Abstract: Three susceptible mosquito populations from China were analyzed for esterase haplotype polymorphism by starch gel electrophoresis and RFLP analysis. At the protein level, 2 and 3 alleles were found for esterase α and β respectively in a Culex tritaeniorhynchus population (n=54), at the DNA level, with the use of one restriction enzyme (EcoRI), only 239% individuals were detected sharing a 1.3 kb single copy band which is homologous with the 1.3 kb cDNA fragment of esterase β1¹ gene. In a Anopheles sinensis population (n=50) with nonspecific esterase of low activity, 1 allele was detected for esterase α and esterase β, at DNA level, no band was found homologous to β1¹ gene. In a Culex pipiens strain of Beijing susceptible population, 5 alleles were found separately for esterase α and β at protein level, 5 alleles at the esterase β locus were detected in a sample of 15 mosquitoes from one population, with the use of only one restriction enzyme. A unique amplification event prior to extensive migration of esterase β haplotype seems the most likely hypothesis to explain the molecular data from Beijing susceptible population. This hypothesis is based on: ① the existence of much neutral polymorphism around the esterase β structural gene in susceptible mosquitoes, and ② the presence of the same amplified haplotype in populations from geographical areas far apart. The first point is supported by this study on population from Beijing. The polymorphism found around the esterase gene is probably neutral to OP insecticides, so that two distinct amplification, even of the same esterase geneallele, will probably generate two distinct amplified haplotypes. Once a haplotype has been amplified and spread in treated populations, some copies may accumulate mutations. This may generate some polymorphism in linkage disequilibrium with the other copies, as described for the β1¹ amplification. If such polymorphism is sufficiently large, it will probably allow us to reconstruct the various historical events for each of the four amplified esterases.

Key words: mosquito, esterase, organophosphate insecticide, RFLP, gene amplification, migration Author for correspondence