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The potential of heptenophos and MK-936 pesticides for control of minor pests in integrated pest control programmes under glass
Agriculture, Ecosystems and Environment, 17 (1986) 287--292
287
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
Short Communication THE POTENTIAL OF HEPTENOPHOS AND MK-936 PESTICIDES FOR CONTROL OF MINOR PESTS IN INTEGRATED PEST CONTROL PROGRAMMES UNDER GLASS
N.L. HELYER and M.S. LEDIEU
Glasshouse Crops Research Institute, Worthing Road, Littlehampton BN1 7 6LP (Great BHtain) (Accepted for publication 14 May 1986)
ABSTRACT
Helyer, N.L. and Ledieu, M.S., 1986. The potential of heptenophos and MK-936 pesticides for control of minor pests in integrated pest control programmes under glass. Agric. Ecosystems Environ., 17: 287--292. In non-replicated glasshouse experiments with tomatoes and cucumbers, the pesticide heptenophos (Hostaquick 55% ec.) with its systemic and short persistence properties was found to be useful in integrated programmes where biological control of major pests was used, but chemical control of minor pests such as leafhopper (Hauptidia maroccana) and thrips (ThHps tabaci) was necessary. A spray interval of 10 days was considered to be the best compromise between kill of pests and depletion of natural enemies. The pesticide MK-936 (avermectin B1) was disruptive to biological control agents and ineffective against the minor pests. It is thus unsuitable for integration, but was found to be very effective as a purely chemical control agent of two-spotted mite.
INTRODUCTION
When biological control of whitefly (Trialeurodes vaporariorum) and/or two-spotted mite (Tetranychus urticae) is adopted on crops such as tomatoes and cucumbers under glass, various minor pests such as thrips (Thrips tabaci), leafhopper (Hauptidia maroccana) and leafminer (Liriomyza bryoniae) can be difficult to control without upsetting the biological control agents. A survey, c o n d u c t e d b y the Agricultural Development and Advisory Service (Gould, 1985), has assessed the usage in the U.K. (by % hectarage treated) of the two major natural enemies on heated glasshouse food crops in 1983. In cucumbers, approximately 70% of the area was treated with Phytoseiulus persimilis and 46% with Encarsia formosa, while in tomatoes the comparable figures were 17% and 35%, respectively. The range of materials which are suitable for integration is limited and, as a result, it is sometimes necessary to resort to judicious use of potentially harmful pesticides by, for instance, separating pesticides from natural enemies in either space or time (Helyer, 1985). 0167-8809/86/$03.50
© 1986 Elsevier Science Publishers B.V.
288
The work reported here was directed at extending the list of pesticides which are selective enough f o r simple integration. The materials chosen were h e p t e n o p h o s (Hostaquick 55% ec.) from Hoechst and MK-936 (avermectin B1) from Merk Sharp & Dohme. This latter is a natural product derived from the actinomycete Streptomyces avermitilis and consists of a mixture of two homologous natural products, avermectin B l a and avermectin B l b . METHODS
Five glasshouse compartments, each of 10 m z, were planted with 6 t o m a t o plants (cv. Marathon) on one side and 5 cucumber plants (cv. Corona) on the other. The plants were grown in 23-cm "whalehide" pots at a set temperature of 20°C with venting at 22°C. Plants in each compartment were similarly infested with adult pests over a 3-week period; thrips and leafhopper twice weekly at 2 per plant. Two-spotted mite was introduced by tapping apical tissue from exhausted stock plants on which the mite population had begun "webbing", over the cucumber and t o m a t o plants (young mites congregate at the apex of the plant when competition for f o o d increases). P. persimilis were introduced twice weekly for two-spotted mite control at 2 per plant, beginning 3 weeks after the first pests were introduced. All the insects were allowed to become established before pesticide treatments commenced. Leafminer and whitefly were also introduced, b u t failed to establish. One of the five compartments was a control, receiving no pesticide; two were sprayed with heptenophos (0.75 ml product 1-1, 0.0375% a.i.), one c o m p a r t m e n t weekly, the other fortnightly; the remaining two compartments received sprays of MK-936 (0.25 ml product 1:1, 0.00045% a.i.) at the same intervals. Assessments of pest and natural enemy populations were made shortly before the first pesticide application and twice-weekly thereafter. In the case of two-spotted mite and P. persimilis on cucumber plants, 25 1-cmdiameter leaf discs were removed from plants and numbers of all stages were recorded under t h e microscope. Thrips and leafhopper, on the other hand, were recorded by direct observation in situ, on the first leaf below each truss up to the fifth truss from 5 plants. Using laboratory pesticide screening methods developed at the GCRI (Ledieu, 1979; Helyer, 1982; Ledieu, 1985) the effect of MK-936 was evaluated against both adults and pupae of E. formosa. Whole plants were sprayed and leaf discs were removed over a 14-day period, adult E. formosa were caged over the leaf material and mortality was assessed daily for 4 days. Pupae or "black scales" were sprayed with MK-936 and the emerged and unemerged scales counted 3 weeks later. RESULTS
Control of two-spotted mite b y predator in the absence of pesticide was
289
