2-TridecanoneGlandular Trichome-Mediated Insect Resistance in

Chapter 11

2-Tridecanone—Glandular Trichome-Mediated Insect Resistance in Tomato Effect on Parasitoids and Predators of Heliothis zea George G. Kennedy , Robert R. Farrar, Jr. , and R. K. Kashyap Downloaded by STANFORD UNIV GREEN LIBR on August 2, 2012 | http://pubs.acs.org Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch011

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Department of Entomology, North Carolina State University, Raleigh, NC 27695-7630 Department of Entomology, Haryana Agricultural University, HISAR 125004, India 1

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2-Tridecanone/glandular trichome-mediated resistance to the tobacco hornworm, Manduca sexta (L.) and the Colorado potato beetle, Leptinotarsa decemlineata (Say) in a wild tomato, Lycopersicon hirsutum f. glabratum C. H. Mull, PI 134417, adversely affects several species of parasitoids and predators of the tomato fruit-worm, Heliothis zea (Boddie). Rates of parasitism or predation, and parasitoid survival, were lower on PI 134417 foliage than rates on susceptible foliage. Removal of trichomes from PI 134417 foliage greatly reduced or eliminated these effects. F i l t e r paper treated with 2-tridecanone at levels comparable to those in PI 134417 foliage had similar effects. Intermediate effects were found on a hybrid line with intermediate densities of trichomes but no 2-tridecanone, indicating at least a partial role of trichome density.

Research on the b i o c h e m i c a l mechanisms o f p l a n t defenses has expanded g r e a t l y i n r e c e n t years and has r e v e a l e d the r i c h d i v e r s i t y and complex n a t u r e o f p l a n t d e f e n s e s . I t has p r o v i d e d i n f o r m a t i o n i m p o r t a n t t o the e f f i c i e n t development and u t i l i z a t i o n o f a r t h r o p o d r e s i s t a n t crop v a r i e t i e s f o r pest management (1) and has c o n t r i b u t e d new i n s i g h t i n t o the r o l e p l a y e d by p l a n t d e f e n s i v e c h e m i s t r y i n the s t r u c t u r i n g o f a r t h r o p o d communities a s s o c i a t e d w i t h p a r t i c u l a r p l a n t s p e c i e s or v a r i e t i e s (2^).

0097-6156/91A)449-0150$06.00/0 © 1991 American Chemical Society In Naturally Occurring Pest Bioregulators; Hedin, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

Downloaded by STANFORD UNIV GREEN LIBR on August 2, 2012 | http://pubs.acs.org Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch011

