the f l o w e r i n g periods by v a r i o u s a u t h o r s  o f A s c l e p i a s s p e c i e s as g i v e n  i n t h e t a x o n o m i c l i t e r a t u r e (Woodson 1954, Munz 1968,  Abrams 1951). B.  Extraction of Cardenolides  from P l a n t M a t e r i a l  P l a n t m a t e r i a l was u s u a l l y c o l l e c t e d a t l o c a t i o n s where i n s e c t s were t a k e n , t o p r o v i d e d i r e c t c o m p a r i s o n s between t h e c a r d e n o l i d e o f t h e p l a n t and t h o s e o f t h e i n s e c t s where p o s s i b l e .  content  To m i n i m i z e  p o s s i b l e d i f f e r e n c e s when comparing e q u i v a l e n t o r g a n s f r o m d i f f e r e n t milkweed s p e c i e s , i t was i m p o r t a n t a s i m i l a r developmental stage.  to attempt to take p l a n t m a t e r i a l o f  Thus, mature o r l o w e r l e a v e s o f s e v e r a l  i n d i v i d u a l p l a n t s w i t h i n a s t a n d were c o l l e c t e d by c u t t i n g whole l e a v e s at the p e t i o l e . bloom o n l y .  Umbels were taken i n t h e same manner, when i n f u l l  Seed samples c o n s i s t e d o f mature seeds ( t h o s e f r o m  dehiscent  pods o r t h o s e i n w h i c h t h e seeds had d a r k e n e d i n c o l o r i m m e d i a t e l y to d e h i s c e n c e )  f r o m s e v e r a l pods, u s u a l l y f r o m d i f f e r e n t p l a n t s .  prior Care  was taken n o t t o s e l e c t samples f r o m p l a n t o r g a n s on which l y g a e i d s o r o t h e r i n s e c t h e r b i v o r e s had been d i r e c t l y f e e d i n g . On r e t u r n t o t h e l a b o r a t o r y , p l a n t m a t e r i a l f o r a n a l y s i s was kept c o o l and d r y , b u t was n o t f r o z e n . suggested  Although  Roeske e t al_. (1976) have  t h a t c a r d e n o l i d e s may be s u b j e c t t o s p o n t a n e o u s breakdown, t h e  r e s u l t s o b t a i n e d i n t h i s t h e s i s s u g g e s t t h a t any l o s s e s i n c u r r e d were no g r e a t e r than t h o s e o f Roeske e t a]_. (1976) who s t o r e d a l l f i e l d l e c t e d p l a n t m a t e r i a l on d r y i c e .  col-  P l a n t samples were d r i e d f o r 12  10 hours a t 80°C i n a f o r c e d d r a f t oven p r i o r t o e x t r a c t i o n . The e x t r a c t i o n o f c a r d e n o l i d e s  from d r i e d p l a n t m a t e r i a l  based on the p r o c e d u r e s o f D u f f e y and S c u d d e r ( 1 9 7 2 ) .  was  To maximize the  extraction e f f i c i e n c y for quantitative analysis, plant material, e s p e c i a l l y d r y s e e d s , r e q u i r e d m e c h a n i c a l breakdown t o i n c r e a s e e x p o s u r e o f the c a r d e n o l i d e - c o n t a i n i n g  the  t i s s u e s t o the e x t r a c t i n g  solvents. Milkweed seeds were ground to a f i n e powder w i t h a commercial g r i n d e r ( C r e s c e n t Dental Mfg. screw-cap t e s t t u b e .  C o . ) , and 0.2 grams p l a c e d i n a 12 ml  The seed m a t e r i a l was e x t r a c t e d w i t h 4 ml  of  p e t r o l e u m e t h e r , the t e s t tube b e i n g shaken v i g o r o u s l y a f t e r a d d i t i o n o f the s o l v e n t , then a l l o w e d  to s e t t l e f o r 6 hours.  This  initial  e x t r a c t i o n removed l a r g e q u a n t i t i e s o f l i p i d s f r o m the seeds which would o t h e r w i s e  have i n t e r f e r e d w i t h the s p e c t r o a s s a y .  c a r b o n e x t r a c t , removed by p i p e t t e , was  This hydro-  d i s c a r d e d b e c a u s e i t was  to l a c k c a r d e n o l i d e s when t e s t e d by both s p e c t r o p h o t o m e t r i c  found  and t h i n -  l a y e r c h r o m a t o g r a p h i c means. The seed r e s i d u e was methanol (10:1 12 h o u r s .  t h e n e x t r a c t e d w i t h 2 ml o f hot  by v o l u m e ) , shaken v i g o r o u s l y , and a l l o w e d  The c h l o r o f o r m  phase was  to stand f o r  then d e c a n t e d , and the r e s i d u e r e -  e x t r a c t e d w i t h 3 ml o f 95 per c e n t aqueous e t h a n o l ethanol  chloroform-  e x t r a c t was added to the c h l o r o f o r m  f o r 12 h o u r s .  e x t r a c t , the  The  pooled  e x t r a c t s e v a p o r a t e d to d r y n e s s a t room t e m p e r a t u r e and r e d i s s o l v e d i n 4 ml o f 95 per c e n t e t h a n o l .  O n e - h a l f o r 1.0 ml a l i q u o t s ( d e p e n d i n g  on the i n t e n s i t y o f a p r e l i m i n a r y c o l o u r r e a c t i o n ) o f p o o l e d  extract  11 were used f o r the s p e c t r o a s s a y o f c a r d e n o l i d e s . D r i e d milkweed l e a v e s and umbels c o n t a i n e d much l e s s l i p i d m a t e r i a l ; d i r e c t e x t r a c t i o n with ethanol provided s u f f i c i e n t l y samples.  The p e t r o l e u m e t h e r e x t r a c t i o n was t h e r e f o r e  pure  unnecessary.  D r i e d milkweed l e a v e s o r umbels were ground t o a f i n e powder i n a commercial  grinder.  Two-tenths o f a gram e x t r a c t e d once w i t h  4 ml o f hot 95 p e r c e n t e t h a n o l were a l l o w e d t o s t a n d 12 hours  before  0.5 o f 1 ml a l i q u o t s were taken d i r e c t l y f o r c a r d e n o l i d e e s t i m a t i o n . O x i d a t i v e d e g r a d a t i o n o f c a r d e n o l i d e s was k e p t t o a minimum by a n a l y z i n g the f i n a l e x t r a c t s w i t h i n 24  hours.  For l e a f and umbel samples, a s i n g l e e s t i m a t i o n o f each sample S i n c e the l y g a e i d bugs fJ. f a s c i a t u s and I.  was made.  k_. k a l m i i a r e  c l o s e l y a s s o c i a t e d w i t h t h e seeds o f milkweed p l a n t s , i t was  important  to o b t a i n c o n c i s e e s t i m a t i o n s o f the c a r d e n o l i d e c o n t e n t o f t h e s e organs. C.  T h e r e f o r e , up t o f i v e e x t r a c t i o n s o f each seed sample was made.  C o l o r i m e t r i c Assay of Cardenolides The c o l o r i m e t r i c a s s a y used was t h a t o f Brower e t al_. (1972) as  m o d i f i e d by Brower and M o f f i t t (1974) and Brower e t al_. (1975).  This  a s s a y , f i r s t d e v e l o p e d by R a b i t s c h and Tambor (1969) i s based on the b l u e c o l o u r formed when 2 , 4 , 2 ' , 4 ' - t e t r a n i t r o d i p h y e n y l  (TNDP)  i s combined w i t h the c a r d e n o l i d e i n the p r e s e n c e o f a base (-0H solution).  The c o l o u r i s formed by t h e r e a c t i o n o f the r e a g e n t s  ions i n with  the u n s a t u r a t e d l a c t o n e ( b u t e n o l i d e ) r i n g a t the C-17 p o s i t i o n on the cardenolide genin. C a r d e n o l i d e e s t i m a t i o n s were based on a s t a n d a r d o f d i g i t o x i n  12 ( N u t r i t i o n a l Biochemical  Corp., Cleveland)  (Figure 1); a l l determinations  a r e e x p r e s s e d as e q u i v a l e n t s o f d i g i t o x i n . Using the procedure  o u t l i n e d by Brower e t a]_. ( 1 9 7 2 ) , d i g i t o x i n  was shown t o obey Beer's Law w i t h i n a range o f 10 t o 250 m i c r o g r a m s i n 4 ml.  I f t h e a b s o r b a n c e o f a sample i n d i c a t e d a q u a n t i t y i n e x c e s s o f  250 m i c r o g r a m s , t h e sample s o l u t i o n was d i l u t e d t o p r o v i d e a q u a n t i t y w i t h i n t h i s range. R e a d i n g s were taken on a Beckman Model B s p e c t r o p h o t o m e t e r  using  Beckman q u a r t z sample c u v e t t e s .  The maximum c o l o u r i n t e n s i t y was  r e a c h e d a f t e r 40 t o 45 m i n u t e s .  A t t h i s p o i n t t h e a b s o r b a n c e was  r e c o r d e d , and t h e c o n c e n t r a t i o n c a l c u l a t e d from t h e l i n e a r r e l a t i o n s h i p e s t a b l i s h e d between c o n c e n t r a t i o n and a b s o r b a n c e u s i n g t h e d i g i t o x i n standard. The c a r d e n o l i d e e s t i m a t i o n s r e p o r t e d here a r e d i r e c t l y c o m p a r a b l e to t h o s e o f Roeske e t aj_. (1976).  The p r o c e d u r e s  were c l o s e l y f o l l o w e d t o a l l o w such c o m p a r i s o n s ,  o f Roeske e t aj_. (1976) as t h i s l a t t e r  study  p r o v i d e s t h e o n l y q u a n t i t a t i v e d a t a on t h e c a r d e n o l i d e c o n t e n t o f N o r t h A m e r i c a n m i l k w e e d s o f t h e genus A s c l e p i a s .  The d a t a o b t a i n e d i n t h e  p r e s e n t r e s e a r c h a r e i n c l o s e agreement w i t h t h a t o f Roeske e_t al_. (1976) f o r p l a n t o r g a n s and s p e c i e s w h i c h a r e common t o both s t u d i e s . D.  E x t r a c t i o n o f C a r d e n o l i d e s from A d u l t 0_. f a s c i a t u s and I.  Lygaeids  k. k a l m i i were c o l l e c t e d on milkweed  p l a n t s ( A s c l e p i a s s p p . ) i n c e n t r a l C a l i f o r n i a between A p r i l and September, 1976. F i e l d - c a u g h t l y g a e i d s were m a i n t a i n e d  in controlled  environmental  13 c a b i n e t s a t 27°C on a 13.5:10.5 LD l i g h t r e g i m e , and p r o v i d e d d i s t i l l e d w a t e r and husked s u n f l o w e r s e e d s .  F i e l d - c a u g h t l y g a e i d s were  a s s a y e d f o r c a r d e n o l i d e s w i t h i n two weeks o f t h e i r c a p t u r e . experiment  with  A control  i n d i c a t e d t h a t t h e r e was no s i g n i f i c a n t l o s s o f c a r d e n o l i d e s  i n l y g a e i d s f e e d i n g on s u n f l o w e r seeds (which l a c k c a r d e n o l i d e s ) f o r t h i s l e n g t h o f time a f t e r h a v i n g p r e v i o u s l y f e d on a c a r d e h o l i d e - c o n t a i n i n g diet.  M a i n t a i n i n g f i e l d - c a u g h t i n s e c t s i n the l a b o r a t o r y on  sunflower  seeds p r i o r t o the c a r d e n o l i d e a s s a y had two a d v a n t a g e s : f i r s t , t h i s p e r i o d a l l o w e d the i n s e c t s t o c l e a r the g u t , so t h a t c a r d e n o l i d e e s t i m a t i o n s would n o t be i n f l u e n c e d by gut c o n t e n t s , and  second,  r e p r o d u c t i v e a d u l t s c o u l d p r o v i d e eggs f o r l a b o r a t o r y r e a r i n g o f l y g a e i d s on milkweed  seeds.  Only a d u l t i n s e c t s were used f o r t h e c a r d e n o l i d e a s s a y . and S c u d d e r (1974) d e m o n s t r a t e d t h a t c a r d e n o l i d e s a r e throughout  Duffey  accumulated  the j u v e n i l e l i f e o f the l y g a e i d fj. f a s c i a t u s , w i t h o v e r h a l f  o f the a d u l t c a r d e n o l i d e complement s e q u e s t e r e d  by the f i f t h and  final  l a r v a l i n s t a r . W h i l e some q u a n t i t i e s o f c a r d e n o l i d e s a r e s e q u e s t e r e d  in  the a d u l t s t a g e , the r a t e o f u p t a k e i s l e s s than t h a t i n t h e l a t e i n s t a r larvae.  The c o l l e c t i o n o f o n l y a d u l t i n s e c t s p r o v i d e s an e s t i m a t e  of  the u l t i m a t e q u a n t i t y o f c a r d e n o l i d e s s t o r e d by t h e s e milkweed f e e d i n g i n s e c t s under n a t u r a l c o n d i t i o n s , and a l l o w e d d i r e c t c o m p a r i s o n s between d i f f e r e n t populations of lygaeids. To i n v e s t i g a t e the c a r d e n o l i d e c o n t e n t o f l y g a e i d s r e a r e d e x c l u s i v e l y on milkweed s e e d s , f i r s t i n s t a r l a r v a e o f fj. f a s c i a t u s and L. k. k a l m i i were r e a r e d t o the a d u l t s t a g e o f the seeds o f d i f f e r e n t  14 milkweed s p e c i e s . bugs were d e t e r m i n e d  The q u a n t i t i e s o f c a r d e n o l i d e found i n t h e s e a d u l t and p r o v i d e an e s t i m a t e o f the u l t i m a t e amount t h a t  t h e s e i n s e c t s m i g h t s e q u e s t e r i n the f i e l d , had t h e y had an u n l i m i t e d s u p p l y o f mature seeds d u r i n g t h e i r l a r v a l l i f e .  F u r t h e r , s i n c e the  milkweed seeds used i n t h i s s t u d y were s u b j e c t e d t o q u a n t i t a t i v e c a r d e n o l i d e a n a l y s i s , i t was p o s s i b l e t o examine the r e l a t i o n s h i p between the c a r d e n o l i d e c o n t e n t o f the seed d i e t and the c o n t e n t o f bugs f e e d i n g on such seeds.  The c o n d i t i o n s under which the l y g a e i d s were  r e a r e d a r e d e s c r i b e d i n d e t a i l i n the f o l l o w i n g s e c t i o n . Ideally, physiological e f f e c t s of cardenolide sequestration s h o u l d be s t u d i e d by i n c l u d i n g d i f f e r i n g known c o n c e n t r a t i o n s o f s i n g l e i s o l a t e d c a r d e n o l i d e s i n a s t a n d a r d i z e d , c h e m i c a l l y i n e r t d i e t which c o u l d be o f f e r e d to the i n s e c t s .  T h i s s t u d y has been much s i m p l e r i n a  t e c h n i c a l s e n s e , b e c a u s e the d i e t ( i . e . milkweed s e e d s ) c o n t a i n s c a r d e n o l i d e s i n a p r e - p a c k a g e d f o r m , and the i n s e c t s w i l l r e a d i l y f e e d on the seeds.  F u r t h e r , the c a r d e n o l i d e s i n g e s t e d by the bugs from  milkweed seeds a r e i n f a c t t h o s e compounds, o c c u r r i n g i n the a c t u a l c o n c e n t r a t i o n s and r e l a t i v e f r e q u e n c i e s t h a t the i n s e c t s would i n the n a t u r a l e n v i r o n m e n t .  encounter  In l i g h t o f the f a c t t h a t the d i e t l e d to  o v e r a t e n - f o l d d i f f e r e n c e i n c a r d e n o l i d e c o n t e n t o f the r e s u l t a n t a d u l t i n s e c t s , i t i s f e l t t h a t the r e s u l t s a r e v a l i d e v i d e n c e t h a t CJ. f a s c i a t u s a r e h i g h l y t o l e r a n t o f the compounds as t h e y a r e  encountered  i n the f i e l d . The method o f S c u d d e r & D u f f e y (1972) was used f o r e x t r a c t i n g c a r d e n o l i d e s from i n s e c t s .  I n s e c t s , e i t h e r l i v e o r d r i e d , were p l a c e d  15 i n d i v i d u a l l y i n 2 ml o f c h l o r o f o r m - m e t h a n o l  (2:1 by v o l u m e ) , a l l o w e d t o  s t a n d f o r 24 h r , then removed from t h i s s o l v e n t and p l a c e d i n an a d d i t i o n a l 2 ml o f c h l o r o f o r m - m e t h a n o l  (2:1).  A f t e r a f u r t h e r 24 h r ,  t h e two e x t r a c t s were p o o l e d , e v a p o r a t e d t o d r y n e s s , and d i s s o l v e d i n 1 ml o f 95 p e r c e n t e t h a n o l .  One h a l f o f t h i s f i n a l s o l u t i o n was  used  f o r the s p e c t r o a s s a y o f g r o s s c a r d e n o l i d e c o n t e n t i n each i n s e c t . More than 95 p e r c e n t o f an i n s e c t ' s c a r d e n o l i d e complement i s e x t r a c t e d u s i n g t h i s p r o c e d u r e s i n c e r e p e a t e d e x t r a c t i o n s f a i l e d t o produce more than 5 p e r c e n t o f the t o t a l q u a n t i t y e s t i m a t e d .  The s p e c t r o a s s a y  was i d e n t i c a l t o t h a t used f o r e s t i m a t i n g g r o s s c a r d e n o l i d e c o n t e n t o f plant  samples. U n l i k e other s t u d i e s of the c a r d e n o l i d e content of i n s e c t s , i n  which the q u a n t i t i e s r e p o r t e d have been based on a f i x e d w e i g h t o f t i s s u e (Brower e t a^. 1975, R o t h s c h i l d e t al_. 1975) o r many i n s e c t s p o o l e d (von Euw e t al_. 1967), c a r d e n o l i d e d e t e r m i n a t i o n s i n t h i s s t u d y were based on whole i n d i v i d u a l i n s e c t s , i r r e s p e c t i v e o f t h e i r body weight.  Two r e a s o n s f o r e s t i m a t i n g t h e c a r d e n o l i d e c o n t e n t o f whole  i n s e c t s were because i t a l l o w e d an e x a m i n a t i o n o f the c o m p o s i t i o n o f l o c a l i z e d i n s e c t p o p u l a t i o n s which i n n a t u r e c o n s i s t o f i n d i v i d u a l s o f d i f f e r e n t w e i g h t s and body s i z e s , and o f more i m p o r t a n c e , the i n d i v i d u a l i n s e c t i s the u n i t t h a t must be sampled E.  by a p r e d a t o r .  Laboratory Rearing of Lygaeids fj. f a s c i a t u s and L_. k_. k a l m i i were r e a r e d i n the l a b o r a t o r y on  the seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s which t h e y m i g h t  encounter  i n the f i e l d and seeds o f H e l i a n t h u s annus (which l a c k c a r d e n o l i d e s ) .  16 T h i s r e a r i n g aimed t o 1.  a s s e s s , i n a g r o s s s e n s e , the n u t r i t i o n a l v a l u e o f each  m i l k w e e d s p e c i e s t o the i n s e c t s .  T h e s e d a t a a r e r e l a t e d to the p a t t e r n  o f c o l o n i z a t i o n o f l y g a e i d s on d i f f e r e n t milkweed s p e c i e s i n the f i e l d ; 2. d e t e r m i n e  i f d i f f e r i n g concentrations of cardenolides  i n the d i e t (seeds) a f f e c t growth and d e v e l o p m e n t o f l a r v a e ; 3.  examine the r e l a t i o n s h i p between c a r d e n o l i d e c o n t e n t i n the  d i e t ( s e e d s ) and the c a r d e n o l i d e c o n t e n t o f i n s e c t s r e a r e d on s p e c i f i e d d i e t s ( i . e . d i f f e r e n t milkweed s p e c i e s ) . Separate r e a r i n g experiments  were c a r r i e d o u t i n 1975 and  1976.  In the autumn o f 1975, CJ. f a s c i a t u s and _L. k_. k a l m i i were r e a r e d i n an environmental  c a b i n e t s e t a t 25±1°C, 6 0 ± 1 0 % RH, and c o n t i n u o u s  light.  Eggs o f CJ. f a s c i a t u s were o b t a i n e d from a l a b o r a t o r y c u l t u r e which had been e s t a b l i s h e d a t l e a s t t h r e e y e a r s e a r l i e r .  