Comparative response of two seasonal spotted wing drosophila (Drosophila suzukii) morphs to different classes of insecticides

Drosophila suzukii Matsumura (Drosophilidae) is a devasting invasive pest affecting berry crops and cherry production throughout North America, South America, and Europe. This species has two different morph phenotypes, winter and summer morphs, which are temperature dependent. Chemical control is the most widely used management approach for managing the spotted wing drosophila, D. suzukii. Little is known regarding the differential response of the two seasonal morphs to insecticides. In this study, we identified a high number of differentially expressed genes likely involved in phase I, II, and III of detoxification pathways and other cuticular proteins in winter morphs as compared to summer morphs. Specifically, several detoxification genes (phase I: Cyp4e3, Cyp4s3, Cyp6d5, Cyp49a1, Cyp318a1; phase II: GstD10, Ugt35Bb, Ugt37b1, Ugt58Fa; phase III: Mdr65) were overexpressed more than two-fold in winter morph. Additionally, we determined the median lethal concentration, LC₅₀, values of Malathion, Cyantraniliprole, Imidan, Zeta-cypermethrin, and Spinetoram insecticides to compare the insecticide susceptibility against two seasonal morphs of D. suzukii. For most of the pesticides tested, there were no differences between the LC₅₀ values, between summer and winter morphs, however, we found that winter morph exhibited an LC₅₀ value of Spinetoram 3.7-fold, significantly higher than that of the summer morph. Overall, we demonstrated that seasonally induced different morphological phenotypes may result in different transcriptional response of phases I, II, and III of the detoxification pathways and other cuticular proteins. However, we found different responses to at least one insecticide, Spinetoram. It remains to be determined what are underlying physiological differences that lead to these changes in response to Spinetoram.