AN INSENSITIVE ACETYLCHOLINESTERASE IN CULEX-PIPIENS (DIPTERA, CULICIDAE) FROM PORTUGAL

Resistance mechanisms of a strain (PRAIAS) of northern house mosquito, Culex pipiens L., collected in Portugal in 1993, and highly resistant to organophosphates and carbamates were investigated by comparing the resistance characteristics to 3 organophosphorus (temephos, chlorpyri fos, malathion) and 1 carbamate (propoxur) insecticides in the presenc e or absence of synergists; and by determining the possible occurrence of overproduced esterases or insensitive acetylcholinesterase (AChE). The reference strain MSE from southern France, with an insensitive AC hE, was included in all analyses for comparison, For organophosphorous insecticides, resistance in PRAIAS was caused by an insensitive AChE and an increase in oxidative metabolism, although the 2nd mechanism ha s only a marginal effect. For propoxur, the insensitive AChE was the o nly resistance mechanism detected. Biochemical properties of both the French and Portuguese insensitive AChEs were similar. We cannot exclud e the possibility that PRAIAS and MSE strains possess exactly the same insensitive AChE allele.