ABSTRACT
Involvement of esterase-mediated hydrolysis as a mechanism of pyrethroidresistance in three species of mosquitoes, viz., Aedes aegypti, Culex quinquefasciatus and Anopheles Stephensi was investigated by microplate assay of β-esterases in individual larva and adult female and male mosquitoes. Assuming an absorbance value of 0·4 and above at 555 nm as the threshold level of elevated esterase activity which confers resistance, frequency distributions of such individual test mosquitoes were constructed in resistant and susceptible populations. The results indicate the involvement of ester hydrolysis of Pyrethroids as a predominant mechanism of pyrethroid-resistance in the larvae of Culex quinquefasciatus but not in Aedes aegypti. However, a marginal role of esterases is indicated in the larvae of Anopheles stephensi.