Eggs o f j.. k_. k a l m i i  were o b t a i n e d from a c u l t u r e i n i t i a t e d i n t h e summer o f 1975 from a d u l t s c o l l e c t e d a t Manning Park and t h e lower Okanagan V a l l e y , B.C. were r e a r e d i n c l e a r p l a s t i c p e t r i d i s h e s , a p p r o x i m a t e l y diameter,  Larvae  9 cm i n  2 cm i n h e i g h t , and e n c l o s e d by a l i d w i t h a s c r e e n e d  3 cm i n d i a m e t e r .  vent,  An e x c e s s o f m i l k w e e d seeds o f one s p e c i e s p e r  c o n t a i n e r was added e v e r y t h r e e days d u r i n g l a r v a l d e v e l o p m e n t ; d e c h l o r i n a t e d w a t e r was c o n s t a n t l y a v a i l a b l e from a s e c t i o n o f c o t t o n d e n t a l r o l l w h i c h was m o i s t e n e d  daily.  C o l l e c t i o n d a t e s and l o c a l i t i e s o f the A s c l e p i a s seeds u t i l i z e d a r e as f o l l o w s .  C o l l e c t e d i n September 1975: A.  fascicularis,  Napa Co. C a l i f . , A. e r i o c a r p a , > T u l a r e Co., C a l i f . , A. s p e c i o s a , 1  17 Cache C r e e k , B.C.  Seeds o f A. e r o s a were c o l l e c t e d i n September 1974  i n T u l a r e Co. C a l i f o r n i a , and t h o s e o f /\. c o r d i f o l i a c o l l e c t e d i n J u l y 1974 i n P l a c e r Co., C a l i f o r n i a .  A l l seeds were d r i e d a t room tem-  p e r a t u r e and s t o r e d i n p l a s t i c bags.  S h e l l e d s u n f l o w e r seeds  ( H e ! i a n t h u s ) were p u r c h a s e d l o c a l l y . W i t h i n 12 h r o f h a t c h i n g t e n f i r s t i n s t a r l a r v a e o f one  species  were p l a c e d t o g e t h e r i n one c o n t a i n e r ; two r e p l i c a t e s were e s t a b l i s h e d f o r each d i f f e r e n t seed d i e t .  The i n s e c t s were c h e c k e d e v e r y 12 h r f o r  i n d i v i d u a l s which had m o u l t e d t o t h e n e x t l a r v a l i n s t a r .  Those which  had m o u l t e d were weighed, and t h e wet w e i g h t and t i m e o f m o u l t i n g n o t e d . The i n s e c t s were then p l a c e d back i n t o t h e i r o r i g i n a l c o n t a i n e r . The d e n s i t y o f i n s e c t s was k e p t c o n s t a n t . In t h e '.autumn o f 1976, 0. f a s c i a t u s were r e a r e d i n an e n v i r o n mental c a b i n e t s e t a t 2 1 ° C ± 1 , 6 0 ± 1 0 % RH and a 16:8 LD l i g h t r e g i m e . T h i s t e m p e r a t u r e r e p r e s e n t s t h e mean ambient t e m p e r a t u r e a t D a v i s , C a l i f o r n i a between t h e months o f A p r i l and September.  Eggs o f fJ.  f a s c i a t u s were o b t a i n e d from t h e o f f s p r i n g o f a d u l t s which were c o l l e c t e d i n Napa County, C a l i f o r n i a i n A u g u s t 1976. In t h i s e x p e r i m e n t , l a r v a e were r e a r e d i n s t y r o f o a m c o n t a i n e r s a p p r o x i m a t e l y 9 cm i n d i a m e t e r , 6 cm i n h e i g h t , and e n c l o s e d by a c l e a r p l a s t i c l i d w i t h a s c r e e n e d v e n t , 3 cm i n d i a m e t e r . An e x c e s s o f milkweed seeds o f one s p e c i e s p e r c o n t a i n e r was added e v e r y f i v e days d u r i n g l a r v a l d e v e l o p m e n t , and d i s t i l l e d w a t e r was c o n s t a n t l y a v a i l a b l e from a p l a s t i c c u l t u r e tube p l u g g e d w i t h c o t t o n , i n s e r t e d through the side of the r e a r i n g c o n t a i n e r .  18 M i l k w e e d seeds used i n t h i s e x p e r i m e n t were c o l l e c t e d between June and September, 1976 a t t h e f o l l o w i n g l o c a l i t i e s i n C a l i f o r n i a : A. f a s c i c u l a r i s , Woodland, Y o l o Co.; A. e r o s a , n r . Ducor, T u l a r e A. s p e c i o s a , D a v i s , Y o l o Co.; A_. c o r d i f o l i a , n r . Moskowite  Co.:  Corner,  Napa Co.; A. e r i o c a r p a , nr. Trimmer, Fresno Co.; A. c a l i f o r n i c a g r e e n e i , Mt. D i a b l o , C o n t r a C o s t a Co.; A. y_. v e s t i t a , n r . Humphrey's S t a t i o n , Fresno Co.; A. c u r a s s a v i c a , D a v i s , Y o l o Co. ( c u l t i v a t e d ) . As i n the p r e v i o u s e x p e r i m e n t , w i t h i n 12 hours o f h a t c h i n g  ten  f i r s t i n s t a r l a r v a e were p l a c e d i n one c o n t a i n e r , w i t h two r e p l i c a t e s e s t a b l i s h e d f o r e a c h seed d i e t .  The l a r v a e were c h e c k e d e v e r y 12 hours  f o r i n d i v i d u a l s w h i c h had m o u l t e d from f i f t h i n s t a r s i n t o a d u l t s . t e n e r a l a d u l t s were weighed l i v e , t h e i r h e m e l y t r a then r e p l a c e d i n t h e i r o r i g i n a l c o n t a i n e r s .  These  marked w i t h i n k , and  T e n e r a l a d u l t s were p e r -  m i t t e d to f e e d on t h e i r r e s p e c t i v e d i e t s f o r an a d d i t i o n a l 10-14  days.  They were then f r o z e n , d r i e d f o r 24 hours a t 60°C i n a f o r c e d d r a f t oven, and k e p t o v e r d e s s i c a n t f o r a f u r t h e r 24 hours b e f o r e  being  reweighed. I t was f e l t t h a t o b t a i n i n g d r y w e i g h t s o f the a d u l t i n s e c t s m i g h t p r o v i d e more a c c u r a t e d a t a than wet w e i g h t s .  F u r t h e r , the a d d i t i o n a l  f e e d i n g t i m e i n the a d u l t s t a g e a l l o w e d the i n s e c t s to s t a b i l i z e t h e i r body w e i g h t s ,  and p e r h a p s t h e i r c a r d e n o l i d e c o n t e n t s as w e l l .  A l l w e i g h t s were measured on a M e t t l e r M i c r o G r a m - A t i c electrobalance.  The p r o n o t a l w i d t h , an i n d e x o f a d u l t body s i z e , was  measured u s i n g a d i s s e c t i n g m i c r o s c o p e f i t t e d w i t h an e y e p i e c e g r a t i c u l e . A d d i t i o n a l 0. f a s c i a t u s and L. k. k a l m i i , used i n c a r d e n o l i d e  19 d e t e r m i n a t i o n s , were r e a r e d from egg t o a d u l t i n an e n v i r o n m e n t a l c a b i n e t s e t a t 27°C,  70% RH and a 13.5:10.5 LD l i g h t regime ( t h i s  c a b i n e t was s h a r e d w i t h o t h e r r e s e a r c h e r s who d e t e r m i n e d  the rearing  conditions). In t h e f i g u r e s , e r r o r i s e x p r e s s e d as ±2 s t a n d a r d e r r o r s o f the mean ( r o u g h l y e q u i v a l e n t t o 95 p e r c e n t c o n f i d e n c e l i m i t s ) .  Where  e r r o r bars do n o t o v e r l a p , means a r e c o n s i d e r e d t o be s i g n i f i c a n t l y different.  20 I I I RESULTS A.  Milkweed F l o r a and L y g a e i d Fauna Nine s p e c i e s o f A s c l e p i a s were e n c o u n t e r e d  d u r i n g the summer o f 1976 a r e a s d i s t u r b e d by man, lying fallow.  (Figure 2).  in central California  Most o f the s p e c i e s o c c u r r e d i n  v i z . r o a d s i d e s , r a i l w a y c u t s , and i n f i e l d s  Most s p e c i e s a r e members o f s e m i - a r i d c h a p a r r e l p l a n t  c o m m u n i t i e s (Munz 1968); e x c e p t i o n s were the montane A. c o r d i f o l i a , which o c c u r r e d i n y e l l o w  Dine  f o r e s t c o m m u n i t i e s , and t h e r e l a t i v e l y  r a r e A. s o l a n o a n a , which was seen on s o u t h - f a c i n g s e r p e n t i n e s l o p e s only. The most common s p e c i e s , w i t h t h e w i d e s t r a n g e o f h a b i t a t s , was A. f a s c i c u l a r i s .  A. e r o s a which i s an economic p e s t i n C a l i f o r n i a ,  o c c a s i o n a l l y o c c u r r e d i n l a r g e p o p u l a t i o n s on c u l t i v a t e d l a n d . D i f f e r e n t s p e c i e s o f A s c l e p i a s were o c c a s i o n a l l y found growing i n sympatry.  On a r a n c h i n F r e n s o c o u n t y , A. y_. v e s t i t a , A. c o r d i f o l i a ,  A. e r i o c a r p a and A. f a s c i c u l a r i s were found w i t h i n a 200 meter r a d i u s . The l y g a e i d fJ. f a s c i a t u s which immigrates  into central  C a l i f o r n i a e v e r y summer from o v e r w i n t e r i n g s i t e s i n the s o u t h  (probably  M e x i c o ) , showed two c o n t r a s t i n g c o l o n i z a t i o n p a t t e r n s on s p e c i e s o f A s c l e p i a s i n the two b a s i c s t u d y a r e a s ( T a b l e I ) . a r e a , CJ. f a s c i a t u s was o n l y found on  In the n o r t h  bay  A. f a s c i c u l a r i s - even i n l o c a t i o n s  where o t h e r b r o a d ! e a f milkweeds such as A. s p e c i o s a and A. e r i o c a r p a were growing s y m p a t r i c a l l y .  In c o n t r a s t , 0. f a s c i a t u s c o l o n i z e d a l l o f  t h e milkweed s p e c i e s i n t h e F r e s n o a r e a , w i t h t h e n o t a b l e e x c e p t i o n o f A. c o r d i f o l i a .  21  TABLE I:  O c c u r r e n c e o f 0_. f a s c i a t u s and L_. JL k a l m i i on d i f f e r e n t s p e c i e s o f A s c l e p i a s i n two a r e a s o f C a l i f o r n i a , summer  Milkweed s p e c i e s  North Bay Area ( Y o l o , Capa, S o l a n o , Contra Costa c o u n t i e s )  J  1976.  Fresno Area (Fresno, Tulare counties)  L  L  A. c o r d i f o l i a  L  L  A. e r i o c a r p a  L  0  L  A. c a l i f o r n i c a g r e e n e i  L  0  L  A. e r o s a  0  L  A. v e s t i t a v e s t i t a  0  L  A. f a s c i c u l a r i s  A. s p e c i o s a  10=0.  f a s c i a t u s , L = L. k. k a l m i i  'L  22  D u r i n g 1976 t e n s t a n d s o f A. c o r d i f o l i a were examined i n f i v e c o u n t i e s , y e t CJ. f a s c i a t u s was never o b s e r v e d on t h i s p l a n t .  Even where  A. c o r d i f o l i a o c c u r r e d i n sympatry w i t h A. v e s t i t a and A. e r i o c a r p a and where both o f t h e s e l a t t e r s p e c i e s s u p p o r t e d CJ. f a s c i a t u s , none o f t h e i n s e c t s were found on t h e A. c o r d i f o l i a . The t i m i n g and d u r a t i o n o f f l o w e r i n g p e r i o d s v a r i e s among m i l k weed s p e c i e s .  T h i s l e a d s t o temporal  season o f t h e r e s p e c t i v e s p e c i e s .  d i f f e r e n c e s i n the f r u i t i n g  A l s o , f l o w e r i n g and f r u i t i n g  v a r i e s w i t h e l e v a t i o n by as much as s i x weeks.  season  A. c o r d i f o l i a and A.  c a l i f o r n i c a g r e e n e i had e a r l y , h i g h l y s y n c h r o n i z e d f l o w e r i n g and f r u i t i n g s e a s o n s , c o m p l e t i n g t h e r e p r o d u c t i v e c y c l e by r e l e a s i n g t h e comose seeds i n June and J u l y ( F i g u r e 3 ) . A. y_. v e s t i t a a l s o had a r a t h e r s h o r t f r u i t i n g season d u r i n g mid summer, c o m p l e t i n g i t s c y c l e i n A u g u s t .  In  c o n t r a s t , A. f a s c i c u l a r i s , A. e r i o c a r p a , A. e r o s a and A_. s p e c i o s a d i d not have s y n c h r o n i z e d f l o w e r i n g and f r u i t i n g p e r i o d s which l e d t o an extended  f r u i t i n g season.  A. f a s c i c u l a r i s and A. e r o s a had t h e l o n g e s t  f l o w e r i n g p e r i o d s , b e a r i n g both f l o w e r s and mature seed pods on t h e same p l a n t as l a t e as mid-September. A t t h e Woodland A_. f a s c i c u l a r i s s i t e , (3. f a s c i a t u s d i d n o t appear u n t i l m i d - J u n e , and remained  i n low numbers u n t i l t h e second  g e n e r a t i o n r e a c h e d i t s peak i n e a r l y September ( F i g u r e 3 ) .  Examinations  o f p o p u l a t i o n s o f CJ. f a s c i a t u s a t o t h e r l o c a l i t i e s on A_. f a s c i c u l a r i s s t r o n g l y s u g g e s t e d t h a t t h i s was t h e p a t t e r n o f p o p u l a t i o n growth i n most o f n o r t h c e n t r a l C a l i f o r n i a  i n 1976 ( K . E . Evans, u n p u b l .  results).  In 1976 t h e p o p u l a t i o n s o f CJ_. f a s c i a t u s d i d n o t r e a c h h i g h d e n s i t i e s i n  FIGURE 3:  F r u i t i n g season i n n a t i v e C a l i f o r n i a n A s c l e p i a s s p e c i e s and the p o p u l a t i o n t r e n d o f fj. f a s c i a t u s a t one milkweed stand.  Stage of f r u i t development: immature dehi s c e n t Milkweed s p e c i e s : V = Asclepias vestita vestita CA = A_. c a l i f o r n i c a g r e e n e i SP = A_. s p e c i o s a EC = A. e r i o c a r p a CO = A. c o r d i f o l i a ES = A_. e r o s a F = A. f a s c i c u l a r i s As f r u i t i n g season can v a r y w i t h e l e v a t i o n , s e a s o n s d e p i c t e d here a r e f o r p l a n t s g r o w i n g a t e l e v a t i o n s below 500 m e t e r s above sea level. Cj. f a s c i a t u s p o p u l a t i o n d a t a from a weekly c e n s u s o f a s t a n d o f A_. f a s c i c u l a r i s i n Woodland, Y o l o County.  Population  t r e n d s o f fj. f a s c i a t u s on A. f a s c i c u l a r i s a t s e v e r a l l o c a l i t i e s i n Napa c o u n t y a r e v e r y s i m i l a r .  FIGURE 3 Species  25 t h i s a r e a u n t i l A. c o r d i f o l i a and A. c a l i f o r m " c a g r e e n e i had  dispensed  most, i f n o t a l l o f t h e i r seed c r o p ( F i g u r e 3 ) . B.  Cardenolide Content of Plant M a t e r i a l The c a r d e n o l i d e c o n t e n t o f p l a n t samples o f A s c l e p i a s from  C a l i f o r n i a v a r i e s o v e r a wide range.  (Tables I I , I I I ) . Within  species  v a r i a t i o n i n c a r d e n o l i d e c o n t e n t o f milkweed seeds was a b o u t equal between s p e c i e s v a r i a t i o n .  Most o f t h e seed samples a n a l y s e d  to  had  c a r d e n o l i d e c o n t e n t s between 1.2 and 4.3 mg per gram o f d r y t i s s u e . However, t h r e e s p e c i e s o f A s c l e p i a s had c a r d e n o l i d e c o n t e n t s w h i c h o c c u r n o t a b l y o u t s i d e o f t h i s range: 0.25  T h e s e a r e A_. f a s c i c u l a r i s  (from  to 0.44 mg per gram) A. v_. v e s t i t a (7.1 mg per gram f o r the s i n g l e  sample a n a l y s e d ) a n d  A_. c u r a s s a v i c a (7.9 mg per gram, s i n g l e  estimation)  Figure 4). Both temporal  and g e o g r a p h i c a l  i n t r a s p e c i f i c d i f f e r e n c e s i n the  c a r d e n o l i d e c o n t e n t o f t h e milkweed seed o c c u r ( T a b l e I I ) .  For example,  the c a r d e n o l i d e c o n t e n t o f seeds o f A. e r o s a , c o l l e c t e d i n the same a r e a , but i n two d i f f e r e n t y e a r s v a r i e d c o n s i d e r a b l y , as d i d the c o n t e n t o f seeds o f A. c a l i f o r m ' c a g r e e n e i , c o l l e c t e d i n t h e same season from geographically isolated populations.  two  However, the two samples o f A.  f a s c i c u l a r i s c o l l e c t e d i n 1975 from d i f f e r e n t c o u n t i e s had  similar  c a r d e n o l i d e c o n t e n t s , whereas the 1976 sample from a d j a c e n t Y o l o  county  c o n t a i n e d a somewhat lower amount o f c a r d e n o l i d e than the f o r m e r  two  (Table I I ) . V a r i a t i o n a l s o e x i s t e d i n the c a r d e n o l i d e content of d i f f e r e n t o r g a n s o f a s i n g l e h o s t pi a n t s p e c i e s ( T a b l e I I I ) .  No  standard  TABLE I I : G r o s s C a r d e n o l i d e c o n t e n t o f seed o f A s c l e p i a s s p e c i e s from C a l i f o r n i a .  ^ c o u n t y i n C a l i f o r n i a and y e a r o f c o l l e c t i o n o f milkweed 2 mg e q u i v a l e n t s o f d i g i t o x i n p e r gram o f d r i e d seed  seeds  3  f o r each c o l l e c t i o n l o c a l i t y , seeds from s e v e r a l p l a n t s were p o o l e d and 1.0 g o f seed ground to a powder; sample  size  N = number o f 0.2 g a l i q u o t s t a k e n from t h e 1 g sample c u l i t v a t e d p l a n t s ; t h i s species i s not n a t i v e to C a l i f o r n i a 5  Cache C r e e k , B r i t i s h C o l u m b i a , Canada  Milkweed S p e c i e s  C o l l e c t i o n Data  C a r d e n o l i d e Contentsmean S.E. N-3  A. c a l i f o r m ' c a g r e e n e i  Contra Costa  1976  4.3-  +  0.40  5  Fresno  1976  3.1  +  0.08  3  Napa Placer  1976  3.1  +  0.15  3  1974  1.3  +  0.05  2  A. c u r a s s a v i c a '  Yolo  1976  7.9  +  0.31  3  A. e r i o c a r p a  Fresno  1976  2.4  +  0.07  5  Yolo Fresno  1976 1975  1.3 3.4  +  0.57  1 3  Tulare Tulare  1976 1974  2.4 1.9  +  0.22 0.14  3 5  Yolo Napa Solano  1976 1975 1975  0.25 0.44 0.44  +  3 5  ±  0.03 0.04 0.04  A. s o l a n o a n a  Tehama  1973  1.2  +  0.13  3  A. s p e c i o s a  Solano B.C.  1976 1975  2.7 1.8  + +  0.15 0.03  3 2  Fresno  1976  7.1  +  0.29  5  A. c o r d i f o l i a .  4  A. e r o s a  A. f a s c i c u l a r i s  5  A. v. v e s t i t a  +  +  3  TABLE I I I : G r o s s c a r d e n o l i d e c o n t e n t o f p l a n t samples o f A s c l e p i a s from C a l i f o r n i a . Leaf  = mature o r l o w e r l e a v e s  Umbel = f l o w e r s a t time o f peak f l o w e r i n g Seed  = seeds f r o m d e h i s c e n t pods o r d a r k e n e d seeds f r o m pods c l o s e t o m a t u r i t y  A l l p l a n t m a t e r i a l c o l l e c t e d i n summer, 1976.  mg e q u i v a l e n t s o f d i g i t o x i n p e r gram o f d r i e d t i s s u e ; d a t a f o r l e a f and umbel r e p r e s e n t s s i n g l e e s t i m a t i o n s !  d a t a from TABLE II  29  Milkweed S p e c i e s  Locality  A. c a l i f o r n i c a g r e e n e i  C o n t r a C o s t a Co. F r e s n o Co  A. e r i o c a r p a  F r e s n o Co. F r e s n o Co.  Leaf  4.3 0.27 3.7  Y o l o Co. A. e r o s a  T u l a r e Co.  Cardenolide Content Umbel Seed  3.0  5.'5  3.'4 2.4  1.7  1.3  0.89  2.4  T u l a r e Co. A. f a s c i c u l a r i s  Y o l o Co.  1.9 0.22  F r e s n o Co. Napa Co. A. v. v e s t i t a  F r e s n o Co.  0.73  0.25  1.0 0.44 6.8  2.6  7.1  FIGURE 4:  Gross c a r d e n o l i d e c o n t e n t o f seed o f A s c l e p i a s s p e c i e s from  California.  Data from TABLE I I ; e r r o r i s e x p r e s s e d as t w i c e t h e s t a n d a r d e r r o r o f t h e mean. differences are depicted.  