Insecticides of Plant Origin - American Chemical Society

Chapter 6

Recent Advances in Research on Botanical Insecticides in China

Downloaded by MONASH UNIV on June 6, 2013 | http://pubs.acs.org Publication Date: February 23, 1989 | doi: 10.1021/bk-1989-0387.ch006

Shin-Foon Chiu Laboratory of Insect Toxicology, South China Agricultural University, Guangzhou, China

Research in China on botanical insecticides has concentrated on species i n c l u d i n g Azadirachta indica, Melia spp., Trypterygium spp. and Tephrosia vogelii possessing insect growth regulating properties. These are active against the Lychee stinkbug, Tessaratoma papilosa and cabbageworm, P i e r i s rapae. Tephrosia extracts were especially active and when applied to cabbageworm larvae caused pupal deformities. Substantial differences in the concentration of insecticidal principles was found in Chinese ecotypes of Melia spp.. New potent insecticidal phytochemicals containing an agarofuran nucleus have been identified from species of Celastraceae. The advantages of pest control systems using botanical pesticides is discussed with reference to the problem of resistance and non-target insects. During the l a s t two decades, problems of r a p i d l y increasing costs o f modern synthetic organic insecticides, pest r e s i s t a n c e t o i n s e c t i c i d e s , pest resurgence and d e t r i m e n t a l effects on non-target organisms and environmental q u a l i t y , a l l d i c t a t e the need f o r e f f e c t i v e , economical, and safe i n s e c t i c i d e s . The search f o r environmentally sound methods f o r c o n t r o l l i n g i n s e c t pests has been c a r r i e d out i n our l a b o r a t o r y f o r more than t e n years ( 1 , 2 ) . In t h i s paper some h i g h l i g h t s of recent i n v e s t i g a t i o n s i n China are presented, i n c l u d i n g experiments with p l a n t s possessing i n s e c t growth r e g u l a t i n g p r o p e r t i e s , s t u d i e s on ecotypes of the china-berry t r e e , M e l i a sp., s t u d i e s on the bioactive principles o f t h e C e l a s t r a c e a e , and experiments on the a p p l i c a t i o n o f b o t a n i c a l s as a new approach t o overcome i n s e c t i c i d e r e s i s t a n c e . 0097-6156/89/0387-0069$06.00/0 « 1989 American Chemical Society

In Insecticides of Plant Origin; Arnason, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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INSECTICIDES OF PLANT ORIGIN


Experiments with Plants Regulating (IGR) P r o p e r t i e s

Possessing

Insect

Growth

With t h e aim o f f i n d i n g botanical insecticides possessing IGR p r o p e r t i e s , laboratory and field experiments have been c a r r i e d out with three species of the Meliaceae: Azadirachta indica (neem), Melia toosendan, and M. azedarach, and s e v e r a l species from other f a m i l i e s i n c l u d i n g Trypterygium w i l l o r d i i , T. hypoglaucum, and Tephrosia v o g e l i i which were used against s e v e r a l a g r i c u l t u r a l i n s e c t pests. Topical application of neem seed o i l t o the prothorax of nymphs of the lychee s t i n k bug (Tessaratoma p a p u l o s a ) showed that the o i l i s a strong ecdysis and growth inhibitor (Table I). The t r e a t e d nymphs exhibited reduced growth and a darkened, wrinkled cuticle. Microscopic examination of the c u t i c l e showed t h a t the s t r u c t u r e was malformed. Death occurred i n succeeding i n s t a r s . Table I. The growth i n h i b i t i n g p r o p e r t i e s i n nymphs of lychee s t i n k bug * Treatment (ul/insect)

Instar Treated

0.005 control

2 2

0.25 control

3 3

0.5 control

4 4

No.of Dead Nymphs /instar 2nd 3rd 4th 5th 1 1

of neem o i l Mortality (%)

