Parker_1991_Pestic.Biochem.Physiol_41_305

Eight esterases identified using native polyacrylamide gel electrophoresis were characterized in a susceptible and an organophosphate-resistant strain of Lucilia cuprina. Developmental profiles and tissue distributions were determined for all eight esterases and substrate and inhibitor specificities were also determined for six of them. Esterases E1 and E2 were isozymes of acetylcholinesterase, with E1 present throughout development and E2 largely confined to adults. Esterases E8, which was mainly confined to the neuromuscular and digestive tissues of early larvae, and E7, which was only recovered from 2- to 3-day-old adults, were not abundant enough for biochemical analysis. E4 and E13, classified as carboxylesterases, were only moderately sensitive to inhibition by organophosphates and found mainly in hemolymph. E3 and E9 were also identified as carboxylesterases but were highly sensitive to inhibition by organophosphates. They were the only enzymes found to differ between the two strains, both being detected only in the organophosphate-susceptible strain. In this strain they were both abundant in pupae, and E3 was also abundant in larvae and sexually mature adults, localized mainly in digestive tissues and the adult reproductive tract. The inhibitor, developmental, and tissue specificities of E3 all support genetic data reported previously that E3 is encoded by the major organophosphate resistance locus, ROP-1. While genetic data are not available for E9, its concentration in pupae suggests that it is unlikely to confer major gene resistance in feeding stages of L. cuprina.