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The s u i t a b i l i t y o f a r t h r o p o d s as prey o r as h o s t s o f i n s e c t p r e d a t o r s and p a r a s i t o i d s has been r e p e a t e d l y shown t o be a f f e c t e d by host plant chemistry. The mechanisms by which p l a n t c h e m i c a l f a c t o r s mediate s u i t a b i l i t y o f h e r b i v o r e s as h o s t s ( p r e y ) f o r t h e i r n a t u r a l enemies f a l l i n t o two b r o a d l y o v e r l a p p i n g c a t e g o r i e s . The f i r s t i n v o l v e s host p l a n t compounds i n g e s t e d , and i n some cases s e q u e s t e r e d , by the h e r b i v o r e s t h a t a r e t o x i c o r d i s t a s t e f u l t o p a r a s i t o i d s o r p r e d a t o r s ( 4 - 6 ) . Such compounds may be a c t i v e as r e p e l l e n t s o r as acute o r c h r o n i c t o x i n s 05, 7-10). The second c a t e gory i n v o l v e s the n u t r i t i o n a l q u a l i t y o f the host p l a n t m e d i a t i n g h e r b i v o r e u t i l i z a t i o n by p a r a s i t o i d s and p r e d a t o r s ( 1 1 - 1 4 ) . Changes i n h e r b i v o r e s i z e due t o host p l a n t e f f e c t s , f o r example, have been a s s o c i a t e d w i t h d i f f e r e n c e s i n s i z e and sex r a t i o o f p a r a s i t o i d s ( 1 5 , 1 2 ) , and d i f f e r e n c e s i n f u n c t i o n a l responses o f p a r a s i t o i d s and p r e d a t o r s (16 ). In a d d i t i o n t o p l a n t c h e m i s t r y , m o r p h o l o g i c a l f e a t u r e s o f the h o s t p l a n t have a l s o been shown t o a f f e c t p a r a s i t o i d s and p r e d a t o r s . However, w i t h the e x c e p t i o n o f t r i c h o m e s , these e f f e c t s have been s t u d i e d l e s s than c h e m i c a l e f f e c t s . Both g l a n d u l a r and n o n g l a n d u l a r t r i c h o m e s have been w i d e l y r e p o r t e d t o i n f l u e n c e the e f f e c t i v e n e s s o f n a t u r a l enemies ( 1 7 - 1 8 ) . Although n o n g l a n d u l a r trichomes have been shown, i n some c a s e s , t o impede s e a r c h i n g by some p a r a s i t o i d s (19-20) and predaceous h e m i p t e r a and c o l e o p t e r a ( 2 1 - 2 3 ) , the e f f e c t i s by no means u n i v e r s a l (24-25). G l a n d u l a r trichomes have a l s o been a s s o c i a t e d w i t h reduced n a t u r a l enemy e f f e c t i v e n e s s . They have been shown t o e n t r a p s e v e r a l s p e c i e s o f hymenopterous p a r a s i t o i d s (26-28) and t o reduce the mobil i t y o f some s p e c i e s o f c o c c i n e l l i d s and c h r y s o p i d s , but not o t h e r s (25, 29-31). In the use o f p l a n t r e s i s t a n c e f o r crop p r o t e c t i o n , i t i s import a n t t o r e c o g n i z e p o t e n t i a l i n c o m p a t i b i l i t i e s t h a t may e x i s t between p a r t i c u l a r r e s i s t a n c e mechanisms and the n a t u r a l enemies o f t a r g e t o r n o n t a r g e t pests o f r e s i s t a n t c r o p s . The i n t e g r a t i o n o f host p l a n t r e s i s t a n c e w i t h b i o l o g i c a l c o n t r o l , i d e a l l y , should combine the cumul a t i v e , d e n s i t y i n d e p e n d e n t , pest p o p u l a t i o n s u p p r e s s i v e f e a t u r e s o f the r e s i s t a n t c u l t i v a r w i t h the d e n s i t y dependent r e g u l a t i o n o f pest p o p u l a t i o n s by n a t u r a l enemies o f the c r o p p e s t s . A l t h o u g h , as d e s c r i b e d above, t h e r e a r e numerous documented cases o f adverse e f f e c t s o f p l a n t r e s i s t a n c e f a c t o r s on h e r b i v o r e n a t u r a l enemies, t h e r e a r e a l s o many examples d e m o n s t r a t i n g the s u c c e s s f u l i n t e g r a t i o n of p l a n t r e s i s t a n c e and b i o l o g i c a l c o n t r o l (24, 32-37, but see 3 8 ) . In g e n e r a l , where r e s i s t a n c e alone w i l l n o t p r o v i d e acceptable c o n t r o l o f the t a r g e t pest s p e c i e s , i t i s i m p o r t a n t t o c o n s i d e r the n a t u r e o f the i n t e r a c t i o n between p l a n t r e s i s t a n c e and b i o l o g i c a l c o n t r o l i n developing s t r a t e g i e s f o r deploying r e s i s t a n c e t o achieve the d e s i r e d l e v e l o f pest c o n t r o l . I n some i n s t a n c e s , i n t e r m e d i a t e l e v e l s o f p l a n t r e s i s t a n c e may permit more e f f i c i e n t b i o l o g i c a l c o n t r o l w i t h the c o m b i n a t i o n r e s u l t i n g i n a h i g h e r l e v e l o f pest c o n t r o l than e i t h e r one a l o n e . A high l e v e l o f r e s i s t a n c e (or other p l a n t c h a r a c t e r s ) may r e s u l t i n a l o s s o r d i m i n u t i o n o f b i o l o g i c a l c o n t r o l w i t h a r e d u c t i o n i n the o v e r a l l l e v e l o f pest c o n t r o l ( 2 3 , 39). The s i t u a t i o n i s f u r t h e r confounded by the r e a l i t y t h a t most crops a r e a t t a c k e d by a complex o f a r t h r o p o d pest s p e c i e s . Plant

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


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NATURALLY OCCURRING PEST BIOREGULATORS