18 1

2 2

0 1

70.0 16.6

4 2

16 0

5 0

86.0 6.6

9 1

14 0

92.0 4.0

* A t o t a l of 30 nymphs was used i n each treatment. The neem o i l ( p u r i f i e d ) was k i n d l y s u p p l i e d by Dr. H. Rembold, Max-Planck I n s t i t u t e , FRG. I t s azadirachtin content was 400 ug/ml. Pure, 1 - cinnamoyl 3 feruloyl - 11hydroxymeliacarpin was i s o l a t e d from seed k e r n e l s of Melia azedarach (supplied by Dr. W. Kraus). Topical a p p l i c a t i o n (50 ug/ml i n acetone, 1 u l / i n s e c t ) t o t h i r d i n s t a r nymphs of the lychee s t i n k bug caused 23.3% of the nymphs t o become deformed, with an only p a r t i a l l y developed prothorax and abnormal antennae. The whole process of molting was a l s o i n h i b i t e d . Topical a p p l i c a t i o n of 20% (w/v) neem o i l (2 ul/larva) to fifth-instar larvae of the imported cabbageworm ( P i e r i s rapae) markedly i n h i b i t e d t h e i r growth and a l l died a f t e r pupation. Neem-seed kernel



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Botanical Insecticides in China

e x t r a c t (AZT-VR-K, s u p p l i e d by Dr. H. Schmutterer) was a l s o found t o be very b i o l o g i c a l l y a c t i v e . Spraying with a 0.3% (w/v) s o l u t i o n of the e x t r a c t proved t o be e f f e c t i v e f o r as long as 21 days under f i e l d c o n d i t i o n s . Laboratory bioassays showed t h a t an acetone e x t r a c t of the leaves of Tephrosia v o g e l i i was a very potent growth inhibitor of the imported cabbageworm. Topical a p p l i c a t i o n of a 0.5% (w/v) e x t r a c t (2 u l / l a r v a ) caused 89% of the l a r v a e t o f a i l t o pupate normally ( F i g u r e 1) and the t r e a t e d population g r a d u a l l y t o d i e out. In the P h i l i p p i n e s , i t was found t h a t the leaves of t h i s legume c o n t a i n 5% rotenone. With the diamondback moth, a 10% acetone e x t r a c t of the leaves of Tephrosia v o g e l i i showed a remarkable growth i n h i b i t i n g e f f e c t on f o u r t h i n s t a r l a r v a e - 86% of the l a r v a e were malformed and d i e d a f t e r f e e d i n g on the t r e a t e d leaves f o r 48 hours. P l a n t s o f f e r a l a r g e number of novel chemical compounds with b i o l o g i c a l a c t i v i t y and China i s a very rich source of plant materials possessing IGR p r o p e r t i e s . In crop p r o t e c t i o n , the p o t e n t i a l f o r the utilization of p l a n t s as insect growth r e g u l a t o r s appears much more p r o m i s i n g than their use as a n t i f e e d a n t s . Research i s now underway t o formulate enriched products from p l a n t s with high l e v e l s of IGR a c t i v i t i e s , f o r p r a c t i c a l a p p l i c a t i o n i n the f i e l d . The chemistry and mechanisms of t o x i c a c t i o n i n i n s e c t s of these p l a n t products are a l s o being s t u d i e d . A f u r t h e r advantage of these IGR P l a n t products i s t h e i r apparent lack of t o x i c i t y t o non-target i n s e c t s . Studies on Ecotypes of M e l i a azedarach and M.

toosendan.

For the p r a c t i c a l u t i l i z a t i o n of p l a n t s as a source of i n s e c t i c i d e s , i f the p l a n t i s d i s t r i b u t e d over a wide geographical area, i t i s important to i n v e s t i g a t e the ecotypes of the p l a n t . A few papers have been published on the ecotypes of neem t r e e by Schmutterer and a s s o c i a t e s , as w e l l as research workers i n I n d i a , with particular r e f e r e n c e t o a z a d i r a c h t i n content (see Proceedings of the 2nd and 3rd I n t e r n a t i o n a l Neem Conferences). The china-berry t r e e s , M. azedarach and M. toosendan, are widely d i s t r i b u t e d i n China i n regions south of the Yellow R i v e r . During the l a s t few years, i n v e s t i g a t i o n s have been c a r r i e d out on the toxic components and i n s e c t i c i d a l p r o p e r t i e s of these two species c o l l e c t e d from different locations. Their content of toosendanin was analyzed by means of HPLC. Aqueous e x t r a c t s were prepared from a i r - d r i e d sanples of bark, f r u i t , and leaves. The e x t r a c t s , a f t e r removal of fats with petroleum ether, were p a r t i t i o n e d with chloroform. The chloroform l a y e r s were f u r t h e r p u r i f i e d by column chromatography. The chloroform l a y e r s and p u r i f i e d f r a c t i o n s were then analyzed by HPLC. R e s u l t s showed t h a t the content of toosendanin i n the bark of Μ·



