Studies on the Mechanisms of Organophosphate Resistance in Oriental Houseflies, Musca domestica vicina MACQUART. (Diptera : Muscidae)

Abstract

In order to elucidate the organophosphate (OP) resistance mechanisms in houseflies, the natures of some enzymes related to the degradation and action of OP insecticides were investigated, i.e. the characters of the resistant strain Daisan Yumenoshima (3-Y) and the susceptible strain Lab-em-7-em (L-7) were compared. The high enzyme activities of carboxylesterase (5-fold) and glutathione S-transferase (11-fold), and the low sensitivity of acetylcholinesterase (AChE) against OP inhibitors (10- to 30-fold) were found to be the main factors of OP resistance in 3-Y strain. The level of esterase activity towards α-naphthyl acetate was almost the same for the two strains, but their level of malathion carboxyl-esterase activity was significantly different. Esterase isozymes separated by electrophoresis showed preferential substrate specificity towards α-naphthyl acetate or malathion. The altered AChE of 3-Y had only about 1.5-fold greater Km and Vmax for acetylthiocholine (ASCh) than those of the normal L-7 AChE, but a remarkable difference was found in the inhibitory parameters; the Kd value of the 3-Y AChE for fenitroxon was 85-fold greater than that of L-7.