The Efficacy of Yeast Phagostimulant Baits in Attract-and-Kill Strategies Varies between Summer- and Winter-Morphs of Drosophila suzukii

SIMPLE SUMMARY: The winter-morph of the soft and stone fruit pest Drosophila suzukii (Matsumura), commonly called spotted wing drosophila, differs in comparison to the summer-morph in terms of its response to olfactory cues. D. suzukii is predominantly controlled using conventional insecticide applications but this is not sustainable due to emerging insecticide resistance and the withdrawal of active ingredients. Combining phagostimulant baits with insecticides can significantly reduce the amount of insecticide used whilst maintaining levels of control. Yeasts are effective phagostimulants and in combination with insecticides may control D. suzukii, but only a limited number of single yeast species have been tested. We investigated the effectiveness of single and combinations of co-fermented yeasts combined with insecticides in laboratory assays and evaluated their effectiveness as phagostimulant baits for use in Integrated Pest Management strategies to control D. suzukii. This study found that some combinations of yeasts were more effective baits that single yeasts, and that certain yeasts were more effective phagostimulants for winter- than summer-morph D. suzukii. These findings suggest that yeast phagostimulants in attract-and-kill strategies should be adjusted to target summer- and winter-morph D. suzukii for more effective control. ABSTRACT: Drosophila suzukii (Matsumura), is a globally invasive pest of soft and stone fruit. To survive winter in temperate zones it enters a reproductive diapause in a morphologically distinct phenotype. Phagostimulant baits can be combined with insecticides in attract-and-kill strategies for control. We investigated the effectiveness of single yeast species and combinations of co-fermented yeast phagostimulant baits when combined with insecticides in laboratory assays against both summer- and winter-morph D. suzukii. Candida zemplininia or Hanseniaspora uvarum + C. zemplininia combined with lambda-cyhalothrin or cyantraniliprole, and H. uvarum combined with cyantraniliprole caused significantly higher mortality in winter- compared to summer-morph D. suzukii. Additionally, lambda-cyhalothrin combined with M. pulcherrima + H. uvarum resulted in greater mortality compared to single yeasts, H. uvarum for both summer- and winter-morphs and C. zemplininia for summer-morphs. M. pulcherrima + H. uvarum with spinosad significantly reduced the time-to-kill (50%) of summer-morphs compared to insecticide alone. Most yeast-based baits were comparable in terms of attract-and-kill efficacy to Combi-protec, a commercially available bait, although M. pulcherrima or H. uvarum + C. zemplininia in with cyantraniliprole were less effective. Our study suggests that yeast phagostimulants in attract-and-kill strategies should be adjusted for summer- and winter-morph D. suzukii for more effective control.