6 Development of Microencapsulated Pheromone Formulations D . R. HALL and B. F . NESBITT—Overseas Development Administration, Tropical Products Institute, London W C 1 X 8 L U , England G . J . M A R R S and A . St. J. G R E E N — I C I Ltd., Plant Protection Division, Bracknell, Berkshire R G 1 2 6 E Y , England
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D. G . C A M P I O N and B. R. C R I T C H L E Y — O v e r s e a s Development Administration, Centre for Overseas Pest Research, London W8 5SJ, England
Microencapsulation provides a means of formulating s y n t h e t i c pheromones f o r a p p l i c a t i o n to l a r g e areas in the c o n t r o l of i n s e c t p o p u l a t i o n s by d i s r u p t i o n of pheromone-mediated communication. Microencapsulated formulations are easily manufactured by known methods of interfacial p o l y m e r i s a t i o n , they can be a p p l i e d to l a r g e areas w i t h c o n v e n t i o n a l spray equipment and they possess numerous v a r i a b l e s that can be used to c o n t r o l the r e l e a s e characteristics. The p h y s i c o chemical p r o p e r t i e s of these formulations have been s t u d i e d by determination of the r e s i d u a l amount of pheromone remaining a f t e r v a r y i n g lengths of exposure: i n c o r p o r a t i o n of light-stable analogues i n t o the formulations and comparison of the r e s u l t s from samples exposed to and s h i e l d e d from d i r e c t s u n l i g h t showed that both pheromone and f o r m u l a t i o n suffered from degradation in s u n l i g h t . Various types of a n t i o x i d a n t were t e s t e d , but only phenylene diamines were e f f e c t i v e in reducing the degradation. Ν , Ν ' - D i s e c o n d a r y phenylene diamines could not be encapsulated, but the corresponding N,N'-ditertiary d e r i v a t i v e s in combination w i t h a dye + carbon b l a c k UV screener gave formulations w i t h g r e a t l y improved stability in s u n l i g h t . Such formulations of the pheromones of Pectinophora gossypiella and Spodoptera littoralis caused h i g h l e v e l s of communication d i s r u p t i o n of these species in the field. A l t h o u g h pheromone t r a p s a r e now w i d e l y u s e d f o r m o n i t o r i n g i n s e c t p o p u l a t i o n s , t h e u s e o f s y n t h e t i c pheromones i n c o n t r o l of i n s e c t p e s t s by d i s r u p t i o n o f pheromone-mediated communication h a s b e e n much s l o w e r t o d e v e l o p , a t l e a s t i n p a r t b e c a u s e o f t h e d i f f i c u l t i e s o f f o r m u l a t i o n . There a r e t h r e e main types o f formulation currently available - hollow f i b r e s , p l a s t i c l a m i n a t e s and m i c r o c a p s u l e s . F o r s e v e r a l y e a r s , t h e UK O v e r s e a s 0097-6156/82/0190-0131$06.00/0 © 1982 American Chemical Society
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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D e v e l o p m e n t A d m i n i s t r a t i o n and I C I L t d . h a v e b e e n i n v o l v e d i n a c o l l a b o r a t i v e p r o j e c t t o develop microencapsulated f o r m u l a t i o n s of l e p i d o p t e r o u s s e x pheromones f o r c o n t r o l o f i n s e c t p e s t s by mating d i s r u p t i o n . M i c r o e n c a p s u l a t e d f o r m u l a t i o n s p r e p a r e d by i n t e r f a c i a l p o l y m e r i s a t i o n were f a v o u r e d f o r t h r e e main reasons : i ) t h e y a r e e a s i l y m a n u f a c t u r e d on a l a r g e s c a l e u s i n g known t e c h n o l o g y ( 1 ) ; i i ) they a r e e a s i l y a p p l i e d over l a r g e areas w i t h c o n v e n t i o n a l spray equipment; i i i ) t h e y p o s s e s s numerous v a r