I n t e r s p e c i f i c and i n t r a s p e c i f i c  32 r e l a t i o n s h i p between the r e l a t i v e amounts o f c a r d e n o l i d e p r e s e n t and p l a n t o r g a n s o c c u r r e d , a t l e a s t i n the few s p e c i e s examined here 4).  the  (Figure  Umbels c o n t a i n e d the g r e a t e s t c o n c e n t r a t i o n s o f c a r d e n o l i d e s i n two  o f the s p e c i e s examined (A. f a s c i c u l a r i s and A_. e r o s a ) , w h i l e the umbels c o n t a i n e d the l o w e s t c o n c e n t r a t i o n s o f c a r d e n o l i d e s i n two  other  s p e c i e s examined (A. e r i o c a r p a and A. v_. v e s t i t a ) ( F i g u r e 5 ) . C.  Cardenolide Content of F i e l d C o l l e c t e d Lygaeids T h e r e was a wide v a r i a t i o n i n the c a r d e n o l i d e c o n t e n t o f the  milkweed bugs 0_. f a s c i a t u s and I.  k.  k a l m i i c o l l e c t e d on A s c l e p i a s  s p e c i e s i n the f i e l d i n c e n t r a l C a l i f o r n i a ( T a b l e I V ) .  Some i n s e c t s  were f o u n d t o e i t h e r l a c k c a r d e n o l i d e s o r have l e v e l s o f c a r d e n o l i d e s below the c o l o r i m e t r i c d e t e c t i o n l i m i t .  O t h e r i n s e c t s were found to  c o n t a i n up to 372 yg o f c a r d e n o l i d e p e r i n d i v i d u a l .  Differences in  c a r d e n o l i d e c o n t e n t between samples o f l y g a e i d bugs taken on a p a r t i c u l a r h o s t s p e c i e s i n d i c a t e d t h a t i n t e r s p e c i f i c d i f f e r e n c e s i n the c a r d e n o l i d e c o n t e n t o f the h o s t s p e c i e s cannot a l o n e a c c o u n t f o r the v a r i a b i l i t y i n t h e i n s e c t s , even between p o p u l a t i o n s f e e d i n g on the same plant  organ. Both fj. f a s c i a t u s and L_. k_. k a l m i i s e q u e s t e r e d the l a r g e s t  q u a n t i t i e s o f c a r d e n o l i d e s from the t h r e e b r o a d l e a f milkweed s p e c i e s A_. v_. v e s t i t a , A_. e r o s a and A. e r i o c a r p a ( F i g u r e s 6,7).  Of the f i v e  l o c a l i t i e s where both fJ. f a s c i a t u s and L_. k_. k a l m i i were c o l l e c t e d and a s s a y e d , I.  k_. k a l m i i s e q u e s t e r e d  fj. f a s c i a t u s i n f o u r ( F i g u r e 8).  larger quantities of cardenolides In two l o c a l i t i e s , ( n e a r P i e d r a ,  F r e s n o Co. on A_. e r i o c a r p a ' and near Ducor, T u l a r e Co. on A. e r o s a ) ,  than  FIGURE 5:  G r o s s c a r d e n o l i d e c o n t e n t o f p l a n t samples o f A s c l e p i a s from C a l i f o r n i a .  Data from TABLE I I I .  TABLE IV:  Gross c a r d e n o l i d e c o n t e n t o f fj. f a s c i a t u s and L_. k_. k a l m i i c o l l e c t e d on A s c l e p i a s i n c e n t r a l C a l i f o r n i a i n 1976.  ^Voucher specimens o f f l o w e r s o f t h e milkweed s p e c i e s a r e i n t h e possession of the author County i n C a l i f o r n i a , month o f c o l l e c t i o n , and p a r t o f p l a n t on which i n s e c t s were p r e d o m i n a n t l y  feeding  3  E x p r e s s e d as e q u i v a l e n t s o f d i g i t o x i n ; NIL = no c a r d e n o l i d e s d e t e c t e d , S.E. = s t a n d a r d e r r o r o f t h e mean, N = number o f i n s e c t s a s s a y e d from  site  4  P l a n t s a t t h i s l o c a l i t y were t a x o n o m i c a l l y between /\. v_. v e s t i t a and A. v_. p a r i s h i i  Woodson.  36  Milkweed S p e c i e s  1  ONCOPELTUS FASCIATUS A. c a l i f o r m " c a g r e e n e i F r e s n o A. e r i o c a r p a Fresno Fresno Fresno Fresno A. e r o s a Tulare Napa A- f a s c i c u l a r i s Fresno Tulare Yolo Solano A. v e s t i t a v e s t i t a Fresno Fresno LYGAEUS KALMII KALMII A. c a l i f o r n i c a g r e e n e i C o n t r a C o s t a A. c o r d i f o l i a Placer Napa A. e r i o c a r p a San L u i s Obispo Yolo Fresno Fresno Yolo Fresno A. e r o s a Tulare Tulare A. f a s c i c u l a r i s Yolo A. v. v e s t i t a San L u i s Obispo^ Fresno  C o l l e c t i o n Data  2  Cardenolide Content (yg p e r i n s e c t ) mean + S.E. N  May May July August August July June July July August August May July  pod umbel umbel pod stem pod umbel pod pod pod pod umbel pod  5.5 20 107 82 15 159 37 61 13 11 18 17 195  +  + +  5.5 8.8 16 8.3 7.0 26 7.7 10 8.3 2.8 5.4 14 32  6 9 9 9 6 9 9 9 9 9 9 6 9  May June June  umbel pod umbel  5.6 3.3  + +  4.3 1.7  9 3 2  June June July July August August July August August  umbel umbel umbel umbel umbel stem umbel pod pod  17 152 162 93 116 74 205 5.7  +  8.4 13 22 23 23 23 31 1.4  2 6 3 4 9 7 9 8 6  June July  pod pod  51 256  + +  23 35  6 9  + + + + + + + + + +  MIL NIL + + + + + + +  FIGURE 6:  Gross c a r d e n o l i d e c o n t e n t o f f i e l d ().  fasciatus.  CA = A s c l e p i a s c a l i f o r n i c a g r e e n e i EC = A. e r i o c a r p a ES = A. e r o s a F = A. f a s c i c u l a r i s V = A. v. v e s t i t a  Data from TABLE IV.  collected  FIGURE 6  ONCOPELTUS  jn jl a  FASCIATUS  may June July august  species CA EC ES organ p u u p s P u p p month m m jl a a jl jn jl jl  u p  umbel pod  p p a  a  u m  FIGURE 7:  Gross cardenolide I.  k.  content o f f i e l d  collected  kalmii.  CA = A s c l e p i a s  c a l i f o r n i c a greenei  CO = A. c o r d i f o l i a EC = A.  eriocarpa  ES = A. e r o s a F = A. f a s c i c u l a r i s V = A. v_. v e s t i t a  O t h e r symbols ( f o r p l a n t o r g a n s , month o f c o l l e c t i o n ) as i n FIGURE 6.  FIGURE 7  LYGAEUS KALMII KALMII  300  -i  species CA organ u month m jn in jn jn jl 1  1  jl  a a  FIGURE 8:  Comparison o f g r o s s c a r d e n o l i d e c o n t e n t s o f CJ_. f a s c i a t u s and L. k. k a l m i i c o l l e c t e d from t h e same l o c a l i t i e s .  F = Asclepias fascicularis ES = A. e r o s a EC = A. e r i o c a r p a V = A. v. v e s i t a P = d e h i s c e n t pods and seed i p = immature pods u = umbels s = stems  Date from TABLE IV.  O. fasciatus FIGURE 8  L. k. kalmii  300 n  200 Z a. D)  100 H  o Species  F  ES  EC  Organ  P  •P  u  EC  V  p ro  43  J_. k_. k a l m i i s e q u e s t e r e d s i g n i f i c a n t l y more c a r d e n o l i d e than d i d CJ. f a s c i a t u s . T h e r e i s e v i d e n c e o f temporal  v a r i a t i o n i n the cardenolide  c o n t e n t o f t h e CJ_. f a s c i a t u s ( T a b l e V ) . A d u l t s o f CJ. f a s c i a t u s c o l l e c t e d i n F r e s n o c o u n t y i n May from t h e t h r e e b r o a d ! e a f  milkweed  s p e c i e s A. c a l i f o r m ' c a g r e e n e i , A.- e r i o c a r p a and A. v_. v e s t i t a c o n t a i n e d small q u a n t i t i e s o f c a r d e n o l i d e s .  However, a d u l t i n s e c t ' s c o l l e c t e d on  A. e r i o c a r p a and A. y_. v e s t i t a l a t e r i n t h e season from t h e same l o c a l i t i e s had much h i g h e r l e v e l s o f c a r d e n o l i d e s i n t h e i r b o d i e s .  On  t h e o t h e r hand, t h i s t r e n d d i d n o t e x i s t among a d u l t s o f CJ. f a s c i a t u s c o l l e c t e d on A. f a s c i c u l a r i s from June t h r o u g h A u g u s t . temporal  Therefore, i f  v a r i a t i o n i n the cardenolide content o f lygaeids i s the  r e s u l t o f some a s p e c t o f t h e p h e n o l o g i e s  o f t h e i r r e s p e c t i v e hosts  ( e . g . a v a i l a b i l i t y o f pods and s e e d ) , t h i s s i t u a t i o n i s l i m i t e d t o t h e c a r d e n o l i d e - r i c h b r o a d l e a f s p e c i e s o f milkweed i n C a l i f o r n i a . In g e n e r a l , both ()_. f a s c i a t u s and L^. k_. k a l m i i c o l l e c t e d i n May and June c o n t a i n e d s u b s t a n t i a l l y lower l e v e l s o f c a r d e n o l i d e s than c o n s p e c i f i c s taken  later  i n t h e season on t h e same h o s t s p e c i e s ( F i g u r e s 6 and 7 ) . The f r e q u e n c y d i s t r i b u t i o n o f c a r d e n o l i d e c o n t e n t i n a l l t h e f i e l d - c o l l e c t e d l y g a e i d s i n t h i s s t u d y i s s t r o n g l y skewed toward t h e l e f t , o r low end o f t h e X - a x i s ( F i g u r e 9 ) . Of t h e 211 i n d i v i d u a l l y g a e i d s a s s a y e d , 52 p e r c e n t o f t h o s e had l e s s than 50 m i c r o g r a m s o f c a r d e n o l i d e i n t h e i r b o d i e s , and 71 p e r c e n t had l e s s than 100 m i c r o g r a m s .  The  o v e r a l l range i n c a r d e n o l i d e content o f the f i e l d - c o l l e c t e d l y g a e i d s f e l l w i t h i n t h e r a n g e o f c a r d e n o l i d e c o n t e n t s i n l a b o r a t o r y - r e a r e d bugs.  44 TABLE V:  Temporal v a r i a t i o n i n g r o s s c a r d e n o l i d e c o n t e n t o f f i e l d c a u g h t fJ. f a s c i a t u s from C e n t r a l C a l i f o r n i a .  Milkweed S p e c i e s  May-June  A. c a l i f o r m ' c a g r e e n e i  5.5  A. e r i o c a r p a  20  A. e r o s a  -  A. f a s c i c u l a r i s  37  A. v. v e s t i t a  17  Cardenolide Content July-August2 107, 82 159 61, 13, 11, 18 195  Lab Reared 251 149 151 34 281  mean i n yg e q u i v a l e n t s o f d i g i t o x i n p e r i n s e c t d a t a from T a b l e IV 'reared from egg t o a d u l t e x c l u s i v e l y on seed from r e s p e c t i v e milkweed s p e c i e s ; d a t a from T a b l e V I .  FIGURE 9:  Gross cardenolide content of f i e l d c o l l e c t e d l y g a e i d s : d i s t r i b u t i o n o f c l a s s e s based on c a r d e n o l i d e  content.  T o t a l sample s i z e o f 211 r e p r e s e n t s a l l i n d i v i d u a l i n s e c t s used t o f o r m u l a t e d a t e i n T a b l e IV.  W h i l e not a random sample o f  l y g a e i d s on m i l k w e e d i n C a l i f o r n i a , t h e s e i n s e c t s c o n s t i t u t e a r e p r e s e n t a t i v e sample owing to the d i s p r o p o r t i o n a t e numbers o f i n s e c t s on d i f f e r e n t A s c l e p i a s s p e c i e s .  Of t h e t o t a l sample, 52 per c e n t c o n t a i n e d l e s s than 50 yg per i n s e c t , and 71 p e r c e n t c o n t a i n e d l e s s t h a t 100 yg p e r i n s e c t .  46  FIGURE 9  120-i  0  100  200  p g per  300 Insect  400  47  D.  Cardenolide Content of Laboratory-Reared  Lygaeids  T a b l e VI shows a n a l y s e s o f t h e c a r d e n o l i d e c o n t e n t o f l y g a e i d s r e a r e d from egg to a d u l t i n t h e l a b o r a t o r y on seed from s p e c i e s o f A s c l e p i a s a t 25°C.  different  CJ. f a s c i a t u s and l^. k_. k a l m i i  sequester  and s t o r e s m a l l q u a n t i t i e s o f c a r d e n o l i d e s from A. f a s c i c u l a r i s , moderate amounts from A. e r o s a , A. c o r d i f o l i a and A. e r i o c a r p a , and  relatively  l a r g e q u a n t i t i e s from /\. c a l i f o r n i c a g r e e n e i and A. y_. v e s t i t a .  There  i s a p o s i t i v e c o r r e l a t i o n between c a r d e n o l i d e c o n t e n t o f l a b o r a t o r y r e a r e d i n s e c t s and the c a r d e n o l i d e c o n t e n t o f t h e seeds o f t h e i r r e s p e c t i v e h o s t s p e c i e s ( F i g u r e 10, T a b l e V I ) . L_. J£. k a l m i i a p p e a r s t o be more e f f i c i e n t a t s e q u e s t e r i n g  these  compounds as i t s t o r e d l a r g e r q u a n t i t i e s o f c a r d e n o l i d e s than CJ. f a s c i a t u s when both i n s e c t s were r e a r e d on the same seed d i e t ( F i g u r e 10).  S i m i l a r l y , fJ. f a s c i a t u s r e a r e d a t 21°C was more e f f i c i e n t a t  s e q u e s t e r i n g c a r d e n o l i d e s than t h o s e r e a r e d a t 25°C ( F i g u r e 10). When the d a t a f o r a d u l t fj. f a s c i a t u s r e a r e d a t 21 °C a r e examined i n d e t a i l , i t i s a p p a r e n t t h a t the c a r d e n o l i d e c o n t e n t o f a d u l t bugs i s s i g n i f i c a n t l y d i f f e r e n t between the sexes i n a l l but one milkweed seed d i e t (Table VII).  Females were more e f f i c i e n t a t s e q u e s t e r i n g  c a r d e n o l i d e s than males on a l l e i g h t s p e c i e s o f A s c l e p i a s ( F i g u r e 11). E.  L a r v a l Growth and Development o f L y g a e i d s on D i f f e r e n t S p e c i e s o f M i l k w e e d i n the L a b o r a t o r y Both fJ. f a s c i a t u s and L. k. k a l m i i were s u c c e s s f u l l y r e a r e d  from  eggs to a d u l t s on a d i e t o f milkweed seeds from s e v e r a l d i f f e r e n t s p e c i e s o f A s c l e p i a s as w e l l as H e l i a n t h u s ( C o m p o s i t a e ) .  None o f the milkweed  48 TABLE V I : Gross c a r d e n o l i d e c o n t e n t o f 0_. f a s c i a t u s and L_. J^. k a l m i i r e a r e d i n t h e l a b o r a t o r y on m i l k w e e d seed. 3  Milkweed  Species  Cardenolide Content 1 2 0.- f a s c i a t u s l^. k. k a l m i i C o l l e c t i o n Data Seed mean + SE N mean + SE N  A. c a l i f o r n i c a g r e n e e i C o n t r a Costa  1976  4.3  251  +  29  9  419  +  92  6  A- c o r d i f o l i a  Placer  1974  1.7  125  +  19  9  78  +  14  9  A- e r i o c a r p a  Fresno  1975  3.4  149  +  13  9  219  +  42  9  A. e r o s a  Tulare  1974  1.9  151  +  23  9  268  +  58  9  A. f a s c i c u l a r i s  Napa  1975  0.4  34  +  5.1 9  50  +  19  9  A. v e s t i t a v e s t i t a  Fresno  1976  7.1  281  +  20 18  765  +  72  9  C a l i f o r n i a n c o l l e c t i o n d a t a f o r m i l k w e e d seed f e d t o i n s e c t s , mg e q u i v a l e n t s o f d i g i t o x i n p e r gram o f d r i e d s e e d ; d a t a f r o m T a b l e I I . V g e q u i v a l e n t s o f d i g i t o x i n p e r i n s e c t : N = no. o f i n s e c t s i n each sample, S.E. = s t a n d a r d e r r o r o f t h e mean.  )  FIGURE 10:  R e l a t i o n s h i p between c a r d e n o l i d e c o n c e n t r a t i o n i n t h e d i e t ( m i l k w e e d s e e d s ) and t h e c a r d e n o l i d e c o n t e n t o f a d u l t fj. f a s c i a t u s and IL. _k. k a l m i i .  I n s e c t s a s s a y e d f o r c a r d e n o l i d e s were r e a r e d from egg t o a d u l t e x c l u s i v e l y on s e e d s o f r e s p e c t i v e s p e c i e s o f A s c l e p i a s . sexes  Values f o r  combined.  I n s e c t d a t a from T a b l e s VI and V I I I , seed d a t a from T a b l e I I ; r = c o r r e l a t i o n c o e f f i c i e n t , m = slope.  D i f f e r e n c e s between t h e  ( F i g u r e 11) c o n t r i b u t e to the l a r g e s t a n d a r d e r r o r s .  O  0. f a s c i a t u s r e a r e d a t  21°C  ©  0. f a s c i a t u s r e a r e d a t 25°C L. k. k a l m i i r e a r e d a t 25°C  fj. f a s c i a t u s s e q u e s t e r s more c a r d e n o l i d e s a t 21 C owing t o a l o n g e r d u r a t i o n o f l a r v a l d e v e l o p m e n t (approx. 40 days to t h e a d u l t m o l t ) compared to c o n s p e c i f i c s r e a r e d a t 25°C (approx.  22 days t o the a d u l t m o l t ) .  L_. k_. k a l m i i a p p e a r s  t o be more e f f i c i e n t a t s e q u e s t e r i n g c a r d e n o l i d e s than fj. f a s c i a t u s a t the same  temperature.  sexes  51 TABLE V I I :  Gross c a r d e n o l i d e c o n t e n t o f CJ. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on milkweed s e e d .  Plant Species  Seed' mean. ± S.E.  N  A d u l t 0. f a s c i a t u s ' mean S.E. ? ? mean ± S.E.  A. f a s c i c u l a r i s  0.25  +  0.03  3  42.3  +  2.5  A. e r o s a  2.4  +  0.07  3  139  +  A. s p e c i o s a  2.7  +  0.15  3  151  A. c o r d i f o l i a  3.1  +  0.15  3  A. e r i o c a r p a  3.4  +  0.57  A. c a l i f o r n i c a  4.3  +  A. v e s t i t a  7.1  A. c u r a s s a v i c a  7.9  cCo*  48.7  +  3.8  20  204  +  14  +  20  250  +  14  152  +  27  363  +  30  3  75  +  6.7  158  +  9.3  0.40  5  215  +  5.6  387  +  32  +  0.29  5  291  +  81  649  +  58  +  0.31  4  386  +  23  707  +  51  mg p e r gram o f d r i e d s e e d ; d a t a from T a b l e I I yg p e r i n s e c t 'N = 3 f o r both  sexes  " d i f f e r e n c e between sexes n o t s i g n i f i c a n t  H  FIGURE 11:  R e l a t i o n s h i p between c a r d e n o l i d e c o n c e n t r a t i o n i n t h e d i e t (milkweed s e e d s ) and t h e c a r d e n o l i d e c o n t e n t o f a d u l t male and f e m a l e 0. f a s c i a t u s r e a t e d a t 21°C.  Data from Tabel V I I . r = c o r r e l a t i o n c o e f f i c i e n t , m = slope.  FIGURE 11  0  2  4  mg per g r a m  6  8  DRY SEED cn co  54 s p e c i e s t e s t e d a p p e a r t o p r e s e n t a n u t r i t i o n a l b a r r i e r t o t h e growth and d e v e l o p m e n t o f CL f a s c i a t u s and j_. k_. k a l m i i . When r e a r e d a t 25°C, CL f a s c i a t u s completed  l a r v a l development  s i g n i f i c a n t l y f a s t e r on seeds o f A., f a s c i c u l a r i s than on t h e o t h e r milkweed seeds p r o v i d e d ( F i g u r e 1 2 ) . T h e r e were no s i g n i f i c a n t d i f f e r e n c e s among t h e s e bugs when r e a r e d on seeds o f o t h e r m i l k w e e d s , v i z . A., e r o s a , /\. c o r d i f o l i a , A. e r i o c a r p a and A. s p e c i o s a ( T a b l e V I I I ) . S u r v i v a l t o t h e a d u l t s t a g e was 75 p e r c e n t o r g r e a t e r on a l l d i e t s . However, d e v e l o p m e n t a l  d u r a t i o n o f t h e l a r v a e was s i g n i f i c a n t l y l o n g e r  f o r bugs r e a r e d on seeds o f H e ! i a n t h u s  annus.  