r e s i s t a n c e mechanisms t h a t p r o v i d e an a c c e p t a b l e l e v e l o f c o n t r o l of the r e s i s t e d pest s p e c i e s may a l s o i n t e r f e r e w i t h the e f f e c t i v e n e s s of n a t u r a l enemies a t t a c k i n g o t h e r pest s p e c i e s t h a t are o t h e r w i s e u n a f f e c t e d by the r e s i s t a n c e mechanisms. Knowledge of such r e l a t i o n s h i p s and t h e i r impact on the o v e r a l l l e v e l of pest c o n t r o l f o r the e n t i r e pest complex a t t a c k i n g the c r o p i s e s s e n t i a l f o r making i n t e l l i g e n t d e c i s i o n s r e g a r d i n g whether or n o t , and how b e s t , t o use a p a r t i c u l a r r e s i s t a n c e mechanism f o r pest management. Some of the complex e c o l o g i c a l i n t e r a c t i o n s mediated by p l a n t defenses are i l l u s t r a t e d by the r e s i s t a n c e of a w i l d tomato, L y c o p e r s i c o n h i r s u t u m f . g l a b r a t u m C. H. M u l l , a c c e s s i o n PI 134417, t o Manduca s e x t a ( L . ) , the tobacco hornworm, and i t s e f f e c t s on s e v e r a l p r e d a t o r s and p a r a s i t o i d s of H e l i o t h i s zea ( B o d d i e ) , the tomato f r u i t w o r m . R e s i s t a n c e i n L. h i r s u t u m f . glabratum A c c e s s i o n PI 134417 i s h i g h l y r e s i s t a n t t o ML_ s e x t a due to the acute t o x i c i t y of i t s f o l i a g e to young l a r v a e (40-41). T h i s r e s i s t a n c e i s c o n d i t i o n e d by the presence of the 13-carbon methyl k e t o n e , 2 - t r i d e c a n o n e , i n the t i p s of type VI (42) g l a n d u l a r t r i c h o mes ( 4 3 - 4 6 ) . 2-Tridecanone a l s o c o n d i t i o n s r e s i s t a n c e to the Colorado p o t a t o b e e t l e , L e p t i n o t a r s a d e c e m l i n e a t a ( S a y ) , c a u s i n g m o r t a l i t y of young l a r v a e which d i s r u p t the g l a n d u l a r trichomes (47-51 ). PI 134417 a l s o possesses f a c t o r s a s s o c i a t e d w i t h l e a f l a m e l l a e t h a t k i l l 1^ d e c e m l i n e a t a l a r v a e d u r i n g the l a t e i n s t a r s . These f a c t o r s are m e c h a n i s t i c a l l y d i s t i n c t from 2 - t r i d e c a n o n e - m e d i a t e d r e s i s t a n c e (51-52). U n l i k e 2 - t r i d e c a n o n e - m e d i a t e d r e s i s t a n c e , which i s i n h e r i t e d r e c e s s i v e l y (45) and k i l l s e a r l y i n s t a r l a r v a e , the l a m e l l a r - b a s e d r e s i s t a n c e i s a dominant or i n c o m p l e t e l y dominant c h a r a c t e r . I t s presence i s observed when l a r v a e are f e d PI 134417 f o l i a g e from which g l a n d u l a r trichomes have been removed, or ¥\ h y b r i d ( L . esculentum χ PI 134417) f o l i a g e , which does not possess 2 - t r i d e c a n o n e - m e d i a t e d resistance (52). PI 134417 i s a l s o h i g h l y r e s i s t a n t to z e a , but the major p o r t i o n of t h i s r e s i s t a n c e i s a s s o c i a t e d w i t h the l e a f l a m e l l a e , not the t r i c h o m e s (50, 5 3 ) . 2-Tridecanone a s s o c i a t e d w i t h PI 134417 occurs i n q u a n t i t i e s p o t e n t i a l l y l e t h a l t o H. z e a . However, few l a r v a e (13-20%) e x p e r i e n c e l e t h a l doses of 2 - t r i d e c a n o n e . Most r e c e i v e s u b l e t h a l exposures t h a t a p p a r e n t l y induce e l e v a t e d l e v e l s of d e t o x i f y i n g enzymes (cytochrome P-450 isozymes) and a l l o w them t o r e c o v e r w i t h i n a few h o u r s . Recovered l a r v a e show i n c r e a s e d t o l e r a n c e t o 2 - t r i d e c a n o n e i n subsequent exposures and are a b l e t o feed on the f o l i a g e f o r s e v e r a l days b e f o r e they succumb t o o t h e r r e s i s t a n c e f a c t o r s a s s o c i a t e d w i t h the f o l i a r l a m e l l a e . These f o l i a r f a c t o r s are independent of 2 - t r i d e c a n o n e (53-55). Because of the 2 - t r i d e c a n o n e - m e d i a t e d i n d u c t i o n of cytochrome P-450, the r e c o v e r e d l a r v a e are a l s o more t o l e r a n t t o some i n s e c t i c i d e s ( 5 5 - 5 8 ) . 2-Undecanone, the 11-carbon methyl k e t o n e , a l s o occurs i n the type VI t r i c h o m e s of PI 134417 and i s a c t i v e a g a i n s t H^_ zea and s e v e r a l o t h e r pest s p e c i e s (59-60). I t i s l e s s a c u t e l y t o x i c than 2 - t r i d e c a n o n e a g a i n s t neonate H. zea (59) and i s l e s s abundant (x = 1.1 ug v s . 6.2 ug/trichome t i p f o r 2 - t r i d e c a n o n e i n PI 134417). However, i n c o m b i n a t i o n , 2 - t r i d e c a n o n e and 2-undecanone are



11.

KENNEDY ET AL.

