Esterases are responsible for malathion resistance in Anopheles stephensi: A proof using biochemical and insecticide inhibition studies.

Abstract

Increase in prevalence and intensity of insecticide-resistance in vectors of vector-borne diseases is a major threat to sustainable disease control; and, for their effective management, studies on resistance mechanisms are important to come out with suitable strategies. Esterases are major class of detoxification enzymes in mosquitoes, which confers protection against insecticides in causing resistance. This study was aimed at biochemical characterization of esterases responsible for malathion resistance in Anopheles stephensi mosquitoes, along with its validation through biochemical techniques and native-PAGE assays. Laboratory maintained susceptible and resistant An. stephensi mosquitoes were used for assessing the activity and effect of α - and β -esterases on malathion. Bioassay, synergist bioassay, biochemical assay and native- PAGE were employed to characterize the role of esterases in conferring malathion-resistance. Notably significant (p < 0.0001) enhancement in α - and β -esterases activity was observed with 2-fold increase in resistant An. StephensiGOA compared to susceptible An. StephensiBB. native-PAGE depicted two major bands 'a' (Rf = 0.80) and 'b' (Rf = 0.72) in susceptible An. stephensiBB , while one intense band 'b' (Rf = 0.72) was visible in resistant An. stephensiGOA. Inhibition assay revealed complete inhibition of α - and β -esterases activity in presence of 1 mM malathion in susceptible strain compared to observed partial inhibition in resistant strain on native-PAGE. This study provides a better understanding on the role of esterase enzyme (carboxylesterase) in conferring malathion-resistance in An. stephensi mosquitoes, as evident from the native-PAGE assay results. The study results could be used in characterizing the resistance mechanisms in vectors and for suggesting alternative chemical insecticide based resistance management strategies for effective vector-borne disease control.