Field evaluation of a phagostimulant for enhancing insecticide efficacy against spotted-wing drosophila (Diptera: Drosophilidae) across multiple berry crops and regions

Since its detection in the continental United States in 2008, spotted-wing drosophila (Drosophila suzukii Matsumura) has become a significant pest of thin-skinned fruits. Current management strategies largely depend on calendar-based insecticide applications, which have disrupted previously established integrated pest management programs. Alternative control tactics, such as behavioral manipulation with phagostimulants, are being explored to reduce dependence on insecticides. In this study, we evaluated the effects of adding the commercial phagostimulant Combi-protec Insect Bait Attractant on the efficacy of insecticides targeting D. suzukii. The study was conducted across 6 US states (New Jersey, Georgia, Michigan, Oregon, Maine, and New York) under field conditions using highbush blueberries, lowbush blueberries, and raspberries. Treatments were applied in the field under caged conditions in 2021 and open conditions in 2022, followed by laboratory bioassays to assess adult mortality, oviposition, and larval infestation/emergence. When adults were exposed to freshly treated materials, insecticide treatments combined with Combi-protec generally performed as well as, or better than, insecticides alone in highbush blueberries (particularly spinetoram and phosmet); however, inconsistent results were observed in lowbush blueberries and raspberries. As materials aged in the field, efficacy across treatments declined, leading to variable results. Oviposition patterns closely mirrored adult mortality, but the treatment effects on developing larvae and emerged progeny were inconsistent or negligible. Overall, Combi-protec enhanced the efficacy of insecticides against adult D. suzukii, though its benefits for subsequent life stages were inconsistent. These findings provide new insights into the potential role of phagostimulants for improving insecticide effectiveness for D. suzukii control.