The toxicity of permethrin to different life stages of Culex quinquefasciatus (Say) was examined in three field insecticide resistant strains, HAmCqG0, MAmCqG0, and BAmCqG0; two permethrin selected strains, HAmCqG8 and MAmCqG6; and a laboratory susceptible strain, S-Lab. The levels of tolerance to permethrin differed among the developmental stages of Culex mosquito larvae with an ascending order from first to fourth instar. A developmentally regulated pattern of permethrin resistance in Culex mosquito larvae was identified, once again increasing from first to fourth instar. Adult mosquitoes had relatively lower levels of resistance in general compared with their larval stages, suggesting that different mechanisms may be involved in the response to insecticide selection pressure between larvae and adults. Inheritance of resistance to permethrin was examined using reciprocal crosses between resistant HAmCqG8 and susceptible S-Lab strains; the resulting logarithm concentration-probit response curves for reciprocal F1 lines were similar to those for the susceptible strain, with degree of dominance values of -0.2 to -0.3, suggesting that the inheritance of permethrin resistance in Cx. quinquefasciatus is incompletely recessive. No significant difference was found in the values of LC50 and the slope of the log concentration—probit lines between reciprocal F1 lines, indicating that the resistance to permethrin was inherited autosomally. Both χ2 goodness-of-fit test and log concentration—probit line analysis on responses of backcross and self-bred progeny to permethrin indicated that permethrin resistance in the HAmCqG8 strain did not follow a monogenic gene inheritance model, revealing that permethrin resistance in Cx. quinquefasciatus is controlled by more than one gene.
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Vol. 47 • No. 6