The s m a l l milkweed bug L_. k_. k a l m i i a l s o d e v e l o p e d  f a s t e r on t h e  seeds o f A_. f a s c i c u l a r i s than on t h e seeds o f o t h e r m i l k w e e d s . c o n t r a s t t o 0. f a s c i a t u s , L_. k. k a l m i i d e v e l o p e d  In  s i g n i f i c a n t l y f a s t e r on  s u n f l o w e r seeds than on t h e milkweed seeds w i t h t h e e x c e p t i o n o f A. f a s c i c u l a r i s ( F i g u r e 1 2 ) . S u r v i v a l t o t h e a d u l t s t a g e on a l l d i e t s was lower than t h a t o f CL f a s c i a t u s ( T a b l e I X ) . A t 2 1 C t h e r e were few s i g n i f i c a n t d i f f e r e n c e s i n t h e l a r v a l U  developmental  times o f CL f a s c i a t u s r e a r e d on e i g h t d i f f e r e n t s p e c i e s o f  A s c l e p i a s ( T a b l e X ) . As t h e c a r d e n o l i d e c o n t e n t o f t h e s e i n s e c t s had been d e t e r m i n e d  ( T a b l e V I I ) , i t was p o s s i b l e t o compare t h e c a r d e n o l i d e  content of the insects with the larval duration.  In t h i s s t u d y , no  s i g n i f i c a n t c o r r e l a t i o n was f o u n d between t h e s e two i n d i c e s ( T a b l e XIV, Figure 14). T h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t h e wet w e i g h t s o f t e n e r a l CJ. f a s c i a t u s o f one sex when r e a r e d on t h e f i v e d i f f e r e n t s p e c i e s  FIGURE 12:  R e l a t i o n s h i p between d u r a t i o n o f l a r v a l  development  and t e n e r a l wet w e i g h t o f CJ. f a s c i a t u s and L^. k.  kalmii  r e a r e d i n t h e l a b o r a t o r y a t 25°C on seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and  Helianthus.  A s c l e p i a s spp. H_. annus  o  0. f a s c i a t u s  •  L_. k. k a l m i i  Data f r o m T a b l e s V I I I and IX: f es c ec s  A. f a s c i c u l a r i s A. e r o s a A. c o r d i f o l i a A. e r i o c a r p a A.  speciosa  TABLE V I I I :  D u r a t i o n o f l a r v a l development and t e n e r a l a d u l t wet w e i g h t o f CJ. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 25°C on t h e seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and H e l i a n t h u s .  Plant Species  Developmental D u r a t i o n ( d a y s ) mean ± S.E. N S u r v i v a l (%) +$mean  A. c o r d i f o l i a  21.9  +  0.28  19  95  65.5  A. e r i o c a r p a  21.7  +  0.37  18  90  68.0  A. e r o s a  22.4  +  0.17  19  95  66.9  A. f a s c i c u l a r i s  19.5  +  0.12  16  80  67.5  A. s p e c i c o s a  22.9  +  0.63  17  85  61.6  H. annus  24.4  +  0.61  15  75  52.3  cr  N = t o t a l number o f i n s e c t s c o m p l e t i n g  Wet W e i g h t (mg) ± + + + + + +  S.E.  ^mean  ?ftnean  ? : cr  2.7  54.1  72.2  1 .33  2.4  60.9  72.6  1 .19  2.7  58.3  74.7  1 .28  2.6  58.1  71.7  1 .23  2.3  54.9  69.8  1 .27  2.4  45.9  55.6  1 .21  d e v e l o p m e n t t o t h e a d u l t s t a g e ( b o t h sexes combined)  See m a t e r i a l s and methods ( S e c t i o n D) f o r c o l l e c t i o n d a t a f o r milkweed  seeds.  S u r v i v a l i s the percentage o f larvae that s u c c e s s f u l l y complete the f i n a l molt i n t o the a d u l t s t a g e . T e n e r a l a d u l t s were weighed w i t h i n 12 hours o f t h e a d u l t m o l t . on  TABLE IX:  D u r a t i o n o f l a r v a l development and t e n e r a l a d u l t wet w e i g h t o f L_. k_. k a l m i i r e a r e d i n the l a b o r a t o r y a t 25°C on the seeds o f d i f f e r e n t s p e c i e s o f A s c l e p i a s and  Helianthus.  Plant Species  Developmental D u r a t i o n (days) mean ± S.E. N S u r v i v a l (%)  A. c o r d i f o l i a  28.5  +  0.16  16  80  43.6  +  1.0  A. e r i o c a r p a  29.6  +  1.6  6  30  44.1  +  2.9  A.  29.3  +  0.88  14  70  47.2  +  1.7  A. f a s c i c u l a r i s  25.8  +  0.12  17  85  44.1  +  0.8  A.  29.1  +  1.5  13  65  41.6  +  1.6  26.5  +  0.43  16  80  42.9  +  1.4  erosa  speciosa  H. annus  M = t o t a l number o f i n s e c t s c o m p l e t i n g  Wet Weight (mg) o*+? mean ± S.E.  d e v e l o p m e n t to the a d u l t s t a g e (both s e x e s combined).  See m a t e r i a l s and methods ( s e c t i o n D) f o r c o l l e c t i o n d a t a f o r milkweed  seeds.  S u r v i v a l i s t h e p e r c e n t a g e o f l a r v a e t h a t s u c c e s s f u l l y c o m p l e t e d the f i n a l m o l t to the a d u l t s t a g e . T e n e r a l a d u l t s were weighed w i t h i n 12 hours o f the a d u l t m o l t .  59 TABLE X:  I n f l u e n c e o f s e q u e s t e r e d c a r d e n o l i d e s on l a r v a l d e v e l o p m e n t o f fj. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21 °C on t h e seeds of Asclepias.  Plant Species  Cardenolide Content mean ± S.E.  12 '  Developmental D u r a t i o n (days) mean ± S.E.  Survival N  (%)  45.5  +  3.5  39.3  +  0.28  20  100  A. e r o s a  171  +  18  40.5  +  0.27  18  90  A. s p e c i o s a  200  +  25  39.2  +  0.37  19  95  A. c o r d i f o l i a  258  +  51  40.3  +  0.26  16  80  A. e r i o c a r p a  117  +  19  40.5  +  0.33  18  90  A. c a l i f o r n i c a greenei  301  +  41  40.3  +  0.20  18  90  A. v. v e s t i t a  470  +  92  40.7  +  0.25  19  95  A. c u r a s s a v i c a  547  +  76  39.8  +  0.25  18  90  A. f a s c i c u l a r i s  3  yg p e r a d u l t i n s e c t d a t a f o r both sexes combined, N = 6 ( d a t a from T a b l e V I I ) 3  s u r v i v a l i s the percentage o f larvae that s u c c e s s f u l l y completed t h e a d u l t m o l t  See m a t e r i a l s and Methods ( s e c t i o n D) f o r c o l l e c t i o n d a t a f o r milkweed seeds.  60 o f A s c l e p i a s a t 25°C ( T a b l e X I I I ) .  However, t h e r e were s i g n i f i c a n t  d i f f e r e n c e s between t h e sexes when r e a r e d on t h e same d i e t , t h e f e m a l e s b e i n g : s i g n i f i c a n t l y h e a v i e r than t h e i r male c o u n t e r p a r t s on a l l t h e diets tested. weight  The r a t i o o f mean f e m a l e wet w e i g h t t o mean male wet  f o r CJ. f a s c i a t u s i n t h i s s t u d y f e l l w i t h i n t h e range o f 1..2:1  t o 1.3:1. O n c o p e l t u s f a s c i a t u s r e a r e d on s u n f l o w e r  seeds were s i g -  n i f i c a n t l y l i g h t e r than t h o s e r e a r e d on t h e d i f f e r e n t milkweed seeds ( F i g u r e 1 2 ) . The f e m a l e t o male w e i g h t r a t i o was s i m i l a r t o t h a t o f CJ_. f a s c i a t u s r e a r e d on t h e milkweed seed d i e t s . L i k e CJ. f a s c i a t u s , t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t e n e r a l wet w e i g h t o f L^. k_. k a l m i i r e a r e d on t h e d i f f e r e n t s p e c i e s o f A s c l e p i a s ( T a b l e I X ) . D i f f e r e n c e s between t h e s e x e s were n o t i n v e s t i g a t e d . In c o n t r a s t t o 0. f a s c i a t u s , t e n e r a l a d u l t s o f l_. k_. k a l m i i r e a r e d on s u n f l o w e r  seeds a r e no l i g h t e r than c o n s p e c i f i c s r e a r e d on  milkweed seeds ( F i g u r e 1 2 ) . T h i s f i n d i n g , t o g e t h e r w i t h t h e r e l a t i v e l y r a p i d l a r v a l d e v e l o p m e n t o f L. k_. k a l m i i on s u n f l o w e r  seeds,  strongly  i n d i c a t e t h a t t h i s i n s e c t i s c a p a b l e o f b e t t e r growth and d e v e l o p m e n t on t h i s non-asclepaidaceous develops  h o s t than i s CJ. f a s c i a t u s .  However, CJ. f a s c i a t u s  f a s t e r and a t t a i n s g r e a t e r body w e i g h t s a t a l l l a r v a l i n s t a r s  compared t o I. Jc. k a l m i i when both a r e r e a r e d on t h e seeds o f /\. f a s c i c u l a r i s under t h e same c o n d i t i o n s ( F i g u r e 1 3 ) . When CJ. f a s c i a t u s was r e a r e d on e i g h t d i f f e r e n t s p e c i e s o f A s c l e p i a s a t 2 1 ° C , t h e r e were some s i g n i f i c a n t d i f f e r e n c e s between t e n e r a l wet w e i g h t s w i t h i n t h e s e x e s ( T a b l e X I ) .  However, a l l  FIGURE 13:  Weight g a i n i n CL f a s c i a t u s and L_. k_. k a l m i i d u r i n g l a r v a l development, reared i n the l a b o r a t o r y a t 25°C on t h e s e e d s o f A. f a s c i c u l a r i s .  A. f a s c i c u l a r i s seed c o l l e c t e d i n Napa c o u n t y i n September, 1975.  62  FIGURE 13  •  O. fasciatus  o  L. k. kalmii  teneral  0  10  20 AGE  (days)  30  adult  FIGURE 14:  R e l a t i o n s h i p between g r o s s c a r d e n o l i d e c o n t e n t  and  d u r a t i o n o f l a r v a l d e v e l o p m e n t o f fj. f a s c i a t u s r e a r e d i n the l a b o r a t o r y a t 21°C on t h e seeds o f d i f f e r e n t species of A s c l e p i a s .  Data f r o m T a b l e X;  m = slope.  LARVAL DURATION  \i9  (days)  TABLE'.XI: A d u l t body w e i g h t o f 0. f a s c i a t u s  r e a r e d i n t h e l a b o r a t o r y a t 21 °C on t h e seeds o f d i f f e r e n t  species of Asclepias. Plant Species  T e n e r a l Wet Weight (mg) mean ± S.E.  n  A d u l t Dry Weight, (mg),  mean ± S.E. n  mean ± S.E.  ?  o*  A. f a s c i c u l a r i s  58.6 + 1 .5  A. e r o s a  59.9 + 1 .7  A. s p e c i o s a  14 1  68.2  +  3.6  24. 8 + 0.8  12  1 .14  26. 8 + 1.3  =p=-i  30. 8 + 2.4  6  2  33. 2 + 1.5  11  31. 6 + 2.4  25. 8 + 1.3-T  9  39. 0 + 2.1  -  7  1 .27  21. 6 + 0.8 J-l  13  34. 6 + 1.3  -|  4  75.0 + 1.2 - 11  1 .21  25. 1 + 1.6  "J  7  35. 9 + 0.7  -|  10  73.3 + 1.7,  9  1 .28  24. 1 + 1.1 1  10  35. 3 + 2.1  ,  10  64.5 + 2.0-'- 8  1 .21  19. 7 + 0.7  'J 10  26. 2 + 0.7  11  68.6 + 5.0  8  1 .18  26. 1 + 1.1  A. c o r d i f o l i a  60.7 + 1 .4  9  72.3 + 3.3  7  1 .19  A. e i r o c a r p a  60.2 + 1 .8 -  1.6 " 4  A. c a l i form'ca greenei  62.1  1  7  A. v. v e s t i t a  57.3 + 1 .2  A. c u r a s s a v i c a  53.2 + 1 .2-  13  •  n  6  57.9 + 1 .4  ,5  —- i 14  1 .16  68.3 + 2.4  1  mean ±JS.E ?  6  6  +  n  a*  76.7  +  2  —  1  1 2  8  2  11 9  I1•  8  b r a c k e t ends j o i n s i g n i f i c a n t l y d i f f e r e n t means 2  no s i g n i f i c a n t d i f f e r e n c e between sexes T e n e r a l wet w e i g h t d e t e r m i n e d w i t h i n 12 hours o f t h e a d u l t m o l t . d e t e r m i n e d between 10 and 14 days f o l l o w i n g t h e a d u l t m o l t .  Adult d r y weight  CTl  66  d i f f e r e n c e s were owing to the l i g h t w e i g h t s o f both males and  females  r e a r e d on A_. c u r a s s a v i c a .  females  As i n the 25°C r e a r i n g e x p e r i m e n t ,  were s i g n i f i c a n t l y h e a v i e r than males on a l l d i e t s t e s t e d .  Adult dry  w e i g h t s y i e l d e d the same r e l a t i o h s h i p as t h e t e n e r a l wet w e i g h t s .  There  were no s i g n i f i c a n t c o r r e l a t i o n s between t e n e r a l wet w e i g h t o r a d u l t d r y w e i g h t and c a r d e n o l i d e c o n t e n t f o r e i t h e r sex  (Table  XIV).  R a t i o s o f mean f e m a l e wet w e i g h t to mean male wet w e i g h t were s i m i l a r to t h o s e i n the 25°C r e a r i n g e x p e r i m e n t , from 1.14  to 1.28  f a l l i n g w i t h i n a range  (Table XI).  Measurement o f a d u l t p r o n o t a l w i d t h showed no s i g n i f i c a n t d i f f e r e n c e s f o r i n s e c t s o f the same sex r e a r e d on the d i f f e r e n t d i e t s (Table XII).  Thus, t h e r e were no c o r r e l a t i o n s between p r o n o t a l  and c a r d e n o l i d e c o n t e n t o f t h e a d u l t i n s e c t s ( T a b l e X I V ) .  width  Females were  s i g n i f i c a n t l y l a r g e r than males on a l l d i e t s . In most group r e a r i n g s , f e m a l e s were s i g n i f i c a n t l y h e a v i e r , l a r g e r , and c o n t a i n e d more c a r d e n o l i d e per i n s e c t than the males ( T a b l e s XI, X I I , V I I , F i g u r e s 15, 11).  The d i f f e r e n c e s between the  sexes i n wet w e i g h t o f t e n e r a l s does n o t a p p e a r to be r e l a t e d to sex d i f f e r e n c e s i n c a r d e n o l i d e c o n t e n t o f the a d u l t i n s e c t s .  0_. f a s c i a t u s  r e a r e d on s u n f l o w e r seeds e x h i b i t a f e m a l e t o male w e i g h t r a t i o equal to that of milkweed-reared  c o n s p e c i f i c s which v a r i e d with r e s p e c t to  cardenolide content (Table X I I I ) . As t h e r e were no s i g n i f i c a n t c o r r e l a t i o n s between c a r d e n o l i d e c o n t e n t and body w e i g h t , body s i z e o r l a r v a l  developmentaliduration  ( T a b l e X I V ) , i t a p p e a r s t h a t t h e r e a r e no m e a s u r a b l e d e t r i m e n t a l a f f e c t s  FIGURE 15:  R e l a t i o n s h i p between g r o s s c a r d e n o l i d e c o n t e n t  and  a d u l t body w e i g h t o f fj. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on t h e s e e d s o f d i f f e r e n t s p e c i e s of Asclepias.  WET = t e n e r a l wet w e i g h t ( w i t h i n 12 hours o f t h e a d u l t molt) DRY = a d u l t d r y w e i g h t (10 t o 14 days f o l l o w i n g t h e adul t m o l t ) .  Data f r o m T a b l e X I ; m = s l o p e .  68  FIGURE 15  • female WET <^ o male DRY <^  • female a male  80 H  1  m= -.003  60 H m=-.016  E I 40 O  t  20 4  m=-.010  0  i  0  m=-.003  200  r  400  pg CARDENOLIDE  i  600 PER INSECT  r  TABLE X I I : P r o n o t a l w i d t h o f a d u l t CJ. f a s c i a t u s r e a r e d i n t h e l a b o r a t o r y a t 21°C on t h e seeds o f d i f f e r e n t  species  of A s c l e p i a s .  o" mean  Plant species  Pronotum Width  (mm)  +  S.E.  $ Mean  1  +  S.E  A. f a s c i c u l a r i s  3.7  +  .06  4.1  +  .04  A. e r o s a  3.6  +  .04  4.1  +  .04  A. s p e c i o s a  3.6  +  .06  3.9  +  .08  A. c o r d i f o l i a  3.6  +  .03  4.0  +  .06  A. e r i o c a r p a  3.6  +  .06  4.1  +  .05  A. c a l i f o r n i c a  3.7  +  .06  4.1  +  .04  A. v e s t i t a  3.6  +  .06  4.0  +  .09  A. c u r a s s a v i c a  3.6  +  .04  4.0  +  .05  N = 5 f o r a l l samples e x c e p t A. e r i o c a r p a - r e a r e d f e m a l e s (N =  4).  TABLE X I I I :  Comparison of female to male r a t i o s for teneral wet weight and cardenolide content of 0. fasciatus reared on d i f f e r e n t seed d i e t s .  Plant Species  Mean Teneral Wet Weight^  Mean Cardenolide Content  y ;  $ : o*  ? : c*  a  1  1.19  152  363  2.39  64.5  1  1.21  386  707  1.83  55.6  2  1.21  NIL  o*  $  A. c o r d i f o l i a  60.7  72.3  A. curassavica  53.2  Helianthus annus  45.9  ^data from Table XI reared at 25°C; data from Table VIII 3 yg per i n s e c t ; data from Table VII  2  4  NIL = no cardenolides detected  $  4  NIC  71 TABLE XIV:  C o r r e l a t i o n s between mean c a r d e n o l i d e c o n t e n t and means o f body w e i g h t , body s i z e and l a r v a l d u r a t i o n i n 0. f a s c i a t u s .  A. C a r d e n o l i d e c o n t e n t o f i n s e c t s vs. cardenolide content i n diet  +0.789  p < .001  B. L a r v a l d u r a t i o n v s . c a r d e n o l i d e content (insects)  +0.264  p > .50  males females  -0.647 -0.163  .10 > p > .05 p > .50  D. A d u l t d r y w e i g h t vs. c a r d e n o l i d e content males females  -0.482 -0.172  .50 > p > .20 p > .50  -0.288 -0.405  .50 > p > .'20 .50 > p > .20  C. T e n e r a l wet w e i g h t v s . c a r d e n o l i d e content:  E. A d u l t pronotum w i d t h v s . c a r d e n o l i d e content males females  r = correlation coefficient  o f c a r d e n o l i d e s e q u e s t r a t i o n on t h e l a r v a l growth and d e v e l o p m e n t o f 0. f a s c i a t u s .  IV DISCUSSION The a b i l i t y o f the l y g a e i d bugs Q_. f a s i c a t u s and L_. k a l m i i to s e q u e s t e r and s t o r e c a r d e n o l i d e s asclepiadaceous 1972,  ( c a r d i a c g l y c o s i d e s ) from t h e i r  h o s t s has been w e l l documented ( D u f f e y and ..Scudder  1974); t h i s a b i l i t y i s c h a r a c t e r i s t i c o f many b r i g h t l y c o l o u r e d  members o f t h e L y g a e i n a e ( S c u d d e r and D u f f e y 1972, Abushama and Ahmed 1976).  F u r t h e r , many s p e c i e s o f A s c l e p i a s , and  o t h e r n a t u r a l h o s t s o f North A m e r i c a n L y g a e i n e s contain cardenolides  von Euw e t al_. 1971,  (Roeske e t al_. 1976,  D u f f e y and S c u d d e r 1972).  T o g e t h e r w i t h t h e w e l l known p h a r m a c o l o g i c a l g l y c o s i d e s (Moe and Farah 1970,  Hoch 1961,  have been shown to  e f f e c t s of cardiac T h o r p and C o b b i n 1 9 6 7 ) ,  the h y p o t h e s i s o f a p a l a t a b i l i t y s p e c t r u m based on p l a n t - d e r i v e d c a r d e n o l i d e s i n t h e s e i n s e c t s a p p e a r s t o be w e l l - f o u n d e d . has d e m o n s t r a t e d t h a t a broad s p e c t r u m e x i s t s i n the  This thesis  cardenolide  c o n t e n t s o f 0. f a c i a t u s and L_. k a l m i i k a l m i i f e e d i n g on A s c l e p i a s i n central C a l i f o r n i a . In terms o f both v a l u e s and v a r i a b i l i t y , the d a t a  presented  h e r e f o r C a l i f o r n i a n s p e c i e s o f A s c l e p i a s a r e l a r g e l y i n agreement w i t h t h o s e o f Roeske e t aj_. (1976).  As such, the c o m p a r i s o n s between  c a r d e n o l i d e c o n t e n t o f p l a n t s and i n s e c t s i n t h i s t h e s i s , and between i n s e c t s i n t h i s t h e s i s and o t h e r r e p o r t s ( e . g . Brower e_t aX. Roeske e t a]_. 1976)  1975,  a r e c o n s i d e r e d t o be v a l i d . .  I t s h o u l d be r e a l i z e d t h a t i n c o l l e c t i n g a d u l t i n s e c t s i n the f i e l d the host p l a n t experience remains u n c e r t a i n .  