Major Profesor: Dr. Patricia Pietrantonio
Culex quinquefasciatus is the prevalent vector of West Nile virus in Harris County, Texas. Mosquito population management by synthetic adulticides is the fastest approach to control disease transmission, however, the development of insecticide resistant mosquito populations could impede control efficacy. The knockdown resistance (kdr)-like mutation in Cx. quiqnuefasciatus (L982F; house fly kdr canonical mutation L1014F) causes pyrethroid insensitivity in the voltage-gated sodium (Nav) channel. To assess the influence of this kdr-like mutation on pyrethroid vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County were treated with the pyrethroid Permanone® 31-66 applied at the operational rate at three distances in field-cage tests. Subsequently females were analyzed by a diagnostic PCR using genomic DNA and newly designed primers that detected the kdr-like mutation (TTA to TTT), or by sequencing the kdr region. All susceptible Sebring strain and more than 99.9% field-collected female Cx. quinquefasciatue were killed at 30.4 m from the pyrethroid source in the tests, while 14% and 35% of field-collected females survived at 60.8 m and 91.2 m, respectively. The detecting accuracy of the diagnostic PCR for the kdr-like mutation was 97.5%. Among mosquitoes analyzed (n=1,028), less than 1% (n= 8) were s-s genotype, 18% were kdr-s genotype, and 81.2% were kdr-kdr genotype. These results indicate the wide distribution of pyrethroid resistant mosquitoes carrying the kdr-like mutation in Harris County. Statistical analyses allowed us to conclude that distance from the treatment source was a key factor influencing survivorship, but an equal survival probability for the kdr–kdr and kdr-s genotyped females was estimated by a logistic regression model. We conclude that the pyrethroid-based arboviral disease control is threatened by the widespread pyrethroid-resistant mosquito population in Harris County.