Naturally Occurring Pest Bioregulators - ACS Publications - American

Chapter 1

Use

of Natural Products in Pest Control Developing Research Trends Paul A. Hedin

Downloaded by GAZI UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch001

Crop Science Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Mississippi State, MS 39762

The rapid growth of knowledge of natural products with biological activities toward pests now provides an option for treatment, a clearer understanding of biochemical mechanisms, and a basis for biorational approaches to the design of pest control agents. Compounds that modify insect behavior are also valuable for pest control because they are normally not toxic to the target insect or to the environment. Natural products are often a key to understanding ecological systems. When the compounds are identified, progress can be made in understanding the metabolic cycles, the enzymes that lead to their biosynthesis, and the underlying genetic controls. An understanding of the interactions should make it possible to devise minimum changes that yield maximum benefits. Some developing research trends in the utilization of natural products for pest control are reviewed. P a r t i c u l a r l y over the p a s t 25 y e a r s , t h e r e has been much a c t i v i t y d i r e c t e d t o c h e m i c a l work on the i s o l a t i o n and i d e n t i f i c a t i o n o f a wide a r r a y o f b i o l o g i c a l l y a c t i v e n a t u r a l p r o d u c t s t h a t i n some way a f f e c t the b e h a v i o r , development and/or r e p r o d u c t i o n o f p e s t s such as i n s e c t s , d i s e a s e s and the growth o f weeds. However w i t h r e g a r d t o crop p l a n t s , a g r o n o m i s t s , e n t o m o l o g i s t s , and o t h e r a g r i c u l t u r a l s c i e n t i s t s have g e n e r a l l y depended on t r a d i t i o n a l methods f o r s e l e c t i n g r e s i s t a n t v a r i e t i e s w i t h adequate y i e l d p r o p e r t i e s . Even though h i g h l y a c t i v e a l l e l o c h e m i c a l s have been i d e n t i f i e d , o n l y i n a l i m i t e d percentage of s i t u a t i o n s has c h e m i c a l guidance been the l e a d i n g f a c t o r i n s c r e e n i n g f o r the p r o p e r t i e s . On the o t h e r hand, agents such as pheromones, a n t i f e e d a n t s , i n s e c t and p l a n t growth r e g u l a t o r s , t o name a few, have found some commercial a p p l i c a t i o n . A l s o , s y n t h e t i c analogues based on the a c t i v i t y o f some n a t u r a l p r o d u c t s have found an even wider market. This chapter not subject to U.S. copyright Published 1991 American Chemical Society In Naturally Occurring Pest Bioregulators; Hedin, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


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NATURALLY OCCURRING PEST BIOREGUIATORS However, perhaps t h e day o f t h e b i o l o g i c a l l y a c t i v e n a t u r a l p r o d u c t has come. E n v i r o n m e n t a l concerns a r e c i r c u m s c r i b i n g t h e use o f t r a d i t i o n a l p e s t i c i d e s . Growing r e s i s t a n c e o f p e s t s t o p r e s e n t p e s t i c i d e s has g i v e n added urgency t o t h e s e a r c h f o r b e t t e r , s a f e r compounds, and b e t t e r , s a f e r d e l i v e r y systems. The need t o t r e a t more p r e c i s e l y has a l s o p r o v i d e d a d d i t i o n a l o p p o r t u n i t i e s f o r t h e use o f n a t u r a l p r o d u c t s . I t should be s t a t e d , however, t h a t r e s i s t a n c e can be expected t o develop t o n a t u r a l p r o d u c t s t h a t have a s i n g l e mode o f a c t i o n . B i o l o g i c a l l y a c t i v e n a t u r a l p r o d u c t s can be c o n s i d e r e d t o be b i o r e g u l a t o r s , t h e name modeled i n p a r t on t h e p l a n t growth hormones t h a t were shown t o r e g u l a t e v a r i o u s p l a n t growth and development p r o c e s s e s . Today, t h e l e v e l s r e q u i r e d f o r a c t i v i t y a r e ever s m a l l e r and s m a l l e r . F o r example, t h e pheromones have been found t o be a c t i v e a t picogram c o n c e n t r a t i o n s and below. Now, t h e neurohomones have been found t o be j u s t as a c t i v e , and t h e s e a r e j u s t two examples. The e l u c i d a t i o n o f compounds o f e x q u i s i t e l y unique s t r u c t u r e s becomes more and more common as access t o p o w e r f u l i n s t r u m e n t a l techniques r a p i d l y increases. As one surveys t h e avalanche o f new, b r i l l i a n t e l u c i d a t i o n s , i t i s t h r i l l i n g t o r e a l i z e t h a t so much power and c a p a b i l i t y has been d e v e l o p e d , p a r t i c u l a r l y i n t h e p a s t decade. The advent o f new c a p a b i l i t i e s i n b i o t e c h n o l o g y f o r e c a s t s a n o t h e r quantum l e a p as t h e c a p a b i l i t y grows t o i n s e r t genes i n t o c r o p p l a n t s . The p r e s e n t prominence o f B a c i l l u s t h u r i n g i e n s i s (BT) might suggest t h a t t h e n a t u r a l p r o d u c t s c h e m i s t can be d i s p e n s e d w i t h , b u t i t can be a n t i c i p a t e d t h a t p e s t s w i l l d e v e l o p r e s i s t a n c e t o BT sooner o r l a t e r . T h e r e f o r e , t h e b i o t e c h n o l o g i s t a p p a r e n t l y w i l l have t o r e l y on t h e c h e m i s t t o i d e n t i f y o t h e r systems t o e x p r e s s . I t thus appears t h a t t h e r e i s a f u t u r e f o r the n a t u r a l p r o d u c t s c h e m i s t . P e s t s can most b r o a d l y be c l a s s i f i e d as those a t t a c k i n g a n i m a l s o r p l a n t s . Those p e s t s t h a t a t t a c k a n i m a l s a r e o f t e n a r t h r o p o d s , u s u a l l y i n s e c t s . Other p e s t s o f a n i m a l s a r e microbes and nematodes. T h e i r t r e a t m e n t i s g e n e r a l l y c o n s i d e r e d a v e t e r i n a r y a c t i v i t y , although n a t u r a l products i n c l u d i n g a n t i m i c r o b i a l s a r e o f t e n used. Thus, a n i m a l h e a l t h c o n c e r n s , u n l e s s they a r e i n s e c t r e l a t e d , a r e g e n e r a l l y c o n s i d e r e d s e p a r a t e l y , and w i l l n o t be emphasized i n t h i s s u r v e y . The p r o t e c t i o n o f p l a n t s from p e s t s has been d i v i d e d i n t o t h r e e c a t e g o r i e s ; c o n t r o l o f (1) i n s e c t s , (2) d i s e a s e s , and (3) weeds. While p e s t c o n t r o l has t r a d i t i o n a l l y been accomplished over t h e p a s t 40-50 y e a r s w i t h p e s t i c i d e s o f s y n t h e t i c o r i g i n , t h i s was n o t the case p r i o r t o t h e development o f s y n t h e t i c p e s t i c i d e s such as DDT. I n r e c e n t y e a r s , a number o f n a t u r a l p r o d u c t s i n c l u d i n g t h o s e from f e r m e n t a t i o n have been f i n d i n g a n i c h e i n t h e market p l a c e , because o f t h e i n c r e a s i n g concerns about c l a s s i c a l p e s t i c i d e s , and more s t r i n g e n t c o n s t r a i n t s about t h e i r u s e . A c c o r d i n g l y , an e f f o r t has been made t o i d e n t i f y t h o s e n a t u r a l p r o d u c t s t h a t have been found u s e f u l f o r t h e c o n t r o l o f a d i v e r s i t y of pests. I t was r e c o g n i z e d t h a t t h e v a l u e o f t h i s r e v i e w would be i n c r e a s e d by t h e i n c l u s i o n o f as many l i t e r a t u r e c i t a t i o n s as