achieved within three weeks of pesticide treatments being applied to other compartments (Fig. 1A). Heptenophos applied weekly resulted in complete disruption of predatory control (Fig. 1B), but when applied fortnightly control was achieved in about six weeks {Fig. 1C). MK-936 applied weekly resulted in control of two-spotted mite within three weeks of starting treatments (Fig. 1D) and thus was comparable to use of the predator alone (cf. Fig. 1A). However, numbers of predators were lower than where no pesticide had been used (Fig. 1D cf Fig. 1A). Similarly, less intensive use of MK-936 (2-week interval) resulted in rapid spider mite control, but poor multiplication of the predator (Fig. 1E). In the absence of pesticides, leafhopper numbers remained at a steady, high level throughout the experiment (Fig. 2A), while thrips underwent an initial period of multiplication before reaching a plateau (Fig. 2B). Weekly sprays of heptenophos resulted in rapid control of both leafhopper and thrips (Figs. 2A and B). Fortnightly sprays were only slightly less effective against leafhopper (Fig. 2A), but much less so against thrips (Fig. 2B). MK-936 sprays of either frequency were ineffective against leafhopper (Fig. 2C) and inadequate against thrips (Fig. 2D). 3.0
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Fig. 1. Effect of heptenophos and MK-936 on predatory control of the two-spotted mite by Phytosieulus persimilis. A, control (water sprayed); B, weekly sprays of heptenophos; C, fortnightly sprays of heptenophos; D, weekly sprays of MK-936; E, fortnightly sprays of MK-936.
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Fig. 2. E f f e c t o f d i f f e r e n t s p r a y r e g i m e ( n o n e , w e e k l y or f o r t n i g h t l y ) o n t h e c o n t r o l o f l e a f h o p p e r a n d t h r i p s b y h e p t e n o p h o s a n d M K - 9 3 6 . A, B, h e p t e n o p h o s o n l e a f h o p p e r an d thrips, r e s p e c t i v e l y , C , D , M K - 9 3 6 o n l e a f h o p p e r and thrips, r e s p e c t i v e l y .
In laboratory tests against E. formosa, MK-936 was found to be 'safe" to adults, using the criteria of Helyer (1982). However, the effect against pupae (black scales) was classified as "harmful" since although 92% of pupae treated with one tenth of the recommended field rate showed emergence holes, all the newly emerged adults were lying dead in the immediate vicinity of their pupal cases. Due to limitations of glasshouse space it was not possible to replicate the treatments and, thus, apply normal statistical tests. However, in the early stages of the experiment, when plants and pest populations were still separate, the effects were consistent from plant to plant. Also, where appropriate, the findings confirm previous experimentation (Ledieu, 1979). DISCUSSION
Heptenophos, with its systemic activity and short persistence, appears an ideal candidate for integration. It has been shown in previous work to be harmful to adults of E. formosa, but only persists for a period of about 4 days. When sprays were repeated weekly (Ledieu, 1979) E. formosa was able to control a whitefly infestation, although control was achieved more slowly than when no pesticide was used. Whereas fortnightly applications of heptenophos controlled leafhoppers reasonably well, they were not frequent enough to give adequate control of thrips. The sharp peaks in leafhopper numbers, separated by samples where none were found, suggests that this may be a reflection of the rate of development of the pest rather than efficacy of the chemical. If timing
291
of the sprays was such that susceptible stages of leafhoppers, but hardy ones of thrips, were present when sprays were applied, results such as those o b t a i n e d would be expected. On the other hand, had other spray intervals been chosen, the opposite results might have ensued. There may be much to be gained from careful study of the susceptibility of different stages of the life cycle to a pesticide in order to ascertain the best spray programme. To achieve adequate control of both leafhopper and thrips, heptenophos should be applied weekly. However, this results in severe reduction in predator efficiency so a compromise must be struck between the effect on the predator and the control of pests. Application of heptenophos at 10-day intervals would probably permit acceptable predator activity and still provide reasonable control of thrips and leafhopper. On the basis of this work, h e p t e n o p h o s n o w has Pesticide Safety Precautions Scheme clearance for leafhopper control on tomatoes and cucumbers with a 14-day spray interval and is n o w in commercial use. MK-936, on the other hand, was not only ineffective against both minor pests tested, b u t also had a deleterious effect on the two major natural enemies used in integrated control programmes. Thus, this material is of little value to anyone practising integrated control in tomatoes or cucumbers. The results of the tests on E. formosa adults and pupae indicate that the harmful nature of MK-936 to this parasite is n o t due to contact action, b u t results from ingestion. However, MK-936 showed good activity against the major pests, performance against two-spotted mite being evident in the results given above (also Green and Dybas, 1984a). Green and Dybas (1984b) have shown that weekly sprays of MK-936 give good control of Liriomyza trifolii, indicating its usefulness for leafminer control. Trumble (1985) had also used weekly sprays of MK-936 and shown suppression of L. trifolii without adverse effects on various stages of several species of leafminer parasite. L.R. Wardlow (personal communication, 1984) has shown that MK-936 will kill y o u n g whitefly larvae b u t is less effective against older larvae, pupae and adults. Thus MK-936 has a useful role as a purely chemical control b u t m a y also be used in certain integrated programmes. ACKNOWLEDGEMENTS
The authors thank T. Green and P. R o u n d for supplying the MK-936 and for sending technical information.
