Tracking the evolution of insecticide resistance in the mosquito Culex pipiens

The evolution of pesticide resistance provides some of the most striking ex amples of darwinian evolution occurring over a human life span. Identificat ion of resistance alleles opens an outstanding framework in which to study the evolution of adaptive mutations from the beginning of pesticide applica tion(1-3), the evolution of interactions between alleles (dominance(4)) or between loci (epistasis(5,6)). Here we shaw that resistance alleles can als o be used as markers to dissect population processes at a microevolutionary scale. We have focused on the antagonistic roles of selection and migratio n involved in the dynamics of local adaptation with reference to allelic fr equencies at two resistance loci in the mosquito Culex pipiens, We find tha t their frequencies follow an annual cycle of large amplitude (25%), and we precisely unravel the seasonal variation of migration and selection underl ying this cycle. Our results provide a firm basis on which to devise an ins ecticide treatment strategy that will better control the evolution of resis tance genes and the growth of mosquito populations.