of these i n s e c t s i n t h e i r l a r v a l  However, i n t h i s s t u d y the p r e s e n c e o f  stages  soft-bodied  74  a d u l t s t o g e t h e r w i t h l a t e i n s t a r l a r v a e f e e d i n g on t h e same seed pod has been taken t o i n d i c a t e t h a t t h e a d u l t s c o l l e c t e d f r o m such a s i t e f o r a n a l y s i s r e p r e s e n t i n s e c t s which developed  e x c l u s i v e l y on t h a t f o o d  source. The q u a n t i t i e s o f c a r d e n o l i d e s i n f i e l d - c o l l e c t e d l y g a e i d s were o f t e n much s m a l l e r than t h o s e p r e d i c t e d by e x t r a p o l a t i n g from t h e r e l a t i o n s h i p between t h e q u a n t i t y i n t h e d i e t and t h e q u a n t i t y s e q u e s t e r e d i n l a b o r a t o r y - r e a r e d bugs. in the lygaeid-milkweed  Thus, t h e r e a p p e a r t o be e c o l o g i c a l p a r a m e t e r s a s s o c i a t i o n which l i m i t , o r i n t e r f e r e with the  i n s e c t s ' o p p o r t u n i t y t o s e q u e s t e r optimum q u a n t i t i e s o f c a r d e n o l i d e s from t h e i r p o t e n t i a l h o s t s . The g r o u n d - d w e l l i n g  l y g a e i d L_. k_. k a l m i i o v e r w i n t e r s  i n and n e a r  milkweed s t a n d s , f e e d i n g on seed on t h e g r o u n d , as w e l l a s t h e seeds o f some n o n - a s c l e p i a d a c e o u s comm.). oleander,  p l a n t s , and dead i n s e c t s (R.B. Root, p e r s .  Among t h e w i n t e r h o s t s i s t h e c a r d e n o l i d e - c o n t a i n i n g  Merium  a u b i q u i t o u s c u l t i v a t e d p l a n t i n c e n t r a l C a l i f o r n i a . In t h e  e a r l y s p r i n g , b e f o r e milkweeds have begun t o s p r o u t , l ^ . k. k a l m i i reproduces  on t h e seeds o f o t h e r p l a n t s , such as t h e common  Senecio v u l g a r i s , which l a c k s c a r d e n o l i d e s Although  groundsel  (K.E. Evans, p e r s . comm.).  t h i s l y g a e i d c a n s u c c e s s f u l l y d e v e l o p and r e p r o d u c e on p l a n t s  o t h e r than m i l k w e e d , milkweed seeds enhance l a r v a l d e v e l o p m e n t (R.B. Root, p e r s . comm.).  L_. k_. k a l m i i c o l o n i z e s most o f t h e s p e c i e s o f A s c l e p i a s i n  C a l i f o r n i a , b u t r e m a i n s a t low d e n s i t i e s u n t i l t h e seed pods l a t e i n the season. develop  develop  Because t h e y have t h e d i e t a r y f e l x i b i 1 i t y t o  i n t h e a b s e n c e o f milkweed p l a n t s and s e e d , a p o r t i o n o f t h e  75  o v e r a l l p o p u l a t i o n o f t h e s e bugs may n o t have t h e o p p o r t u n i t y t o s e q u e s t e r and s t o r e c a r d e n o l i d e s . The f a c t t h a t J^. k_. k a l m i i i s more e f f i c i e n t t h a t (D. f a s c i a t u s a t s e q u e s t e r i n g c a r d e n o l i d e s from p l a n t m a t e r i a l may have p e r m i t t e d t h i s s p e c i e s t o e x p l o i t a wider range o f host s p e c i e s , i n c l u d i n g those w h i c h do n o t p r o v i d e t h e i n s e c t w i t h c a r d e n o l i d e s .  Since cardenolides  may be r e t a i n e d i n t h e d o r s o - l a t e r a l spaces o f t h e s e i n s e c t s f o r a p e r i o d o f weeks ( e x p e r i m e n t a l  evidence undescribed i n t h i s t h e s i s ) , a  s h o r t e x p o s u r e t o a c a r d e n o l i d e - r i c h d i e t combined w i t h e f f i c i e n t s e q u e s t r a t i o n might allow t h i s i n s e c t to b u i l d a c o n s i d e r a b l e  cardenolide  s t o r e which i s m a i n t a i n e d w h i l e t h e i n s e c t e x p l o i t s a l t e r n a t e h o s t species. However, t h e f i e l d d a t a show t h a t L_. k. k a l m i i c o l l e c t e d i n t h e l a t e s p r i n g on milkweed p l a n t s o f s e v e r a l s p e c i e s , e i t h e r c o n t a i n e d q u a n t i t i e s o f c a r d e n o l i d e s , o r l a c k e d t h e s e compounds a l t o g e t h e r .  small This  f i n d i n g suggests that these i n d i v i d u a l s e i t h e r l o s t t h e i r s t o r e o f cardenolides obtained before the winter, or are the o f f s p r i n g o f overw i n t e r i n g a d u l t s w h i c h d e p o s i t e d eggs on n o n - a s c l e p i a d a c e o u s  hosts.  In c o n t r a s t , t h e h o s t p l a n t r a n g e o f 0. f a s c i a t u s i n t e m p e r a t e N o r t h A m e r i c a i s r e s t r i c t e d t o members o f t h e genus A s c l e p i a s 1976).  (Ralph  In C a l i f o r n i a t h i s l y g a e i d has been seen on f i v e s p e c i e s o f  milkweed (A. f a s c i c u l a r i s , A. e r o s a , A. e r i o c a r p a , A. v e s t i t a v e s t i t a and A^. c a l i f o r n i c a g r e e n e i ) , and t h e l a b o r a t o r y - r e a r i n g  experiments  s u g g e s t t h a t a t l e a s t two o t h e r s p e c i e s (A. s p e c i o s a and A. c o r d i f o l i a ) w i l l support l a r v a l development,  0_. f a s c i a t u s i s known t o c o l o n i z e  76 A. s p e c i o s a i n o t h e r p a r t s o f t h i s i n s e c t ' s g e o g r a p h i c a l r a n g e (Andre  1934).  CJ. f a s c i a t u s i s a l o n g d i s t a n c e m i g r a n t s p e c i e s , r e c o l o n i z i n g milkweed s t a n d s i n C a l i f o r n i a e v e r y summer from i t s s i t e s o f o v e r w i n t e r i n g i n t h e s o u t h (perhaps M e x i c o ) .  The h o s t - p l a n t a s s o c i a t i o n s o f CJ. f a s c i a t u s  a t i t s s i t e s o f o v e r w i n t e r i n g a r e unknown. i n t o C a l i f o r n i a had d e v e l o p e d  I f the a d u l t s w h i c h i m m i g r a t e  on milkweed p l a n t s p r i o r to t h e i r l o n g  d i s p e r s a l f l i g h t s , one would e x p e c t to f i n d moderate q u a n t i t i e s o f l i d e s i n these i n s e c t s .  cardeno-  However, the f i r s t a r r i v i n g c o l o n i z e r s a t a l l  milkweed s t a n d s sampled c o n t a i n e d s m a l l q u a n t i t i e s o f c a r d e n o l i d e s . ther, comparison of t h i n - l a y e r chromatographic  Fur-  p r o f i l e s of cardenolides  between the e a r l y c o l o n i z e r s and l a b o r a t o r y - r e a r e d i n s e c t s s u g g e s t t h e s e s m a l l q u a n t i t i e s o f c a r d e n o l i d e s were a c c u m u l a t e d  that  on t h e p l a n t s on  which the i n s e c t s were c o l l e c t e d , r a t h e r than on some o v e r w i n t e r i n g  host:  the c a r d e n o l i d e p r o f i l e s o f i n s e c t s were i d e n t i c a l t o p r o f i l e s o f bugs r e a r e d i n t h e l a b o r a t o r y on t h e C a l i f o r n i a n s p e c i e s o f A s c l e p i a s .  This  s u g g e s t s t h a t t h e o v e r w i n t e r i n g h o s t s e i t h e r l a c k c a r d e n o l i d e s , o r have v e r y s m a l l q u a n t i t i e s ( c f . A.  fascicularis).  U n l i k e p o p u l a t i o n s o f CJ. f a s c i a t u s i n e a s t e r n N o r t h  America,  e a r l y c o l o n i z i n g 0_. f a s c i a t u s i n C a l i f o r n i a o f t e n a r r i v e a t milkweed s t a n d s b e f o r e d e v e l o p i n g pods and seeds a r e a v a i l a b l e ( R a l p h K.E.  Evans, unpubl. r e s u l t s , p e r s . o b s e r v . ) .  1976,  Where t h i s i n s e c t a r r i v e s  i n advance o f the f r u i t i n g season o f i t s h o s t , i t i s a b l e t o  reproduce  and l e a v e o f f s p r i n g which must d e v e l o p on p l a n t o r g a n s o t h e r than pods. However, i t i s o n l y the seeds o f t h e milkweed p l a n t which o p t i m a l growth and d e v e l o p m e n t o f l a r v a e ( R a l p h 1976), and  support populations  o f bugs o n l y i n c r e a s e a t a r a p i d r a t e when mature pods and seed a r e  77 present. Determination  o f the c a r d e n o l i d e content o f l a b o r a t o r y seed-  r e a r e d fj. f a s c i a t u s and bugs c o l l e c t e d on t h e same h o s t s i n t h e f i e l d shows t h a t fj. f a s c i a t u s can u s u a l l y s e q u e s t e r moderate t o l a r g e q u a n t i t i e s o f c a r d e n o l i d e s from some o f t h e i r h o s t s p e c i e s d u r i n g t h e f r u i t i n g season.  However, t h e l a b o r a t o r y s e e d - r e a r e d  insects often  c o n t a i n more c a r d e n o l i d e than i n s e c t s c o l l e c t e d i n t h e f i e l d ,  sug-  g e s t i n g t h a t bugs i n t h e n a t u r a l e n v i r o n m e n t may n o t f e e d e x c l u s i v e l y on s e e d , even when i t i s a v a i l a b l e .  L y g a e i d s o b t a i n w a t e r by t a p p i n g  the pod w a l l , l e a v e s , and stems o f milkweed p l a n t s and i n g e s t i n g t h e m i l k y s a p . In so d o i n g , they p r o b a b l y r e c e i v e some n u t r i e n t s i n t h e sap, w h i c h may n o t c o n t a i n t h e same c o n c e n t r a t i o n s o f c a r d e n o l i d e s as the seeds.  A l t e r n a t e l y , t h e t h i c k pod w a l l o f s e v e r a l s p e c i e s o f  A s c l e p i a s i n C a l i f o r n i a ( p a r t i c u l a r l y A. e r o s a , A. v_. v e s t i t a , A. c a l i f o r n i c a g r e e n e i and A_. s p e c i o s a ) may p r e v e n t l y g a e i d s from f e e d i n g on t h e seeds u n t i l t h e e a r l i e s t m a t u r i n g 1976).  pods b e g i n t o d e h i s c e  (Ralph  F u r t h e r , t h e p e r i o d o f time i n w h i c h 0_. f a s c i a t u s can f e e d  d i r e c t l y on seeds c a n be s e v e r l y l i m i t e d on milkweed s p e c i e s w h i c h have h i g h l y s y n c h r o n o u s pod d e h i s e n c e a n d / o r r a p i d seed d i s p e r s a l from d e h i s c i n g pods.  A l l o f these f a c t o r s probably l i m i t the a b i l i t y o f  both 0_. f a s c i a t u s and L. k_. k a l m i i t o s e q u e s t e r q u a n t i t i e s o f c a r d e n o l i d e s within the p h y s i o l o g i c a l l i m i t s o f the i n s e c t s . B e f o r e pods and seed a r e a v a i l a b l e , 0_. f a s c i a t u s f e e d s  almost  e x c l u s i v e l y on t h e d e v e l o p i n g f l o w e r buds and open f l o w e r s (Brown e t a l . 1976,  Evans, unpubl. r e s u l t s , p e r s . o b s e r v . ) .  T h i s s t u d y has shown t h a t  78 f o r ' a t l e a s t f o u r s p e c i e s o f A s c l e p i a s i n C a l i f o r n i a , the umbels (buds and f l o w e r s ) c o n t a i n r e l a t i v e l y l a r g e q u a n t i t i e s o f c a r d e n o l i d e s , y e t i n most samples, the bugs d i d n o t s e q u e s t e r p r o p o r t i o n a l q u a n t i t i e s o f c a r d e n o l i d e s from t h e s e s o u r c e s .  Ralph (1976) r e p o r t e d t h a t CJ. f a s c i a t u s  f e e d i n g on f l o w e r s o f A. s y r i a c a d i d n o t i n g e s t m a t e r i a l from o v a r i e s , but i n s t e a d f e d p r i m a r i l y on t h e n e c t a r , which may  the  lack  c a r d e n o l i d e s e n t i r e l y . Thus, t h e mode o f f e e d i n g o f CJ.' f a s c i a t u s m i g h t make the a v a i l a b i l i t y o f seed o f t h e h o s t p l a n t c r i t i c a l f o r t h e sequestration of cardenolides. IL. k_. k a l m i i has been shown t o s e q u e s t e r g r e a t e r q u a n t i t i e s o f c a r d e n o l i d e s from t h e umbels o f milkweeds than CJ. f a s c i a t u s .  Whether  t h i s i s a r e f l e c t i o n o f the h i g h e r s e q u e s t r a t i o n e f f i c i e n c y o f L^. k_. ka 1 m i i , o r a more e f f i c i e n t mode o f f e e d i n g than 0_. f a s c i a t u s r e q u i r e s more d e t a i l e d i n v e s t i g a t i o n . As p r e v i o u s l y i n d i c a t e d , l ^ . k^. k a l m i i was seen on a l l but one o f t h e n i n e s p e c i e s o f A s c l e p i a s examined (A. s o l a n o a n a  being  the e x c e p t i o n ) , and was r e p r e s e n t e d by a t l e a s t some i n d i v i d u a l s a t a l m o s t e v e r y milkweed s t a n d v i s i t e d .  The l a r g e s t numbers o f bugs were  seen a t s t a n d s o f A. f a s c i c u l a r i s , A. c o r d i f o l i a and A. g r e e n e i which bore mature seed pods.  californica  On the o t h e r hand, 0. f a s c i a t u s  i s a more s e l e c t i v e h e r b i v o r e , i n terms o f t h e numbers o f h o s t species u t i l i z e d . In t h e m i l k w e e d - r i c h  F r e n s o a r e a , l a r g e p o p u l a t i o n s o f CJ.  f a s c i a t u s o c c u r on f o u r b r o a d - l e a f s p e c i e s (A. y_. v e s i t a , A. e r o s a , A. e r i o c a r p a , and A_. c a l i f o r n i c a g r e e n e i ) as w e l l as the  narrow-leaved  79 A. f a s c i c u l a r i s . A l l o f t h e s e h o s t s p e c i e s a p p e a r e d to be c o l o n i z e d to more o r l e s s the same e x t e n t .  In the more n o r t h e r l y c o l l e c t i n g a r e a  (Napa v a l l e y and a d j a c e n t Y o l o , S o l a n o and C o t n r a C o s t a c o u n t i e s ) , t h e o n l y m i l k w e e d c o l o n i z e d by 0. f a s c i a t u s i s A. f a s c i c u l a r i s . L a r g e s t a n d s o f A. c o r d i f o l i a , A. s p e c i o s a , and A. e r i o c a r p a were n o t c o l o n i z e d d u r i n g the summer o f 1976,  even though many o f t h e s e p l a n t s bore l a r g e  numbers o f pods and o f t e n grew w i t h i n a few k i l o m e t e r s o f A. f a s c i c u l a r i s s t a n d s w h i c h were i n f e s t e d w i t h fj. f a s c i a t u s . observations  Furthermore, f i e l d  i n d i c a t e d t h a t even the s m a l l e s t , most i s o l a t e d milkweed  s t a n d s i n the F r e n s o a r e a were c o l o n i z e d by some bugs, s u g g e s t i n g the b r o a d - l e a f s p e c i e s i n the n o r t h bay a r e a were not s i m p l y by i m m i g r a t i n g  that  overlooked  Cj. f a s c i a t u s on t h e b a s i s o f t h e i r p o p u l a t i o n s i z e o r  habitat. The f a i l u r e t o f i n d CJ. f a s c i a t u s on A. c o r d i f o l i a a t any t i m e at l o c a l i t i e s studied i s p a r t i c u l a r l y mysterious.  In t h e l a r v a l r e a r i n g  e x p e r i m e n t s d e s c r i b e d i n t h i s t h e s i s , seeds o f A. c o r d i f o l i a  supported  l a r v a l growth and d e v e l o p m e n t o f CJ. f a s c i a t u s equal to t h a t o f most o t h e r s p e c i e s o f A s c l e p i a s , s u g g e s t i n g t h a t t h e r e i s no n u t r i t i o n a l b a r r i e r p r e v e n t i n g Cj. f a s c i a t u s from e x p l o i t i n g t h i s milkweed s p e c i e s . Perhaps A. c o r d i f o l i a l a c k s some v i s u a l o r o l f a c t o r y cues w h i c h Q_. f a s c i a t u s may  use i n o r i e n t a t i o n t o i t s h o s t s ( P a n t l e and F e i r 1976).  One m i g h t even c o n c l u d e  t h a t CJ. f a s c i a t u s i n t h i s r e g i o n does not  u t i l i z e an optimum f o r a g i n g s t r a t e g y , f o r i t does n o t c o l o n i z e h o s t s p e c i e s w h i c h a r e c a p a b l e o f s u p p o r t i n g p o p u l a t i o n s o f bugs.  On  the  o t h e r hand, l a b o r a t o r y r e a r i n g o f Cj. f a s c i a t u s a t 25°C i n d i c a t e d t h a t  80 l a r v a l d e v e l o p m e n t was more r a p i d on A. f a s c i c u l a r i s compared t o o t h e r milkweed s p e c i e s t e s t e d , which would s u g g e s t a s h o r t e r g e n e r a t i o n  time  o f 0. f a s c i a t u s f e e d i n g on t h i s h o s t i n the n a t u r a l e n v i r o n m e n t . A. f a s c i c u l a r i s s t a n d s i n t h e Napa V a l l e y s u p p o r t l a r g e r e p r o d u c i n g p o p u l a t i o n s o f fj_. f a s c i a t u s (K.E. E v a n s , u n p u b l .  results).  The a n a l y s i s o f p l a n t and i n s e c t m a t e r i a l d e s c r i b e d i n t h i s t h e s i s has shown t h a t t h e s e i n s e c t s c o n t a i n r e l a t i v e l y small q u a n t i t i e s o f c a r d e n o l i d e s i n t h e i r b o d i e s , r e f l e c t i v e o f the c a r d e n o l i d e c o n t e n t o f the h o s t p l a n t .  T h e r e f o r e , i t i s suggested  part of i t s geographical  t h a t CJ. f a s c i a t u s i n t h i s  r a n g e does n o t maximize i t s o p p o r t u n i t i e s to  s e q u e s t e r l a r g e q u a n t i t i e s o f c a r d e n o l i d e s , f o r i t does n o t c o l o n i z e the s p e c i e s o f A s c l e p i a s which a r e r i c h e r i n t h e s e s e c o n d a r y  plant  substances. 52 per c e n t o f the f i e l d - c o l l e c t e d l y g a e i d s i n t h i s s t u d y were found to c o n t a i n l e s s than 50 yg o f c a r d e n o l i d e p e r i n s e c t .  While t h i s  sample o f l y g a e i d s i n C a l i f o r n i a i s not a random one, i t i s a r e p r e s e n t a t i v e one, based on t h e o c c u r r e n c e o f 0_. f a s c i a t u s and L_k_. k a l m i i on the d i f f e r e n t milkweed s p e c i e s o b s e r v e d :  a l a r g e p r o p o r t i o n o f t h i s 52  per c e n t was 0_. f a s c i a t u s from A. f a s c i c u l a r i s . widespread  T h i s p l a n t i s t h e most  s p e c i e s o f milkweed i n C a l i f o r n i a , and a l t h o u g h i t p r o b a b l y  does n o t c o n s t i t u t e the l a r g e s t s p e c i e s i n the s t a t e i n terms o f biomass, i t c e r t a i n l y o c c u r s i n h i g h d e n s i t i e s i n many d i f f e r e n t h a b i t a t s and p l a n t communities.  I t has been s u g g e s t e d  t h a t the abundance and  d i s t r i b u t i o n o f A_. f a s c i c u l a r i s c o u l d a c c o u n t i n p a r t f o r the h i g h p r o p o r t i o n (47 p e r c e n t ) o f monarch b u t t e r f l i e s c o l l e c t e d i n C a l i f o r n i a  81 w i t h o n l y small to immeasurable q u a n t i t i e s o f c a r d e n o l i d e s i n a s t u d y o f w i l d monarchs by Brower and M o f f i t t (1974). The p r e s e n t work has shown t h a t t h e l y g a e i d bugs 0. f a s c i a t u s and L_. k_. k a l m i i i n c e n t r a l C a l i f o r n i a c o n t a i n v a r i e d q u a n t i t i e s o f cardenolides.  The r o l e o f c a r d e n o l i d e s i n t h e s e m i l k w e e d - f e e d i n g  remains l a r g e l y i n q u e s t i o n .  