79 - No two assays are the same: a multi-assay assessment of pyrethroid resistance in Culex pipiens

Abstract: Insecticide resistance is an increasing problem globally, making control of arthropod-borne diseases and their vectors more difficult. Reduced susceptibility to pyrethroids has been reported in Culex pipiens across the country based on the standardized laboratory method: the CDC bottle bioassay. This bioassays uses a rapid phenotypic outcome to reveal evidence for resistance, but how this information translates to product effectiveness or the severity of resistance is unclear. Therefore, other methods for resistance monitoring are recommended. To compare CDC bottle bioassays, topical applications, and caged field trials, we conducted each resistance assay to six Culex pipiens populations the Chicago, IL region. Caged field trials were conducted using Anvil 10+10 (sumithrin + PBO), CDC bottle bioassays were conducted with sumithrin and etofenprox, and topical applications were made with sumithrin, etofenprox, and deltamethrin. All assays revealed pyrethroid resistance in all six mosquito populations, but the conclusions drawn from each assay are considerably different. Based on this data and our experience using each assay, we created a decision-making tree for mosquito control professionals which will help guide selection of the most optimal assay for resistance surveillance based on goals, needs, and resources.