Next generation sequencing as a tool to proactively assess the risk of insecticide resistance in Drosophila suzukii (Diptera: Drosophilidae)

The recently invasive insect pest Drosophila suzukii, commonly known as spotted wing Drosophila (SWD) is a serious threat to fruit production in the United States. The fruits damaged by D. suzukii include blueberries, blackberries, raspberries, cherries, strawberries, peaches and grapes. As an approach to proactively assess the risk of insecticide resistance development, we used RNA sequencing transcriptomics to analyze the response of D. suzukii at the gene expression level upon treatment with three different classes of chemical insecticides that are commonly applied against D. suzukii. We identified differentially expressed genes (DEGs) upon insecticide treatment in two sets of samples: (1) lab-reared D. suzukii and (2) field-collected D. suzukii that were treated with zeta-cypermethrin, spinosad and malathion as compared to untreated control. Gene Ontology (GO) enrichment analysis identified gene classes that are overrepresented in DEGs. We then focused our analyses on detoxification, receptor and defense related genes due to their known functions in conferring insecticide resistance and found that many of these genes are significantly up-regulated upon insecticide treatment, and are common between the different insecticide treatments. In general, higher number of significantly DEGs were identified in field population when compared to lab population, suggesting that field population is at higher risk for insecticide resistance and cross-resistance development. This higher potential for adaptive change in the field populations is likely due to their higher genetic diversity.