Permethrin resistance variation and susceptible reference line isolation in a field population of the mosquito, Culex quinquefasciatus (Diptera: Culicidae).

This study examines the genetic variations and mechanisms involved in the development of permethrin resistance in individual mosquitoes from a field population of Culex quinquefasciatus, HAmCq(G0) , and characterizes susceptible reference lines of mosquitoes with a similar genetic background to the field HAmCq(G0) strain. Six upregulated cytochrome P450 genes, CYP9M10, CYP9J34, CYP6P14, CYP9J40, CYP6AA7, and CYP4C52v1, previously identified as being upregulated in the larvae of resistant HAmCq(G8) mosquitoes were examined in the larvae of 3 strains (susceptible S-Lab, parental HAmCq(G0) and permethrin-selected highly resistant HAmCq(G8) ) and 8 HAmCq(G0) single-egg raft colonies, covering a range of levels of susceptibility/resistance to permethrin and exhibiting different variations in the expression of A and/or T alleles at the L-to-F kdr locus of the sodium channel. The 2 lines with the lowest tolerance to permethrin and bearing solely the susceptible A allele at the L-to-F kdr locus of the sodium channels, from colonies Cx_SERC5 and Cx_SERC8, showed lower or similar levels of all 6 of the P450 genes tested compared with the S-Lab strain, suggesting that these 2 lines could be used as the reference mosquitoes in future studies characterizing insecticide resistance in HAmCq mosquitoes. This study also provides a detailed investigation of the mechanisms involved in insecticide resistance in individuals within a population: individuals with elevated levels of resistance to permethrin all displayed one or more potential resistance mechanisms-either elevated levels of P450 gene expression, or L-to-F mutations in the sodium channel, or both.