In Naturally Occurring Pest Bioregulators; Hedin, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

1.

HEDIN

Use of Natural Products in Pest Control

p o s s i b l e . Many of the c i t a t i o n s are of r e c e n t meeting a b s t r a c t s , p a r t i c u l a r l y ACS meetings. These should p r o v i d e an e n t r a n c e i n t o the l i t e r a t u r e . An e f f o r t has been made t o a c h i e v e a r e l a t i v e l y e q u a l emphasis f o r a l l a r e a s t h a t have been i d e n t i f i e d , but t h i s i s intended as a survey t o show impact and not t o be an e x h a u s t i v e review.


C o n t r o l of

Insects

Sex, A s s e m b l i n g , and Other Pheromones. The r e c e n t l i t e r a t u r e ( 1 4) c o n t a i n s hundreds of c i t a t i o n s a t t e s t i n g t o the s p e c i f i c i t y , u n i q u e n e s s , and e f f i c a c y o f t h e s e compounds, a few o f which are l i s t e d i n Chapters 2 and 3 of t h i s volume. Two of the major drawbacks t o u t i l i z a t i o n o f pheromones are t h a t m a r k e t i n g o p p o r t u n i t i e s are l i m i t e d and t h a t the c o n t r o l a c h i e v e d i s u s u a l l y l e s s than complete. Pheromones may o c c a s i o n a l l y be s u i t a b l e f o r c o n t r o l , but may be most a p p l i c a b l e i n survey a p p l i c a t i o n s o r as p a r t of i n t e g r a t e d pest management programs. Pheromones have r e p e a t e d l y been used t o demonstrate the presence o f i n s e c t s where s c o u t i n g and o t h e r p h y s i c a l procedures are i n e f f e c t i v e . I t has been demonstrated t h a t pheromones can be used both f o r a t t r a c t i o n and f o r c o n f u s i o n . For c o n f u s i o n , e i t h e r l a r g e q u a n t i t i e s of the pheromone o r isomers can be used. I t has been f u r t h e r suggested t h a t where s e v e r a l i n s e c t s a t t a c k a c r o p , a l l of the pheromones may be f o r m u l a t e d t o g e t h e r . Where s e v e r a l components are r e q u i r e d f o r an i n s e c t r e s p o n s e , c o n f u s i o n may be a c h i e v e d by a l t e r i n g the r a t i o o r w i t h h o l d i n g one o r more components. In a d d i t i o n t o c o n t i n u i n g work t o i d e n t i f y pheromones, c o n s i d e r a b l e work on pheromone b i o s y n t h e s i s i s i n p r o g r e s s . Two r e c e n t symposia each i n c l u d e m u l t i p l e papers d e s c r i b i n g v a r i o u s a s p e c t s (4, 5 ) . Chapters 4-6 i n t h i s volume d e s c r i b e r e g u l a t o r y f a c t o r s of pheromone b i o s y n t h e s i s t h a t when more c o m p l e t e l y understood may f i n d f i e l d a p p l i c a t i o n s i m i l a r t o t h a t of i n s e c t growth r e g u l a t o r s . A l l e l o c h e m i c a l s . Food a t t r a c t a n t s , r e p e l l e n t s , f e e d i n g stimulants, feeding deterrents (antifeedants), o v i p o s i t i o n s t i m u l a n t s and d e t e r r e n t s , t o x i c a n t s , and n u t r i t i o n a l f a c t o r s are examples of a l l e l o c h e m i c a l s . They are u s u a l l y secondary p l a n t c o n s t i t u e n t s ( n o n - n u t r i t i o n a l chemicals a f f e c t i n g i n s e c t behavior and development). A l l e l o c h e m i c a l s g i v i n g the h o s t p l a n t an a d a p t i v e advantage are c a l l e d a l l o m o n e s , and f a c t o r s g i v i n g the i n s e c t an a d a p t i v e advantage are c a l l e d kairomones. A number of books and symposia have d e s c r i b e d work on t h e i r i s o l a t i o n , i d e n t i f i c a t i o n , and a p p l i c a t i o n (6-13). For many y e a r s , the U.S. Department of A g r i c u l t u r e conducted a r e s e a r c h program t o i d e n t i f y a t t r a c t a n t s and r e p e l l e n t s by b i o a s s a y i n g p l a n t e x t r a c t s and s y n t h e t i c compounds, many r e l a t e d t o known p l a n t compounds. A t t r a c t a n t s f o r the M e d i t e r r a n e a n f r u i t f l y , o r i e n t a l f r u i t f l y , and Japanese b e e t l e and many o t h e r s were s e l e c t e d as the r e s u l t of t h e s e programs and w i d e l y used. However, i n r e c e n t y e a r s , food a t t r a c t a n t s (kairomones) have found o n l y i n f r e q u e n t a p p l i c a t i o n s . On the o t h e r hand, a n t i f e e d a n t compounds w i t h very h i g h a c t i v i t y , n o t a b l y a z a d i r a c h t i n from neem


