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INSECT ANTIFEEDANTS1 FROM PLANTS
I N S E C T B IO L O G Y IN T H E F U T U R E
INSECT ANTIFEEDANTS1 FROM PLANTS
Koji Nakanishi Department of Chemistry Columbia University New York, N.Y.
I.
INTRODUCTION
In recent years we have been searching for various bio active compounds from tropical plant sources guided by simple and quick bioassays which can be carried out in a chemical laboratory by chemists. The crude extracts are also submitted to 10-20 different pharmacological assays carried out else where, and if the activity is significant the particular activity is also pursued in the isolation; however, this latter process necessarily takes a much longer time because each fraction has to be sent out until the activity can be correlated with a specific spectroscopic property. It is not surprising to expect that tropical flora, in contrast to their temperate zone counterparts, have developed a more efficient and varied defense mechanism because of the far more severe conditions for survival. They have indeed turned out to provide a rich and intriguing source for iso lating natural products which exhibit interesting properties such as plant or insect growth regulatory, cytotoxic, antimi crobial, molluscicidal (snail-killing) and other activities. The current studies on insect antifeedants being carried out in New York were initiated at the International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya,where I was a Research Director from 1969 (when ICIPE started) to 1977
^supported by NIH Grant AI-10187 Copyright
603
© 1980 by A cadem ic Press, Inc.
A ll rights o f reproduction in any form reserved. ISBN 0 -1 2 -454340-5
KOJI NAKANISHI
604
and Dr. Isao Kubo was a Senior Research Scientist for the years 1975/1976. The plants currently under investigation originated mostly from East Africa and Mexico, and a few from South America.
II. COLLECTION OF PLANTS AND BIOASSAY
Plants are collected on the basis of information gathered from literature survey and on local knowledge on insect re sistant species. In our laboratory in the Chemistry Department we maintain colonies of the Southern army-worm (Spodoptera eridania), the spruce bud-worm (Choristoneura fumigerana) and the Mexican bean bettle (Epilachna varivestes) for antifeedant studies. The first two are maintained on artificial diet whereas the bettle is fed with pole beans. The simplest bioassay system is schematically depicted in Fig. 1. In certain cases the crude extract is mixed with the artificial diet but the
FIGURE I. The vial with the leaf is put in a petri dish which contains water to keep the larvae from escaping. The larvae are placed at the branching point of the leaves, and the treated and untreated leaves are scored at appropriate time intervals. feeding of the insect is considerably affected by the shape of
present address:
Division Entomology & Parasitology University of California,Berkeley,CA.
605
INSECT ANTIFEED ANTS FROM PLANTS
the diet. Alternatively, in the assay employing natural leaves, e.g., spruce and Lima beans, we have noticed vari ations depending on the freshness of the leaf. Hence, unless the antifeedant is extremely potent, complications arising from securing reproducible results have been encountered. Probably a more revealing assay is the one based on elec trophysiology. Namely, initial studies carried out at ICIPE (Ma, 1977) on the monophagous (and therefore sensitive) Afri can army-worm (S.exempta) turned out to be very promising since the activity could be followed time-wise by impulse/ second readings recorded as oscillographs. In the case of the potent warburganal (see Fig.2)he found that contact of the medial sensilla with a filter paper impregnated with the com pound led to a drastic drop in the readings in a few minutes; the sense of taste recovered in ten minutes but two more contacts resulted in irreversible damage in the electrophysi ology readings. This in practiceleads to an interesting case; when the varacious larvae are left on corn-leaves treated with warburganal for 1 hour and then transferred to untreated leaves, they will not eat and starve. The electrophysiological assay is being continued at our place by Dr. Camilla Zack who has built a unit and has started working with 5. eridania. Preliminary studies have revealed that there are probably multiple mechanisms for antifeeding activities (Zack,1980). In addition to antifeedant assays, we are also looking for antiecdysones (if any - with Bombyx mori or silk worm), helicocides (Nakanishi and Kubo,1977) (with Biomphalaria pfeifferei - a snail which is a host for schistosomes, parasitic nematodes responsible for the wide-spread occurrence of shistosomiasis) and plant growth regulators. The crude plant extract which is obtained by immersion of the air-dried material in 40% aqueous MeOH is then extracted with the following four solvents and each extract is pro cessed separately: PLANT (air-dried) 40% aq. MeOH EXTRACT
Ί hexane
ether
- - - - 1- - 1 MeOH
water
a) Each extract bioassayed separately. b) Isolation is based on bioassay. c) Pure compound assayed for other activities; also submitted to Ames test.
