P 3 - Selection Pressure for Insecticide Resistance in Major Mosquito Vectors of the Salt River Valley

Resistance to insecticides is a growing global issue in mosquito populations. It is caused by selective pressures from increasing overuse and untargeted use of insecticidal chemicals to decrease the prevalence of vector-borne diseases and of other pesticidal chemicals to hinder crop destruction and kill nuisance arthropods. Populations of Aedes aegypti in the Salt River Valley in metropolitan Phoenix, AZ, have been shown to have high levels of target-site resistance mutations at the 410, 1016, and 1534 loci of the kdr gene. However, the status of insecticide resistance in Culex spp. in the Valley is largely unknown, a quite concerning issue due to the genus’s role as the West Nile Virus vector. Insecticide resistance in Cx. spp. is thought to be primarily controlled by metabolic enzyme pathways. Here, we will present our ongoing work to determine the level and spatial distribution of pyrethroid resistance in Cx. spp. in the highly populated urban areas of the Salt River Valley. Phenotypic resistance is determined by establishing dose-response curves using topical application bioassays. Mosquitoes are further genotyped using melt-curve analysis for common kdr target-site mutations, and metabolic resistance is assessed using colorimetric enzyme activity assays. Levels of resistance will be correlated with past fogging frequency from the public health vector control program. However, public health insecticide use may not be the main driver of resistance. We will be assessing the insecticide exposure to mosquitoes from fogging in both semi-field and operational field studies to estimate the evolutionary pressures exerted by programmatic fogging.