Monitoring Culex mosquito resistance to pyrethroids: within-population variation in response informs modifications of the time-response CDC Bottle Bioassay

Resistance to pyrethroid insecticides in Culex pipiens and Cx. tarsalis is a growing problem in California, where these mosquitoes are the primary vectors of West Nile virus. Many of the state’s 60 local mosquito and vector control agencies use the time-response CDC Bottle Bioassay to detect and track pyrethroid resistance.  It is essential that these agencies have a reliable and accurate method to determine resistance in their local mosquito populations. This study evaluates population variation in pesticide response to further refine the CDC Bottle Bioassay and identify the replication necessary to collect reproducible data about pesticide resistance over time.  Test populations included field-collected Culex mosquitoes as well as colony populations lacking any known history of exposure to pyrethroid insecticides.  These data will help improve future resistance monitoring programs.