606
KOJI NAKANISHI
If any of the assays give a positive response, the ex traction is followed through and the pure principle is structurally determined with the minimum possible quantity. The remainder of the sample is submitted to more extensive antifeedant and other assays and are also sent out for wider screening such as antibiotic activities. We have found that compounds isolated on the basis of insect antifeedant activity almost invariably exhibit other activities. A typical case was the leaf extract of the East African Croton macrostachys. The antifeedant principle was isolated according to bioassays with 5. exempta and the structure was fully determined to be the 1-benzylAteof 1,2,3, 4-diepoxy-5,6-diacetoxycyclohexane (unpublished). To our surprise we then found that the same compound had been iso lated from the same tree by the late Kupchan and NCI by following tumor-inhibiting antileukemic activities. There are several other cases. Hence we now regard the "antifeedant" assays as a quick means of isolating bioactive compounds from plants in general. Compounds isolated as weak antifeedants have been shown to be potent antibiotics occasionally.
III.ANTIFEEDANTS
Studies on antifeedants from plants have been carried out extensively by Munakata and co-workers (1970). We have also reviewed our studies in this area (Nakanishi,1977; Kubo and Nakanishi,1977? Kubo and Nakanishi,1979). Several compounds which we have isolated are shown in Figs. 2 and 3. Brief comments are given for some selected compounds Azadirachtin (Zanno,et al.1975; Nakanishi,1975). This is a we11-documented insect antifeedant (Gill and Lewis,1971; Ruscoe,1972; Morgan and Thornton,1973) which is contained in the leaves and berries of Azadirachta indica (Indian neem tree) and Melia azedarach (China-berry tree). Extensive structural studies were carried out by Morgan and co-workers (Butterworth, et al.1972) but the noncrystalline compound was too difficult to deal with in the days preceding 13c-NMR. We were able to isolate 800 mg from 300 g of the large fruit seeds of fresh berries collected from trees near Mombasa. However, the yield is usually much lower, and it may well be due to seasonal variation. It is one of the most potent antifeedants against the African desert locust Schistocerca gregaria, the limiting concentration to cause 100% inhibition of feeding being 40 yg/liter or when impreg nated onto filter paper 1 nanogram/cm2 (Morgan and Thornton, 1973). There is great interest in this tree, or the anti-
INSECT ANTI FEED ANTS FROM PLANTS
607
harrisonin
azadirachtin
_,
Heterocycles, 5 485(1976)
J. Am.Chem.Soc., 97,1975(1975)
N-methylflindersine J. Am.Chem.Soc., 98,6704(1976) J. Am.Chem.Soc., 100, 7079(1978) 0
H
Heterocycles, 7, 969(1977)
M
0Cv—
/H
CH20H
CH2°H
0
s c h k u r in -I
R = Ac
Ϋ Π
/H e
R= - C - C - C C
0
ÖH
" Me
HETEROCYCLES, 11,471(1978)
ojugarin-I -H (6-OH) -IH(4,l7-diol) J.C.S.CHEM.COMM., 949 (1976)
FIGURE 2.
Some Antifeedants isolated from East Plants.
African
KOJI NAKANISHI
608
Warburaia uaandensis (Canellaceae) CHO ..OH CHO
CHO ,ΌΗ
CHO
warburganal Chem. Comm. 1013(1976)
muzigadial Tet. Lei., 4553(1977)
Me Biological Activity of Warburganal - I Insect antifeedant "choice test" S p o d o p t e r a e x c m p t a (oligophagous) 0.1 ppm S . l i t t o r a l i s (polyphagous) 10 ppm S c h i s t o c e r c a g r e g a r i a (polyphagous) and L o c u s t a m i g r a t o r i a (gramnivorous) 85-90% inhibition at 0.01% dry weight of fiber disc containing 5% sucrose IDr.E.A. Bernays, COPR, London] weakly or nonactive against S. e r i d a n i a Schistocerca
vaga
Epilachna var ivestis Manduca sexta
Antimicrobial Saccharomyces cerevisiae Ca nd id a utilis S c l e r o t i nia l i b e r t i a n a Mucor mucedo
.