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153

s y n e r g i s t i c i n t h e i r t o x i c i t y t o s e v e r a l i n s e c t s p e c i e s , i n c l u d i n g H. zea (60-61). At l e v e l s f r e q u e n t l y found i n P I 134417, 2-undecanone a l s o causes e x t e n s i v e m o r t a l i t y o f H^_ zea pupae when i n g e s t e d by f i f t h i n s t a r l a r v a e (61-62). Because 2 - t r i d e c a n o n e - m e d i a t e d r e s i s t a n c e t o s e x t a and L. d e c e m l i n e a t a i s g e n e t i c a l l y d i s t i n c t from the l a m e l l a r - b a s e d resistance to z e a , i t would be p o s s i b l e t o develop tomato c u l t i vars r e s i s t a n t to s e x t a and d e c e m l i n e a t a but s u s c e p t i b l e t o H. z e a . On such c u l t i v a r s , the 2 - t r i d e c a n o n e - m e d i a t e d i n d u c t i o n o f e l e v a t e d t o l e r a n c e t o some i n s e c t i c i d e s might make c o n t r o l o f zea more d i f f i c u l t ( 5 5 , 5 8 ) . The s e v e r i t y o f H. zea as a pest problem on such c u l t i v a r s would be f u r t h e r e x a c e r b a t e d i f 2 - t r i d e c a n o n e a s s o c i a t e d w i t h the r e s i s t a n t f o l i a g e s e r i o u s l y i n t e r f e r e d w i t h i n s e c t p a r a s i t o i d s and p r e d a t o r s i m p o r t a n t i n s u p p r e s s i n g n a t u r a l p o p u l a t i o n s o f îî^ z e a . Because of i t s o c c u r r e n c e i n the f o l i a r g l a n d u l a r t r i c h o m e s , and because o f i t s broad spectrum t o x i c i t y t o i n s e c t s , we c o n s i d e r e d i t l i k e l y t h a t p a r a s i t o i d s and predaceous i n s e c t s s e a r c h i n g the r e s i s t a n t f o l i a g e f o r prey would be exposed t o potent i a l l y t o x i c l e v e l s of 2-tridecanone. E f f e c t s o f PI 134417 and 2-Tridecanone

on an Egg P a r a s i t o i d o f H. zea

P a r a s i t i s m o f eggs by Trichogramma spp. i s a major source o f m o r t a l i t y among zea p o p u l a t i o n s on tomato i n the C o a s t a l P l a i n o f N. C a r o l i n a . In f i e l d s t u d i e s i n v o l v i n g tomato l i n e s v a r y i n g i n the l e v e l of 2-tridecanone-mediated r e s i s t a n c e to sexta, parasitism of H. zea eggs by Trichogramma s p p . ( p r i m a r i l y T^ p r e t i o s u m R i l e y ) was g r e a t l y reduced on p l a n t s e x p r e s s i n g h i g h l e v e l s o f 2 - t r i d e c a n o n e and h i g h d e n s i t i e s o f g l a n d u l a r trichomes (Table I , 63). In t h i s s t u d y , t h e r e was a s i g n i f i c a n t n e g a t i v e r e l a t i o n s h i p between p e r c e n t p a r a s i t i s m by Trichogramma and g l a n d u l a r t r i c h o m e d e n s i t y (% p a r a s i t i s m = -2.6 ( t r i c h o m e d e n s i t y ) + 82.1, R = 0.64, Ρ < 0.0001), but not b e t ween percent p a r a s i t i s m and d e n s i t y o f host eggs ( R = 0.07, Ρ > 0.16). However, because 2 - t r i d e c a n o n e i s c o n t a i n e d w i t h i n the g l a n d u l a r trichome t i p s of t h e more r e s i s t a n t l i n e s , i t was not p o s s i b l e t o s e p a r a t e the e f f e c t s o f 2 - t r i d e c a n o n e from those o f the trichome d e n s i t y alone (63 ). High d e n s i t i e s o f f o l i a r trichomes have been shown t o a d v e r s e l y a f f e c t Trichogramma spp. i n o t h e r p l a n t s p e c i e s ( 2 8 ) , and i t i s c l e a r t h a t they have an e f f e c t i n t h i s system. This i s shown by the r e d u c t i o n o f p a r a s i t i z a t i o n on the F i l i n e , which has a much h i g h e r trichome d e n s i t y than L. esculentum, but no 2-tridecanone. In a s e r i e s o f s t u d i e s t o determine i f the methyl ketones 2 - t r i d e c a n o n e and 2-undecanone were c o n t r i b u t i n g t o the reduced p a r a s i t i z a t i o n by Trichogramma on r e s i s t a n t p l a n t l i n e s , we found t h a t a d u l t T^ p r e t i o s u m c o n t a c t i n g P I 134417 f o l i a g e or exposed t o f o l i a r v o l a t i l e s of P I 134417 ( r i c h i n 2 - t r i d e c a n o n e vapors (54) s u f f e r e d e l e v a t e d l e v e l s o f m o r t a l i t y . When f o l i a g e from which the g l a n d u l a r t r i c h o m e s had been removed was used, t h i s m o r t a l i t y was e l i m i n a t e d among i n s e c t s exposed t o f o l i a r v o l a t i l e s , and g r e a t l y reduced among i n s e c t s h e l d i n c o n t a c t w i t h f o l i a g e (Table I I ) . In a d d i t i o n , fewer p a r a s i t i z e d eggs i n c u b a t e d on PI 134417 f o l i a g e w i t h trichomes i n t a c t produced p a r a s i t o i d a d u l t s than was the case f o r p a r a s i t i z e d eggs i n c u b a t e d on P I 134417 from which the g l a n d u l a r trichomes were 2

2


154


removed o r on L. esculentum f o l i a g e (Table I I I ) . T h i s d i f f e r e n c e i s a p p a r e n t l y a t t r i b u t a b l e t o m o r t a l i t y o f immature p a r a s i t o i d s w i t h i n h o s t eggs.


