CHANGE IN GENETIC ARCHITECTURE RESULTING FROM THE EVOLUTION OF INSECTICIDE RESISTANCE - A THEORETICAL AND EMPIRICAL-ANALYSIS

Under selection for insecticide resistance, the spread of a major resi stance allele that has strong pleiotropic effects on life history char acters will affect the genetic architecture of fitness. A model is dev eloped showing that the spread of such an allele induces a change in t he mean and in the additive genetic variance (heritability) of the lif e history characters, and in the genetic covariance (correlation) betw een these characters. The model was tested using a quantitative geneti c study that compared, in a lepidopteran species (Choristoneura rosace ana), the genetic architecture of diapause propensity and larval weigh t within and among insecticide-free and insecticide-treated population s from the same geographical area. Significant genetic correlations be tween resistance to the insecticides and the life history traits were found within the populations, suggesting that the resistance allele(s) has pleiotropic effects on the life history characters. As resistance develops from an initial value of zero, the model predicts a positive relationship between the degree of resistance within the populations and, (1) the magnitude of the fitness costs, (2) the heritability of t he life history traits, and (3) the absolute value of-the genetic corr elations between pairs of life history traits. All these predictions w ere confirmed. Moreover, the evolution of resistance apparently affect ed the environmental variance in larval weight. Hence, the novel evolu tion of insecticide resistance appears to result in major changes in t he genetic architecture of fitness, which may limit to some extent the colonization of insecticide-treated habitats.