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azedarach and i n bark of M . toosendan varies geographically. The bark of M. azedarach growing i n Yanhe, Guizhou Province (south-western China), and i n X i x i a n g , Shanxi Province (north-western China) c o n t a i n s the h i g h e s t amounts of toosendanin, 5.16 mg/g and 4.710 mg/g, r e s p e c t i v e l y , whereas bark from Lechang, Guangdong Province (south China), c o n t a i n s only 1.26 mg/g. In M. toosendan, samples of the bark from northern and n o r t h western China-Zhengzhou, Henan Province, and Yibin, Sichuan province, c o n t a i n the h i g h e s t amount, 4.22 mg/g and 3.03 mg/g, r e s p e c t i v e l y . Samples from c e n t r a l and southern China, Hangzhou, Zhejiang Province and Lechang, Guangdong Province, provide low y i e l d s of toosendanin, 0.57 mg/g and 0.61 mg/g, respectively. However, the i n s e c t i c i d a l potency of the p l a n t , as shown by t o x i c i t y t o the l a r v a e of the imported cabbageworm, was found t o be not directly correlated with the content of toosendanin. Toosendanin was mainly found i n the bark of c h i n a berry ( 3 ) . None or very l i t t l e was found i n the leaves and f r u i t , but these p l a n t m a t e r i a l s a l s o showed some t o x i c i t y t o the l a r v a e . Some e x t r a c t s and crude products from the e x t r a c t s of the bark showed stronger b i o a c t i v i t y than pure toosendanin (compared on the b a s i s of the same amount of toosendanin). T h i s i n d i c a t e s t h a t besides toosendanin, the e x t r a c t s and crude products may c o n t a i n other b i o a c t i v e substances with synergistic effects. I t i s i n t e r e s t i n g t o note that the f r u i t s of M. azedarach from the southern most p a r t of China, Sanya, Hainan I s l a n d Province, possess f a i r l y high t o x i c i t y t o i n s e c t s , although the content of toosendanin i n the bark i s q u i t e low. A 1% chloroform e x t r a c t of the f r u i t s from Sanya and Haikou, Hainan Province, showed very high f e e d i n g r e p e l l e n c e was f i f t h i n s t a r l a r v a e of Spodoptera litura i n a non-choice test. M o r t a l i t i e s of 90.6% and 96.8%, compared with 37.9%, were obtained when f i f t h i n s t a r larvae of imported cabbageworm were t r e a t e d with a 1% chloroform e x t r a c t of f r u i t s of M. azedarach from Sanya and Haikou, Hainan Province, or Zhengzhou, c e n t r a l China, r e s p e c t i v e l y . From the above p r e l i m i n a r y r e s u l t s of our s t u d i e s on samples of M e l i a c o l l e c t e d from d i f f e r e n t r e g i o n s , i t can be concluded t h a t there are d i s t i n c t ecotypes i n China, which vary i n both the nature and q u a n t i t y of their insecticidal constituents, Genotype, climatic c o n d i t i o n s , and s o i l type a l l may p l a y a r o l e i n the e v o l u t i o n of the ecotypes. More d e t a i l e d s t u d i e s on ecotypes w i l l be of great value i n the u t i l i z a t i o n of i n s e c t i c i d a l plants f o r insect control. r

Studies on B i o a c t i v e P r i n c i p l e from the Celastraceae Plants of the C e l a s t r a c e a e are moderately well d i s t r i b u t e d i n t r o p i c a l and temperate regions of the world. In China there are 12 genera, composed of 183


