Genetic and phenotypic assessment of the insecticide susceptibility of Culex pipiens and Culex restuans in Illinois

Mosquitoes are major vectors of disease and thus a major concern for public health globally. Currently the most effective way to control for these vectors is with the use of insecticides. However, insecticide use can easily lead to the development of resistance. It is important to understand and monitor the level of susceptibility that local mosquito populations have to insecticides so that both local abatement districts and public health departments will be able to make the most informed decisions if an outbreak occurs. Culex pipiens and Culex restuans are common mosquito species found in Illinois and primary vectors of West Nile Virus. To better understand the levels of insecticide resistance of the Culex populations, egg collections were made throughout the state from 2018-2020. Collections were taken from all seven of the Illinois Department of Public Health’s main health regions. Eggs collected were reared under constant laboratory conditions and adults were tested for insecticide resistance using the CDC’s bottle bioassay protocol. Results from the bottle assays show that resistance is common in Illinois, but the degree of resistance is highly variable. To understand the importance of environmental conditions in relation to genetic variation and determining resistance to insecticides, a family comparison study was performed using Culex restuans which determined how the heritability of insecticide resistance differs by environmental conditions.