Insecticide susceptibility and carboxylesterase activity in leafminers (Diptera: Agromyzidae) and their associated hymenopteran parasitoids

• Leafminers were more tolerant to malathion than their most common parasitoids.
• Halticoptera circulus was more tolerant to malathion than other parasitoids.
• Leafminers and H. circulus exhibited high carboxylesterase activities.

Laboratory cultures of three dipteran leafminers, Liriomyza trifolii, Liriomyza sativae and Chromatomyia horticola, and their four most common hymenopteran parasitoids in Japan, Diglyphus isaea, Chrysocharis pentheus, Neochrysocharis formosa and Hemiptarsenus varicornis, were evaluated for their susceptibility to three conventional insecticides following topical application. All the leafminers were far less sensitive to malathion and moderately less sensitive to permethrin compared with the parasitoids. The marked disparity in insecticide susceptibility convincingly explains the increased abundance of leafminers in the field after applications of these insecticides. L. trifolii and C. horticola were also less sensitive to emamectin-benzoate than the parasitoids, although L. sativae was as sensitive as the parasitoids. We also evaluated the susceptibility of a more minor parasitoid species attacking leafminers in Japan, Halticoptera circulus, to malathion and it was less sensitive than the four more common parasitoid species and may, therefore, be suitable for augmentative biological control of leafminers in IPM programmes that include insecticides. In addition, carboxylesterase activity of each insect species was determined and correlations with their insecticide susceptibility discussed.

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