31 Insect Feeding Deterrents from Semiarid and Arid Land Plants ELOY RODRIGUEZ
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Phytochemical Laboratory, Department of Ecology and Biology, University of California, Irvine, CA 92717 Phytochemical investigations of plant species of Parthenium, Εncelia and Dicοria (Asteraceae) from semi-arid and arid zones of the United States and Mexico has resulted in the isolation and identification of numerous sesquiterpene lactones and benzopyrans that are active insect feeding deterrents. The chemistry, biological effects and possible mode of action of bioactive pseudoguaianolides and chromenes are reviewed. During t h ecourse of e v o l u t i o n , a r i d land p l a n t s , l i k e many o t h e r s p e c i e s o f p l a n t s f r o m d i v e r s e e n v i r o n m e n t a l zones, have evolved an a r r a y of natural organic chemicals that function p r i m a r i l y i n regulating insect growth and r e p r o d u c t i o n . Natural constituents like prenylated q u i n o n e s and b e n z o f u r a n s from d e s e r t plants a r e k n o w n t o be e x t r e m e l y t o x i c when t o p i c a l l y applied to l e p i d o p t e r a n l a r v a e and p a t h o g e n i c microorganisms (1_). I n many c a s e s o f d e s e r t p l a n t - i n s e c t i n t e r a c t i o n s , it i s becoming apparent that secondary chemicals p r i m a r i l y function i nrepelling a large percentage of herbivorous i n s e c t s , with theplant s u f f e r i n g a c e r t a i n degree o f l e a f , f l o w e r and seed l o s s . I n s u r v e y i n g t h e l i t e r a t u r e f o r r e p e l l e n t s and a n t i f e e d a n t s from s e m i a r i d and a r i d land p l a n t s , i t i s s u r p r i s i n g t o f i n d t h a t very little research h a s been done on t h e c h e m i s t r y , mode o f a c t i o n and d i s t r i b u t i o n of desert plant a n t i f e e d a n t s and r e p e l l e n t s . F o rexample, i na recent survey of n a t u r a l l y occurring insecticides, insect r e p e l l e n t s and a t t r a c t a n t s i nhigher p l a n t s , Jacobson (2^) l i s t s o n l y o n e s p e c i e s t h a t i s f r o m a n a r i d zone, while theother species examined for b i o a c t i v i t y a r e from s u b - t r o p i c a l and t r o p i c a l areas. This i s indeed very s u r p r i s i n g when o n e c o n s i d e r s that i n North A m e r i c a , about 2 5 % o f t h e U n i t e d S t a t e s i s s e m i - a r i d t o a r i d , while i n Mexico, approximately 46% i sd r y l a n d (3).
Library
1155 16th St., N.W. Washington, D.C. 20030
Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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BIOREGULATORS FOR PEST CONTROL
Desert regions which a r e of great i m p o r t a n c e t ot h e United S t a t e s and Mexico a r e t h e a r i d Lands o f t h e Southwest and Baja C a l i f o r n i a , Mexico- I t i s i n these a r i d r e g i o n s t h a t we h a v e c o n c e n t r a t e d our research e f f o r t s i n i s o l a t i n g and e l u c i d a t i n g t h e s t r u c t u r e s o f new p h y t o c h e m i c a l s t h a t i n h i b i t i n s e c t and f u n g a l g r o w t h
(4). I n t h i s b r i e f c o m m u n i c a t i o n we s u m m a r i z e s o m e o f o u r r e c e n t f i n d i n g s on s e s q u i t e r p e n o i d s from s p e c i e s of P a r t h e n i u m, En c e I i a a n d D i c o r i a ( A s t e r a c e a e ) f r o m t h e Chihuahuan and Sonoran D e s e r t s , that exhibit insect r e p e l l e n t and a n t i f e e d a n t activities.
Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch031
Sesquiterpene
Lactones
as I n s e c t
Feeding
Deterrents
Sesquiterpene lactones are structurally d i v e r s e and b i t t e r constituents of the Asteraceae t h a t a r e known t o e x h i b i t numerous b i o l o g i c a l a c t i v i t i e s . These m e v a l o n i c a c i d d e r i v e d c o n s t i t u e n t s have been d e m o n s t r a t e d t o have c y t o t o x i c and a n t i t u m o r a c t i v i t i e s , a r e p o t e n t elicitors of a l l e r g i c c o n t a c t d e r m a t i t i s i n humans and have been implicated i n livestock poisonings (5_). S e v e r a l studies also i n d i c a t e that sesquiterpene lactones are important defensive constituents against known i n s e c t pests, because o f t h e i r f e e d i n g d e t e r r e n t and i n s e c t g r o w t h i n h i b i t i n g p r o p e r t i e s (£). F o r e x a m p l e , g l a u c o l i d e A (1), a germ a c r a n o l i d e p r e s e n t i n various species of Vernonia (Asteraceae), i s a feeding d e t e r r e n t and ovipositionaI deterrent to the f a l l , south and y e l l o w s t r i p e d army worms ^Ζ.ζ2.^· Parthenin ( 2 ) , a pseudoguaianolide present i n s p e c i e s o f P a r t h e n i urn, Hymenoclea a n d Amb ro s i a, i s physiologiclly active a g a i n s t Me l a n o p l u s s a n g u i n i p e s (10). B a k k e n o l i d e A (3), a sesquiterpene s p i r o l a c t o n e f r o m H y m o g y n e a I p i na ( L . ) C a s s , w a s r e c e n t l y s h o w n t o be an e f f e c t i v e r e p e l l e n t against the granary weevil a d u l t b e e t l e (S i t op h i l u s g r a n a r i u s ) t h e f l o u r b e e t l e l a r v a e a n d a d u l t s ( T r l b o I i urn conf usum) and t h e K h a p r a b e e t l e l a r v a e (T r opcode r m a granarium) (12). Recent studies i n our laboratory have also d e m o n s t r a t e d that C