i a b l e s t h a t c a n be manipulated to c o n t r o l the release c h a r a c t e r i s t i c s ( 2 ) , e.g. c a p s u l e w a l l t h i c k n e s s , c a p s u l e w a l l c o m p o s i t i o n , c a p s u l e s i z e and i n t e r n a l c o m p o s i t i o n . Persistence Studies I n most o f t h e w o r k , t h e p h y s i c o c h e m i c a l b e h a v i o u r o f t h e f o r m u l a t i o n s was s t u d i e d by gas c h r o m a t o g r a p h i c e s t i m a t i o n a t i n t e r v a l s o f t h e r e s i d u a l pheromone r e m a i n i n g i n f o r m u l a t i o n s sprayed onto f i l t e r papers. The l a t t e r w e r e o f t h e s i l i c o n e t r e a t e d " p h a s e - s e p a r a t i n g " type as these best s i m u l a t e d a l e a f s u r f a c e . When t h e f o r m u l a t i o n s w e r e e x p o s e d i n a l a b o r a t o r y w i n d - t u n n e l t h e r e was l i t t l e pheromone l o s s o t h e r t h a n by r e l e a s e , a t l e a s t f o r t h e m o n o u n s a t u r a t e d a c e t a t e s u s e d i n most of t h e p r e l i m i n a r y w o r k , and s u c h a n a l y s e s p r o v i d e d a c c u r a t e i n f o r m a t i o n on r e l e a s e r a t e s u n d e r t h e s e c o n d i t i o n s . However, u s e o f t h i s t e c h n i q u e i n t h e f i e l d showed t h a t l o s s o f pheromone was v e r y much more r a p i d t h a n u n d e r c o m p a r a b l e c o n d i t i o n s o f t e m p e r a t u r e and w i n d s p e e d i n t h e w i n d - t u n n e l ( 2 ) . T h e s e r e s u l t s w e r e t a k e n t o i n d i c a t e t h a t t h e r e was s i g n i f i c a n t l o s s o f pheromone by d e g r a d a t i o n u n d e r f i e l d c o n d i t i o n s . The e x t e n t o f pheromone d e g r a d a t i o n u n d e r f i e l d c o n d i t i o n s was i n v e s t i g a t e d w i t h a m i c r o e n c a p s u l a t e d f o r m u l a t i o n c o n t a i n i n g a s a t u r a t e d h y d r o c a r b o n and a c e t a t e ( o c t a d e c a n e and t e t r a d e c y l a c e t a t e (14:Ac)), the corresponding monounsaturated hydrocarbon and a c e t a t e ( ( Z ) - 4 - o c t a d e c e n e a n d ( Z ) - 9 - t e t r a d e c e n y l a c e t a t e ( Z 9 - 1 4 : A c ) ) and a d i u n s a t u r a t e d a c e t a t e ((Z,E)-9,11-tetradecad i e n y l a c e t a t e ( Z E 9 , 1 1 - 1 4 : A c ) ) , c h o s e n so t h a t a l l t h e components had s i m i l a r v o l a t i l i t i e s . On e x p o s u r e t o s u n l i g h t , l o s s o f t h e d i e n e was more r a p i d t h a n l o s s o f t h e m o n o u n s a t u r a t e d components w h i c h i n t u r n d i s a p p e a r e d f a s t e r t h a n t h e s a t u r a t e d components ( F i g . 1 ) . A l l components d i s a p p e a r e d a t a s i m i l a r , s l o w e r r a t e when s h i e l d e d f r o m d i r e c t s u n l i g h t . Thus s u b s e q u e n t e x p e r i m e n t s w e r e c a r r i e d o u t w i t h two important m o d i f i c a t i o n s . i ) F o r m u l a t i o n s were sprayed onto f i l t e r p a p e r s , h a l f of w h i c h were exposed t o d i r e c t s u n l i g h t w h i l e t h e o t h e r h a l f w e r e e x p o s e d t o t h e same c o n d i t i o n s o f t e m p e r a t u r e , w i n d s p e e d and h u m i d i t y , b u t s h i e l d e d
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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from d i r e c t s u n l i g h t ; r a t e s of disappearance o f e n c a p s u l a t e d components i n e x p o s e d and s h i e l d e d samples were then compared, L i g h t - s t a b l e analogues were i n c o r p o r a t e d i n t o t h e f o r m u l a t i o n s , e.g. t h e c o r r e s p o n d i n g s a t u r a t e d acetates i n formulations of unsaturated acetates.
