Molecular and behavioral studies reveal differences in olfaction between winter and summer morphs of Drosophila suzukii

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major economic pest of several fruit crops in Europe, North and South America, and other parts of the world because it oviposits in ripening thin-skinned fruits. This vinegar fly exhibits two distinct morphotypes: a summer and a winter morph. Although adaptations associated with the winter morph enhance this invasive pest's capacity to survive in cold climates, winter is still a natural population bottleneck. Since monitoring early spring populations is important for accurate population forecasts, understanding the winter morph's response to olfactory cues may improve current D. suzukii management programs. In this study, a comparative transcriptome analysis was conducted to assess gene expression differences between the female heads of the two D. suzukii morphs, which showed significant differences in 738 genes (p <= 0.0001). Out of twelve genes related to olfaction determined to be differentially expressed in the transcriptome, i.e., those related to location of food sources, chemosensory abilities, and mating behavior, nine genes were upregulated in the winter morph while three were downregulated. Three candidate olfactory-related genes that were most upregulated or downregulated in the winter morph were further validated using RT-qPCR. In addition, behavioral assays were performed at a range of temperatures to confirm a differing behavioral response of the two morphs to food odors. Our behavioral assays showed that, although winter morphs were more active at lower temperatures, the summer morphs were generally more attracted to food odors. This study provides new insights into the molecular and behavioral differences in response to olfactory cues between the two D. suzukii morphs that will assist in formulating more effective monitoring and physiological -based control tools.