Characterization and inheritance of elevated esterases in organophosphorus and carbamate insecticide resistant Culex quinquefasciatus (Diptera: Culicidae) from Sri Lanka

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Abstract
Culex quinquefasciatus Say from Peliyagoda, Sri Lanka, has elevated esterases A2 and B2. In vitro insecticide metabolism studies on the temephos-selected Sri Lankan Cutex quinquefasciatus strain, Pel RR, showed that fenitrothion was hydrolysed more rapidly than malathion. A significantly larger amount of fenitrothion was metabolized in Pel RR compared to the insecticide susceptible Pel SS strain, but the amount of malathion metabolized in the two strains was not significantly different. There was more esterase hydrolysis of fenitrothion than oxidase or glutathione S-transferase metabolism in Pel RR, which suggests that the elevated esterases in this strain have both metabolic and sequestering functions and that the relative importance of the two roles depends on the insecticide used. Genetic crosses of the temephos resistant and susceptible strains, showed that both resistance and elevated esterase activity were inherited as semi-dominant multi-genic characters. Hydrolysis of 2-naphthyl acetate was highest in the Pel RR strain, lowest in the Pel SS and intermediate in the F1 cross of the two strains. A minor maternal effect on resistance occurred with backcrosses involving resistant (F1) females, which gave consistently and significantly lower mortalities than those involving resistant (F1) males.