Improving Monitoring of Spotted Wing Drosophila (Drosophila suzukii, Diptera: Drosophilidae) in Michigan Fruit Crop

The spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is currently one of the most important invasive insects with a global distribution. Methods for detection and trapping D. suzukii have not yet been optimized for this devastating pest of berry crops and cherries. Laboratory assays quantifying alightment on sticky, odorless disks of various colors, D. suzukii consistently alighted most on red, purple, and black disks. Under field conditions, baited, red sticky sphere traps consistently captured 3-6x more D. suzukii than clear deli-cup traps baited with the same lure. In another test, baited, red sphere traps captured significantly more D. suzukii than deli-cup traps baited with a lure or with yeast sugar bait, and baited red panel traps captured significantly more D. suzukii than deli-cup traps baited with a lure in cherry orchards. In raspberry high tunnels, baited red sphere traps captured significantly more D. suzukii than deli-cup traps baited with the same lure. In cherry orchards and raspberry high tunnels, baited red panel traps and combination panel plus sphere traps captured significantly more D. suzukii than deli-cup traps and yellow panel traps when all traps were baited with the same lure. Baited red traps consistently captured more D. suzukii , demonstrating traps integrating both visual and olfactory cues are superior monitoring tools and a simple, dry trap requires far less labor and maintenance than deli-cup traps containing liquid bait. Central-trap, multiple release-recapture experiments used to interpret D. suzukii captures in a monitoring trap in tart cherry orchards revealed the plume reach was short (< 3 m) and the maximum dispersive distance for D. suzukii was about 90 m, yielding a trapping area of 2.7 ha. Capturing one D. suzukii in a monitoring trap translates to approximately 192 D. suzukii per trapping area, indicating that control actions should be implemented if the fruit is at a vulnerable stage. These data provide the first information about the dispersal distance and monitoring trap efficacy, and capture data per single monitoring trap can now be used to estimate absolute pest density in cherries. Between two seasonally induced morphs, responses of female D. suzukii to six volatiles were evaluated separately for electroantennogram (EAG) and behavioral assays. Isoamyl acetate, acetic acid and geosmin elicited significantly different responses from summer morphs compared with those of winter morphs, and winter morphs exhibited a reduced antennal response to the volatiles overall. As determined by scanning electron microscopy, summer morphs had more basiconic sensilla, but not statistically so. Geosmin and bornyl acetate elicited significantly different behavioral responses between the two morphs in no-choice tests. T-maze assays with geosmin further revealed significantly different responses between the morphs with summer morphs showing aversion and winter morphs no aversion to geosmin. Overall, these studies demonstrated the responses of two seasonally induced morphs of D. suzukii are different, and future studies are justified to further understand how these differences contribute to pest management for the two seasonal D. suzukii morphs.