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s p e c i e s , of t h i s f a m i l y . They are t r e e s , shrubs and climbers. There are about 30 C e l a s t r u s species widely d i s t r i b u t e d i n the c e n t r a l and northwestern regions of china. The r o o t bark of Chinese b i t t e r s w e e t , C e l a s t r u s angulatus Maxim, and Ç. qlaucophyllus Rehd. e t Wils have been used by farmers t o c o n t r o l i n s e c t pests of vegetables f o r many years (4). I t has a l s o been reported t h a t the r o o t bark powder (and i t s ethanol e x t r a c t ) of C. angulatus was e f f e c t i v e as an a n t i f e e d a n t with the adults and nymphs of Locusta migratoria manilensis and the l a r v a e of P i e r i s rapae. They a l s o i n h i b i t the reproduction of the maize weevil ( S i t o p h i l u s zeamais) and a c t as an a n t i f e e d a n t and stomach poison, producing a n a r c o t i c e f f e c t . An e t h y l ether e x t r a c t incorporated in rice at 2.6 mg/g caused complete i n h i b i t i o n of reproduction of the w e e v i l . This extract i s f a i r l y s t a b l e to s u n l i g h t and heat (5). Recently a d e t a i l e d study has been conducted on the b i o a c t i v e p r i n c i p l e s of the r o o t barks of C e l a s t r u s angulatus and Ç. qlaucophyllus i n the Department of Phytochemistry, Kunming I n s t i t u t e of Botany, Yunnan Province. A l t o g e t h e r seven sesquiterpene a l k a l o i d s and four sesquiterpene esters have been isolated and indentified. Representative compounds are maytansine, t r i p t o l i d e , maytoline and evonine. A l l these compounds c o n t a i n a common mother nucleus - agarofuran (6)(Figure 2). Nine samples from t h i s group of compounds have been bioassayed i n our l a b o r a t o r y and some of them were found t o be e f f e c t i v e against the imported cabbageworm and the A s i a t i c corn borer ( O s t r i n i a f u r n a c a l i s ) as a n t i f e e d a n t s and stomach poisons. A new sesquiterpene, " c e l a n g a l i n " , supposed to be the most a c t i v e compound of the root bark of Ç. angulatus was r e c e n t l y i s o l a t e d (5). I t i s i n t e r e s t i n g t o note t h a t the e m u l s i f i e d seed o i l fromÇ. angulatus was reported to be a safe and e f f e c t i v e i n s e c t i c i d e f o r cucumber b e e t l e s and other i n s e c t pests of vegetable crops (7). Thus both the r o o t bark and seed o i l of Chinese b i t t e r s w e e t may serve as potential botanical insecticides. Regarding the types of t o x i c symptoms and the modes of a c t i o n of t h i s c l a s s of n a t u r a l products, i t seems t h a t they are c l o s e l y r e l a t e d t o the a c t i v e p r i n c i p l e s i n the r o o t bark of thunder-god-vine (Trypterygium w i l f o r d i i ) and the yellow azalea (Rhododendron m o l l e ) . A l l these b o t a n i c a l i n s e c t i c i d e s possess a n t i f e e d a n t and stomach poison effects. They probably act on the central nervous system but not on cholinesterase activity. The t r e a t e d i n s e c t s undergo n a r c o s i s , r e v i v e b r i e f l y , then d i e . P


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r

r




74

Figure 1. The e f f e c t of t o p i c a l a p p l i c a t i o n of an acetone e x t r a c t of Tephrosia v o g e l i i on the growth and development of P i e r i s rapae L. A p p l i c a t i o n s were made t o the l a r v a l stage a t r a t e s equivalent t o 2.5 ug dry weight l e a v e s / i n s e c t ( l e f t ) , 25 (middle) or 100 ( r i g h t ) .

Ο

Dihydro-p-agarofuran

New compound from C e l a s t r u s angulatus

Figure 2. Compounds from the Celastraceae.


