Integrating plant and microbial metabolites as a biorational control for striped cucumber beetle

Striped cucumber beetle (Acalymma vittatum) is a serious pest of cucurbits in the northeastern United States. Synthetic insecticides, including neonicotinoids and pyrethroids, provide fairly consistent control of adult beetles. However, there are concerns that an over-reliance on these materials threatens beneficial insects and will lead to insecticide resistance. A number of microbial metabolites have been formulated into biorational insecticides, several of which are approved for use in organic production. Spinosad is a broad-spectrum, foliar insecticide that is derived from fermentation of the naturally occurring soil bacterium Saccharopolyspora spinosa. Spinosad has relatively low toxicity towards several beneficial insect species and a novel mode of action, making it a valuable tool in resistance management. It is effective against beetles closely related to A. vittatum, including Colorado potato beetle. However, efforts to manage A. vittatum with spinosad have generally been unsuccessful. We hypothesize this failure stems from insufficient ingestion of the insecticide material, and that by integrating a cucurbitacin feeding stimulant, we could increase spinosad’s efficacy against A. vittatum. In field efficacy trials, spraying spinosad and cucurbitacin at four times the maximum labeled rate significantly reduced the number of live A. vittatum relative to untreated controls. In subsequent laboratory bioassays, we generated dose response curves for beetle mortality in response to spinosad and spinosad with cucurbitacin. Cucurbitacin significantly reduced the LC-50 of spinosad, though gender influenced the mortality response. Though further work is needed, these results suggest that integrating spinosad and cucurbitacin into baits for A. vittatum is a promising tool for pest management.