lygaeids  I t must be emphasized t h a t o n l y when t h e  n a t u r a l p r e d a t o r s o f t h e s e i n s e c t s a r e known w i l l we be a b l e t o t e s t the e f f e c t i v e n e s s o f c a r d e n o l i d e s as a p o t e n t i a l c h e m i c a l d e f e n c e agent i n these i n s e c t s .  No i n c i d e n t s o f p r e d a t i o n o f l y g a e i d s were seen  t h e c o u r s e o f f i e l d work d u r i n g t h i s s t u d y .  during  S a u e r and F e i r (1972)  s t u d i e d p r e d a t i o n o f 0_. f a s c i a t u s i n a s t a n d o f A. s y r i a c a i n M i s s o u r i o v e r a p e r i o d o f f i v e months and r e p o r t e d t h a t t h e o n l y p r e d a t o r s o f 0_. f a s c i a t u s o b s e r v e d were i n s e c t p r e d a t o r s , e.g. brown l a c e w i n g (Hemerobiidae).  In the p r e s e n t s t u d y , s e v e r a l a n t h r o p o d  o b s e r v e d f r e q u e n t l y on milkweed p l a n t s , i n c l u d i n g m a n t i d s  larvae  p r e d a t o r s were (Stagomantis  c a l i f o r m " c a Rehn & Heb.), a s s a s i n bugs ( Z e l u s s p . ) , ambush bugs (Phymata e r o s a L . ) , c r a b s p i d e r s (Misumena sp.) and jumping s p i d e r s ( P h i d i p p u s s p . ) . I n d i v i d u a l s o f t h e f o r m e r t h r e e were t a k e n i n t o the l a b o r a t o r y and o f f e r e d a d u l t , o r second and t h i r d i n s t a r 0_. f a s c i a t u s , but none o f the c o u l d be i n d u c e d to a t t a c k t h e l y g a e i d s .  predators  M a n t i d s c o l l e c t e d on A_. e r o s a  p l a n t s were a s s a y e d f o r c a r d e n o l i d e s , but were f o u n d to l a c k t h e s e compounds,  s u g g e s t i n g t h a t t h e i r p r e y items c o n s i s t e d s o l e l y o f  p o l l i n a t o r s of Asclepias.  P o l l i n a t o r s such as the honey bee,  Apis  m e l l i f e r a L. were f r e q u e n t l y c a u g h t by c r a b s p i d e r s h i d i n g i n milkweed umbels.  82  Gelperin  (1968)  reported that the mantids Paratanodera  sinensis  S a u s s u r e and M a n t i s r e l i g i o s a L. would a t t a c k a d u l t CJ. f a s c i a t u s , b u t subsequently  r e j e c t t h e l y g a e i d a s a p r e y i t e m , o o s s i b l y on t h e b a s i s o f  o l f a c t o r y cues.  M a n t i d s l e a r n e d t o r e j e c t CJ. f a s c i a t u s on s i g h t a l o n e ,  but i n h i b i t i o n o f t h e s t r i k e r e s p o n s e was dependant on t h e n u t r i t i o n a l state o f the mantid. No i n c i d e n c e o f p r e d a t i o n o f l y g a e i d s by v e r t e b r a t e s were observed  i n t h i s f i e l d s t u d y , o r i n t h e s t u d y o f S a u e r and F e i r  (1972).  However, g u t a n a l y s e s o f b i r d s and a m p h i b i a n s (R.T. M i t c h e l l , u n p u b l i s h e d r e s u l t s ) i n d i c a t e t h a t l a r g e numbers o f L_. k a l m i i r a t e s , i n p a r t i c u l a r t h e sage g r o u s e C e n t r o c e r c u s  a r e e a t e n by v e r t e b urophasianus  Bona..,  the s c a l e d q u a i l C a l l i p e p ! a squamata V i g o r s , and t h e r o a d r u n n e r G e o c o c c y x c a l i f o r n i a n u s L e s s o n . I t was n o t known w h e t h e r any o f t h e s e i n s e c t s c o n t a i n e d c a r d e n o l i d e s o r n o t . Because i t i s n o t known what level o f cardenolide content i n the C a l i f o r n i a n lygaeids i s required to c a u s e an e m e t i c o r d i s t r e s s f u l r e s p o n s e  i n a vertebrate predator, the  f u l l i m p l i c a t i o n o f t h e c a r d e n o l i d e v a r i a t i o n cannot y e t be e s t a b l i s h e d . Perhaps t h e b e s t documented b i o a s s a y o f A s c l e p i a s c a r d e n o l i d e s and c a r d e n o l i d e s s t o r e d by an i n s e c t f e e d i n g on A s c l e p i a s i s t h e b l u e j a y e m e t i c d o s e ^ t e s t o f Brower e t a l .  (1968).  In e x a m i n i n g t h e e m e t i c r e s p o n s e o f t h e b l u e j a y ( C y a n o c i t t a c r i s t a t a ) t o t h e monarch b u t t e r f l y (D_. p l e x i p p u s ) r e a r e d on t h e neot r o p i c a l milkweed A. c u r a s s a v i c a , Brower e t aJL e m e t i c dose  (ED^Q)  f o r a n 85 g b i r d .  r e q u i r e d between  68  and  84  (1975)  r e p o r t e d t h a t one  yg equivalents o f d i g i t o x i n  A d d i t i o n a l c a l c u l a t i o n s from t h e d a t a o f Brower and  83  Glazier  i n d i c a t e t h a t f o r the abdomen o f such a b u t t e r f l y , a  (1975)  s i n g l e ED^Q  c o n s i s t s o f from 44 t o 54-yg  o f c a r d e n o l i d e whereas a s i n g l e  EDgQ from the c a r d e n o l i d e s s t o r e d i n t h e wings o f the same i n s e c t r e q u i r e s from 232 to 238  yg.  I t has been e s t a b l i s h e d t h a t owing t o p h y s i o l o g i c a l b a r r i e r s i n vertebrates  p o l a r c a r d e n o l i d e s tend to have lower e m e t i c p o t e n c i e s  do n o n - p o l a r o n e s , when a d m i n i s t e r e d v i a the o r a l r o u t e ( s e e D u f f e y f o r a complete d i s c u s s i o n ) .  than 1976  T h i s r e l a t i o n s h i p i s l a r g e l y because o f the  more r a p i d a b s o r p t i o n o f l i p o p h i l i c c a r d e n o l i d e s a c r o s s the g u t , and t h e i r more e f f e c t i v e p r o t e i n Gisvold  1952,  b i n d i n g i n the b l o o d s t r e a m  Parsons and Summers  (White  and  1971).  P r e l i m i n a r y s t u d i e s (Parsons 1965,  R e i c h s t e i n e t al_, 1968)  have  shown t h a t the p r i n c i p l e c a r d e n o l i d e s s t o r e d by the monarch r e a r e d on A. c u r a s s a v i c a a r e the r e l a t i v e l y n o n - p o l a r c h e m i c a l s c a l o t r o p i n and c a l a c t i n ( F i g u r e 1 ) , w h i c h c o u l d a c c o u n t f o r the r e l a t i v e l y h i g h p o t e n t i a l o f t h e whole b u t t e r f l y the wings  (232-238  (68-84  y g per  ED^Q)  emetic  compared to t h a t o f  y g per E D ) . 5 Q  I t i s c o n c e i v a b l e t h a t the lower e m e t i c i t y o f the c a r d e n o l i d e s i n the wings o f t h e monarch b u t t e r f l i e s may be owing to the p r e s e n c e o f a l a r g e r p r o p o r t i o n of p o l a r c a r d e n o l i d e s i n these organs i n comparison t o t h e c a r d e n o l i d e compliment o f t h e e m e t i c a l l y - p o t e n t abdomen.  Thus t h e  monarch may p a r t i t i o n i t s c a r d e n o l i d e s ' i n a f a s h i o n s i m i l a r to 0_. f a s c i a t u s which p r e f e r e n t i a l l y s e q u e s t e r s more p o l a r compounds i n the d o r s o - l a t e r a l s p a c e f l u i d , w h i l e more l i p o p h i l i c c a r d e n o l i d e s o c c u r i n t h e f a t body ( D u f f e y , unpubl.  results).  84 The r e l a t i o n s h i p  between e m e t i c a c t i v i t y and p o l a r i t y o f  A s c l e p i a s c a r d e n o l i d e s may be c o n s i d e r a b l y more complex t h o u g h .  Roeske  et^ al_. (1976) r e a r e d D_. p l e x i p p u s i n t h e l a b o r a t o r y on t h e l e a v e s o f A. c u r a s s a v i c a and t h e A f r i c a n a s c l e p i a d Gomphocarpus s p . , and found t h e c a r d e n o l i d e s s t o r e d by t h e b u t t e r f l i e s r e a r e d on A. c u r a s s a v i c a t o be 2.6 times more e m e t i c a l l y p o t e n t ( p e r mg o f c a r d e n o l i d e ) than s t o r e d by t h e monarchs r e a r e d on Gomphocarpus.  those  However, t h e c a r d e n o l i d e  p r o f i l e s o f t h e s e i n s e c t s show t h a t t h e c a r d e n o l i d e s s t o r e d by t h e b u t t e r f l i e s from t h e d i f f e r e n t p l a n t s o c c u r o v e r t h e same p o l a r i t y  range,  w i t h r o u g h l y t h e same p r o p o r t i o n o f p o l a r t o n o n - p o l a r compounds.  There-  fore, t h e i r r e s u l t s indicate that the cardenolides sequestered  by t h e  b u t t e r f l y from t h e d i f f e r e n t p l a n t s d i f f e r q u a l i t a t i v e l y i n terms o f t h e i r emetic potencies, i r r e s p e c t i v e o f t h e i r p o l a r i t y .  C a l o t r o p i n and  i t s s t e r e o i s o m e r c a l a c t i n a c c o u n t f o r a l m o s t 65 p e r c e n t o f t h e c a r d e n o l i d e s s t o r e d by t h e b u t t e r f l i e s r e a r e d on A. c u r a s s a v i c a , whereas t h e s e compounds were found t o be a b s e n t i n monarchs r e a r e d on Gomphocarpus (Roeske e t al_. 1976). In an e a r l i e r s t u d y , Brower and M o f f i t t (1974) r e p o r t e d a causal r e l a t i o n s h i p  between c a r d e n o l i d e c o n t e n t o f w i l d monarch b u t t e r -  f l i e s and t h e i r e m e t i c p o t e n c y .  However, b u t t e r f l i e s c o l l e c t e d i n  C a l i f o r n i a were 4.6 t o 6.5 times more e m e t i c o v e r t h e same r a n g e o f c a r d e n o l i d e c o n t e n t as b u t t e r f l i e s t a k e n i n M a s s a c h u s e t t s ; r e a r i n g study, the c a r d e n o l i d e p r o f i l e s o f the C a l i f o r n i a n Massachusetts  As i n t h e and  monarchs c o v e r e d t h e same p o l a r i t y r a n g e , w i t h  approxi-  m a t e l y equal p r o p o r t i o n s o f p o l a r t o n o n - p o l a r compounds i n each g r o u p  85 (Roeske e_t a]_. 1976).  A g a i n the h i g h e r p o t e n c i e s p e r m i l l i g r a m o f  c a r d e n o l i d e i n t h e C a l i f o r m " a n monarchs r e f l e c t q u a l i t a t i v e d i f f e r e n c e s i n t h e c a r d e n o l i d e s s t o r e d by the two groups o f b u t t e r f l i e s . C a l o t r o p i n and c a l c a t i n were a b s e n t f r o m the b u t t e r f l i e s c o l l e c t e d i n  Massachusetts,  w h i l e some o f the b u t t e r f l i e s i n the C a l i f o r n i a sample c o n t a i n e d a l a r g e p r o p o r t i o n o f t h e s e compounds amongst t h e i r c a r d e n o l i d e  stores.  S i m i l a r l y , the A f r i c a n g r a s s h o p p e r P o e k i l o c e r u s b u f o n i u s  stores  l a r g e q u a n t i t i e s o f c a l o t r o p i n and c a l a c t i n , when r e a r e d on the milkweeds A_. c u r a s s a v i c a and C a l o t r o p i s p r o c e r a (von Euw e t a]_. 1967); t h i s i n s e c t has been shown t o c a u s e e m e s i s i n w h i t e mice and the European j a y ( G a r r u l u s g l a n d a r i u s L.) ( R o t h s c h i l d 1966).  While l a r g e l y c i r c u m s t a n t i a l ,  t h i s e v i d e n c e a l o n g w i t h the d i f f e r e n t e m e t i c p o t e n c i e s o f t h e body p a r t s o f JJ. p l e x i p p u s as r e p o r t e d by Brower and G l a z i e r s u g g e s t t h a t t h e p r e s e n c e o f c a l o t r o p i n and c a l a c t i n may f o r the e m e t i c r e s p o n s e seen i n t h e b l u e j a y .  separate (1975),  l a r g e l y account  R o t h s c h i l d e t aj_. (1975  and u n p u b l . r e s . ) r e a r e d JJ. p l e x i p p u s on t h e i r 'Oxford s t r a i n ' o f A. c u r a s s a v i c a , w h i c h l a c k s c a l a c t i n e n t i r e l y . T h i s compound was  also  a b s e n t from the b u t t e r f l i e s , w h i c h f a i l e d t o i n d u c e e m e s i s i n  pigeons  (Columba 1 i v e a  Gm.).  Examination  o f whole body e x t r a c t s o f f i e l d c o l l e c t e d 0_.  f a s c i a t u s and J_. k_. k a l m i i ( n o t d e s c r i b e d i n t h i s t h e s i s ) shows t h a t a l l o f the c a r d e n o l i d e s s t o r e d i n t h e s e i n s e c t s a r e more p o l a r t h a t c a l o t r o p i n o r c a l a c t i n . Should t h e s e more p o l a r c a r d e n o l i d e s f r o m t h e C a l i f o r n i a n s p e c i e s o f A s c l e p i a s by l y g a e i d s be found have s i m i l a r p h a r m a c o l o g i c a l  p r o p e r t i e s t o the c a r d e n o l i d e  derived to  compliment  86  i n the wings o f t h e monarch b u t t e r f l y r e a r e d on A. c u r a s s a v i c a (Brower and G l a z i e r 1975), i t would seem p o s s i b l e t h a t few, i f any o f t h e i n d i v i d u a l l y g a e i d s c o l l e c t e d i n t h i s s t u d y c o n t a i n e d enough c a r d e n o l i d e o f t h e r e q u i r e d t y p e t o e l i c i t an e m e t i c r e s p o n s e f r o m a p r e d a t o r w i t h a s e n s i t i v i t y s i m i l a r t o the b l u e j a y .  R o u g h l y 50 p e r c e n t o f the  f i e l d - c a u g h t milkweed bugs examined were f o u n d to c o n t a i n l e s s than 50 yg o f c a r d e n o l i d e per i n s e c t .  However, t h e s e i n s e c t s c o u l d i n c r e a s e  t h e i r e m e t i c p o t e n t i a l by way o f t h e i r g r e g a r i o u s b e h a v i o u r ; a p r e d a t o r m i g h t i n g e s t s e v e r a l i n d i v i d u a l s a t one f e e d i n g , w i t h the t o t a l c a r d e n o l i d e pool o f s e v e r a l i n s e c t s e l i c i t i n g an e m e t i c r e s p o n s e e t al_. 1973).  (Pough  On the o t h e r hand, the number o f i n s e c t s needed to  c o n d i t i o n the p r e d a t o r to a v o i d the s p e c i e s as a p r e y i t e m m i g h t o u t w e i g h the a d v a n t a g e o f such  gregariousness.  Even i f t h e a d u l t s o f CJ. f a s c i a t u s and L_. k_. k a l m i i w i t h g r e a t e r than 100 yg per i n s e c t a r e f o u n d t o have some c h e m i c a l  protection  from p r e d a t o r s , the d a t a p r e s e n t e d i n t h i s t h e s i s s u g g e s t t h a t the e f f e c t i v e n e s s o f c a r d e n o l i d e s e q u e s t r a t i o n as a c h e m i c a l d e f e n s e  strategy  may v a r y o v e r t h e g e o g r a p h i c a l r a n g e o f t h e s e s p e c i e s , and may v a r y i n the c o u r s e o f a season a t a p a r t i c u l a r l o c a t i o n . A f u r t h e r c o m p l i c a t i o n to u n d e r s t a n d i n g  the e f f e c t i v e n e s s o f  c a r d e n o l i d e s s t o r e d by l y g a e i d s i s the v a r i a t i o n o f s e n s i t i v i t i e s to c a r d e n o l i d e s among p o t e n t i a l v e r t e b r a t e p r e d a t o r s .  The b l u e j a y (C_.  c r i s t a t a ) and European j a y (G_. g l a n d a r i u s ) a r e c o n s i d e r e d to be s p e c i e s w h i c h a r e s e n s i t i v e to c a r d e n o l i d e s , the European hedgehog ( E r i n a c e u s e u r o p a e u s L.) and l a b o r a t o r y r a t a r e n o t , and the J a p a n e s e q u a i l  87 ( C o t u r n i x j a p o n i c u s Tern.) can t o l e r a t e q u a n t i t i e s o f d i g i t o x i n up t o 50 times g r e a t e r than t h e human l e t h a l dose ( R o t h s c h i l d and K e l l e t t 1972). D u f f e y (1970) found t h a t fj_. f a s c i a t u s r e a r e d i n the l a b o r a t o r y on seeds o f A. s y r i a c a ( t h e i n s e c t s c o n t a i n e d a mean o f 284 yg o f c a r d e n o l i d e i n s e c t ) were c o m p l e t e l y  per  p a l a t a b l e to both f r o g s (Rana p i p i e n s S c h r e b e r )  and toads (Bufo b o r e a s B a i r d & G i r a r d ) .  Thus i n c o n s i d e r i n g the p o s i t i o n  o f m i l k w e e d - f e e d i n g l y g a e i d s i n m i m i c r y complexes one can o n l y the s t a t e m e n t o f R e t t e n m e y e r (1970), who  repeat  wrote:  "... i n s t e a d o f r e f e r r i n g to an i n s e c t as a B a t e s i a n i t would be more n e a r l y a c c u r a t e to s t a t e t h a t under s p e c i f i e d c o n d i t i o n s the i n s e c t , o r some p a r t o f i t s i n a c e r t a i n l o c a l i t y has a B a t e s i a n r e l a t i o n s h i p t o predator."  mimic, the population a specific  I t may n o t be v a l i d to a s s e s s p l a n t - d e r i v e d c a r d e n o l i d e s as a d e f e n s i v e s t r a t e g y o f l y g a e i d s s t r i c t l y on t h e b a s i s o f t h e i r e m e t i c p o t e n t i a l to a v e r t e b r a t e .  It i s e n t i r e l y possible that predators  could  become c o n d i t i o n e d t o a v o i d b r i g h t l y c o l o u r e d l y g a e i d s and o t h e r m i l k w e e d v  f e e d i n g i n s e c t s on t h e b a s i s o f g a s t r i c d i s t r e s s ( i . e . nausea) o r t o x i c o s i s , n e i t h e r o f which need be o u t w a r d l y (cf.  delayed  v i s i b l e to an e x p e r i m e n t o r  emesis). Cardiac glycosides are capable of causing d i r e c t i r r i t a t i o n of  g a s t r i c t i s s u e ( G o l d e t aj_. 1950), and have been shown t o c a u s e s t r o n g c o n t r a c t i o n o f v e r t e b r a t e smooth m u s c l e i n i s o l a t e d p r e p a r a t i o n s ( H a u s t e i n ejt al_. 1966, a l . 1963).  G o d f r a i n d and G o d f r a i n d - d e  B e c k e r 1961,  S h i g e i ejt  Rowe e t al_. (1970) s t u d i e d the t o x i c i t y o f the milkweed A.  b r a c h y s t e p h a n a Englem i n s h e e p , and r e p o r t e d t h a t symptoms o f s u b - l e t h a l doses o f c a r d e n o l i d e - c o n t a i n i n g  p l a n t m a t e r i a l (from which t h e  animal  88 f u l l y r e c o v e r e d ) , i n c l u d e d d i a r r h e a and l a b o u r e d b r e a t h i n g . While d i f f i c u l t to q u a n t i f y , e f f e c t s o f t h i s nature might p o s s i b l y l e a d t o the c o n d i t i o n e d a v e r s i o n o f p r e d a t o r t o c a r d e n o l i d e c o n t a i n i n g i n s e c t s . C z a p l i c k i e_t aj_. (1975) d e m o n s t r a t e d v i a b i l i t y o f the c o n c e p t o f o l f a c t o r y m i m i c r y .  the t h e o r e t i c a l  In an a r t i f i c i a l  s i t u a t i o n , g a r t e r snakes (Thamnophis sp.) were c o n d i t i o n e d t o r e j e c t e d i b l e p r e y items t h a t bore an o l f a c t o r y resemblance  t o worms a f t e r  h a v i n g e x p e r i e n c e d a d e l a y e d t o x i c o s i s f o l l o w i n g t h e i r i n g e s t i o n o f the worms.  