Table I .

P a r a s i t i s m of zea eggs by Trichogramma spp. on tomato l i n e s selected f o r v a r y i n g l e v e l s of 2-tridecanone-mediated r e s i s t a n c e t o M^ s e x t a - C l i n t o n , NC - 19861/ Mean Trichome Density no. /mm 1.2 10.2 15.2 23.3 2

Plant l i n e L. esculentum Fl BC2 PI 134417 2/

P e r c e n t m o r t a l i t y o f T\_ p r e t i o s u m a d u l t s f o l l o w i n g con finement on PI 134417 o r esculentum f o l i a g e o r exposure to f o l i a r v o l a t i l e s f o r 4 hours

Treatment C o n f i n e d on f o l i a g e Exposed t o f o l i a r volatiles

Foliage

Emergence o f T^ p r e t i o s u m a d u l t s from p a r a s i t i z e d zea eggs i n c u b a t e d on P I 134417 o r L. esculentum f o l i a g e ! ?

Type

PI 134417 trichomes present trichomes removed L. esculentum

ί'

Type of F o l i a g e PI 134417 Trichomes Trichomes AbsentiZ L. esculentum Present*/ 5.1 c 10 b 35 a 5 b 6 16 a

Mean s e p a r a t i o n h o r i z o n t a l by LSD a t Ρ < 0.05; v a l u e s a r e means f o r 10 r e p l i c a t e s w i t h 25 T. p r e t i o s u m a d u l t s per r e p l i c a t e .

Table I I I .

i/

2

Mean Percent P a r a s i t i s m Aug 8 Aug 13 J u l y 29 96 83 82 78 82 42 70 51 0 8 55 19

Data from Kauffman and Kennedy (63)

Table I I .

\J

Mean 2-tridecanone ng/mm 0 0 80.2 352.8

P e r c e n t p a r a s i t i z e d eggs yielding adults / 2

56 a 84 b 86 b

Eggs exposed, on a n e u t r a l s u b s t r a t e , t o p a r s i t i z a t i o n by T. p r e t i o s u m over a 24 h p e r i o d p r i o r t o t r a n s f e r t o the f o l i a g e treatments f o r i n c u b a t i o n . V a l u e s a r e means o f 10 r e p l i c a t e s w i t h 25 p a r a s i t i z e d eggs per t r e a t m e n t . Mean s e p a r a t i o n by LSD a t Ρ < 0.05.


11.

KENNEDY ET AL.

155



S i m i l a r but more d r a m a t i c e f f e c t s were observed when T^_ p r e t i o s u m a d u l t s were c o n f i n e d on f i l t e r paper d i s k s t r e a t e d w i t h 2 - t r i d e c a n o n e a t c o n c e n t r a t i o n s comparable t o those found i n P I 134417 f o l i a g e and when p a r a s i t i z e d H. zea eggs were i n c u b a t e d on 2 - t r i d e c a n o n e t r e a t e d f i l t e r paper d i s k s (Table I V ) . In s i m i l a r t e s t s , 2-undecanone, a t r a t e s comparable t o those a s s o c i a t e d w i t h PI 134417 f o l i a g e , had no e f f e c t on m o r t a l i t y o f a d u l t T. p r e t i o s u m but caused a s i g n i f i c a n t r e d u c t i o n i n the percentage o f p a r a s i t i z e d eggs y i e l d i n g a d u l t p a r a s i t o i d s (Table V ) .

T a b l e IV. M o r t a l i t y o f T^ p r e t i o s u m a d u l t s on, and emergence o f T. p r e t i o s u m from, p a r a s i t i z e d zea eggs i n c u b a t e d on f i l t e r paper t r e a t e d w i t h 2 - t r i d e c a n o n e , 2-Tridecanonei/ (ug/cm!) 0 45 90

