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

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Abstract
To elucidate the organophosphate (OP) resistance mechanism in houseflies, the nature of some enzymes related to the degradation and action of OP insecticides were invetigated, i.e., the characters of the resistant strain Daisan Yumenoshima (3-Y) and the susceptible strain Lam-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 the main factors of OP resistance in the 3-Y strain. The level of esterase activity towards .alpha.-naphthyl acetate was almost the same for the 2 strains, but their level of malathion carboxylesterase activity was significantly different. Esterase isozymes separated by electrophoresis showed preferential substrate specificity towards .alpha.-napthyl acetate or malathion. The altered AChE of 3-Y had only .apprx. 1.5-fold greater Km and Vmax for acetylthiocholine (ASCh) than those of the normal L-7 AChE, but a difference was found in the inhibitory parameters; the Kd value of the 3-Y AChE, but a 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.