POLYMORPHISMS AND FLUCTUATIONS IN COPY NUMBER OF AMPLIFIED ESTERASE GENES IN CULEX-PIPIENS MOSQUITOS

In Culex pipiens mosquitoes, A2 esterase alleles are co-amplified with 82 esterase alleles in response to selection with organophosphate ins ecticides. In this study the amplified A2 and 82 sequences were compar ed between twelve strains from four continents by restriction mapping, The restriction maps were almost identical in each strain throughout 22 kb surrounding the genes, suggesting that this represents a constan t core sequence. A polymorphism was found in two strains collected fro m Egypt and Kenya in the mid 1980s. This polymorphism was present in a ll copies of the amplicon, which suggests that a mechanism of sequence homogenization was operating, i.e. concerted evolution, These two str ains were almost certainly descendants from the same population and mi gration probably occurred along the River Nile. Although the maps were almost identical in each strain, dot blotting demonstrated that ampli fication levels differed by up to 13-fold between strains, Thus the pr esence of the A2-B2 haplotype cannot be used to indicate the level of amplification or any particular degree of resistance.