POPULATION-STRUCTURE AND DYNAMICS OF SELECTED GENES IN THE MOSQUITO CULEX-PIPIENS

To determine the outcome of the combined effects of gene flow, genetic drift, and selection on the evolution of insecticide-resistance genes in the mosquito Culex pipiens, samples were collected along three tra nsects crossing treated and nontreated areas in northern Spain and sou thern France. Electrophoretic polymorphisms of five presumably neutral genes disclosed that differentiation among samples was low, and that both Wright F-statistics and Slatkin private-alleles methods provided a high estimate for Nm. In contrast, there was a strong differentiatio n in the distribution of resistance genes closely associated with inse cticide treatments. These divergent situations are explained in relati on to both the very recent origin of some resistance genes that are st ill localized geographically (A2-B2 and C1), and the high fitness cost of the older and ubiquitous ones in nontreated areas (Al, A4-B4, and Ace(R)).