Using population genetics and directed evolution to better understand insecticide resistance in Culex pipiens

The Northern House Mosquito, Culex pipiens, is a vector of West Nile virus, filariasis and avian malaria. In the Northeastern states of the USA, control of this pest depends on pyrethroid sprays, but the underlying genomic variation contributing to pyrethroid resistance is not well understood. To better understand how insecticide resistance evolves, we are currently conducting population genetics studies and a directed evolution experiment. We have collected mosquitoes from representative sites in the Northeastern USA and analysed their whole genome sequences, with an initial focus on known pyrethroid resistance markers. When comparing highly resistant mosquitoes from Suffolk, VA to moderately resistant mosquitoes collected in New Haven, CT, we found a high prevalence of homozygous mutants at the key resistance marker 1014F. An extended haplotype analysis of para revealed deletions in putative regulatory regions. Directed evolution experiments have also begun. Populations from a subset of sampling sites are established in the laboratory and subjected to pyrethroid pressure at each generation. Males and females are exposed to insecticide using a topical application. Surviving mosquitoes are then allowed to mate, blood feed and produce eggs, thereby maintaining resistant progeny over the course of 12 generations. Whole genome sequencing of the resulting highly resistant mosquitoes is expected to reveal several pathways to elevated resistance. This research is expected to advance our understanding of the genetic basis of insecticide resistance in a part of the USA where pyrethroid sprays are losing efficacy, and provide insights into the suite of genes contributing to pyrethroid resistance.