REFERENCES Gould, H.J., 1985. The advisory problem. In: N.W. Hussey and N. Scopes (Editors), Biological Pest Control. The Glasshouse Experience. Blandford Press, Dorset, pp. 213--219.
292 Green, A.St.J. and Dybas, R.A., 1984a. Avermectin BI: control of mites on ornamentals. Proc. British Crop Protection Conference, Pests and Diseases 1984, Brighton. 3, 1129--1133. Green, A.St.J. and Dybas, R.A., 1984b. The control of Liriomyza leafminers and other insect species with avermectin B1. Proc. British Crop Protection Conference, Pests and Diseases 1984, Brighton, 3: 1135--1141. Helyer, N.L., 1982. Laboratory screening of pesticides for use in integrated control programmes with Encarsia formosa (Hymenoptera, Aphelinidae) and Phytoseiulus persimilis (Acarina, Phytoseiidae). Tests of agrochemicals and cultivars. Ann. Appl. Biol., 100, Suppl., 3: 64--65. Helyer, N.L., 1985. The ecological selectivity of pesticides in integrated pest management. In: N.W. Hussey and N. Scopes (Editors), Biological Pest Control. The Glasshouse Experience. Blandford Press, Dorset, pp. 162--165. Ledieu, M.S., 1979. Laboratory and glasshouse screening of pesticides for adverse effects on the parasite Encarsia formosa Gahan. Pest. Sci., 10: 123--132. Ledieu, M.S., 1985. Integration with chemical control of diseases and minor pests. In: N.W. Hussey and N. Scopes (Editors), Biological Pest Control. The Glasshouse Experience. Blandford Press, Dorset, pp. 153--161. Trumble, J.T., 1985. Integrated pest management of Liriomyza trifolii: influence of avermectin, cyromazine and methomyl on leafminer ecology in celery. Agric. Ecosystems Environ., 12 : 181--188.
287
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
Short Communication THE POTENTIAL OF HEPTENOPHOS AND MK-936 PESTICIDES FOR CONTROL OF MINOR PESTS IN INTEGRATED PEST CONTROL PROGRAMMES UNDER GLASS
N.L. HELYER and M.S. LEDIEU
Glasshouse Crops Research Institute, Worthing Road, Littlehampton BN1 7 6LP (Great BHtain) (Accepted for publication 14 May 1986)
ABSTRACT
Helyer, N.L. and Ledieu, M.S., 1986. The potential of heptenophos and MK-936 pesticides for control of minor pests in integrated pest control programmes under glass. Agric. Ecosystems Environ., 17: 287--292. In non-replicated glasshouse experiments with tomatoes and cucumbers, the pesticide heptenophos (Hostaquick 55% ec.) with its systemic and short persistence properties was found to be useful in integrated programmes where biological control of major pests was used, but chemical control of minor pests such as leafhopper (Hauptidia maroccana) and thrips (ThHps tabaci) was necessary. A spray interval of 10 days was considered to be the best compromise between kill of pests and depletion of natural enemies. The pesticide MK-936 (avermectin B1) was disruptive to biological control agents and ineffective against the minor pests. It is thus unsuitable for integration, but was found to be very effective as a purely chemical control agent of two-spotted mite.