% Mortality of T. p r e t i o s i u m a d u l t s / 26 a 85 b 96 b 2

% P a r a s i t i z e d eggs y i e l d i n g adult parasitoid^./ 93 a 10 b 0 b

1/

2

PI 134417 f o l i a g e c o n t a i n s a mean o f 44.6 ug 2 - t r i d e c a n o n e / c m o f foliage (50). % ! M o r t a l i t y a f t e r 4 hours o f confinement i n 5.5 cm P e t r i d i s h con t a i n i n g 5 cm f i l t e r paper d i s k t r e a t e d w i t h 2 - t r i d e c a n o n e a t the i n d i c a t e d c o n c e n t r a t i o n . Values a r e means o f 10 r e p l i c a t e s w i t h 50 a d u l t s / r e p l i c a t e . Mean s e p a r a t i o n v e r t i c a l by LSD a t Ρ < 0.05. 1! Values a r e p e r c e n t p a r a s i t i z e d zea eggs p r o d u c i n g one or more a d u l t T^ p r e t i o s u m when i n c u b a t e d on 2 - t r i d e c a n o n e t r e a t e d f i l t e r paper. Values a r e means o f 10 r e p l i c a t e s w i t h 25 p a r a s i t i z e d eggs per r e p l i c a t e . Mean s e p a r a t i o n v e r t i c a l by LSD a t Ρ < 0.05.

Table V.

E f f e c t o f 2-undecanone on emergence o f T^_ p r e t i o s u m a d u l t s from p a r a s i t i z e d H. zea eggs i n c u b a t e d on 2-undecanone t r e a t e d f i l t e r paper

2-undecanone (ug/cm )i/ 2

Percent p a r a s i t i z e d eggs y i e l d i n g wasps ./ 2

0 4.47 8.942/ 17.88 !/

P e r c e n t eggs c o n t a i n i n g dead p a r a s i t o i d pupae ./ 2

1 a 82 b 53 b 80 b

81 a 7 b 38 b 11 b

Mean c o n c e n t r a t i o n s a s s o c i a t e d w i t h P I 134417 f o l i a g e range from 1.9 t o 9.6 ug/cm l e a f l e t s u r f a c e ( 6 3 ) . Values a r e means o f 5 r e p l i c a t e s w i t h 25 p a r a s i t i z e d eggs per r e p l i c a t e . Mean s e p a r a t i o n v e r t i c a l by LSD, Ρ < 0.05. Approximate c o n c e n t r a t i o n found i n P I 134417 f o l i a g e . 2

2/ If

A l t h o u g h the l e v e l o f exposure t o the methyl ketones e x p e r i e n c e d by T^_ p r e t i o s u m i n these " t r e a t e d f i l t e r paper t e s t s ' i s l i k e l y t o be h i g h e r than those e x p e r i e n c e d by p a r a s i t o i d s on PI 134417 f o l i a g e , 1


156


the types of e f f e c t s caused by 2 - t r i d e c a n o n e and 2-undecanone are the same as those caused by normal PI 134417 f o l i a g e but not by f o l i a g e from which the g l a n d u l a r t r i c h o m e s have been removed. T h e r e f o r e , i t i s l i k e l y t h a t 2 - t r i d e c a n o n e and t o a l e s s e r e x t e n t 2-undecanone c o n t r i b u t e t o the adverse e f f e c t s of PI 134417 on Trichogramma.


E f f e c t s o f PI 134417 and 2-Tridecanone zea

on L a r v a l P a r a s i t o i d s of H.

A l t h o u g h p a r a s i t i s m of H. zea l a r v a e on tomato i s v a r i a b l e and o f t e n low i n N o r t h C a r o l i n a , we have c o n s i s t e n t l y observed lower l e v e l s o f l a r v a l p a r a s i t i s m by an a r r a y o f p a r a s i t o i d s on p l a n t l i n e s s e l e c t e d f o r e l e v a t e d l e v e l s of 2 - t r i d e c a n o n e - m e d i a t e d r e s i s t a n c e t o M. s e x t a ( T a b l e V I ) ( 6 4 ) . To i n v e s t i g a t e the causes of reduced p a r a s i t i s m , we focused on two s p e c i e s of l a r v a l p a r a s i t o i d s : Campoletis s o n o r e n s i s (Cameron), an ichneumonid, and A r c h y t a s marmoratus (Townsend), a t a c h i n i d .

Table V I .

Percent p a r a s i t i s m of zea l a r v a e c o l l e c t e d from PI 134417, L. esculentum or F i p l a n t s , C l i n t o n , NC, 1987

Plant Line L. esculentum Fi PI 134417 }J

Mean P e r c e n t P a r a s i t i s m j / 15.5 a 12.6 a 3.4 b

Values are means o f 6 r e p l i c a t e s ; mean s e p a r a t i o n by LSD at Ρ < 0.05. They r e f l e c t t o t a l p a r a s i t i s m by a complex o f l a r v a l p a r a s i t o i d s c o n s i s t i n g of C o t e s i a m a r g i n i v e n t r i s , C a m p o l e t i s sonoren s i s , M i c r o p l i t i s c r o c e i p e s and Meteorus autographae.