12.5 pg/rnl 12 pg/ml 3.1 3 , 50 100
Molluscicidal Biompharis glabratus B. p f e i f f e r i Lymnaca natalensis
5 ppm - 2 hrs 5 ppm - 2 hrs 10 ppm ppm - 2 hrs
Cytotoxicity 0.01 yg/ml KB test Acute toxicity subcutaneous injection in mice, LD5 q 20.4 mg/kg FIGURE 3.
Activities of Warburganal.
INSECT ANTIFEEDANTS FROM PLANTS
609
feedant(s), for potential use as a means of controlling pest insects. The structure is too complex to be synthesized on a practical basis but studies are ongoing at various places to cultivate the tree, isolate other active principles, etc. In fact the Frist International Neem Conference will be held in June, 1980 in West Germany to discuss future approaches. Warburganal (Kubo, et al.1976,1977). This sesquiterpene is one of the strongest against the African army-worm (see above) and besides exhibits a broad spectrum of activity. Its synthesis has also been completed by at least three groups (Tanis and Nakanishi,1979; Nakata, et al.1979; Ohsuka and Matsukawa,1979). The bark of the tree is a favorite spice used by East Africans; it has a pleasant hot taste which is also true for warburganal. The too broad activity may severely restrict its use as a practical antifeedant.
IV. SUMMARY
The tropical flora offer a rich source of bioactive com pounds. Although natural products chemist have indeed been studying plants extensively it is only recent that the isolation is being followed on a more purpose oriented and systematic manner. The natural products thus isolated will serve to suggest entirely new types of active compounds, an aspect which has been so fruitful in microbial antibiotics; another case, exemplified by azadirachtin, is the cultivation of the plant itself to let nature take care of the synthesis. As far as I am aware of, no commercial antifeedant is known; obviously numerous untested difficulties have to be overcome even if a potentially useful compound was discovered. How ever, the antifeedant may well provide an additional means for the integrated control of insects. One advantage is that they are frequently extracted from plants which have been used over the years in folk medicine and hence are less likely to be toxic to animals.
ACKNOWLEDGMENTS
The systematic studies carried out in our laboratory was led by Professor Isao Kubo who was here for the years 1977 1979 before going to Berkeley. I am grateful to my other colleagues who are quoted in the references and to the entire ICIPE organization.
610
KOJI NAKANISHI
REFERENCES
Butterworth, J.H., and Morgan, E.D. (1968). Isolation of a substance that suppresses feeding in locusts. Chem.Commun. 23 - 24. Butterworth, J.H., and Morgan, E.D. (1971). J. Insect Physiol. 17, 969. Butterworth, J.H., Morgan, E.D., and Percy, G.R. (1972). The structure of azadirachtin; the functional groups. J. Chem. Soc. Perkin Trans.I, 2445 - 2450. Gill, G.S., and Lewis, C.T. (1971). Systemic action of an insect feeding deterrent. Nature 232, 402 - 403. Kubo, I., Lee, Y.-W., Pettei, M.J., Pilkiewicz, F., and Naka nishi, K. (1976). Potent army worm antifeedants from the East African Warburgia Plants. Chem.Commun., 1013 - 1014. Kubo, I., Miura, I., Pettei, M.J., Lee, Y.-W., Pilkiewicz, F., and Nakanishi, K. (1977). Muzigadial and warburganal, potent antifungal, antiyeast, and African army worm anti feedant agents. Tetrahedron Lett., 4553 - 4556. Kubo, I., and Nakanishi, K. (1977). Insect antifeedants and repellents from African plants. In "Host plant resistance to pests", Am. Chem. Soc. Symposium Series, 62, (P.A. Hedin, ed.) pp 165 - 178. Kubo, I., and Nakanishi, K. (1979). Some terpenoid insect antifeedants from tropical plants. In "Advances in pesti cide Science" Part 2, (H. Geissbuhler,ed.), pp. 284 - 294. Pergamon Press, Oxford. Kupchan, S.M., Hemingway, R.J., and Smith, R.M. (1969). Tumor inhibitors.XLV crotepoxide, a novel cyclohexane diepoxide tumor inhibitor from Croton macrostachys. J. Org. Chem. 34, 3898 - 3902. Ma, W.