INTRODUCTION
When biological control of whitefly (Trialeurodes vaporariorum) and/or two-spotted mite (Tetranychus urticae) is adopted on crops such as tomatoes and cucumbers under glass, various minor pests such as thrips (Thrips tabaci), leafhopper (Hauptidia maroccana) and leafminer (Liriomyza bryoniae) can be difficult to control without upsetting the biological control agents. A survey, c o n d u c t e d b y the Agricultural Development and Advisory Service (Gould, 1985), has assessed the usage in the U.K. (by % hectarage treated) of the two major natural enemies on heated glasshouse food crops in 1983. In cucumbers, approximately 70% of the area was treated with Phytoseiulus persimilis and 46% with Encarsia formosa, while in tomatoes the comparable figures were 17% and 35%, respectively. The range of materials which are suitable for integration is limited and, as a result, it is sometimes necessary to resort to judicious use of potentially harmful pesticides by, for instance, separating pesticides from natural enemies in either space or time (Helyer, 1985). 0167-8809/86/$03.50
© 1986 Elsevier Science Publishers B.V.
288
The work reported here was directed at extending the list of pesticides which are selective enough f o r simple integration. The materials chosen were h e p t e n o p h o s (Hostaquick 55% ec.) from Hoechst and MK-936 (avermectin B1) from Merk Sharp & Dohme. This latter is a natural product derived from the actinomycete Streptomyces avermitilis and consists of a mixture of two homologous natural products, avermectin B l a and avermectin B l b . METHODS
Five glasshouse compartments, each of 10 m z, were planted with 6 t o m a t o plants (cv. Marathon) on one side and 5 cucumber plants (cv. Corona) on the other. The plants were grown in 23-cm "whalehide" pots at a set temperature of 20°C with venting at 22°C. Plants in each compartment were similarly infested with adult pests over a 3-week period; thrips and leafhopper twice weekly at 2 per plant. Two-spotted mite was introduced by tapping apical tissue from exhausted stock plants on which the mite population had begun "webbing", over the cucumber and t o m a t o plants (young mites congregate at the apex of the plant when competition for f o o d increases). P. persimilis were introduced twice weekly for two-spotted mite control at 2 per plant, beginning 3 weeks after the first pests were introduced. All the insects were allowed to become established before pesticide treatments commenced. Leafminer and whitefly were also introduced, b u t failed to establish. One of the five compartments was a control, receiving no pesticide; two were sprayed with heptenophos (0.75 ml product 1-1, 0.0375% a.i.), one c o m p a r t m e n t weekly, the other fortnightly; the remaining two compartments received sprays of MK-936 (0.25 ml product 1:1, 0.00045% a.i.) at the same intervals. Assessments of pest and natural enemy populations were made shortly before the first pesticide application and twice-weekly thereafter. In the case of two-spotted mite and P. persimilis on cucumber plants, 25 1-cmdiameter leaf discs were removed from plants and numbers of all stages were recorded under t h e microscope. Thrips and leafhopper, on the other hand, were recorded by direct observation in situ, on the first leaf below each truss up to the fifth truss from 5 plants. Using laboratory pesticide screening methods developed at the GCRI (Ledieu, 1979; Helyer, 1982; Ledieu, 1985) the effect of MK-936 was evaluated against both adults and pupae of E. formosa. Whole plants were sprayed and leaf discs were removed over a 14-day period, adult E. formosa were caged over the leaf material and mortality was assessed daily for 4 days. Pupae or "black scales" were sprayed with MK-936 and the emerged and unemerged scales counted 3 weeks later. RESULTS
Control of two-spotted mite b y predator in the absence of pesticide was
289
achieved within three weeks of pesticide treatments being applied to other compartments (Fig. 1A). Heptenophos applied weekly resulted in complete disruption of predatory control (Fig. 1B), but when applied fortnightly control was achieved in about six weeks {Fig. 1C). MK-936 applied weekly resulted in control of two-spotted mite within three weeks of starting treatments (Fig. 1D) and thus was comparable to use of the predator alone (cf. Fig. 1A). However, numbers of predators were lower than where no pesticide had been used (Fig. 1D cf Fig. 1A). Similarly, less intensive use of MK-936 (2-week interval) resulted in rapid spider mite control, but poor multiplication of the predator (Fig. 1E). In the absence of pesticides, leafhopper numbers remained at a steady, high level throughout the experiment (Fig. 2A), while thrips underwent an initial period of multiplication before reaching a plateau (Fig. 2B). Weekly sprays of heptenophos resulted in rapid control of both leafhopper and thrips (Figs. 2A and B). Fortnightly sprays were only slightly less effective against leafhopper (Fig. 2A), but much less so against thrips (Fig. 2B). MK-936 sprays of either frequency were ineffective against leafhopper (Fig. 2C) and inadequate against thrips (Fig. 2D). 3.0
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Fig. 1. Effect of heptenophos and MK-936 on predatory control of the two-spotted mite by Phytosieulus persimilis. A, control (water sprayed); B, weekly sprays of heptenophos; C, fortnightly sprays of heptenophos; D, weekly sprays of MK-936; E, fortnightly sprays of MK-936.