In f i e l d cage s t u d i e s i n which zea l a r v a e on s e v e r a l p l a n t l i n e s were exposed t o a d u l t p a r a s i t o i d s (one p l a n t l i n e per c a g e ) , p e r c e n t p a r a s i t i z a t i o n by both s p e c i e s was s i g n i f i c a n t l y lower on BC2, (a b a c k c r o s s ( ( L . esculentum χ PI 134417) χ PI 134417) l i n e w i t h i n t e r m e d i a t e l e v e l s of 2 - t r i d e c a n o n e and g l a n d u l a r trichome d e n s i t y ) , and PI 134417 than on L. esculentum and the F i h y b r i d ( L . esculentum χ PI 134417) ( T a b l e V l t l . T h i s p a t t e r n r e f l e c t s l e v e l s of 2 - t r i d e c a n o n e - m e d i a t e d r e s i s t a n c e t o M^ s e x t a . These d a t a i n d i c a t e t h a t fewer 11^ zea l a r v a e are p a r a s i t i z e d on the more r e s i s t a n t p l a n t l i n e s but do not i n d i c a t e whether t h i s i s due to e l e v a t e d d e n s i t i e s of g l a n d u l a r t r i c h o m e s or methyl k e t o n e s , or b o t h . Because of t h e i r l i f e h i s t o r i e s , l a r v a e of both p a r a s i t o i d s d i r e c t l y c o n t a c t the f o l i a g e of the food p l a n t s of t h e i r host l a r v a e . Thus, p o t e n t i a l e x i s t s f o r both t o be a f f e c t e d d i r e c t l y by the methyl ketones p r e s e n t i n the g l a n d u l a r t r i c h o m e s of the r e s i s t a n t p l a n t s . C. s o n o r e n s i s o v i p o s i t s i n second and e a r l y t h i r d i n s t a r zea l a r v a e . The p a r a s i t o i d l a r v a e k i l l and emerge from l a t e t h i r d and e a r l y f o u r t h i n s t a r host l a r v a e , c r a w l onto the f o l i a g e , and s p i n a cocoon i n which p u p a t i o n o c c u r s . C l o s e o b s e r v a t i o n of s o n o r e n s i s l a r v a e emerging from t h e i r h o s t s on PI 134417 f o l i a g e i n d i c a t e d t h a t they d i s r u p t a l a r g e number of g l a n d u l a r trichomes d u r i n g the cocoon s p i n n i n g process and c o n t a c t



11.

KENNEDY ET AL.

157


the methyl ketones c o n t a i n e d t h e r e i n . In s t u d i e s i n which p a r a s i tized zea l a r v a e were r e a r e d on a r t i f i c i a l d i e t and t r a n s f e r r e d t o f o l i a g e of L. esculentum, BC2 o r P I 134417, s i g n i f i c a n t l y h i g h e r l e v e l s o f p a r a s i t o i d m o r t a l i t y were observed on f o l i a g e from p l a n t l i n e s possessing elevated l e v e l s of 2-tridecanone-mediated r e s i s t a n c e (Table V I I I ) . I t i s noteworthy t h a t on P I 134417 f o l i a g e , which con t a i n e d the h i g h e s t l e v e l s o f methyl ketones (Table I ) , v i r t u a l l y a l l p a r a s i t o i d m o r t a l i t y o c c u r r e d among l a r v a e d u r i n g the cocoon s p i n n i n g process. I n c o n t r a s t , on BC2 f o l i a g e , which has lower l e v e l s o f m e t h y l ketones (Table I ) , a s i g n i f i c a n t p o r t i o n o f t o t a l p a r a s i t o i d m o r t a l i t y o c c u r r e d among pupae and a d u l t s w i t h i n the cocoon. This d i f f e r e n c e may be a t t r i b u t a b l e t o reduced dosages o f methyl ketones e x p e r i e n c e d on BC2 ( 6 4 ) .

Table V I I .

Percent p a r a s i t i z a t i o n of zea l a r v a e by sonorensis and marmoratus i n n o n c h o i c e f i e l d cage s t u d i e s Percent P a r a s i t i z a t i o n Π. s o n o r e n s i s - ^ A. m a r m o r a t u s i ^ 66.6 a 76 a 66.2 a 73 a 47.5 b 54 b 38.9 c 57 b

Plant Line L. esculentum Fi BC2

PI 134417 }J

Mean s e p a r a t i o n v e r t i c a l by LSD a t Ρ < 0.05. See Table 1 f o r trichome d e n s i t i e s and methyl ketone l e v e l s a s s o c i a t e d w i t h each plant l i n e .

Table V I I I .

M o r t a l i t y of s o n o r e n s i s on f o l i a g e f o r cocoon s p i n n i n g f o l l o w i n g development o f p a r a s i t o i d s i n l a r v a e r e a r e d on a r t i f i c i a l d i e t A/

Plant Line L. esculentum BC2

PI 134417 y y y y

larvae^/. 0.7 a 43.6 b 98 c

Percent Mortality.^/ i n cocoon^/ 9.5 a 16.3 b 0.7 c

zea

Total 10.2 a 59.9 b 98.7 c

Data from Kauffman and Kennedy ( 6 3 ) . Mean s e p a r a t i o n v e r t i c a l Ρ £ 0.05 by Duncan's m u l t i p l e range test. Data i n c l u d e a l l p a r a s i t o i d l a r v a e t h a t d i e d p r i o r t o cocoon construction. Data i n c l u d e m o r t a l i t y o f l a r v a e , pupae and a d u l t s w i t h i n the cocoon.

