Effects of eight insecticides on Drosophila suzukii and its major pupal parasitoid Trichopria drosophilae

Abstract Drosophila suzukii is an important fruit pest of global significance. The combined application of insecticides and natural enemies can control D. suzukii efficiently and reduce chemical insecticide residues. The pupal parasitoid Trichopria drosophilae has been evaluated for the biological control of D. suzukii. However, little is known about the toxicity of common insecticides to T. drosophilae. In this study, the toxicity of eight common insecticides to D. suzukii as well as the effects of semi-lethal and sublethal doses on T. drosophilae were evaluated. The eight insecticides had higher toxicities to D. suzukii larvae with lower LC50 values than those for adults. Adults and larvae were sensitive to emamectin benzoate, spinetoram, lambda-cyhalothrin, abamectin, and sophocarpidine. Based on the median lethal dose (LR50) and safety factor (SF) of insecticides, lambda-cyhalothrin and imidacloprid were classified as medium risk and the other six insecticides were classified as low risk against T. drosophilae adults. Although these insecticides exhibited low toxicity to D. suzukii pupae, the exposure of pupae or larvae to chlorantraniliprole, emamectin benzoate, sophocarpidine, abamectin, azadirachtin, and spinetoram at semi-lethal and sublethal doses could decrease the parasitism or eclosion rate of T. drosophilae. These results improve our understanding of the effects of insecticide residues on T. drosophilae development and provide a basis for combined use of chemical and biological methods for the management of D. suzukii.