Characterization of novel esterases in insecticide-resistant mosquitoes

In the mosquito Culex pipiens complex (Diptera: Culicidae), the amplification of carboxylesterase genes is an important mechanism providing resistance to organophosphate insecticides. Various amplified alleles at the Ester locus have been identified over the world. In this study, two newly detected Ester alleles, EsterB10 and Ester11 (including associated EsterA11 and EsterB11), coding for esterases B10 and A11-B11, respectively, are characterized qualitatively and quantitatively. A high molecular identity is observed both at the nucleotide level and at the deduced amino acid level among the known Ester alleles. Real-time quantitative PCR results suggest 2.5-fold amplification of the EsterB10 allele, 36.5-fold amplification of the EsterA11 allele, and 19.1-fold amplification of the EsterB11 allele. The ca. 2-fold difference in amplification level between EsterA11 and EsterB11 may indicate a new model for the esterase amplification. Bioassays show that these two resistant Ester alleles only can confer moderate or low resistance to the tested organophosphate insecticides.