-C. (1977). Alterations of chemoreceptor function in army worm larvae (Spodoptera exempta) by a plant-derived sesquiterpenoid and by sulfhydryl reagents. Physiol Entomol. 2, 199 - 207. Ma, W.-C., and Kubo, I. (1977). Phagostimulants for Spodopt era exempta: Identification of adenosine from Zea and mays. Entomol. Exp. Appl. 22, 107 - 112. Morgan, E.D., and Thornton, M.D. (1973). Azadirachtin in the fruit of Melia azadarach. Phytochem. 12, 391 - 392. Munakata, K. (1970). Insect antifeedants in plants. In "Control of Insect Behavior by Natural Products" (D.L. Wood,ed.) pp. 179 - 187. Academic Press, New York, N.Y. Nakanishi,K. (1975). In "Recent Advances in Phytochemistry" (V.C. Runeckles, ed.), 9, 283.
INSECT ANTIFEED ANTS FROM PLANTS
611
Nakanishi, K. (1977). Insect growth regulators from plants. Pontificiae Academiae Scientiarvm Scripta Varia 41, 185198. Nakanishi, Κ., and Kubo, I. (1977). Studies on warburganal, muzigadial and related compounds. Israel J. Chem. 16, 28 - 31. Nakata, T., Akita, H., Naito, T., and Oishi, T. (1979). A total synthesis of (±)-warburganal. J.Am. Chem. Soc. 101, 4400 - 4401. Ohsuka, A., and Matsukawa, A. (1979). Synthesis of (i)®rburganal and (±) isotadeonal. Chem. Lett., 635 - 636. Ruscoe, C.N.E. (1972). Growth disruption effects of an insect antifeedant. Nature (London), New Biol. 236, 159 - 160. Tanis, S.P., and Nakanishi, K. (1979). Stereospecific total synthesis of (i)-warburganal and related compounds. J. Am. Chem. Soc. 101, 4398 - 4400. Zack, C. (1980). Unpublished. Zanno, P.R., Miura, I., Nakanishi, Κ., and Elder, D.L. (1975). Structure of the insect phagorepellent ctzadirachtin. Application of PRFT/CWD carbon-13 nuclear magnetic reso nance. J. Am. Chem. Soc. 97, 1975 - 1977.
INSECT ANTIFEEDANTS1 FROM PLANTS
Koji Nakanishi Department of Chemistry Columbia University New York, N.Y.
I.
INTRODUCTION
In recent years we have been searching for various bio active compounds from tropical plant sources guided by simple and quick bioassays which can be carried out in a chemical laboratory by chemists. The crude extracts are also submitted to 10-20 different pharmacological assays carried out else where, and if the activity is significant the particular activity is also pursued in the isolation; however, this latter process necessarily takes a much longer time because each fraction has to be sent out until the activity can be correlated with a specific spectroscopic property. It is not surprising to expect that tropical flora, in contrast to their temperate zone counterparts, have developed a more efficient and varied defense mechanism because of the far more severe conditions for survival. They have indeed turned out to provide a rich and intriguing source for iso lating natural products which exhibit interesting properties such as plant or insect growth regulatory, cytotoxic, antimi crobial, molluscicidal (snail-killing) and other activities. The current studies on insect antifeedants being carried out in New York were initiated at the International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya,where I was a Research Director from 1969 (when ICIPE started) to 1977
^supported by NIH Grant AI-10187 Copyright
603
© 1980 by A cadem ic Press, Inc.
