Esterase polymorphism in insecticide susceptible populations of the mosquitoCulex pipiens

Abstract

Gene amplification involving a particular haplotype has been found at the esterase B locus of mosquitoes from various countries. This similarity has been explained by a unique amplification event followed by migration and selection by organophosphate (OP) insecticides. This assumes that the polymorphism of non-amplified esterase haplotypes is so large that the chance of independent amplification in two distinct populations is negligible. In order to test this assumption, three susceptible populations from northern Europe were sampled and analysed for esterase and haplotype polymorphism. At the protein level, 18 and 16 alleles were found for esterase A and B respectively in one French population (n = 74), and 16 and 14 in an English one (n = 50). At the DNA level, 24 alleles at the esterase B locus were detected in a sample of 72 mosquitoes from one population, with the use of only one restriction enzyme (EcoR V). Restriction maps of two nonamplified haplotypes randomly sampled from a single breeding site in Belgium were built with six restriction enzymes. 60% of all restriction sites were different among the two maps. The huge polymorphism found in northern Europe requires specific explanations for its stability, but it considerably strengthens the hypothesis of migration of amplified haplotypes.

Insecticide resistance in the mosquito Culex pipiens: What have we learned about adaptation?

“…At the Ester locus, independent amplifications have occurred only a few times, as indicated by the known list of distinct amplified alleles (Table 2) and the huge polymorphism existing among non-amplified alleles (Raymond, Qiao & Callaghan, 1996). This relatively low number of independent de novo amplification events, inventoried on a world scale for a pest species with large population sizes, indicates that there is somehow a limitation on the rate of occurrence of new advantageous mutation.…”

Quantitative analysis of gene amplification in insecticide-resistant Culex mosquitoes

“…The most prevalent amplified esterase genes are estα2" and estβ2", which occur worldwide [1,14,15]. Some insects have variants of estβ1 (alleles of estβ2") that might or might not have a co-amplified estα3 [16].…”

Polymorphisms and fluctuations in copy number of amplified esterase genes in Culex pipiens mosquitoes

“…Sequences in and around the A2 and B2 alleles were mapped using RFLP techniques. Previous work by Raymond et al (1991Raymond et al ( , 1996 demonstrated that the B2 allele had spread worldwide by migration since the restriction maps collected from strains throughout four continents were identical. Similar maps of the A2 allele were constructed.…”