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NATURALLY OCCURRING PEST BIOREGULATORS ( 1 3 ) , have r e c e n t l y become the s u b j e c t o f renewed i n t e r e s t , and s e v e r a l have now been r e g i s t e r e d f o r commercial use. The i n t e r e s t s of s e v e r a l i n d u s t r i a l companies have been i n s t r u m e n t a l i n t h i s new t r e n d . The a n t i f e e d a n t s t e s t e d t o date are sometimes s p e c i f i c f o r c e r t a i n i n s e c t s . These v a r i a b l e a c t i v i t i e s may serve as the b a s i s both f o r s t r u c t u r e - a c t i v i t y s t u d i e s and m e c h a n i s t i c s t u d i e s a t the r e c e p t o r l e v e l . The use of a n t i f e e d a n t s has an added advantage o v e r t h a t of t o x i c a n t s i n t h a t the i n s e c t consumes l i t t l e i f any of the p l a n t , t h u s l i m i t i n g damage. Pest c o n t r o l m a t e r i a l s which are s p e c i f i c f o r i n s e c t s and which a f f e c t m e t a b o l i c pathways o r a n a t o m i c a l s t r u c t u r e s ( i n c l u d i n g c e l l u l a r ) which are unique t o i n s e c t s may p o s s e s s l e s s t o x i c i t y f o r mammals, and thus may be s u p e r i o r as p e s t i c i d e s . I t has a l s o been s p e c u l a t e d t h a t h i g h l y s p e c i f i c l i p o l y t i c and p r o t e o l y t i c enzymes w i l l be found t o c o n t r o l s p e c i f i c p r o c e s s e s i n i n s e c t s , as they do i n mammals; thus t h e y w i l l be i m p o r t a n t t a r g e t s f o r r e s e a r c h . Chapters 2 and 9-20 i n t h i s volume d i s c u s s the c o n t r o l of i n s e c t s w i t h a l l e l o c h e m i c a l s , and the mechanisms by which p l a n t s b i o s y n t h e s i z e t h e s e compounds and use them t o become r e s i s t a n t t o t h e i r pests. Toxicants. The d i s c u s s i o n o f t h i s s u b j e c t has been separated from t h a t of a l l e l o c h e m i c a l s t o emphasize t h a t n o v e l compounds p o s s e s s i n g s t r o n g t o x i c a c t i v i t y , and o f t e n accompanying a n t i f e e d a n t a c t i o n , have been i s o l a t e d from p l a n t s t h a t are o f t e n t r o p i c a l o r d e s e r t i n o r i g i n (12-15). One of the apparent e x p l a n a t i o n s f o r the l a r g e number o f t r o p i c a l and d e s e r t p l a n t s p o s s e s s i n g h i g h l y t o x i c compounds i s t h a t they must c o e x i s t w i t h h i g h e r i n s e c t and d i s e a s e i n f e s t a t i o n s t h a n p l a n t s grown i n temperate c l i m a t e s . In e v o l u t i o n a r y t i m e , p l a n t s t h a t are most a b l e t o c o e x i s t ( i n p a r t because of t h e i r b i o s y n t h e s i s of t o x i c a n t s ) have been s e l e c t e d . An i n c r e a s e i n the a c c e s s i b i l i t y o f t h e s e p l a n t m a t e r i a l s w i l l depend l a r g e l y on the a c t i v i t y of b o t a n i c a l and p h a r m a c e u t i c a l c o l l e c t i o n programs. Chapters 21 and 28 i n t h i s volume are p e r t i n e n t examples of d i r e c t e d e f f o r t s t o i d e n t i f y n a t u r a l t o x i n s from t r o p i c a l p l a n t s o u r c e s . A prominent example of a s y n t h e t i c p e s t i c i d e whose s t r u c t u r e was based on a n a t u r a l p r o d u c t i s the f a m i l y of p y r e t h r o i d s ( 1 6 ) . A f t e r the e l u c i d a t i o n of the n a t u r a l p r o d u c t s t r u c t u r e , a s e a r c h f o r compounds w i t h optimum p r o p e r t i e s has c o n t i n u e d f o r many y e a r s and has r e s u l t e d i n wide c o m m e r c i a l i z a t i o n . N a t u r a l l y O c c u r r i n g Hormonal Agents from I n s e c t s and P l a n t s . The j u v e n i l e , m o l t i n g , b r a i n , and diapause hormones, antihormones such as the p r e c o c e n e s , and the p r o s t a g l a n d i n s are examples of t h e s e a g e n t s . S e v e r a l books and symposia ( 5 , 10, 12, 17) p r o v i d e a summary o f the s t a t u s of t h e s e c l a s s e s of compounds. I t i s p r o b a b l e t h a t a d d i t i o n a l hormonal and a n t i h o r m o n a l agents w i t h h i g h a c t i v i t y and s p e c i f i c i t y w i l l be i s o l a t e d from p l a n t s o r i n s e c t s . Some w i l l a c t i n a d i r e c t manner w h i l e o t h e r s may promote b i o s y n t h e s i s of a secondary compound(s) w i t h t o x i c i t y o r o t h e r a c t i v i t y toward the i n s e c t . The h i g h a c t i v i t y and g r e a t s p e c i f i c i t y of t h e s e compounds make i t p r o b a b l e t h a t f i e l d


1.

