COAMPLIFICATION OF ESTERASE-A AND ESTERASE-B GENES AS A SINGLE-UNIT IN CULEX-PIPIENS MOSQUITOS

In Culex pipiens mosquitoes, resistance to organophosphorous insectici des often results from increased detoxification by two types of estera ses, A and B, which are closely linked. Overproduction of all esterase s B so far investigated (B1, B2, B4, B5 and B6) is from gene amplifica tion. An esterase A gene (esterase A2) has recently been cloned from m osquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences o f three additional esterase genes from insecticide-resistant strains o f Culex pipiens originating from France and California which show at l east 93 per cent homology with the esterase A2 gene sequence. Restrict ion enzyme mapping shows that the esterase A gene lies within 2.2 kb o f the esterase B gene. In mosquitoes with overproduced esterases A2 an d B2, the amplification level of esterase A is equal to that of estera se B suggesting that the genes are coamplified. Furthermore, we show t hat in one strain with an overproduced A esterase (A1), gene amplifica tion cannot account for the increased protein level. This indicates th at overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism - the natur e of which remains to be identified.