Buzz kill: Insecticide resistance in Culex mosquito populations

Insecticides play an important role in mitigating mosquito-borne disease outbreaks. However, the continued use of insecticides across sectors has raised concerns regarding selection for insecticide resistance within mosquito populations. West Nile virus (WNV) is currently the leading cause of mosquito-borne disease in the continental United States and Culex mosquitoes are key components in maintaining its natural cycle. Insecticide resistance has been reported in Culex populations worldwide requiring the development of effective resistance management approaches. Important questions regarding this include: what is the degree of resistance in different Culex mosquito populations, what mechanisms are responsible, and what are the consequences for transmission potential associated with these resistance levels? I addressed this by surveying populations throughout Illinois and determining phenotypic resistance. Assay results indicate variable resistance levels to permethrin and malathion throughout the state. Population differences in rates of knockdown resistance mutations and metabolic resistance mechanisms drive this variation in resistance. In another experiment, Culex pipiens were used in a nested parental half-sibling design to determine the importance of heritability and environmental effects on resistance. Results show that the families respond differently to the two environments indicating a genotype-by-environment interaction. Additional work determined the effects of sublethal exposure on different components of vectorial capacity after exposing larvae to permethrin. The resulting adults were used to test the probability of daily survival, the extrinsic incubation period of WNV, vector competence, and fecundity at two different temperatures. These results will enhance our understanding of insecticide resistance and exposure and can inform resistance management strategies.