A ll rights o f reproduction in any form reserved. ISBN 0 -1 2 -454340-5
KOJI NAKANISHI
604
and Dr. Isao Kubo was a Senior Research Scientist for the years 1975/1976. The plants currently under investigation originated mostly from East Africa and Mexico, and a few from South America.
II. COLLECTION OF PLANTS AND BIOASSAY
Plants are collected on the basis of information gathered from literature survey and on local knowledge on insect re sistant species. In our laboratory in the Chemistry Department we maintain colonies of the Southern army-worm (Spodoptera eridania), the spruce bud-worm (Choristoneura fumigerana) and the Mexican bean bettle (Epilachna varivestes) for antifeedant studies. The first two are maintained on artificial diet whereas the bettle is fed with pole beans. The simplest bioassay system is schematically depicted in Fig. 1. In certain cases the crude extract is mixed with the artificial diet but the
FIGURE I. The vial with the leaf is put in a petri dish which contains water to keep the larvae from escaping. The larvae are placed at the branching point of the leaves, and the treated and untreated leaves are scored at appropriate time intervals. feeding of the insect is considerably affected by the shape of
present address:
Division Entomology & Parasitology University of California,Berkeley,CA.
605
INSECT ANTIFEED ANTS FROM PLANTS
the diet. Alternatively, in the assay employing natural leaves, e.g., spruce and Lima beans, we have noticed vari ations depending on the freshness of the leaf. Hence, unless the antifeedant is extremely potent, complications arising from securing reproducible results have been encountered. Probably a more revealing assay is the one based on elec trophysiology. Namely, initial studies carried out at ICIPE (Ma, 1977) on the monophagous (and therefore sensitive) Afri can army-worm (S.exempta) turned out to be very promising since the activity could be followed time-wise by impulse/ second readings recorded as oscillographs. In the case of the potent warburganal (see Fig.2)he found that contact of the medial sensilla with a filter paper impregnated with the com pound led to a drastic drop in the readings in a few minutes; the sense of taste recovered in ten minutes but two more contacts resulted in irreversible damage in the electrophysi ology readings. This in practiceleads to an interesting case; when the varacious larvae are left on corn-leaves treated with warburganal for 1 hour and then transferred to untreated leaves, they will not eat and starve. The electrophysiological assay is being continued at our place by Dr. Camilla Zack who has built a unit and has started working with 5. eridania. Preliminary studies have revealed that there are probably multiple mechanisms for antifeeding activities (Zack,1980). In addition to antifeedant assays, we are also looking for antiecdysones (if any - with Bombyx mori or silk worm), helicocides (Nakanishi and Kubo,1977) (with Biomphalaria pfeifferei - a snail which is a host for schistosomes, parasitic nematodes responsible for the wide-spread occurrence of shistosomiasis) and plant growth regulators. The crude plant extract which is obtained by immersion of the air-dried material in 40% aqueous MeOH is then extracted with the following four solvents and each extract is pro cessed separately: PLANT (air-dried) 40% aq. MeOH EXTRACT
Ί hexane
ether
- - - - 1- - 1 MeOH
water
a) Each extract bioassayed separately. b) Isolation is based on bioassay. c) Pure compound assayed for other activities; also submitted to Ames test.
606
KOJI NAKANISHI
If any of the assays give a positive response, the ex traction is followed through and the pure principle is structurally determined with the minimum possible quantity. The remainder of the sample is submitted to more extensive antifeedant and other assays and are also sent out for wider screening such as antibiotic activities. We have found that compounds isolated on the basis of insect antifeedant activity almost invariably exhibit other activities. A typical case was the leaf extract of the East African Croton macrostachys. The antifeedant principle was isolated according to bioassays with 5. exempta and the structure was fully determined to be the 1-benzylAteof 1,2,3, 4-diepoxy-5,6-diacetoxycyclohexane (unpublished). To our surprise we then found that the same compound had been iso lated from the same tree by the late Kupchan and NCI by following tumor-inhibiting antileukemic activities. There are several other cases. Hence we now regard the "antifeedant" assays as a quick means of isolating bioactive compounds from plants in general. Compounds isolated as weak antifeedants have been shown to be potent antibiotics occasionally.
