Detection of pyrethroid resistance associated SNPs in the Nav channel and resistance ratios in Culex quinquefasciatus female mosquitoes from Harris County, TX, USA

In Harris County, Texas, Culex quinquefasciatus is the primary vector of West Nile virus and application of synthetic pesticide to control the population is one of the methods to slow the disease transmission. However, the population control efficacy could be impeded by the development of insecticide resistant mosquito populations. Previous study analyzed knockdown resistance (kdr)-like mutation, one of the causative mutations of pyrethroid resistance, in the field-cage tested mosquitoes from different operational areas in Harris County. The result of the same genotyped, kdr-kdr or kdr-s, mosquitoes from different areas had different survival probabilities implies the involvement of other pyrethroid resistant mechanisms or the involvement of other SNPs on the voltage-gated sodium channel to increase the target site insensitivity. The W1573R located at LIII/IV can cause high pyrethroid resistance in mosquitoes, however, this mutation was not detected in any of the 49 analyzed mosquitoes from area 55, 109 and 708. Instead, primers for amplifying and sequencing exons encoded PyRI and PyRII were designed to detect other potential SNPs in mosquitoes tested in the field-cage assays. Previous result of different survival probabilities of mosquitoes from different areas also implies the possibility of mosquitoes among areas contain different resistant ratios. To understand the resistant ratios associated with the mosquito survivorships of field-cage assays, Permanone^® deposited at the 3 distances during the field-cage tests were quantified to explain the different survivorships, and the resistant ratios were determined by testing no pesticide exposed cohort mosquitoes with probit analyses.