L a b o r a t o r y r a t s and q u a i l can a l s o l e a r n t o a s s o c i a t e g u s t a t o r y  and v i s u a l cues w i t h d e l a y e d t o x i c o s i s , l e a d i n g t o t h e i r  subsequent  r e j e c t i o n o f f o o d and water which c o n t a i n s t h e s e cues (Wilcoxon e t a l . 1974). To d a t e , the o n l y p h a r m a c o l o g i c a l i n v e s t i g a t i o n s u s i n g c a r d e n o l i d e s from A s c l e p i a s - f e e d i n g i n s e c t s a r e t h o s e o f Brower and c o workers u s i n g t h e b l u e j a y e m e t i c dose^Q b i o a s s a y (Brower ejt al_.  1968).  A p i l o t s t u d y o f t h e t o x i c i t y o f ' l y g a e i n i n ' ( t e n t a t i v e name f o r a compound i s o l a t e d by t h e a u t h o r from both 0_. f a s c i a t u s and L^. k_. k a l m i i , s e q u e s t e r e d from s e v e r a l C a l i f o r n i a n s p e c i e s o f A s c l e p i a s ) u s i n g the embryonic  c h i c k h e a r t b i o a s s a y o f Lehman and P a f f (1942), i n d i c a t e d t h a t  t h i s compound was as p o t e n t as c o m m e r c i a l l y o b t a i n e d d i g i t o x i n cribed experiment).  (under-  However, the i n t r a v e n o u s e m e t i c p o t e n c y o f  c a l a c t i n i n the c a t i s t h r e e t i m e s g r e a t e r than t h a t o f d i g i t o x i n ( P a r s o n s and Summers 1971).  C l e a r l y , a l l o f the pharmacological  effects  o f A s c l e p i a s c a r d e n o l i d e s and t h o s e o b t a i n e d by i n s e c t s from milkweed p l a n t s a r e i n need o f i n v e s t i g a t i o n b e f o r e the e c o l o g i c a l r o l e o f the  89 compounds i n the i n s e c t s w i l l be One p h a r m a c o l o g i c a l g r e a t l y underestimated  understood.  e f f e c t o f c a r d e n o l i d e s w h i c h may  is their bitter taste.  have been  Most c a r d e n o l i d e s  (Brower  and G l a z i e r 1975 c i t e T. R e i c h s t e i n ) , l i k e o t h e r p l a n t g l y c o s i d e s (Kingsbury  1964)  a r e b i t t e r t o the human t a s t e .  shown t o have w e l l d e v e l o p e d Duncan 1960,  Yang & Kare 1968,  Some b i r d s have been  t a s t e r e c e p t o r s ( K i t c h e l l e t a]_. Wenzel 1973)  1959,  and have shown an a v e r s i o n  to b i t t e r compounds (Wenzel 1973); such a r e s p o n s e has been used to investigate  l e a r n i n g a b i l i t y i n some s p e c i e s ( e . g . A l c o c k 1971;  Brower and G l a z i e r f o r s e v e r a l o t h e r r e f e r e n c e s ) .  see  Brower and G l a z i e r  (1975) have r i g h t l y a d o p t e d t h i s argument t o s u g g e s t t h a t some b i r d s c o u l d use t h e b i t t e r t a s t e o f c a r d e n o l i d e s to d i s c r i m i n a t e between emetic and n o n - e m e t i c monarch b u t t e r f l i e s .  T h e i r f i n d i n g s t h a t the  wings o f t h e monarch c o n t a i n the l a r g e s t c o n c e n t r a t i o n s o r c a r d e n o l i d e s , but t h e l e a s t e m e t i c among t h o s e i n t h e body, s u p p o r t the c o n c e p t o f an a n t i - p r e d a t o r s t r a t e g y based on the t a s t e o f c a r d e n o l i d e s .  Similarly,  the h i g h e s t c o n c e n t r a t i o n s o f c a r d e n o l i d e s i n the l y g a e i d bugs fJ. f a s c i a t u s and J_. k_. k a l m i i a r e found i n t h e f l u i d o f the d o r s o - l a t e r a l s p a c e s ( D u f f e y and S c u d d e r 1974): when r o u g h l y h a n d l e d ,  the f l u i d f r o m  t h e s e s p a c e s i s r e l e a s e d as d i s c r e t e d r o p l e t s o n t o the c u t i c l e f r o m the d o r s o - l a t e r a l edge o f t h e m e t a t h o r a x and abdominal segments ( S c u d d e r and D u f f e y 1972,  Graham and Staddon 1974).  The a d v a n t a g e o f h a v i n g the h i g h e s t c o n c e n t r a t i o n s o f b i t t e r t a s t i n g c a r d e n o l i d e s i n both t h e wings o f the monarch and the s e c r e t e d s p a c e f l u i d o f t h e l y g a e i d i s t h a t t h e p r e d a t o r can sample the i n s e c t without  the f o r m e r s a c r i f i c i n g i t s l i f e .  90 Other v e r t e b r a t e s may be h i g h l y s e n s i t i v e t o t h e b i t t e r t a s t e o f cardiac glycosides.  In t h e v e t e r i n a r y l i t e r a t u r e , most a u t h o r s  suggest  t h a t p l a n t m a t e r i a l o f A s c l e p i a s may l o s e i t s d i s a g r e e a b l e f l a v o r when d r y , w h i l e r e t a i n i n g i t s t o x i c i t y ( H u l b e r t and Oehme 1965, V a i l 1942). The r e a s o n f o r t h i s o b s e r v a t i o n c o u l d be t h a t t h e a v a i l a b i l i t y o f t h e b i t t e r c a r d e n o l i d e s t o t h e t a s t e r e c e p t o r s i s l e s s e n e d when i n t h e dry s t a t e . I t i s c o n c e i v a b l e t h a t c a r d e n o l i d e s i n l y g a e i d bugs, s e c r e t e d i n h i g h l y c o n c e n t r a t e d d r o p l e t s o n t o t h e c u t i c l e , c o u l d g i v e r i s e t o an e x t r e m e l y r a p i d r e s p o n s e by a p r e d a t o r t a k i n g t h e i n s e c t i n t o i t s mouth. A l t h o u g h no q u a n t i t a t i v e s t u d i e s have been u n d e r t a k e n ,  small q u a n t i t i e s  o f c a r d e n o l i d e s , such as t h o s e found i n many o f t h e C a l i f o r n i a n l y g a e i d s , may be enough t o e l i c i t an e f f e c t i v e r e s p o n s e from a v e r t e b r a t e  predator,  even though t h e q u a n t i t y and q u a l i t y o f t h o s e c a r d e n o l i d e s i s f a r below that necessary to cause  emesis.  I f p l a n t d e r i v e d c a r d e n o l i d e s a r e n o t b e i n g employed by l y g a e i d bugs an an : a n t i - p r e d a t o r , s t r a t e g y , then:.what. s t r a t e g i e s m i g h t t h e s e warningly-coloured  i n s e c t s r e l y upon t o a v o i d p r e d a t i o n ?  L i k e most  H e m i p t e r a , 0_. f a s c i a t u s and _L. k_. k a l m i i p o s s e s s m e t a - t h o r a c i c g l a n d s i n t h e a d u l t s t a g e (Games and Staddon 1973). e x c r e t e v o l a t i l e a l k y l compounds ( e . g . h e x a n o l s )  scent  These glands, which  could provide the basis  for unpalatabi1ity i n certain responsive vertebrate predators.  Duffey  (1970) found t h a t among s e v e r a l grades o f v e r t e b r a t e p r e d a t o r s , none r e s p o n d e d t o t h e c a r d e n o l i d e s o f CL f a s c i a t u s when r e a r e d on seeds o f A. s y r i a c a , whereas some p r e d a t o r s ( t u r t l e s and c h i c k e n s ) a v o i d e d  this  91 i n s e c t because of i t s v o l a t i l e scent gland s e c r e t i o n s .  Similar results  have been shown f o r a n o l i s l i z a r d s p r e s e n t e d w i t h s u n f l o w e r - r e a r e d 0_. f a s c i a t u s (Weber 1975).  I t i s c o n c e i v a b l e t h e n , t h a t some p r e d a t o r s  i n the n a t u r a l e n v i r o n m e n t  c o u l d r e j e c t 0_. f a s c i a t u s and II. _k. k a l m i i  because o f t h e s e s e c r e t i o n s , i r r e s p e c t i v e o f t h e c a r d e n o l i d e c o n t e n t o f the i n s e c t s . Graham and Staddon (1974) have d e m o n s t r a t e d of a histamine analogue  the  presence  i n t h e d o r s o - l a t e r a l s p a c e , f l u i d , and o t h e r  body f l u i d s o f a d u l t and l a r v a e o f fJ. f a s c i a t u s . T h i s compound  was  shown t o produce s t r o n g c o n t r a c t i o n s i n v e r t e b r a t e smooth m u s c l e ,  and  as no such a c t i v i t y was found i n the s u n f l o w e r seeds on w h i c h the i n s e c t s were r e a r e d ( e x c l u d i n g the p o s s i b i l i t y o f c a r d e n o l i d e s p r o d u c i n g the e f f e c t s ) , t h e a u t h o r s s u g g e s t e d t h a t t h i s p r e v i o u s l y u n d e s c r i b e d compound may  be s y n t h e s i z e d by t h e bug (Graham and Staddon 1974).  H i s t a m i n e has a l s o been found i n the d e f e n s i v e s e c r e t i o n s o f the g r a s s hopper 'P_. b u f o n i u s ,  w h i c h l i k e CJ. f a s c i a t u s , s e q u e s t e r s c a r d e n o l i d e s  from i t s milkweed h o s t (von Euw e t al_. 1967).  Perhaps t h e r e i s a  s y n e r g i s t i c e f f e c t o f t h e s e compounds, i . e . c a r d e n o l i d e s p r e s e n t i n t h e s e c r e t i o n s enhance the c o n t r a c t i l e e f f e c t s o f h i s t a m i n e on v e r t e b r a t e smooth muscle.  The p r e s e n c e o f an e f f e c t i v e compound l i k e  histamine  c o u l d o f f e r one e x p l a n a t i o n as t o why an i n s e c t such as f j . f a s c i a t u s can a f f o r d t o be an i n c o n s i s t e n t s t o r e r o f c a r d e n o l i d e s , as shown i n t h i s t h e s i s , w h i l e m a i n t a i n i n g i t s c o n s p i c u o u s c o l o r a t i o n and  behaviour.  A n o t h e r p o s s i b i l i t y i s t h a t many o f the p o p u l a t i o n s o f 0_. f a s c i a t u s and L. k. k a l m i i , mimic t h e i r c o n s p e c i f i c s w h i c h c o n t a i n  92 pharmacologically e f f e c t i v e quantities of cardenolides.  One p r o b l e m o f  t h i s h y p o t h e s i s t h o u g h , i s t h a t i t r e q u i r e s s e l e c t i o n p r e s s u r e from a m i g r a t o r y p r e d a t o r , one w h i c h c o u l d sample i n s e c t s from many g e o g r a p h i cally d i s t i n c t populations.  Otherwise,  a p r e d a t o r m i g h t n e v e r come i n t o  c o n t a c t with a p o p u l a t i o n of l y g a e i d s which c o n t a i n s i g n i f i c a n t q u n a t i t i e s of cardenolides.  W h i l e t h i s t y p e o f m i m e t i c s y s t e m seems a p p r o p r i a t e f o r  t h e m i g r a t i n g monarch b u t t e r f l y (Pough e t al_. 1973, Brower and M o f f i t t 1974), i t s s t a t u s as an a n t i - p r e d a t o r s t r a t e g y i n l y g a e i d s r e q u i r e s a b e t t e r knowledge o f t h e p o t e n t i a l p r e d a t o r s o f t h e s e bugs. A f u r t h e r p o s s i b i l i t y i s that predators capable of v i s u a l d i s c r i m i n a t i o n may g e n e r a l i z e t h e i r a v o i d a n c e t i n g combinations  t o a l l p r e y items w i t h c o n t r a s -  o f w h i t e , y e l l o w , o r a n g e , r e d and b l a c k .  Phyrrhocorid  bugs o f the genus D y s d e r c u s G u e r i n M e n e v i l l e s h a r e a body s i z e , shape and c o l o r a t i o n s i m i l a r t o many l y g a e i n e s , and the g e o g r a p h i c a l ranges o f t h e s e two g r o u p s l a r g e l y o v e r l a p (van Doesburg 1968).  Although  do n o t s e q u e s t e r c a r d e n o l i d e s ( D u f f e y and S c u d d e r 1972) v o l a t i l e ketones and a l d e h y d e s  Dysdercus species t h e y do s e c r e t e  ( e . g . h e x - 2 - e n - l - a l , Calam and S c o t t ,  w h i c h may e f f e c t i v e l y d e t e r p r e d a t o r s ( P a r s o n s 1940),  Sexton  1969)  (1964) r e p o r -  t e d t h a t the l i z a r d A n o l i s c a r o l i n e n s i s V o i g t r e j e c t e d a l l m u l t i - c o l o u r e d prey items.  In a l a b o r a t o r y s i t u a t i o n , t h e common f e n c e l i z a r d  Sceloporus  o c c i d e n t a l i s B a i r d & G i r a r d a v o i d s a d u l t 0. f a s c i a t u s on s i g h t a l o n e , b u t w i l l a c c e p t mealworm l a r v a e ( T e n e b r i o m o l i t o r L.) under t h e same conditions (undescribed experiment).  F e i r and Suen (1971) a l s o i n d i c a t e d  t h a t the f e n c e l i z a r d s w i l l not a c c e p t 0. f a s c i a t u s as a f o o d i t e m .  In  f a c t , most i n s e c t h e r b i v o r e s f e e d i n g on m i l k w e e d a r e b r i g h t l y c o l o u r e d ,  93 s u g g e s t i n g t h a t t h e y p a r t i c i p a t e i n some form o f m i m i c r y complex ( P r i c e 1975).  However, r e c e n t e v i d e n c e s t r o n g l y s u g g e s t s t h a t such a m i m i c r y  complex c o u l d n o t be based on p l a n t - d e r i v e d c a r d e n o l i d e s , as few memb e r s o f t h e milkweed i n s e c t fauna s t o r e s i g n i f i c a n t q u a n t i t i e s o f t h e s e compounds ( I s m a n e t a l _ .  1977).  F i n a l l y , three observations suggest t h a t c a r d e n o l i d e sequest r a t i o n i s n o t an i m p o r t a n t a n t i - p r e d a t o r s t r a t e g y among l y g a e i d bugs in central California.  F i r s t l y , i f predators are able to exert a  s e l e c t i o n p r e s s u r e on l y g a e i d s t o s e q u e s t e r l a r g e q u a n t i t i e s o f  cardeno-  l i d e s , then we would e x p e c t t h i s p r e s s u r e to be o p e r a t i n g most e f f e c t i v e l y when the d e n s i t y o f i n s e c t s i s low.  For l y g a e i d s , t h i s period  would be i n t h e l a t e s p r i n g and e a r l y summer, when i m m i g r a t i n g f i r s t c o l o n i z e milkweed s t a n d s .  adults  However, as t h e d a t a i n t h i s t h e s i s  have shown, l y g a e i d s sampled i n May and June e i t h e r l a c k e d  cardenolides  or contained small q u a n t i t i e s of c a r d e n o l i d e s , only a c q u i r i n g l a r g e r q u a n t i t i e s l a t e r i n the season when the r e p r o d u c t i v e s t r u c t u r e s o f A s c l e p i a s are well Secondly,  developed. p r e d a t o r s do n o t a p p e a r to h i n d e r p o p u l a t i o n growth o f  CJ. f a s c i a t u s on s t a n d s o f A. f a s c i c u l a r i s i n t h e n o r t h bay a r e a , even though t h e s e i n s e c t s have been shown by the p r e s e n t work t o c o n t a i n r e l a t i v e l y small q u a n t i t i e s of c a r d e n o l i d e s .  Once e s t a b l i s h e d , 0_.  f a s c i a t u s p o p u l a t i o n s on A. f a s c i c u l a r i s i n c r e a s e i n number exponent i a l l y (K.E. Evans, u n p u b l . r e s u l t s ) .  This f i n d i n g i s c o n s i s t e n t with  p o p u l a t i o n growth o f Cj. f a s c i a t u s i n t h e m i d w e s t e r n U n i t e d S t a t e s , where i t most f r e q u e n t l y c o l o n i z e s A. s y r i a c a  (Brown e_t aj_. 1976).  94 T h i r d l y , t h e r e does n o t a p p e a r to be a p h y s i o l o g i c a l o r m e t a b o l i c c o s t i n v o l v e d i n t h e s e q u e s t r a t i o n and s t o r a g e o f c a r d e n o l i d e s by 0_. f a s c i a t u s and L^. Ik. k a l m i i , (which would be o u t w e i g h e d by t h e a d v a n t a g e s o f p r o t e c t i o n from p r e d a t i o n ) .  No m e a s u r a b l e d i f f e r e n c e s i n t h e amount  o r r a t e o f growth o f l a r v a l and a d u l t CJ. f a s c i a t u s were d e t e c t e d when t h i s i n s e c t was r e a r e d on t h e seeds o f e i g h t d i f f e r e n t s p e c i e s o f A s c l e p i a s , a l 1 o f which are p o t e n t i a l n a t u r a l host p l a n t s of t h i s i n s e c t . The f a c t t h a t c a r d e n o l i d e c o n t e n t o f the f o o d does n o t i n f l u e n c e the amount o r r a t e o f growth o f 0_. f a s c i a t u s i s i n agreement w i t h the d a t a o b t a i n e d by E r i c k s o n (1973).  E r i c k s o n (1973) compared the l a r v a l  d e v e l o p m e n t and growth o f t h e monarch b u t t e r f l y ID.  p l e x i p p u s on f o u r  d i f f e r e n t s p e c i e s o f A s c l e p i a s on w h i c h t h i s i n s e c t i s known t o f e e d , and f a i l e d t o show s i g n i f i c a n t d i f f e r e n c e s . Thus, t h e d a t a p r e s e n t e d i n t h i s t h e s i s p r o v i d e s t r o n g  evidence  a g a i n s t t h e p o s s i b i l i t y t h a t t h e s e q u e s t r a t i o n and s t o r a g e o f c a r d e n o l i d e s has an a d v e r s e e f f e c t upon growth and d e v e l o p m e n t o f CJ_. f a s c i a t u s , even though 0_. f a s c i a t u s i n t h i s s t u d y s t o r e d up to seven t i m e s as much c a r d e n o l i d e by w e i g h t as the monarch b u t t e r f l y . F u r t h e r , t h e range o f c a r d e n o l i d e c o n t e n t i n t h e f i e l d c o l l e c t e d bugs f a l l s w e l l w i t h i n t h a t o f the l a b o r a t o r y reared i n s e c t s .  The l a r g e s t q u a n t i t y o f c a r d e n o l i d e s  d e t e c t e d i n a f i e l d c o l l e c t e d l y g a e i d was 372-yg, whereas l a b o r a t o r y r e a r e d CJ. f a s c i a t u s have been known to c o n t a i n as much as 800 yg o f cardenolide.  T h e r e f o r e , t h i s f i n d i n g i s c o n s i d e r e d t o be v a l i d f o r  ly.gaeids.i- f e e d i n g on A s c l e p i a s i n the n a t u r a l e n v i r o n m e n t . As s u g g e s t e d  by Feeny / (1976), the t o x i c compounds o f  early  95 s u c c e s s i o n a l herbs ( e . g . c a r d e n o l i d e s i n A s c l e p i a s ) may a c t as a ' q u a l i t a t i v e ' b a r r i e r to g e n e r a l i s t i n s e c t h e r b i v o r e s w h i l e  having  l i t t l e o r no e f f e c t on the growth and f i t n e s s o f h i g h l y adapted species.  herbivore  The i n a b i l i t y o f the p r e s e n t s t u d y o r the f i n d i n g s o f E r i c k s o n  (1973) t o d e m o n s t r a t e a d e t r i m e n t a l e f f e c t o f c a r d e n o l i d e s on the growth and d e v e l o p m e n t o f t h e m i l k w e e d - f e e d i n g  i n s e c t s fj. f a s c i a t u s and D_.  plexippus support t h i s hypothesis. I f t h e n , c a r d e n o l i d e s a r e n o t s t o r e d by l y g a e i d s as an a n t i p r e d a t o r s t r a t e g y , and t h e s e compounds do n o t a f f e c t the growth and d e v e l o p m e n t o f the i n s e c t s , then how does one e x p l a i n the p r e s e n c e t h e s e compounds i n t h e l y g a e i d s ?  