III.ANTIFEEDANTS
Studies on antifeedants from plants have been carried out extensively by Munakata and co-workers (1970). We have also reviewed our studies in this area (Nakanishi,1977; Kubo and Nakanishi,1977? Kubo and Nakanishi,1979). Several compounds which we have isolated are shown in Figs. 2 and 3. Brief comments are given for some selected compounds Azadirachtin (Zanno,et al.1975; Nakanishi,1975). This is a we11-documented insect antifeedant (Gill and Lewis,1971; Ruscoe,1972; Morgan and Thornton,1973) which is contained in the leaves and berries of Azadirachta indica (Indian neem tree) and Melia azedarach (China-berry tree). Extensive structural studies were carried out by Morgan and co-workers (Butterworth, et al.1972) but the noncrystalline compound was too difficult to deal with in the days preceding 13c-NMR. We were able to isolate 800 mg from 300 g of the large fruit seeds of fresh berries collected from trees near Mombasa. However, the yield is usually much lower, and it may well be due to seasonal variation. It is one of the most potent antifeedants against the African desert locust Schistocerca gregaria, the limiting concentration to cause 100% inhibition of feeding being 40 yg/liter or when impreg nated onto filter paper 1 nanogram/cm2 (Morgan and Thornton, 1973). There is great interest in this tree, or the anti-
INSECT ANTI FEED ANTS FROM PLANTS
607
harrisonin
azadirachtin
_,
Heterocycles, 5 485(1976)
J. Am.Chem.Soc., 97,1975(1975)
N-methylflindersine J. Am.Chem.Soc., 98,6704(1976) J. Am.Chem.Soc., 100, 7079(1978) 0
H
Heterocycles, 7, 969(1977)
M
0Cv—
/H
CH20H
CH2°H
0
s c h k u r in -I
R = Ac
Ϋ Π
/H e
R= - C - C - C C
0
ÖH
" Me
HETEROCYCLES, 11,471(1978)
ojugarin-I -H (6-OH) -IH(4,l7-diol) J.C.S.CHEM.COMM., 949 (1976)
FIGURE 2.
Some Antifeedants isolated from East Plants.
African
KOJI NAKANISHI
608
Warburaia uaandensis (Canellaceae) CHO ..OH CHO
CHO ,ΌΗ
CHO
warburganal Chem. Comm. 1013(1976)
muzigadial Tet. Lei., 4553(1977)
Me Biological Activity of Warburganal - I Insect antifeedant "choice test" S p o d o p t e r a e x c m p t a (oligophagous) 0.1 ppm S . l i t t o r a l i s (polyphagous) 10 ppm S c h i s t o c e r c a g r e g a r i a (polyphagous) and L o c u s t a m i g r a t o r i a (gramnivorous) 85-90% inhibition at 0.01% dry weight of fiber disc containing 5% sucrose IDr.E.A. Bernays, COPR, London] weakly or nonactive against S. e r i d a n i a Schistocerca
vaga
Epilachna var ivestis Manduca sexta
Antimicrobial Saccharomyces cerevisiae Ca nd id a utilis S c l e r o t i nia l i b e r t i a n a Mucor mucedo
.
12.5 pg/rnl 12 pg/ml 3.1 3 , 50 100
Molluscicidal Biompharis glabratus B. p f e i f f e r i Lymnaca natalensis
5 ppm - 2 hrs 5 ppm - 2 hrs 10 ppm ppm - 2 hrs
Cytotoxicity 0.01 yg/ml KB test Acute toxicity subcutaneous injection in mice, LD5 q 20.4 mg/kg FIGURE 3.
Activities of Warburganal.
INSECT ANTIFEEDANTS FROM PLANTS
609
feedant(s), for potential use as a means of controlling pest insects. The structure is too complex to be synthesized on a practical basis but studies are ongoing at various places to cultivate the tree, isolate other active principles, etc. In fact the Frist International Neem Conference will be held in June, 1980 in West Germany to discuss future approaches. Warburganal (Kubo, et al.1976,1977). This sesquiterpene is one of the strongest against the African army-worm (see above) and besides exhibits a broad spectrum of activity. Its synthesis has also been completed by at least three groups (Tanis and Nakanishi,1979; Nakata, et al.1979; Ohsuka and Matsukawa,1979). The bark of the tree is a favorite spice used by East Africans; it has a pleasant hot taste which is also true for warburganal. The too broad activity may severely restrict its use as a practical antifeedant.
