Identification of Resistance Mechanisms in Culex pipiens (Diptera: Culicidae) from Southern France: Insensitive Acetylcholinesterase and Detoxifying Oxidases

Abstract

Resistance mechanisms of a strain (MSE) of Culex pipiens L., collected in southern France in 1979 and highly resistant to chlorpyrifos, were investigated by comparing the resistance characteristics to various organophosphates and carbamates in the absence or presence of synergists and determining the biochemical characteristics of four enzymes (esterases, glutathione-S-transferases, mixed function oxidases, and acetylcholinesterase) compared with a susceptible strain and a chlorpyrifos-resistant strain (S54) collected in the same area in 1960 and 1974, respectively. Chlorpyrifos resistance in S54 was due to a detoxifying esterase as previously described, whereas resistance in MSE was associated with an acetylcholinesterase insensitive to the inhibition by chlorpyrifoxon and some carbamates (propoxur, carbosulfan, and carbaryl), and with an increase of oxidative metabolism.