LIFE-HISTORY COSTS ASSOCIATED WITH THE EVOLUTION OF INSECTICIDE RESISTANCE

Strong directional selection for insecticide resistance in agricultura l systems favours an increase in frequency of resistance allele(s). Pr ovided that the resistance allele(s) has negative pleiotropic effects on life-history traits, such a change in gene frequency is expected to result in a progressive increase in fitness costs. Therefore, negativ e impacts on fitness components should increase with the degree of res istance across populations exposed to different insecticide regimes. T he aim of this study was to assess whether selection for insecticide r esistance resulted in such an evolutionary change in life-history trai ts in the obliquebanded leafroller, Choristoneura rosaceana. Within a local geographic area there was significant variation in pesticide res istance. Compared with unsprayed populations, which were highly suscep tible to pesticides, resistant populations had lower 16 day live mass, smaller pupal mass, and longer development time. Thus, in C. rosacean a pesticide resistance is associated with life-history costs. This sug gests that an alternation of insecticides to which the obliquebanded l eafroller is not resistant could be a valuable strategy to manage this species. There were also significant across-population correlations b etween the fitness components and resistance. These relations may illu strate a mechanism that can limit evolutionary responses of population s by natural selection.