IV. SUMMARY
The tropical flora offer a rich source of bioactive com pounds. Although natural products chemist have indeed been studying plants extensively it is only recent that the isolation is being followed on a more purpose oriented and systematic manner. The natural products thus isolated will serve to suggest entirely new types of active compounds, an aspect which has been so fruitful in microbial antibiotics; another case, exemplified by azadirachtin, is the cultivation of the plant itself to let nature take care of the synthesis. As far as I am aware of, no commercial antifeedant is known; obviously numerous untested difficulties have to be overcome even if a potentially useful compound was discovered. How ever, the antifeedant may well provide an additional means for the integrated control of insects. One advantage is that they are frequently extracted from plants which have been used over the years in folk medicine and hence are less likely to be toxic to animals.
ACKNOWLEDGMENTS
The systematic studies carried out in our laboratory was led by Professor Isao Kubo who was here for the years 1977 1979 before going to Berkeley. I am grateful to my other colleagues who are quoted in the references and to the entire ICIPE organization.
610
KOJI NAKANISHI
REFERENCES
Butterworth, J.H., and Morgan, E.D. (1968). Isolation of a substance that suppresses feeding in locusts. Chem.Commun. 23 - 24. Butterworth, J.H., and Morgan, E.D. (1971). J. Insect Physiol. 17, 969. Butterworth, J.H., Morgan, E.D., and Percy, G.R. (1972). The structure of azadirachtin; the functional groups. J. Chem. Soc. Perkin Trans.I, 2445 - 2450. Gill, G.S., and Lewis, C.T. (1971). Systemic action of an insect feeding deterrent. Nature 232, 402 - 403. Kubo, I., Lee, Y.-W., Pettei, M.J., Pilkiewicz, F., and Naka nishi, K. (1976). Potent army worm antifeedants from the East African Warburgia Plants. Chem.Commun., 1013 - 1014. Kubo, I., Miura, I., Pettei, M.J., Lee, Y.-W., Pilkiewicz, F., and Nakanishi, K. (1977). Muzigadial and warburganal, potent antifungal, antiyeast, and African army worm anti feedant agents. Tetrahedron Lett., 4553 - 4556. Kubo, I., and Nakanishi, K. (1977). Insect antifeedants and repellents from African plants. In "Host plant resistance to pests", Am. Chem. Soc. Symposium Series, 62, (P.A. Hedin, ed.) pp 165 - 178. Kubo, I., and Nakanishi, K. (1979). Some terpenoid insect antifeedants from tropical plants. In "Advances in pesti cide Science" Part 2, (H. Geissbuhler,ed.), pp. 284 - 294. Pergamon Press, Oxford. Kupchan, S.M., Hemingway, R.J., and Smith, R.M. (1969). Tumor inhibitors.XLV crotepoxide, a novel cyclohexane diepoxide tumor inhibitor from Croton macrostachys. J. Org. Chem. 34, 3898 - 3902. Ma, W.-C. (1977). Alterations of chemoreceptor function in army worm larvae (Spodoptera exempta) by a plant-derived sesquiterpenoid and by sulfhydryl reagents. Physiol Entomol. 2, 199 - 207. Ma, W.-C., and Kubo, I. (1977). Phagostimulants for Spodopt era exempta: Identification of adenosine from Zea and mays. Entomol. Exp. Appl. 22, 107 - 112. Morgan, E.D., and Thornton, M.D. (1973). Azadirachtin in the fruit of Melia azadarach. Phytochem. 12, 391 - 392. Munakata, K. (1970). Insect antifeedants in plants. In "Control of Insect Behavior by Natural Products" (D.L. Wood,ed.) pp. 179 - 187. Academic Press, New York, N.Y. Nakanishi,K. (1975). In "Recent Advances in Phytochemistry" (V.C. Runeckles, ed.), 9, 283.
INSECT ANTIFEED ANTS FROM PLANTS
611
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