Current Status of Tobacco Thrips (Frankliniella fusca Hinds) Neonicotinoid Resistance in the Eastern US

Tobacco thrips (Frankliniella fusca) resistance to neonicotinoid insecticides has become a key issue for cotton producers throughout the Mid-South and Southeast. In response to this emerging issue, university and industry researchers collaborated on a regional survey of resistance to imidacloprid (Gaucho^® 600FS, Bayer CropScience) and thiamethoxam (Cruiser^® 5FS, Syngenta Crop Protection). In 2014 and 2015, a diagnostic dose bioassay was used to screen 100 thrips samples from 86 independent locations in ten states for reduced neonicotinoid sensitivity. Results of the survey showed resistance widespread, 57% and 65% of populations had reduced sensitivity to imidacloprid and thiamethoxam, respectively. Significant variation in susceptibility was observed between states in the Mid-South and Southeast. Multiple dose assays documented up to 55-fold and 39-fold resistance ratios for imidacloprid and thiamethoxam, respectively. For a subset of locations, paired populations were collected from treated and untreated host plants. Survivorship between treated and untreated host plants was not significantly different. Bioassays of these populations revealed that the outcome of diagnostic dose assays were not strongly affected by within-season thrips management activities. Overall, our results indicate that neonicotinoid resistance in the Mid-South and Southeast is now common. Stewardship of future management tools for tobacco thrips will benefit from a finer-scale documentation of local-selection factors driving insecticide resistance in cotton agroecosystems.