UC Riverside

Culex tarsalis is a major public health concern as it transmits viral pathogens causing encephalitis in humans, birds, and animals. This study aims to shed light on the genetic structure and insecticide resistance profiles of Cx. tarsalis populations, particularly in the western United States where it plays a key role in transmitting viruses like western equine encephalitis virus (WEEV) and St. Louis encephalitis virus (SLEV).Using restriction-site associated DNA sequencing (RADseq) data collected from 32 populations across 13 states and two locations in Canada, this research identified major clusters as: (i) Coachella, (ii) Pacific Northwest, Rocky Mountain, and coastal California, and (iii) Midwest and desert southwest. Gene flow among neighboring populations was found to be widespread, thought to be facilitated by movement of mosquitoes among adjacent populations. Prevalence of permethrin resistance in female Cx. tarsalis was explored from five field sites across two regions in Riverside County with individual mosquitoes categorized based on their survival time post-exposure diagnostic dose of permethrin. Significant variation in resistance levels between populations from the Coachella Valley and the Inland Valley were identified and could potentially be attributed to differences in insecticide usage regionally. Additionally, the impact of age and sex on susceptibility to permethrin for Cx. tarsalis was explored. Older mosquitoes exhibited lower survival rates while similar survival rates were seen between males and females. The presence of knockdown resistance mutations (kdr) was assessed from mosquitoes tested in previous bottle bioassays using melt curve analysis and sequencing. All mosquitoes displaying resistance contained at least one copy of the phenylalanine (F) mutation. The challenges in accurately identifying heterozygous genotypes using melt curve analysis was examined. Overall, this research provides valuable insights into the genetic structure and insecticide resistance profiles of Cx. tarsalis populations. Continued monitoring and research efforts are crucial for effective mosquito control strategies and the management of insecticide resistance. Moreover, this study underscores the need for innovative approaches to combat the development of resistance and mitigate public health risks associated with mosquito-borne diseases.