Karunaratne_1996_Pestic.Biochem.Physiol_54_4

Amplification of two carboxylesterases, Estalpha21and Estbeta1, is the major insecticide resistance mechanism in the field-collected Pel strain of the mosquitoCulex quinquefasciatus.Three colonies were selected from the Pel strain with three different insecticides. Both esterases Estalpha21and Estbeta21were partially purified from each colony and their bimolecular rate constants (ka's) for the interaction with insecticides were measured. Significant intercolony differences were observed for thekavalues suggesting that different esterase isoenzymes or mixtures of isoenzymes occur within each colony. This may be due to different proportions of the nonamplified carboxylesterases Estalpha3 and Estbeta13being present in the predominantly Estalpha21and Estbeta21preparations. An altered acetylcholinesterase mechanism, which was present at a very low initial frequency in the parental colony, was also differentially selected and contributed to the differences in resistance in the colonies. Neither glutathioneS-transferases nor monooxygenases appear to be involved in this resistance.