In a r e l a t e d s t u d y , Kauffman and Kennedy (65) demonstrated t h a t the t o x i c i t y o f PI 134417 and BC2 f o l i a g e t o sonorensis larvae d u r i n g cocoon s p i n n i n g was e l i m i n a t e d when the g l a n d u l a r t r i c h o m e s were removed. They f u r t h e r demonstrated the acute t o x i c i t y o f 2 - t r i d e c a n o n e and 2-undecanone t o C. s o n o r e n s i s l a r v a e on t r e a t e d f i l t e r paper d i s k s ( 2 - t r i d e c a n o n e LC50 = 13.0, 95% f i d u c i a l l i m i t s =


158

NATURALLY OCCURRING PEST BIOREGULATORS 2

10.88, 17.95); 2-undecanone LC50 « 38.9 (32.34, 47.79 ug/cm ) and showed l e v e l s o f p a r a s i t o i d m o r t a l i t y on methyl ketone t r e a t e d f i l t e r paper d i s k s t h a t were q u a n t i t a t i v e l y s i m i l a r t o those observed on r e s i s t a n t foliage (65). A l t h o u g h the t o x i c i t y o f 2 - t r i d e c a n o n e t o s o n o r e n s i s and H. zea i s s i m i l a r (LC50 13.9 and 17.1 ug/cm , t r e a t e d s u r f a c e , r e s p e c t i v e l y (59, 65) i n t r e a t e d f i l t e r paper b i o a s s a y s , C. s o n o r e n s i s i s a f f e c t e d t o a much g r e a t e r degree than i t s h o s t . U n l i k e f i f t h i n s t a r C. s o n o r e n s i s l a r v a e , which d i s c h a r g e numerous g l a n d u l a r trichomes and d i r e c t l y c o n t a c t s u b s t a n t i a l q u a n t i t i e s of 2 - t r i d e c a n o n e , neonate H. zea are v e r y s m a l l and r a r e l y d i s c h a r g e trichome t i p s b e f o r e 2 - t r i d e c a n o n e vapors s u r r o u n d i n g the f o l i a g e induce e l e v a t e d l e v e l s of cytochrome P-450 which a l l o w s the l a r v a e t o t o l e r a t e subsequent exposures to 2 - t r i d e c a n o n e ( 5 8 ) . A r c h y t a s marmoratus l a r v i p o s i t s f i r s t i n s t a r maggots ( p l a n i d i a ) on the h o s t ' s food p l a n t . P l a n i d i a remain on the f o l i a g e u n t i l they c o n t a c t and a t t a c h themselves t o second or subsequent i n s t a r s of t h e i r h o s t . L a r v a l development takes p l a c e w i t h i n host pupae ( 6 6 ) . Since zea pupate i n the s o i l , the o n l y immature stage of A^_ marmoratus t o c o n t a c t p l a n t f o l i a g e i s the p l a n i d i u m . On F i and PI 134417 f o l i a g e , A. marmoratus p l a n i d i a s u f f e r e x t e n s i v e m o r t a l i t y as compared t o t h a t observed on 1^ esculentum f o l i a g e . S i n c e e l e v a t e d m o r t a l i t y i s not observed among p l a n i d i a on F i and PI 134417 f o l i a g e from which the g l a n d u l a r trichomes have been removed (Table I X ) , the trichomes are an i m p o r t a n t cause of the mortality. Trichome f a c t o r s o t h e r than the methyl ketones must be l a r g e l y r e s p o n s i b l e , however, because e x t e n s i v e m o r t a l i t y o c c u r r e d on F i h y b r i d f o l i a g e , which c o n t a i n s n e i t h e r 2 - t r i d e c a n o n e nor 2-undecanone (Table I ) .


s

Table IX.

2

M o r t a l i t y of A^ marmoratus p l a n i d i a on f o l i a g e of t h r e e tomato l i n e s w i t h and w i t h o u t trichomes % Mortality!/

Plant Line B e t t e r Boy Fl PI 134417 A' **

With Trichomes 48.9 a 83.0 b 95.8 c

Without Trichomes 36.8 a 35.1 a** 36.8 a**

Means s e p a r a t i o n v e r t i c a l by LSD; means w i t h the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (P>0.05). Means f o r f o l i a g e w i t h and w i t h o u t trichomes are s i g n i f i c a n t l y d i f f e r e n t by F - t e s t (P

2-TridecanoneGlandular Trichome-Mediated Insect Resistance in

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