HEDIN



a p p l i c a t i o n s can be c a r r i e d out under o p t i m a l c o n d i t i o n s , o f t e n as a p a r t of p e s t management systems. D u r i n g the past few y e a r s , a number of p e p t i d e s have been i s o l a t e d from i n s e c t s and p l a n t s w i t h v e r y p o w e r f u l hormonal o r t o x i c e f f e c t s (18, 19). Chapter 7 i n t h i s volume d e s c r i b e s work on the e f f e c t s of enzymes on c u t i c l e t a n n i n g t h a t are hormonal l i k e i n a c t i o n s and have a c t i v i t y a t low c o n c e n t r a t i o n s . M i c r o b i a l and V i r a l Agents f o r the C o n t r o l of I n s e c t P e s t s . M i c r o b i a l agents t r a d i t i o n a l l y have been v i s u a l i z e d as c o n t r i b u t i n g t o b i o l o g i c a l c o n t r o l of p e s t s . Many o f these m i c r o b i a l agents can now be d e f i n e d c h e m i c a l l y . Work i s a l s o p r o g r e s s i n g on f l y c o n t r o l i n a n i m a l p r o d u c t i o n and a n t i g e n s f o r nematodes and i n s e c t s ( 1 9 ) . The development of BT p r e p a r a t i o n s f o r c o n t r o l of i n s e c t p e s t s has a c c e l e r a t e d g r e a t l y i n the past 3-5 y e a r s , p a r t i c u l a r l y s i n c e f o r m u l a t i o n s have been developed t o extend f i e l d l i f e . Other m i c r o b i a l and v i r a l agents are a l s o b e i n g developed and show v a r y i n g degrees of promise f o r f i e l d a p p l i c a t i o n s (18-21). N a t u r a l Products as Inducers of I n s e c t R e s i s t a n c e . P l a n t growth r e g u l a t o r s have been shown t o i n c r e a s e the b i o s y n t h e s i s of c e r t a i n secondary p l a n t c o n s t i t u e n t s t h a t i n t u r n decrease p l a n t a t t a c k by i n s e c t s . $ - N a p h t h a l e n e a c e t i c a c i d , f o r example, e l i c i t s i n c r e a s e d t e r p e n e b i o s y n t h e s i s i n c i t r u s , thus d e c r e a s i n g a t t a c k by f r u i t flies. The approach of u s i n g both n a t u r a l and s y n t h e t i c p l a n t growth r e g u l a t o r s may c o n t i n u e t o f i n d a p p l i c a t i o n s i n i n s e c t control. A g e n e r a l term f o r compounds whose b i o s y n t h e s i s i s e l i c i t e d o r i n d u c e d i n p l a n t s as the r e s u l t of a t t a c k by a pest i s " p h y t o a l e x i n " . These h i g h e r p l a n t m e t a b o l i t e s are a n t i b i o t i c t o c e r t a i n p o t e n t i a l p l a n t pathogens and a l s o on o c c a s i o n t o i n s e c t s (Chapter 13 of t h i s volume). The p h y t o a l e x i n s t y p i c a l l y are b i o s y n t h e s i z e d i n g r e a t e r c o n c e n t r a t i o n s when the p l a n t i s s u b j e c t e d t o s t r e s s . T h e r e f o r e , the a t t a c k i n g agent ( f u n g i , b a c t e r i a , o r v i r u s e s i n most work t o date) e l i c i t s the i n i t i a t i o n o r i n c r e a s e d s y n t h e s i s o f p h y t o a l e x i n s ( a n t i b i o t i c compounds). I t has r e c e n t l y been shown t h a t a t t a c k by i n s e c t s and nematodes a l s o can e l i c i t the f o r m a t i o n o f p h y t o a l e x i n s . A number of c h e m i c a l e l i c i t o r s o f p h y t o a l e x i n s have a l s o been i d e n t i f i e d (11, 12, 22, 23). Induced A u t o i n t o x i c a t i o n . The g o a l of t h i s approach i s t o a p p l y p r e c u r s o r s t h a t develop a c t i v i t y o n l y i n the t a r g e t s p e c i e s . A l t h o u g h p h o t o s e n s i t i z a t i o n i s not always r e q u i r e d t o develop a c t i v i t y , t h i s type of s e n s i t i z a t i o n was r e p o r t e d a number of y e a r s ago as o c c u r r i n g when h o u s e f l i e s were f e d v a r i o u s dyes (24). A c e t y l e n e s and furanocoumarins have been shown t o a f f e c t the i n s e c t m e l a n i n s and they are p h o t o t o x i c ( 2 5 ) . The advantage of t h i s approach f o r p r a c t i c a l a p p l i c a t i o n i s t h a t i t may p e r m i t f o l i a r a p p l i c a t i o n o f compounds w i t h low t o x i c i t y and perhaps h i g h s p e c i f i c i t y f o r the t a r g e t i n s e c t . Continued s t u d i e s of the mechanisms of a c t i v a t i o n can be expected t o generate more e f f i c i e n t p r e c u r s o r s . Much of the r e c e n t work has been summarized


5

6

NATURALLY OCCURRING PEST BIOREGULATORS i n two symposia and a subsequent book (26, 2 7 ) , and i n Chapters 25 and 26 o f t h i s volume.