F i g u r e 2 shows t h e f o u r c u r v e s o b t a i n e d f r o m s u c h an experiment c a r r i e d out i n Egypt w i t h a p o l y u r e a m i c r o e n c a p s u l a t e d f o r m u l a t i o n o f Z9-14:Ac and 14:Ac. The e x t e n t o f d e g r a d a t i o n o f t h e u n s a t u r a t e d Z9-14:Ac i s i n d i c a t e d by t h e d i f f e r e n c e b e t w e e n t h e c u r v e f o r t h i s component and t h e c o r r e s p o n d i n g c u r v e f o r t h e l i g h t - s t a b l e 14:Ac. I n t h i s e x p e r i m e n t - c f . F i g . 1 f r o m an e x p e r i m e n t c a r r i e d o u t i n London d u r i n g w i n t e r - t h e r e i s e v e n s i g n i f i c a n t d e g r a d a t i o n o f t h e u n s a t u r a t e d component i n t h e f o r m u l a t i o n s h i e l d e d from d i r e c t s u n l i g h t a l t h o u g h s t i l l exposed to r e f l e c t e d l i g h t . The d i f f e r e n c e b e t w e e n t h e c u r v e f o r t h e d i s a p p e a r a n c e o f t h e 14:Ac i n t h e e x p o s e d s a m p l e s and t h a t f o r t h e s h i e l d e d s a m p l e s i s a measure o f t h e d e g r a d a t i o n o f t h e microcapsules themselves i n d i r e c t s u n l i g h t . Stabiliser
Studies
R a p i d d e g r a d a t i o n o f s i m p l e m o n o - o l e f i n s i n s u n l i g h t was u n e x p e c t e d a s t h e y show a b s o r b a n c e maxima w e l l b e l o w t h e 300 nm c u t - o f f o b s e r v e d f o r n a t u r a l s u n l i g h t . However, t h e e f f e c t was e a s i l y d e m o n s t r a t e d by e x p o s i n g m i x t u r e s o f u n s a t u r a t e d compounds and l i g h t - s t a b l e a n a l o g u e s a s t h i n f i l m s i n open p e t r i d i s h e s and a n a l y s i n g t h e r e l a t i v e amounts o f t h e two components r e m a i n i n g . V a r i o u s a n t i o x i d a n t s were t e s t e d i n t h i s s y s t e m , i n c l u d i n g h i n d e r e d p h e n o l s , g a l l a t e e s t e r s and p h e n y l e n e d i a m i n e s . Only t h e l a t t e r h a d any s i g n i f i c a n t e f f e c t i n r e d u c i n g d e g r a d a t i o n , and t h e b e s t w e r e t h o s e w i t h a d d i t i o n a l a r o m a t i c s u b s t i t u e n t s on nitrogen. T a b l e I shows t h e r e s u l t s o f a n e x p e r i m e n t i n w h i c h m i x t u r e s o f 1 mg e a c h o f Z9-14:Ac and 14:Ac w i t h 0.2 mg o f t h e a n t i o x i d a n t w e r e e x p o s e d a s t h i n f i l m s i n open 4 c m - d i a m e t e r p e t r i d i s h e s on t h e l a b o r a t o r y r o o f i n L o n d o n . A f t e r e x p o s u r e f o r 10 d a y l i g h t h o u r s t h e amounts o f Z9-14:Ac and 14:Ac r e m a i n i n g w e r e d e t e r m i n e d b y g a s c h r o m a t o g r a p h y . The r a t i o b e t w e e n t h e amount o f t h e u n s a t u r a t e d component and t h a t o f t h e s a t u r a t e d component r e m a i n i n g p r o v i d e s a measure o f t h e e x t e n t o f t h e d e g r a d a t i o n of the former s i n c e t h e r a t e s of e v a p o r a t i o n o f the two components w i l l be s i m i l a r . A f i n a l r a t i o o f 1.0 ( t h e s t a r t i n g r a t i o ) i n d i c a t e s no d e g r a d a t i o n , and a r a t i o o f 0.0 i n d i c a t e s c o m p l e t e d e g r a d a t i o n o f t h e u n s a t u r a t e d component d u r i n g the experiment. Of t h e c o m m e r c i a l l y - a v a i l a b l e p h e n y l e n e d i a m i n e s t e s t e d , t h e N , N - d i p h e n y l compound i s a n i n s o l u b l e , h i g h m e l t i n g - p o i n t , c r y s t a l l i n e s o l i d , whereas t h e u n s y m m e t r i c a l l y s u b s t i t u t e d N-phenyl-N -(2-octyl) derivative i s a l i q u i d , r e a d i l y m i s c i b l e f
f
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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time (days) Figure 1. Exposure of unstabilized microcapsule formulation on TPI roof in London. Key: octadecane, 14:Ac, (O); (L)-4-octadecene, Z9-14:Ac, (/\); ZE9,11-14:Ac, (Πλ' and all components shielded, (%).
