Evolution of resistance under insecticide selection pressure in Culex pipiens quinquefasciatus (Diptera, Culicidae) from Martinique.

Population surveys of Culex pipiens quinquefasciatus carried out in 1991 and 1999 were compared with data collected in 1990 before the beginning of the control program against this mosquito. Larval samples collected in 1999 displayed resistance to the four tested insecticides: permethrin, propoxur, temephos, and chlorpyrifos. Temephos resistance ratio at LC50 (RR50) ranged between 8.1- and 42-fold compared with 2.9- and 4.6-fold in 1990, and chlorpyrifos RR50 ranged between 8.6- and 123-fold compared with 6.4- and 19-fold in 1990. This increased resistance to organophosphorus insecticides was associated with a sharp decrease of susceptible genotypes at two loci (Ester and ace-1), as well as to an allele replacement at the Ester locus.

Genetic differentiation of Anopheles claviger s.s. in Europe.

Two groups of Anopheles claviger sensu stricto Meigen (Diptera: Culicidae) were recently found in France, representing unclear genetic entities. To better understand this situation, sampling was extended to 13 European countries, and 47 samples were analyzed by investigating the polymorphism of 11 autosomal and 1 sex-linked allozyme loci. Genetic differentiation, as measured by F(st), between these two groups was confirmed, with no isolation by distance within each group. Among the twelve loci studied, none had diagnostic alleles. Group I is mainly located in western Europe (UK and south-west of France), and Group II covers eastern France and eastern and northern Europe. Intermediate populations, sampled at the overlapping range between them, do not display a heterozygote deficit, suggesting that these two groups are probably not genetically isolated. The origin of each group and its biological significance is discussed within the context of differentiation in refugia during recent glaciations.

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 transects crossing treated and nontreated areas in northern Spain and southern 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 differentiation in the distribution of resistance genes closely associated with insecticide treatments. These divergent situations are explained in relation to both the very recent origin of some resistance genes that are still localized geographically (A2-B2 and C1), and the high fitness cost of the older and ubiquitous ones in nontreated areas (A1, A4-B4, and AceR ).