C o n t r o l o f Weeds Weed c o n t r o l i s d e f i n e d as t h e s e l e c t i v e a p p l i c a t i o n o f s t r e s s agents t h a t can be c h e m i c a l ( s y n t h e t i c o r n a t u r a l ) , t i l l a g e , f e r t i l i z e r , c u l t u r a l p r a c t i c e , or other. I t has been suggested and i s g e n e r a l l y r e c o g n i z e d t h a t c o n t r o l o f weeds must f o l l o w t h e approach o f i n t e g r a t e d p e s t management. Some o f t h e d e s i r e d r e s u l t s a r e t h a t t h e system be energy e f f i c i e n t , c o n s e r v a t i v e t o s o i l , e n v i r o n m e n t a l l y s a f e , i n e x p e n s i v e , e f f e c t i v e , broad spectrum where d e s i r a b l e , and s e l e c t i v e . The c o n t r o l o f weeds has g e n e r a l l y been c o n s i d e r e d t o be t h e domain o f s y n t h e t i c c h e m i c a l s , but n a t u r a l p r o d u c t s a r e b e g i n n i n g t o have an impact (28, 2 9 ) . N a t u r a l P r o d u c t s t h a t R e g u l a t e P l a n t Growth. N a t u r a l p r o d u c t s t h a t possess growth r e g u l a t i n g a c t i v i t y can be b r o a d l y c a t e g o r i z e d i n t o two groups: (1) growth substances such as a u x i n s , g i b b e r e l l i n s , c y t o k i n i n s , a b s c i s i c a c i d , e t h y l e n e , and t h e i r s y n t h e t i c analogues o r mimics, and (2) t h e s o - c a l l e d secondary p l a n t growth substances such as t h e p h e n o l s , a l i p h a t i c and a r o m a t i c c a r b o x y l i c a c i d s and t h e i r d e r i v a t i v e s , s t e r o i d s , a l k a l o i d s , t e r p e n o i d s , amino a c i d s , and l i p i d s . Of t h e secondary p l a n t growth s u b s t a n c e s , some o f t h e u n s a t u r a t e d l a c t o n e s , t e r p e n o i d s , s t e r o i d s , and a l k a l o i d s tend t o have l i m i t e d s p e c i e s d i s t r i b u t i o n , a r e produced i n s m a l l q u a n t i t i e s , b u t may possess some s p e c i f i c a c t i v i t y . N e a r l y a l l o f t h e s o - c a l l e d secondary p l a n t growth substances can be viewed as o r i g i n a t i n g from t h e a c e t a t e and s h i k i m i c a c i d pathways. Mandava (30) has l i s t e d a number o f t h e s e compounds w i t h t h e i r s p e c i f i c a c t i v i t i e s . Duke (Chapter 26 i n t h i s volume) r e p o r t e d on s e v e r a l t e t r a p y r r o l e i n t e r m e d i a t e s o f heme b i o s y n t h e s i s t h a t generate h i g h l e v e l s o f s i n g l e t oxygen. Many compounds t h a t e f f e c t heme and/or c h l o r o p h y l l pathways a r e s t r o n g l y h e r b i c i d a l due t o a c c u m u l a t i o n of p h y t o t o x i c l e v e l s o f these t e t r a p y r r o l e s . I n v e s t i g a t i o n s of the r o l e that these n a t u r a l products play i n t h e metabolism o f t h e p l a n t s where t h e y a r e produced and t h e e x t e n t t o which they c o n t r o l growth and developmental p r o c e s s e s appear o f i n t e r e s t . A l s o , t h e n a t u r e o f t h e c o n t r o l mechanisms and t h e i r e f f i c a c y f o r h e r b i c i d a l a c t i v i t y may warrant i n v e s t i g a t i o n . The r e c e n t i n t e r e s t i n b r a s s i n o s t e r o i d s as p l a n t growth r e g u l a t o r s may a l s o l e a d t o an a p p l i c a t i o n f o r weed c o n t r o l (31). A l l e l o p a t h i c Agents. Weeds (and o t h e r p l a n t s ) s e c r e t e c h e m i c a l s from t h e r o o t s and t o p s t h a t i n h i b i t seed g e r m i n a t i o n and growth of proximate p l a n t s . These c h e m i c a l s can be shown t o be v e r y e f f e c t i v e i n t h e l a b o r a t o r y and t h e i r f i e l d e f f e c t s i n - s i t u a r e e v i d e n t , but a d a p t a t i o n f o r commercial use has been slow t o f o l l o w . Nevertheless, there i s a continuing e f f o r t t o i d e n t i f y a l l e l o p a t h i c a g e n t s . Two comprehensive books by Thompson (28) and W a l l e r (29) summarize much o f t h e r e c e n t l i t e r a t u r e .


1.

