Malathion resistance conferred by a carboxylesterase in<i>Anopheles culicifacies</i>Giles (species B) (Diptera: Culicidae)

Abstract

Abstract A strain of Anopheles culicifacies Giles (species B) originally collected from Aurangabad, Maharashtra State, India, showed highly specific resistance to malathion. Homogenates of one-day-old adults metabolized 14 C-labelled malathion at a level comparable with strains of A. stephensi Liston and A. arabiensis Patton known to possess the malathion carboxylesterase resistance mechanism and at a higher rate (6.4 and 7.8 times, respectively) than malathion-susceptible strains of these species. The major metabolite obtained was malathion dicarboxylic acid, a carboxylesterase product, which suggests that this may be the principal resistance mechanism in this strain. Levels of non-specific esterase activity in larvae and adults were similar to those shown by both the susceptible and resistant strains of A. stephensi , implying that no quantitative increase in esterases had occurred. Microtitre plate assays on individual mosquitoes provided no evidence for the presence of the insensitive acetylcholinesterase resistance mechanism.