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Experiments on the A p p l i c a t i o n of P l a n t Products and Mixtures of B o t a n i c a l and Conventional I n s e c t i c i d e s - A New Approach t o Solve the Problem of Insecticide Resistance. In chemical control of i n s e c t pests, i n s e c t i c i d e r e s i s t a n c e i s a very s e r i o u s problem. In our s t u d i e s on b o t a n i c a l s , attempts have been made to solve this problem. One way i s t o make good formulations that c o n t r o l r e s i s t a n t s t r a i n s of i n s e c t s and a l s o delay the occurrence of r e s i s t a n c e i n s u s c e p t i b l e populations. Results of l a b o r a t o r y and f i e l d experiments with mixtures of toosendanin, e t h a n o l i c e x t r a c t of the root bark of Trypterygium w i l f o r d i i and c h l o r p y r i f o s , showed marked s y n e r g i s t i c e f f e c t s i n c o n t r o l l i n g the imported cabbageworm. I t was found t h a t , although conventional i n s e c t i c i d e s such as cartap and c h l o r p y r i f o s e x h i b i t a r a p i d t o x i c a c t i o n on the cabbageworm, those that s u r v i v e the treatment feed and develop normally, with pupal weight s i m i l a r to t h a t of the untreated l a r v a e . With b o t a n i c a l i n s e c t i c i d e s , however, e i t h e r a p p l i e d alone or i n a mixture with other i n s e c t i c i d e s , the percentage of pupation of the l a r v a e which s u r v i v e d the treatments was s i g n i f i c a n t l y decreased and the weight of the pupae was found t o be l e s s than t h a t of the untreated c o n t r o l s . For example, a f t e r treatment of f i f t h i n s t a r l a r v a e of the imported cabbageworm with 50 ug/g crude w i l f o r i n e the average weight of the pupae of the surviving i n d i v i d u a l s was 116. mg, as compared t o an average weight of 162. mg of the pupae of the untreated l a r v a e . Emergence of a d u l t s from the t r e a t e d l a r v a e was 62.5%, as compared t o 93.62% f o r the untreated c o n t r o l s . The r e s u l t s of treatment of f o u r t h i n s t a r l a r v a e of the cabbageworm with a mixture of 300 ppm toosendanin and 0.5% ethanol e x t r a c t of the r o o t bark of Trypterygium showed t h a t a f t e r e i g h t days, the percentage of pupation was decreased to 0.00-7.69% as compared to the c o n t r o l value of 91.2%; the average weight of the pupae was 115.0 mg as compared to 183.4 for controls. The e f f i c a c y of c o n t r o l of the r i c e g a l l midge ( O r s e o l i a oryzae) was g r e a t l y increased by spraying with a mixture of a 0.5% s o l u t i o n of china-berry seed o i l with 167 ug/ml d i a z i n o n , as compared t o spraying with 500 ug/ml d i a z i n o n alone. Because of the f a c t t h a t p l a n t d e r i v e d i n s e c t i c i d e s contain a number of compounds possessing bioactive p r o p e r t i e s , i n s e c t s have d i f f i c u l t y i n adapting t o them, and are not exposed to the same s e l e c t i o n pressure as with conventional insecticides. Hence the use of b o t a n i c a l may avoid or delay the development of i n s e c t resistance. The mixing of conventional i n s e c t i c i d e s , such as organophosphates and carbamates, at low concentrations with b o t a n i c a l s can serve t o increase the acute t o x i c i t y of the treatment, k i l l i n g the i n s e c t s f



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more q u i c k l y . Furthermore, p l a n t products are u s u a l l y fairly s e l e c t i v e i n a c t i o n ; many of them have low t o x i c i t y t o the n a t u r a l enemies of i n s e c t pests. Field t r i a l s conducted i n Guangdong i n 1984 showed t h a t a spray of 0.5% china-berry seed o i l showed little t o x i c i t y t o the predaceous mite, Amblyseius newsami (Erans), and other s p e c i e s of Amblyseius. By keeping the population d e n s i t y of i t s predator at a f u n c t i o n a l level, the damage caused by the citrus red mite (Panonychus c i t r i McG.) might be kept below the economic t h r e s h o l d , and i t i s q u i t e p o s s i b l e t h a t the s e r i o u s problem of resistance to organic and inorganic i n s e c t i c i d e s may be thus a l l e v i a t e d . Our discovery of the decreases i n pupal weight, percentage of emergence and egg-laying capacity of imported cabbageworm survors a f t e r treatment, with botanical i n s e c t i c i d e s , i n sharp c o n t r a s t to those t r e a t e d with conventional organo-phosphorous compounds, may have f a r - r e a c h i n g a f f e c t s on the formation of resistant strains. There may be a genetic reason why r e s i s t a n t s t r a i n s do not develop f o l l o w i n g treatment with n a t u r a l products. I t has been demonstrated t h a t diamondback moth l a r v a e d i d not develop r e s i s t a n c e a f t e r treatment with neem extracts (AZT-VR-K) f o r 35 generations, whereas with deltamethrin r e s i s t a n c e of the larvae built up within 20-35 generations. More research on the a p p l i c a t i o n of n a t u r a l products f o r s o l v i n g the r e s i s t a n c e problem should be undertaken and could be very rewarding. P l a n t s o f f e r a r i c h source of compounds possessing i n s e c t growth i n h i b i t i n g p r o p e r t i e s . Besides neem, china-berry, Tephrosia v o g e l i i , and other p l a n t products mentioned in this paper, the p o t e n t i a l of using phytoecdysones as IGRs must not be overlooked. I t has been reported t h a t there are more than 1000 species of plants containing these b i o a c t i v e substances. In agriculture IGRs g e n e r a l l y are compatible with the agroecosystem and may play an important role in i n t e r g r a t e d management programs. Recently i t was found that Derris extract, a time-honored botanical i n s e c t i c i d e , a l s o possesses IGR a c t i v i t y . D e r r i s and rotenone-containing products possess many outstanding p r o p e r t i e s , one of which i s t h e i r low persistance. Renewed e f f o r t s i n studying t h i s group of p l a n t s i s needed. Conclusions A p p l i c a t i o n of b o t a n i c a l i n s e c t i c i d e s has never given r i s e t o the problem of r e s i s t a n c e i n a g r i c u l t u r a l i n s e c t pests. This may have biochemical, genetic and ecological implications. The r a t i o n a l a p p l i c a t i o n of these n a t u r a l products e i t h e r alone or i n admixture with other i n s e c t i c i d e s may lead t o new s t r a t e g i e s f o r the prevention of the i n s e c t i c i d e r e s i s t a n c e problem.