HEDIN Disease

Use of Natural Products in Pest Control Control


D i s e a s e s i n p l a n t s may be c a t e g o r i z e d as r e s u l t i n g c h i e f l y from v i r u s e s , b a c t e r i a and f u n g i . I t has been s t a t e d t h a t modern o r g a n i c f u n g i c i d e s have i n e f f e c t b i o r a t i o n a l l y e v o l v e d from the p a s t use of s u l f u r , copper s u l f a t e , and copper s u l f a t e h y d r a t e d l i m e . Over the p a s t 30-40 y e a r s , a s u c c e s s i o n of s y n t h e t i c f u n g i c i d e s and o t h e r d i s e a s e c o n t r o l agents have been developed. They have c a p t u r e d most of the market and c o n t i n u e t o h o l d i t . N e v e r t h e l e s s , l a r g e numbers of n a t u r a l p r o d u c t s have been screened f o r v a r i o u s d i s e a s e c o n t r o l a c t i v i t i e s (12, 30, 32). F u n g i c i d e s from T r o p i c a l and S u b t r o p i c a l P l a n t s . As d i s c u s s e d e a r l i e r , p l a n t s from t r o p i c a l r e g i o n s of the w o r l d are s u b j e c t e d t o severe d i s e a s e p r e s s u r e s , p a r t i c a l l y because of the heat and h u m i d i t y ( o t h e r d i s e a s e organisms r e q u i r e c o o l , humid c o n d i t i o n s ) . These p l a n t s may adapt t o p r e s s u r e of d i s e a s e s i n e v o l u t i o n a r y time by d e v e l o p i n g defense systems. One mechanism of defense i s the b i o s y n t h e s i s of h i g h l y a c t i v e a n t i f e e d a n t s f o r i n s e c t s . A number have been i d e n t i f i e d (14, 32) which suggests t h a t o t h e r t y p e s of b i o l o g i c a l a c t i v i t y such as a n t i f u n g a l a c t i v i t y a l s o may be found i n these p l a n t s . The a v a i l a b i l i t y of p l a n t m a t e r i a l from the t r o p i c s has i n c r e a s e d because of i n d u s t r i a l and p u b l i c s e c t o r groups s e c u r i n g them f o r e x a m i n a t i o n o f t h e i r p h a r m a c e u t i c a l and a n t i c a n c e r p r o p e r t i e s . The work o f M i l e s e t . a l . (Chapter 28 i n t h i s volume), who screened P e r u v i a n p l a n t s f o r s e v e r a l a n t i m i c r o b i a l a c t i v i t i e s , i s an example of t h i s approach. Snook and Chortyk (Chapter 27 of t h i s volume) found s e v e r a l tobacco r o o t p h e n o l i c s t o be a c t i v e a g a i n s t the b l a c k shank fungus. Hasegawa e t a l (Chapter 29 of t h i s volume) i s o l a t e d a n t a g o n i s t i c microorganisms from the r h i z o s p h e r e s o i l of Adzuke-bean r o o t t h a t c o n t r o l l e d Fusarium w i l t and i s o l a t e d s e v e r a l a n t i b i o t i c c o n s t i t u e n t s . A l s o , a number of a n t i f u n g a l c o n s t i t u e n t s were r e p o r t e d i n the symposium book o f C u t l e r ( 1 2 ) . A n t i b i o t i c s . The s u c c e s s f u l use of a n t i b i o t i c s a g a i n s t b a c t e r i a l d i s e a s e s of humans has l e d t o l a r g e - s c a l e s c r e e n i n g of a n t i b i o t i c s f o r p l a n t d i s e a s e c o n t r o l . They are n o r m a l l y produced c o m m e r c i a l l y f o r use by m i c r o b i o l o g i c a l p r o c e s s e s . Some o f the a n t i f u n g a l a n t i b i o t i c s are c y c l o h e x i m i d e , g r i s e o f u l v i n , b l a s t i c i d i n S, kasugamycin, p o l y o x i n , ezomycin, and v a l i d a m y c i n A. The a n t i b a c t e r i a l a n t i b i o t i c s i n c l u d e s t r e p t o m y c i n , c e l l o c i d i n , c h l o r a m p h e n i c o l , and n o v o b i o c i n . In another a r e a , S t r o b e l and Myers (33) i s o l a t e d a b a c t e r i u m n o r m a l l y found on l e a v e s of wheat, b a r l e y , and o a t s t h a t can d e f e a t the fungus r e s p o n s i b l e f o r Dutch elm d i s e a s e . The b a c t e r i u m i s a pseudomonad t h a t produces f u n g u s - k i l l i n g a n t i b i o t i c s . A l t e r n a t i v e l y , the b a c t e r i a c o u l d be d i r e c t l y used o r the b a c t e r i a l a n t i b i o t i c c o u l d be m i c r o b i o l o g i c a l l y produced and used f o r c o n t r o l . The success w i t h Dutch elm d i s e a s e fungus suggests t h a t s u i t a b l e s c r e e n i n g programs may i d e n t i f y s t i l l o t h e r d i s e a s e - k i l l i n g agents. E l i c i t a t i o n of P h y t o a l e x i n s . P h y t o a l e x i n s ( p r e v i o u s l y d i s c u s s e d b r i e f l y w i t h r e g a r d t o a c t i v i t i e s a g a i n s t i n s e c t s ) are g e n e r a l l y


7


8

NATURALLY OCCURRING PEST BIOREGULATORS d e f i n e d as low m o l e c u l a r weight p r o d u c t s o f p l a n t b i o s y n t h e s i s t h a t have a n t i b i o t i c p r o p e r t i e s t o one o r s e v e r a l groups o f m i c r o o r g a n i s m s . The preformed l e v e l s o f p h y t o a l e x i n s a r e g e n e r a l l y low o r n o n - d e t e c t a b l e i n h e a l t h y p l a n t t i s s u e , b u t they accumulate t o h i g h l e v e l s a t t h e s i t e o f a t t a c k o f t h e p l a n t by an i n v a d i n g m i c r o o r g a n i s m . B e l l e t a l . ( 3 4 ) d e f i n e s t h o s e components o f r e s i s t a n c e t h a t a r e p r e s e n t i n h e a l t h y p l a n t s as p a r t o f a " c o n s t i t u t i v e d e f e n s e " . Chemicals t h a t e f f e c t a c t i v e defense responses a r e r e f e r r e d t o as e l i c i t o r s , and may be e i t h e r b i o t i c o r a b i o t i c i n o r i g i n . B e l l e t a l . (34) have i d e n t i f i e d a number of a b i o t i c e l i c i t o r s o f t e r p e n o i d and t a n n i n s y n t h e s i s i n c o t t o n such as c h i l l i n g i n j u r y , UV i r r a d i a t i o n , c u p r i c i o n s , polymers from m i c r o b i a l c e l l w a l l s such as p o l y s a c c h a r i d e s , and p e s t i c i d e s . I n a sense, many o f those b i o r e g u l a t o r s , n a t u r a l and s y n t h e t i c , t h a t i n c r e a s e p l a n t r e s i s t a n c e t o p e s t s c a n be viewed as e l i c i t o r s o f p h y t o a l e x i n s . Of s p e c i a l i n t e r e s t a r e t h e p o l y s a c c h a r i d e s t h a t a c t as e l i c i t o r s . V a r i o u s heterogeneous polymers o b t a i n e d from f u n g a l and b a c t e r i a l c e l l w a l l s a l s o a c t as e l i c i t o r s . These i n c l u d e e x t r a c e l l u l a r p o l y s a c c h a r i d e s , l i p o p r o t e i n p o l y s a c c h a r i d e s , and glycoproteins. S t u d i e s w i t h o t h e r p l a n t - p a t h o g e n systems have shown t h a t o l i g o m e r s from c h i t o s a n and 3-1,3-glucans can be potent e l i c i t o r s ( 3 5 ) . Both c h i t i n and t h e g l u c a n s a r e common c o n s t i t u e n t s o f f u n g a l c e l l w a l l s and a r e c l e a v e d by c h i t i n a s e s and 3-1,3-glucanases t h a t o c c u r i n p l a n t s ; c o n c e n t r a t i o n s o f t h e s e enzymes i n c r e a s e i n many p l a n t s soon a f t e r i n f e c t i o n . A s p e c i f i c o l i g o m e r s i z e ( u s u a l l y 5-8 s u b u n i t s ) o f c h i t o s a n o r 3-1,3-glucans i s required for appreciable a c t i v i t y . I s i s p o s s i b l e t h a t such s i z e s a r e c l e a v e d from l i p o p r o t e i n p o l y s a c c h a r i d e s , e x t r a c e l l u l a r p o l y s a c c h a r i d e s , and dead c e l l s o f f u n g a l and b a c t e r i a l pathogens t o a c t i v a t e defense responses i n c o t t o n . A 3-Na c e t y l g l u c o s a m i n i d a s e has been demonstrated i n c o t t o n t i s s u e ( 3 4 ) . P e c t a t e o l i g o m e r s a l s o may a c t as e l i c i t o r s and can be formed by t h e a c t i o n o f f u n g a l o r h o s t p e c t i n a s e enzymes on p e c t i n (33). Summary. N a t u r a l l y o c c u r r i n g pest b i o r e g u l a t o r s have been i s o l a t e d from a wide d i v e r s i t y o f s o u r c e s , o f t e n from g e o g r a p h i c a l l y s t r e s s e d r e g i o n s which f a v o r r a p i d growth o f p e s t populations. I n o r d e r f o r p l a n t s ( o r a n i m a l s ) t o s u r v i v e , they must develop mechanisms t o a v o i d o r cope w i t h t h e s e p e s t s . These mechanisms o f t e n i n v o l v e c h e m i c a l s t h a t d e t e r f e e d i n g , t h a t a r e t o x i c , o r t h a t slow growth and m a t u r a t i o n o f t h e p e s t . N a t u r a l p r o d u c t s a r e a l s o a key t o u n d e r s t a n d i n g e c o l o g i c a l systems. With t h e i d e n t i f i c a t i o n o f t h e c o n s t i t u e n t s , p r o g r e s s has been made i n u n d e r s t a n d i n g t h e m e t a b o l i c c y c l e s , t h e enzymes t h a t l e a d t o t h e i r b i o s y n t h e s i s , and t h e u n d e r l y i n g g e n e t i c c o n t r o l s . F o r a p p l i c a t i o n o f these n a t u r a l p r o d u c t s t o p e s t c o n t r o l , an u n d e r s t a n d i n g o f t h e p h y s i o l o g y and b e h a v i o r a r e e s s e n t i a l t o e l u c i d a t e t h e u n d e r l y i n g c h e m i c a l l y mediated i n t e r a c t i o n s between h o s t and p e s t . N a t u r a l p r o d u c t s have p r o v i d e d l e a d s t o new p e s t i c i d e s . Knowledge o f t h e b i o s y n t h e t i c p r o c e s s e s o f n a t u r a l p r o d u c t s and