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Fig. 2. E f f e c t o f d i f f e r e n t s p r a y r e g i m e ( n o n e , w e e k l y or f o r t n i g h t l y ) o n t h e c o n t r o l o f l e a f h o p p e r a n d t h r i p s b y h e p t e n o p h o s a n d M K - 9 3 6 . A, B, h e p t e n o p h o s o n l e a f h o p p e r an d thrips, r e s p e c t i v e l y , C , D , M K - 9 3 6 o n l e a f h o p p e r and thrips, r e s p e c t i v e l y .
In laboratory tests against E. formosa, MK-936 was found to be 'safe" to adults, using the criteria of Helyer (1982). However, the effect against pupae (black scales) was classified as "harmful" since although 92% of pupae treated with one tenth of the recommended field rate showed emergence holes, all the newly emerged adults were lying dead in the immediate vicinity of their pupal cases. Due to limitations of glasshouse space it was not possible to replicate the treatments and, thus, apply normal statistical tests. However, in the early stages of the experiment, when plants and pest populations were still separate, the effects were consistent from plant to plant. Also, where appropriate, the findings confirm previous experimentation (Ledieu, 1979). DISCUSSION
Heptenophos, with its systemic activity and short persistence, appears an ideal candidate for integration. It has been shown in previous work to be harmful to adults of E. formosa, but only persists for a period of about 4 days. When sprays were repeated weekly (Ledieu, 1979) E. formosa was able to control a whitefly infestation, although control was achieved more slowly than when no pesticide was used. Whereas fortnightly applications of heptenophos controlled leafhoppers reasonably well, they were not frequent enough to give adequate control of thrips. The sharp peaks in leafhopper numbers, separated by samples where none were found, suggests that this may be a reflection of the rate of development of the pest rather than efficacy of the chemical. If timing
291
of the sprays was such that susceptible stages of leafhoppers, but hardy ones of thrips, were present when sprays were applied, results such as those o b t a i n e d would be expected. On the other hand, had other spray intervals been chosen, the opposite results might have ensued. There may be much to be gained from careful study of the susceptibility of different stages of the life cycle to a pesticide in order to ascertain the best spray programme. To achieve adequate control of both leafhopper and thrips, heptenophos should be applied weekly. However, this results in severe reduction in predator efficiency so a compromise must be struck between the effect on the predator and the control of pests. Application of heptenophos at 10-day intervals would probably permit acceptable predator activity and still provide reasonable control of thrips and leafhopper. On the basis of this work, h e p t e n o p h o s n o w has Pesticide Safety Precautions Scheme clearance for leafhopper control on tomatoes and cucumbers with a 14-day spray interval and is n o w in commercial use. MK-936, on the other hand, was not only ineffective against both minor pests tested, b u t also had a deleterious effect on the two major natural enemies used in integrated control programmes. Thus, this material is of little value to anyone practising integrated control in tomatoes or cucumbers. The results of the tests on E. formosa adults and pupae indicate that the harmful nature of MK-936 to this parasite is n o t due to contact action, b u t results from ingestion. However, MK-936 showed good activity against the major pests, performance against two-spotted mite being evident in the results given above (also Green and Dybas, 1984a). Green and Dybas (1984b) have shown that weekly sprays of MK-936 give good control of Liriomyza trifolii, indicating its usefulness for leafminer control. Trumble (1985) had also used weekly sprays of MK-936 and shown suppression of L. trifolii without adverse effects on various stages of several species of leafminer parasite. L.R. Wardlow (personal communication, 1984) has shown that MK-936 will kill y o u n g whitefly larvae b u t is less effective against older larvae, pupae and adults. Thus MK-936 has a useful role as a purely chemical control b u t m a y also be used in certain integrated programmes. ACKNOWLEDGEMENTS
The authors thank T. Green and P. R o u n d for supplying the MK-936 and for sending technical information.
REFERENCES Gould, H.J., 1985. The advisory problem. In: N.W. Hussey and N. Scopes (Editors), Biological Pest Control. The Glasshouse Experience. Blandford Press, Dorset, pp. 213--219.
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