MICROPLATE ASSAY OF ELEVATED ESTERASE-ACTIVITY IN INDIVIDUAL PYRETHROID-RESISTANT MOSQUITOS

Involvement of esterase-mediated hydrolysis as a mechanism of pyrethro id-resistance in three species of mosquitoes, viz., Aedes aegypti, Cul ex quinquefasciatus and Anopheles stephensi was investigated by microp late assay of beta-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 result s indicate the involvement of ester hydrolysis of pyrethroids as a pre dominant mechanism of pyrethroid-resistance in the larvae of Culex qui nquefasciatus, but not in Aedes aegypti. However, a marginal role of e sterases is indicated in the larvae of Anopheles stephensi.