CHARACTERIZATION OF CARBOXYLESTERASES FROM MALATHION-RESISTANT CULEX-QUINQUEFASCIATUS SAY (DIPTERA, CULICIDAE) MOSQUITOS

The activities of carboxylesterases (CaE, EC 3.1.1.1) from laboratory cultured susceptible and malathion-resistant Culex quinquefasciatus we re estimated, and esterase bands were identified by electrophores. Tot al CaE activity in malathion-resistant larvae increased significantly with different CaE substrates, i.e., naphthyl acetate, naphthyl propio nate, and naphthyl butyrate. Michaelis constant (K-m) values of CaE fo r different naphthyl ester substrates showed that naphthyl propionate and butyrate are more specific substrates for CaE than naphthyl acetat e. Arrhenius temperature plots showed decreased breakpoints for CaE fr om the malathion-resistant larvae with all three naphthyl ester substr ates studied. Polyacrylamide gel electrophoresis of partially purified CaE revealed a less intense esterase hand (B-2) in the resistant larv ae when the eletrophoretograms were stained with naphthyl butyrate. Th e possible use of these results for detection of insecticide resistanc e in mosquitoes is discussed. (C) 1997 Academic Press.