1. HEDIN

Use of Naturd Products in Pest Control

r e l a t e d i n f o r m a t i o n has o f t e n l e d t o an u n d e r s t a n d i n g o f t h e mode o f a c t i o n . A knowledge o f t h e r e q u i r e d f u n c t i o n a l groups has l e d t o t h e d e s i g n o f s y n t h e t i c p e s t i c i d e s w i t h h i g h a c t i v i t y and specificity. N a t u r a l p r o d u c t s may a l s o f i n d t h e i r p l a c e i n t h e market p l a c e . E c o n o m i c a l l y f e a s i b l e b i o r e g u l a t o r s may be produced by m i c r o b i o l o g i c a l p r o c e s s e s such as f e r m e n t a t i o n . I n o t h e r i n s t a n c e s , p r o c e s s i n g o f p l a n t m a t e r i a l may p r o v i d e c o m m e r c i a l l y adequate y i e l d s . F o r o t h e r a p p l i c a t i o n s such as t h e p r o d u c t i o n o f pheromones, hormones, o r p e p t i d e s , s y n t h e s i s o f t h e n a t u r a l p r o d u c t s may be t h e b e s t s t r a t e g y . Another a p p l i c a t i o n o f n a t u r a l p r o d u c t s t o p e s t c o n t r o l may be t h r o u g h t h e i n s e r t i o n o f genes i n t o p l a n t s e x p r e s s i n g t h e compound. T h i s approach i s j u s t now r e c e i v i n g i n c r e a s e d emphasis. When a b i o l o g i c a l l y a c t i v e n a t u r a l p r o d u c t i s i d e n t i f i e d , o f t e n more i s g a i n e d than knowledge about t h e s p e c i f i c s t r u c t u r e . An u n d e r s t a n d i n g o f how t h e n a t i o n a l p r o d u c t i s b i o s y n t h e s i z e d and by which mechanism(s) i t e x p r e s s e s i t s a c t i v i t y s h o u l d make i t p o s s i b l e t o d e v i s e a d d i t i o n a l minimal changes t h a t y i e l d maximum b e n e f i t s . Thus, those changes t h a t b e n e f i t people may be s e l e c t e d which do minimum o r no damage t o t h e ecosystem. Literature Cited 1.

Beroza, M. Pest Management with Insect Sex Attractants; ACS Symposium Series No. 23; American Chemical Society: Washington, DC, 1976; 192 pp. 2. Inscoe, M. N. In Insect Suppression with Controlled Release Pheromone Systems; Kydonieus, A. E., Beroza, M., Eds.; CRC Press: New York, Vol. I I , p. 201-295. 3. Leonhardt, Β. Α.; Beroza, M. Insect Pheromone Technology: Chemistry and Application; ACS Symposium Series No. 190, American Chemical Society: Washington, DC, 1982; 260 pp. 4. Hedin, P. Α.; Menn, J . J . ; Editors, Insect Chemical Communication: Unifying Concepts; Special Issue, J . Chemical Ecology 1988, 14, 1979-2145. 5. Carlson, D. A. Symposium on Biosynthesis and Catabolism of Insect Pheromones and Hormones; Abstracts of Papers, 199th National Meeting of the American Chemical Society: Boston, MA, A p r i l 1990, AGRO 36-40, 55-60, 74-79. 6. Wallace, J . W.; Mansell, R. L. Biochemical Interactions Between Plants and Insects; Recent Advances i n Phytochemistry, Vol. 10, Plenum Press, Ν. Υ., 1976; 425 pp. 7. Hedin, P. A. Host Plant Resistance to Pests; ACS Symposium Series No. 62; American Chemical Society: Washington, DC, 1977; 286 pp. 8. Rosenthal, G. Α., Janzen, D. H. Herbivores: Their Interaction with Secondary Plant Metabolites; Academic Press: New York, 1979; 718 pp. 9. Hedin, P. A. Plant Resistance to Insects; ACS Symposium Series No. 208; American Chemical Society: Washington, DC, 1983; 375 pp. 10. Hedin, P. A. Bioregulators f o r Pest Control; ACS Symposium Series No. 276; American Chemical Society: Washington, DC, 1985; 540 pp.


