PLEIOTROPY OF ADAPTIVE-CHANGES IN POPULATIONS - COMPARISONS AMONG INSECTICIDE RESISTANCE GENES IN CULEX-PIPIENS

Resistance to toxicants is a convenient model for investigating whethe r adaptive changes are associated with pleiotropic fitness costs. Desp ite the voluminous literature devoted to this subject, intraspecific c omparisons among toxicant resistance genes are rare. We report here re sults on the pleiotropic effect on adult survival of Culex pipiens mut ants involved in the same adaptation: the resistance to organophosphor us insecticides. This held study was performed in southern France wher e four resistance genes sequentially appeared and increased in frequen cy in response to intense insecticide control. By repeated sampling of overwintering females through winter, we analysed the impact of each of three resistance genes on adult survival. We showed that (i) the mo st recent gene seems to be of no disadvantage during winter, (ii) the oldest affects survival in some environmental conditions, and (iii) th e third induces a constant, severe and dominant survival cost. Such va riability is discussed in relation to the physiological changes involv ed in resistance.