5
10
15
20
time (days) Figure 2. Z9-14:Ac,
Exposure of unstabilized microcapsule formulation in Egypt. Key: exposed (À) and shielded (A); and 14:Ac, exposed (O) and shielded
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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TABLE I STABILISATION OF
Z9-14:Ac BY VARIOUS PHENYLENE DIAMINE
e1 ANTIOXIDANTS 2
M _X »
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Η
Η
antioxidant ,1 .2 R R
C
H
" 8 17
-Ph
" 8 17
- 8 17
-Ph
Z9-14:Ac 14:Ac
C
H
°-
6 2
C
H
°'
9 0
-Ph
no a n t i o x i d a n t
0.92 0.47
1 mg Z9-14:Ac + 1 mg 14:Ac + 0.2 mg a n t i o x i d a n t e x p o s e d i n open p e t r i d i s h e s on TPI r o o f f o r 10 d a y l i g h t h o u r s
w i t h t y p i c a l n o n - p o l a r pheromones. T h i s compound i s c o m m e r c i a l l y a v a i l a b l e as t h e a n t i o z o n a n t UOP 688, b u t , as a s e c o n d a r y a m i n e , i t c a n n o t be e n c a p s u l a t e d u s i n g i n t e r f a c i a l p o l y m e r i s a t i o n s i n c e i t r e a c t s w i t h one o f t h e monomers. F u l l y s u b s t i t u t i n g t h e n i t r o g e n s i n t h e UOP 688 c a u s e d some r e d u c t i o n i n t h e s t a b i l i s i n g e f f e c t on pheromone d e g r a d a t i o n ( T a b l e I I ) , b u t t h e r e s u l t i n g t e r t i a r y a m i n e s c o u l d be e n c a p s u l a t e d and s t i l l r e t a i n e d u s e f u l s t a b i l i s i n g a c t i v i t y (Table I I I ) . A r a n g e o f s u b s t i t u e n t s on n i t r o g e n was t e s t e d ( T a b l e I V ) and a l l the d e r i v a t i v e s possessed s t a b i l i s i n g a c t i v i t y . F u r t h e r work was c a r r i e d o u t w i t h t h e Ν,Ν'-dimethyl compound as t h i s was most c o n v e n i e n t l y p r e p a r e d (I) . V a r i o u s UV s c r e e n e r s w e r e a l s o t e s t e d f o r t h e i r s t a b i l i s i n g a c t i v i t y , i n c l u d i n g hydroxybenzophenones, aminobenzoates, dyes and c a r b o n b l a c k . O n l y c o m b i n a t i o n s o f d y e s and c a r b o n b l a c k showed any e f f e c t , t h e b e s t b e i n g t h e c o m m e r c i a l l y - a v a i l a b l e Waxoline Black (Table V).
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
INSECT P H E R O M O N E T E C H N O L O G Y
TABLE I I STABILISATION OF Z9-14:Ac BY VARIOUS PHENYLENE DIAMINE ANTIOXIDANTS 2 R Z
Ph ,
)
-