of  One p o s s i b l e e x p l a n a t i o n i s t h a t  c a r d e n o l i d e s e q u e s t r a t i o n i s o r was used by t h e s e l y g a e i d s o r c l o s e l y related species in previous predator-prey  i n t e r a c t i o n s over e v o l u t i o n a r y  t i m e , o r a t t h e p r e s e n t day, i n o t h e r a r e a s o f t h e s p e c i e s ' g e o g r a p h i c a l range. Most L y g a e i n e s a r e t r o p i c a l i n s e c t s ; few s p e c i e s have s u c c e s s f u l l y i n v a d e d t e m p e r a t e r e g i o n s o f the w o r l d .  In t h e t r o p i c a l  environ-  ment, where s e v e r a l s p e c i e s o f b r i g h t l y - c o l o u r e d l y g a e i d s o c c u r sympatt i c a l l y , t h e s e i n s e c t s may depend on p l a n t - d e r i v e d c a r d e n o l i d e s as a d e f e n s i v e s t r a t e g y , as t h e y c o u l d be s u b j e c t to p r e d a t i o n from a w i d e r v a r i e t y o f p r e d a t o r s than i n a t e m p e r a t e h a b i t a t ( e . g . c e n t r a l California).  A l t e r n a t e l y fJ. f a s c i a t u s and L. Ik.  k a l m i i may have d e s c e n d e d  from a n c e s t r a l s p e c i e s w h i c h b e n e f i t e d from c a r d e n o l i d e s t o r a g e as an anti-predator device.  Such a p h y s i o l o g i c a l s y s t e m , w h i c h does n o t  i n t e r f e r e w i t h the normal d e v e l o p m e n t o f the i n s e c t , c o u l d c o n c e i v a b l y  96  e x i s t i n p r e s e n t day l y g a e i d s as an a r t i f a c t o f a p r e v i o u s  predator-prey  i n t e r a c t i o n , l o n g a f t e r the p r e d a t o r e v o l v e d d i f f e r e n t f e e d i n g h a b i t s which d i d n o t i n c l u d e l y g a e i d s . In c o n c l u s i o n , t h e r o l e o f c a r d e n o l i d e s i n CJ. f a s c i a t u s and I.  L  k a l m i i f e e d i n g on milkweeds i n c e n t r a l C a l i f o r n i a r e m a i n s i n  q u e s t i o n , a l t h o u g h t h e c o l o u r a t i o n and b e h a v i o u r o f t h e s e s p e c i e s s t r o n g l y s u g g e s t t h a t t h e y b e n e f i t from w a r n i n g c o l o u r a t i o n and some form o f m i m i c r y w h i c h can c o n d i t i o n p r e d a t o r s t o a v o i d t h e s e i n s e c t s .  Cardenolide  s e q u e s t r a t i o n does n o t a p p e a r to be an i m p o r t a n t o r g a n i z i n g f a c t o r i n t h e f e e d i n g and p o p u l a t i o n e c o l o g y o f t h e s e l y g a e i d s p e c i e s i n t h i s p a r t o f t h e i r geographical  range.  97 REFERENCES Abrams, L. 1951. I l l u s t r a t e d F l o r a of the P a c i f i c S t a t e s , V o l . I I I . Stanford Univ. Press. Abushama, F.T. and A.A. Ahmed. 1976. F o o d - p l a n t p r e f e r e n c e and d e f e n s e mechanism i n t h e l y g a e i d bug S p i l o s t e t h u s pandurus ( S c o p . ) . Z. Angew. Entomol. 80: 206-213. A l c o c k , J . 1971. I n t e r s p e c i f i c differences in avian feeding and the e v o l u t i o n o f B a t e s i a n m i m i c r y . B e h a v i o u r 4 C A n d r e , F. 1934. Notes on t h e b i o l o g y o f O n c o p e l t u s Iowa S t a t e C o l l . J . S c i . 9: 73-87. B o r i s o n , H.L. and S.C. Wang. v o m i t i n g . Pharmacol. Brower, L.P., 1969.  behaviour 1-9.  fasciatus (Dallas).  1953. P h y s i o l o g y and p h a r m a c o l o g y o f Rev. 5; 193-230.  Ecological chemistry.  S c i . Amer. 220: 22-29.  Brower, L.P., W.N. R y e r s o n , L.L. C o p p i n g e r and S.C. G l a z i e r . 1968. E c o l o g i c a l c h e m i s t r y and t h e p a l a t a b i l i t y s p e c t r u m . Science (Wash.) 161: 1349-1351. Brower, L.P., P.B. McEvoy, K.L. W i l l i a m s o n and M.A. F l a n n e r y . 1972. V a r i a t i o n i n c a r d i a c g l y c o s i d e c o n t e n t o f monarch b u t t e r f l i e s from n a t u r a l p o p u l a t i o n s i n e a s t e r n N o r t h A m e r i c a . Science (Wash.) 177: 426-429. Brower, L.P. and C M . M o f f i t t . 1974. P a l a t a b i l i t y dynamics o f c a r d e n o l i d e s i n t h e monarch b u t t e r f l y . N a t u r e ( L o n d . ) 249: 280-283. Brower L.P., M. Edmunds and C M . M o f f i t t . 1975. C a r d e n o l i d e c o n t e n t and p a l a t a b i l i t y o f a p o p u l a t i o n o f Danaus c h r y s i p p u s b u t t e r f l i e s from West A f r i c a . J . Entomol. (A) 49: 183-196. Brower, L.P. and S.C. G l a z i e r . 1975. L o c a l i z a t i o n o f h e a r t p o i s o n s i n the monarch b u t t e r f l y . S c i e n c e (Wash.). 188: 19-25. Brown, K.M., R.L. C a l d w e l l and H. D i n g l e . 1976. P o p u l a t i o n e c o l o g y o f t h e m i l k w e e d bugs O n c o p e l t u s f a s c i a t u s and Lygaeus k a l m i i . Unpublished manuscript. Calam, D.H. and F.C. S c o t t . 1969. The s c e n t g l a n d complex o f the a d u l t c o t t o n s t a i n e r bug Dysdercus i n t e r m e d i u s . J . I n s e c t P h y s i o l . 15: 1659-1702.  98 C z a p l i c k i , J.A., R.H. P o r t e r and H.C. W i l c o x o n . 1975. O l f a c t o r y m i m i c r y i n v o l v i n g g a r t e r snakes and a r t i f i c i a l models and m i m i c s . B e h a v i o u r 54: 60-71. D e t w e i l e r , D.K. 1967. C o m p a r a t i v e p h a r m a c o l o g y o f c a r d i a c g l y c o s i d e s . Fed. P r o c . 26: 1119-1124. van D o e s b u r g , P.H. 1968. A r e v i s i o n o f t h e new w o r l d s p e c i e s o f Dysdercus Guerin M e n e v i l l e (Heteroptera, P y r r h o c o r i d a e ) . Z o o l o g i s c h e V e r h a n d e l i n g e n 9 7 : 1-215. D u f f e y , S.S. 1970. A p l a n t ( A s c l e p i a s ) - i n s e c t ( O n c o p e l t u s ) c h e m i c a l r e l a t i o n s h i p . M. S c . t h e s i s , U n i v . o f B r i t i s h C o l u m b i a . D u f f e y , S.S. 1976. A l l o m o n e s : c h e m i c a l e f f r o n t e r i e s and a n t a g o n i s t s . P r o c . XV I n t . C o n g r . E n t o m o l . , pp. 323-394. D u f f e y , S.S. and G.G.E. S c u d d e r . 1972. C a r d i a c g l y c o s i d e s i n North American Asclepiadaceae, a b a s i s f o r u n p a l a t a b i l i t y i n b r i g h t l y c o l o u r e d H e m i p t e r a and C o l e o p t e r a . J . I n s e c t P h y s i o l . 18: 63-78. D u f f e y , S.S. and G.G.E. S c u d d e r . 1974. C a r d i a c g l y c o s i d e s i n O n c o p e l t u s f a s c i a t u s ( D a l l a s ) (Hemiptera: Lygaeidae). I . The u p t a k e and d i s t r i b u t i o n o f n a t u r a l c a r d e n o l i d e s i n t h e body. Can. J . Z o o l . 52: 283-290. Duncan, C . J . 1960. P r e f e r e n c e t e s t and t h e s e n s e o f t a s t e i n t h e f e r a l p i g e o n (Columba l i v e a v a r . G m e t i n ) . Anim. Behav. 8_: 54-60. Eggermann, W. and J . B o n g e r s . 1971. Wasser-und nahrugsaufnahme an pflanzen unter besonderer Berucksichtigung der W i r t s s p e z i f i t a t von O n c o p e l t u s f a s c i a t u s D a l l a s . O e c o l o g i a ( B e r l . ) 6 j 303-317.. E r i c k s o n , J.M. 1973. The u t i l i z a t i o n o f v a r i o u s A s c l e p i a s s p e c i e s ( A s c l e p i a d a c e a e ) by l a r v a e o f t h e monarch b u t t e r f l y Danaus p l e x i p p u s ( L e p . , D a n a i d a e ) . Psyche 80: 230-244. von Euw, J . , L. F i s h e l s o n , J.A. P a r s o n s , T. R e i c h s t e i n and M. R o t h s c h i l d . 1967. C a r d o n o l i d e s ( h e a r t p o i s o n s ) i n a g r a s s h o p p e r f e e d i n g on m i l k w e e d s . N a t u r e (Lond.) 214: 35-39. von Euw, J . , T. R e i c h s t e i n and M. R o t h s c h i l d . 1971. H e a r t p o i s o n s ( c a r d i a c g l y c o s i d e s ) i n t h e l y g a e i d bugs C a e n o c o r i s n e r i i and S p i l o s t e t h u s p a n d u r u s . I n s e c t Biochem. 1_: 373-384. Feeny, P. 1976. P l a n t a p p a r e n c y and c h e m i c a l Phytochem. 10.: 1-40.  defense.  Rec. Adv.  99  F e i r , D. and J . Suen. 1971. C a r d e n o l i d e s i n t h e milkweed p l a n t and f e e d i n g by t h e milkweed bug. Ann. E n t . Soc. Amer. 64: 1 1 7 3 1174.  Games, D.E. and B.W. Staddon. 1973. C o m p o s i t i o n o f s c e n t s from t h e l a r v a o f t h e milkweed bug O n c o p e l t u s f a s c i a t u s ; ' J . I n s e c t P h y s i o l . 19: 1 5 2 7 - 1 5 3 2 . G e l p e r i n , A. 1968. F e e d i n g b e h a v i o u r o f a p r e y i n g m a n t i s : a l e a r n e d m o d i f i c a t i o n . N a t u r e (Lond.) 219: 3 9 9 - 4 0 0 . G o d f r a i n d , T. and A. G o d f r a i n d - d e B e c k e r . 1961. g l y c o s i d e s on a smooth m u s c l e . Biochem.  Action of cardiac P h a r m a c o l . *3: 156.  G o l d , H., M. C a t t e l l , W. Modell, T. G r e i n e r and R. Guevara. 1 9 5 9 . Local emetic a c t i v i t y of g l y c o s i d e s of the d i g i t a l i s s e r i e s . J . P h a r m a c o l . E x p t l . T h e r a p . 98: 3 3 7 - 3 4 5 . Graham, J.D.P. and B.W. Staddon. 1974. P h a r m a c o l o g i c a l o b s e r v a t i o n s on body f l u i d s from t h e milkweed bug, O n c o p e l t u s f a s c i a t u s ( D a l l a s ) ( H e t e r o p t e r a : L y g a e i d a e ) . J . Entomol. (A) 48: 1 7 7 - 1 8 4 . H a u s t e i n , K.O., F. Markwardt and K. Repke. 1966. Uber d i e darmwirksamk e i t von d i g i t o x i n , p e n t a - a c e t y l - g i t o x i n und a c e t y l - g i t o x i n e n . Naunyn-Schmiedeberg's A r c h . EXD. P a t h . u. Pharmak. 252; 4 2 4 - 4 3 2 . Hoch, J.H. 1961. A S u r v e y o f C a r d i a c G l y c o s i d e s and G e n i n s . South C a r o l i n a P r e s s .  Univ. o f  H u b e r t , L.C. and F.W. Oehme. 1965. P l a n t s P o i s o n o u s t o L i v e s t o c k . Kansas S t a t e U n i v . P r e s s , Manhattan, Kansas. Isman, M.B., S.S. D u f f e y and G.G.E. S c u d d e r . 1977. C a r d e n o l i d e c o n t e n t o f some l e a f - and s t e m - f e e d i n g i n s e c t s o n t e m p e r a t e N o r t h American milkweeds ( A s c l e p i a s s p p . ) . Can. J . Z o o l . 55_: i n p r e s s . K i n g s b u r y , J.M. 1964. P o i s o n o u s P l a n t s o f t h e U n i t e d S t a t e s and P r e n t i c e - H a l l , Englewood C l i f f s , New J e r s e y .  Canada.  K i t c h e l l , R.L., L. Strom and Y. Z o t t e r m a n . 1959. Electrophysiological s t u d i e s o f thermal and t a s t e r e c e p t o r s i n c h i c k e n s and p i g e o n s . A c t a . P h y s i o l . Scand. 46: 1 3 3 - 1 5 1 . Lehman, R.A. and G.H. P a f f . 1942. A p r a c t i c a l t e c h n i q u e and d e s i g n f o r t h e a s s a y o f d i g i t a l i s on t h e embryonic c h i c k h e a r t . J . P h a r m a c o l . E x p t l . T h e r a p . 75: 2 0 7 - 2 1 8 . Moe, G.K.  and A.E. F a r a h . 1970. D i g i t a l i s and a l l i e d c a r d i a c g l y c o s i d e s . Ch. 31. I n : The P h a r m a c o l o g i c a l B a s i s o f T h e r a p e u t i c s . S. Goodman and A. Gilman ( E d s . ) , M a c M i l l a n , New York.  100 Munz, P.A. 1968. Berkeley.  A C a l i f o r n i a F l o r a and Supplement.  Univ. C a l i f .  Press,  P a n t l e , C. and D. F e i r . 1976. O l f a c t o r y r e s p o n s e s t o milkweed seed e x t r a c t s i n the milkweed bug. J . I n s e c t P h y s i o l . 22: 285-289. Parsons, C T . 1940. coloration.  O b s e r v a t i o n s i n Cuba on m i m i c r y and Psyche 47_: 1-7.  protective  P a r s o n s , J.A. 1965. A d i g i t a l i s - l i k e t o x i n i n the monarch b u t t e r f l y , Danaus p l e x i p p u s . J . P h y s i o l . 178: 290-304. P a r s o n s , J.A. and R.J. Summers. 1971. Cat a s s a y f o r the e m e t i c a c t i o n o f d i g i t a l i s and r e l a t e d g l y c o s i d e s ( d i g i t o x i n , d i g o x i n , l a n a t o s i d e C, o u a b a i n and c a l a c t i n ) . B r i t . J . P h a r m a c o l . Chemother. 42: 143-152. P a t t e r s o n , B.D., S.K. Wahba K h a u l , L . J . S c h e r m e i s t e r and M.S. Q u r a i s h i . 1975. P l a n t - i n s e c t i n t e r a c t i o n s . I. B i o l o g i c a l and p h y t o c h e m i c a l e v a l u a t i o n o f s e l e c t e d p l a n t s . L l o y d i a 38; 391-403. Pough, H.F., L.P. Brower, H.R. Meek and S.R. K e s s e l l . 1973. Theoretical i n v e s t i g a t i o n s o f a u t o m i m i c r y : m u l t i p l e t r i a l l e a r n i n g and the p a l a t a b i l i t y s p e c t r u m . P r o c . N a t l . Acad. S c i . U.S.A. 70_: 22612265. P r i c e , P.W.  1975.  Insect Ecology  Wiley-Interscience,  New  York.  R a b i t z s c h , G. and U. Tambor. 1969. Method f o r the q u a n t i t a t i v e d e t e r m i n a t i o n o f c a r d i a c g l y c o s i d e s and g e n i n s o f the c a r d e n o l i d e type with 2,4,2',4'-tetranitrodiDhenyl. D i e P h a r m a z i e . 24: 262-269. R a l p h , C P . 1976. N a t u r a l f o o d r e q u i r e m e n t s o f the l a r g e milkweed bug, Oncopeltus f a s c i a t u s (Hemiptera: Lygaeidae) i n t h e i r r e l a t i o n t o g r e g a r i o u s n e s s and h o s t p l a n t m o r p h o l o g y . O e c o l o g i a , ( B e r l . ) 26: 157-176. R e i c h s t e i n , T.,.Jivon Euw,J.A. P a r s o n s and M. R o t h s c h i l d . 1968. p o i s o n s i n the monarch b u t t e r f l y . S c i e n c e (Wash.) 161: R e t t e n m e y e r , CW.  1970.  Insect mimicry.  Ann.  Rev.  Heart 861-865.  E n t o m o l . 1_5: 43-74.  Roeske, C.N., J.N. S e i b e r , L.P. Brower and C M . M o f f i t t . 1976. Milkweed c a r d e n o l i d e s and t h e i r c o m p a r a t i v e p r o c e s s i n g by monarch b u t t e r f l i e s (Danaus p l e x i p p u s L . ) . Rec. Adv. Phytochem. 10: 93-167.  101 Root, R.B. and S . J . C h a p l i n . 1976. The l i f e s t y l e s o f t r o p i c a l milkweed bugs, O n c o p e l t u s (HemiDtera: L y g a e i d a e ) u t i l i z i n g t h e same h o s t s . E c o l o g y 57: 132-140. R o t h s c h i l d , M. 1972. Secondary p l a n t s u b s t a n c e s and w a r n i n g c o l o r a t i o n i n i n s e c t s . Symp. R. E n t . S o c . (Lond.) 6_: 59-83. R o t h s c h i l d , M. and D.N. K e l l e t t . 1972. R e a c t i o n s o f v a r i o u s p r e d a t o r s t o i n s e c t s s t o r i n g h e a r t Doisons ( c a r d i a c g l y c o s i d e s ) i n t h e i r t i s s u e s . J . Entomol. (A) 46: 103-110. R o t h s c h i l d , M., J . von Euw, T. R e i c h s t e i r v , D.A.S. Smith and J . P i e r r e . 1975. C a r d e n o l i d e s t o r a g e i n Danaus c h r y s i p p u s ( L . ) w i t h a d d i t i o n a l n o t e s on D_. P l e x i p p u s ( L . ) . P r o c . R. E n t . S o c . (Lond.) B 190: 1-31. Rowe, L.D., P.D. Ohlenbusch and J.W. D o l l a h i t e . 1970. T o x i c i t y o f A s c l e p i a s b r a c h y s t e p h a n a ( s h o r t c r o w n m i l k w e e d ) f o r sheep. S o u t h w e s t V e t . 23: 219-224. Sauer, D. and D. F e i r . 1972. F i e l d o b s e r v a t i o n s on p r e d a t i o n on t h e l a r g e m i l k w e e d bug O n c o p e l t u s f a s c i a t u s . E n v i r o n . Entomol. J_: 268. Scudder, G.G.E. and S.S. D u f f e y . 1972. C a r d i a c g l y c o s i d e s i n t h e L y g a e i n a e ( H e m i p t e r a : L y g a e i d a e ) . Can. J . Z o o l . 50: 35-42. S e x t o n , O.J. 1964. D i f f e r e n t i a l p r e d a t i o n by t h e 1 i z a r d A n o l i s c a r o l i n e n s i s , upon u n i c o l o r e d and p o l y c o l o r e d i n s e c t s a f t e r an i n t e r v a l o f no c o n t a c t . Anim. Behav. ]2_: 101-110. S h i g e i , T., S. Imai and H. Murase. 1963. C o n t r a c t u r e o f slow muscle f i b r e i n d u c e d by c a r d i a c a c t i v e s t e r o i d s . N a u n y n - S c h m i e d e b e r g s A r c h . Exp. P a t h . u. Pharmak. 244: 510-518. 1  Simanton,  W. and F. Andre. 1936. A b i o l o g i c a l s t u d y o f Lygaeus k a l m i i S t a l . ( H e m i p t e r a : L y g a e i d a e ) . B u l l . B r o o k l y n E n t . S o c . 31: 99-107.  S i n g h , B. and R.P. R a s t o g i . 1970. C a r d e n o l i d e s - g l y c o s i d e s and g e n i n s . Phytochem. 9_: 315-331. Thorp, R.H. and L.B. C o b b i n . 1967. C a r d i a c S t i m u l a n t Academic P r e s s , New York.  Substances.  V a i l , E.L. 1942. W o o l l y - p o d o r b r o a d - l e a v e d milkweed ( A s c l e p i a s e r i o c a r p a ) p o i s o n i n g o f r a b b i t s . N. Amer. V e t . 23: 539-542.  102 Weber, R.R. 1975. P r e d a t i o n e x p e r i m e n t s w i t h t h e milkweed bug ( O n c o p e l t u s f a s c i a t u s ) . B.Sc. t h e s i s , U n i v . o f B r i t . C o l . W e i s s , H.B. and E.L. D i c k e r s o n . 1921. Notes on milkweed i n s e c t s i n New J e r s e y . J . N.Y. E n t . S o c . 29: 125-144. Wenzel, B.M. 1973. C h e m o r e c e p t i o n , Ch. 6. I n : A v i a n B i o l o g y , V o l . I I I . D.S. F a r n e r , J.R. King and K.C. P a r k e s ( E d s . ) , Academic P r e s s , New York. W h i t e , W.F. and 0. G i s v o l d . 1952. A b s o r p t i o n r a t e s t u d i e s o f o r a l l y a d m i n i s t e r e d c a r d i a c g l y c o s i d e s i n c a t s . J . Amer. Pharm. A s s n . , S c i . Ed. 4J_: 42-46. W i l c o x o n , H.C., W.B. D r a g o i n and P.A. K r a i . 1971. I l l n e s s - i n d u c e d a v e r s i o n s i n r a t and q u a i l : r e l a t i v e s a l i e n c e o f v i s u a l and g u s t a t o r y c u e s . S c i e n c e (Wash.) 171: 826-i828. Woodson, R.E. 1954. The North A m e r i c a n sDecies o f A s c l e p i a s Mo. B o t . Gard. 41_: 1-211.  L.  Yang, R.S.H. and M.R. Kare 1968. T a s t e r e s p o n s e s o f a b i r d t o c o n s t i t u e n t s o f a r t h r o p o d d e f e n s i v e s e c r e t i o n s . Ann. E n t . Soc. Amer. 61: 781-782.  Ann.  

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