ESTERASE POLYMORPHISM IN INSECTICIDE SUSCEPTIBLE POPULATIONS OF THE MOSQUITO CULEX-PIPIENS

Gene amplification involving a particular haplotype has been found at the esterase B locus of mosquitoes from various countries. This simila rity has been explained by a unique amplification event followed by mi gration and selection by organophosphate (OF) insecticides. This assum es that the polymorphism of non-amplified esterase haplotypes is so la rge that the chance of independent amplification in two distinct popul ations is negligible. In order to test this assumption, three suscepti ble populations from northern Europe were sampled and analysed for est erase and haplotype polymorphism. At the protein level, 18 and 16 alle les were found for esterase A and B respectively in one French populat ion (n = 74), and 16 and 14 in an English one (n = 50). At the DNA lev el, 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 rando mly sampled from a single breeding site in Belgium were built with six restriction enzymes, 60 % of all restriction sites were different amo ng the two maps. The huge polymorphism found in northern Europe requir es specific explanations for its stability, but it considerably streng thens the hypothesis of migration of amplified haplotypes.