| Abstract: | Abstract The stability of resistance in the organophosphate resistant strain of Culex pipiens pallens with amplification of single gene coding for esterase B2 was determined under relaxation of insecticide selection. Insecticide resistance and amplification of esterase were both lost when strains were not homozygous for the presence of amplified gene, probably due to biological disadvantage of the esterase gene. LC50 and LC95 of chlorpyrifos for this strain were 0. 2099 mg/L and 0.9036 mg/L in the F0 generation respectively, but 0. 0207 mg/L and 2. 8027 mg/L respectively in the F16 generation. In the homozygous strain, insecticide resistance was still stable and amplification of esterase remained after 16 generations under relaxation of insecticide selection, which indicated that copy of esterase gene was not lost in the offspring of this strain. The evolution of insecticide resistance in mosquitoes is discussed. |
