DUPLICATION OF THE ACE.1 LOCUS IN CULEX-PIPIENS MOSQUITOS FROM THE CARIBBEAN

In Culex pipiens mosquitoes, AChE1 encoded by the locus Ace.1 is the t arget of organophosphorus and carbamate insecticides. In several resis tant strains homozygous for Ace.1(RR), insensitive AChE1 is exclusivel y found. An unusual situation occurs in two Caribbean resistant strain s where each mosquito, at each generation, displays a mixture of sensi tive and insensitive AChE1. These mosquitoes are not heterozygotes, Ac e.1(RS), as preimaginal mortalities cannot account for the lethality o f both homozygous classes. This situation is best explained by the exi stence of two Ace.1 loci, coding, respectively, a sensitive and an ins ensitive AChE1. Thus, we suggest that in the Caribbean a duplication o f the Ace.1 locus occurred before the appearance of insecticide resist ance at one of the two copies.