Insecticide bioassays are frequently used to measure levels of insecticide resistance in mosquito populations, examining the ability of mosquitoes to survive exposure to insecticides. Laboratory bioassays measure insects' responses to insecticides in resistant (field) populations and laboratory susceptible strains using serial doses or concentrations across the range of >0 and <100% mortality. This protocol measures the toxicity of insecticides to mosquito larvae and determines the level of insecticide resistance. Generally, laboratory-reared mosquito larvae of known age or instar are exposed to H2O containing various concentrations of an insecticide, and the response (mortality) is recorded 24 h after the test. Larval bioassay tests can (1) identify the lethal concentrations of larvicide that cause 50% and 90% mortality (LC50 and LC90, respectively); (2) determine the diagnostic concentration needed to monitor susceptibility in mosquito larvae in the field; and (3) investigate the resistance status and the mechanisms governing insecticide resistance to a specific insecticide.
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