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NATURALLY OCCURRING PEST BIOREGULATORS 11. Green, M. B.; Hedin, P. A. Natural Resistance to Pest: Roles of Allelochemics; ACS Symposium Series No. 296; American Chemical Society: Washington, DC, 1986; 243 pp. 12. Cutler, H. G. B i o l o g i c a l l y Active Natural Products: Potential Uses i n Agriculture; ACS Symposium Series No. 380; American Chemical Society: Washington, DC, 1988; 483 pp. 13. Morgan, E. D.; Mandava, Ν. B. Handbook of Natural Pesticides: Vol. VI, Insect Attractants and Repellents; CRC Press: Boca Raton, FL.; 249 pp. 14. Kubo, I.; Nakanishi, K. In Host Plant Resistance to Pests; Hedin, P. Α., Ed.; ACS Symposium Series No. 62; American Chemical Society: Washington, DC, 1977; pp 165-178. 15. Mabry, T. J . ; Burnett, W. C.; Jones, S. B.; Gill, J . E. In Host Plant Resistance to Pests; Hedin, P. Α., Ed., ACS Symposium Series No. 62; American Chemical Society: Washington, DC, 1977; pp. 179-184. 16. Elliott, M. Synthetic Pyrethroids; ACS Symposium Series No. 42; American Chemical Society: Washington, DC, 1977; 229 pp. 17. G i l b e r t , L. I. The Juvenile Hormones; Plenum Press: New York, 1976; 572 pp. 18. Osburn, Β. I. Symposium on Natural Antimicrobial Peptides and t h e i r Application i n Agriculture; Abstracts of Papers, 197th National Meeting, American Chemical Society: Dallas, TX, A p r i l 1989, AGRO 13-17, 30-33. 19. Menn, J.J.; Kelly, T. J . ; Masler, E. P.; Edwards, J . V.; Cherry, J . P; Eto, M., Hammock, B. D.; Okai, H. Symposium on B i o l o g i c a l l y Active Peptides i n Insects, Plants, and Food; Abstracts of Papers, 197th International Chemical Congress of P a c i f i c Basin Societies: Honolulu, HI, December 1989, AGRO 43-47, 82-88, 105-110, 133-138, 140-145, 382-390, 398-404. 20. Cross, B.; Cody, S. Symposium on Formulation of Proteins f o r A g r i c u l t u r a l Applications; Abstracts of Papers, 200th National Meeting, American Chemical Society: Washington, DC, August 1990, AGRO 5-8, 14-18, 40-44. 21. Hedin, P. Α.; Menn, J . J . ; Hollingworth, R. M. Biotechnology for Crop Protection; ACS Symposium Series No. 379; American Chemical Society: Washington, DC, 1988, 471 pp. 22. Keen, N. T.; Bruegger, B. In "Host Plant Resistance to Pests"; Hedin, P. Α., Ed.; ACS Symposium Series No. 62; American Chemical Society: Washington, DC, 1977; pp 1-26. 23. Hedin, P. Α.; Jenkins, J . N.,; Thompson, A. C.; McCarty, J . C.; Smith, D. H.; Parrott, W. L.; Shepherd, R. L. J . Agric. Food Chem. 1988, 36, 1055-1061. 24. Carpenter, T. L; Heitz, J . R. "Abstracts of Papers", 178th National Meeting, American Chemical Society: Washington, DC, Sept. 1979; PEST 34. 25. Berenbaum, M. Science (Washington, DC): 1978, 201, 532-533. 26. Heitz, J . R.; Downum, K. R. Light Activated Pesticides; ACS Symposium Series No. 339; American Chemical Society; Washington, DC, 1987; 355 pp. 27. Towers, G. Η. N.; Kubo, I.; Tang, C. S.; Mizutani, J . Symposium on Chemical Aspects of Plant-Microogaranism, PlantInsect, and Plant-Plant Interactions; Abstracts of Papers,


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1989 International Chemical Congress of P a c i f i c Basin Societies: Honolulu, HI, December 1989, AGRO 164-171, 195-202. Thompson, A. C. The Chemistry of Allelopathy: Biochemical Interactions Among Plants; ACS Symposium Series No. 268; American Chemical Society: Washington, DC, 1985; 471 pp. Waller, G. R. Allelochemicals: Role i n Agriculture and Forestry; ACS Symposium Series No. 330; American Chemical Society: Washington, DC, 606 pp. Mandava, Ν. B. In "Plant Growth Substances"; Mandava, Ν. B., Ed.; ACS Symposium Series No. 111; American Chemical Society: Washington, DC, 1979; pp 135-213. Cutler, H. G. Symposium on Brassinosteroids; Abstracts of Papers, 200th National Meeeting, American Chemical Society: Washington, DC, August 1990, AGRO 76-79, 100-102, 119-122, 131-133. Jacobson, M. In Host Plant Resistance to Pests; Hedin, P. Α., Ed.; ACS Symposium Series No. 62; American Chemical Society: Washington, DC, 1977; pp 153-164. Strobel, G.; Myers, D. F. Science News (Washington, DC): 1980, 117, 362. B e l l , Α. Α.; Mace, M. E.; Stipanovic, R. D. In Natural Resistance of Plants to Pests: Roles of Allelochemicals; Green, M. B, Hedin, P. Α., Eds.; ACS Symposium Series No. 296; American Chemical Society; Washington, DC, pp 36-54. Keen, N. T.; Yoshikawa, M.; Want, M. C. Plant Physiol. 1983, 71, 466-471.

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