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For some p l a n t s o f wide d i s t r i b u t i o n such as neem and china-berry, i n v e s t i g a t i o n o f t h e i r ecotypes should be based on an a n a l y s i s o f t h e i r main b i o a c t i v e c o n s t i t u e n t s as w e l l as t h e i r b i o l o g i c a l p r o p e r t i e s . Both are e s s e n t i a l . A d e t a i l e d knowledge o f the ecotypes would help us t o evaluate the b i o s y n t h e s i s o f the t o x i c components under d i f f e r e n t c l i m a t i c c o n d i t i o n s and t o supply information on how t o f u l l y u t i l i z e the raw m a t e r i a l l o c a l l y a v a i l a b l e f o r i n s e c t c o n t r o l . In China there i s a very r i c h f l o r a and farmers have been using p l a n t products as p e s t i c i d e s f o r more than one hundred years ( 8 ) , but s t u d i e s on p l a n t s possessing i n s e c t i c i d a l p r o p e r t i e s have been e x p l o i t e d only t o a l i m i t e d extent. The b i o a c t i v e p r i n c i p l e s and i n s e c t i c i d a l a c t i o n o f C e l a s t r u s angulatus and other species belonging t o Celastraceae i s an example o f the ample p o t e n t i a l f o r research on new compounds from p l a n t s as i n s e c t c o n t r o l agents i n China. However, i n t e r n a t i o n a l cooperation and c o o r d i n a t i o n i s very important i n the implementation of research i n t h i s f i e l d . There i s a need f o r m u l t i d i s c i p l i n a r y i n t e r n a t i o n a l team e f f o r t s t o b u i l d up and complement the v a l u a b l e research c u r r e n t l y underway a t various i n s t i t u t i o n s i n d i f f e r e n t countries. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

Anonymous, Recent advances in the investigations of botanical insecticides. South China A g r i . Univ. Research B u l l . , 1987, No.4 19 pp Guangzhou, China. Chiu, S . F . Z e i t . fur Pflanzenkr. und Pflanzenschutz. 1985,92(3), 310-319. Chiu, S . F . ; Zhang,X. J. South-China A g r i . Univ., 1987, 8(2), 57-67. Chiu, S . F . J. S c i . Food Agric. 1950, 9, 276-286. Wu, W . J . ; Cao, G . J . Acta Phytophylacica Sinica 1985, 12(1), 57-62. L i u , J. Investigations on the bioactive p r i c i p l e s of Celastraceae 1988. Ph.D. thesis. Institute of Organic Chemistry, Lanzhou University, China. Ke, Ζ . ; Nan, U . ; Lu, L.; Wu, D. Acta Phytophylacica Sinica 1987, 14(3), 208-216. Huang, H.T. in Science and C i v i l i z a t i o n in China 1987, 6(1), 471-519.

RECEIVED December 27, 1988


Insecticides of Plant Origin - American Chemical Society

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