Permethrin Resistance Profiles in a Field Population of Mosquitoes, Culex quinquefasciatus (Diptera: Culicidae)

Insecticides, especially pyrethroids, are important components in the vector-control effort. To better understand the development of resistance, the current study characterized resistance profiles in individual single-egg-raft colonies of a field population of Culex quinquefasciatus Say, HAmCq(G0). Our study, with 104 colonies derived from each of the single-egg-rafts of HAmCq(G0), indicated that the levels of resistance to permethrin in fourth instar larvae ranged from 0.4- to 280-fold compared with laboratory susceptible S-Lab larvae. We characterized the distribution of single-egg-raft colonies with different levels of resistance in the HAmCq(G0) population and found that 65% individual colonies had <10-fold levels of resistance to permethrin, 16% from 10- to 20-fold, 7% from 20- to 30-fold, and 12% >= 30-fold. We further characterized the frequency of the L-to-F kdr allelic expression of sodium channels in the single-egg-raft colonies with different levels of resistance to determine its possible role in resistance. The correlation between allelic expression and levels of resistance clearly showed the importance of L-to-F kdr mutation mediated sodium channel insensitivity in resistance development. However, our results also suggested that the sodium channel insensitivity is unlikely to be the sole mechanism and multiple mechanisms may present among the single colonies in response to insecticide resistance.