Roles of selection intensity, major genes, and minor genes in evolution ofinsecticide resistance

A prominent hypothesis about insecticide resistance is that genes of major effect play a key role in held-evolved resistance because the intensity of selection is extremely high in the field. A corollary hypothesis is that th e lower intensity of selection in laboratory selection experiments favors p olygenic control of insecticide resistance. Contrary to these hypotheses, a literature review revealed that the intensity of selection for insecticide resistance in the field varies widely and overlaps broadly with selection intensities in the laboratory. Also contrary to these hypotheses, results F rom simulations of population genetic models suggest that selection intensi ties typical of laboratory selection experiments favor resistance that is c onferred by major genes. Major genes dominated responses to selection for r esistance across a wide range of simulated selection intensities. with and without fitness costs and refuges. The simulation results also suggest that the intensity of selection, rather than the number of loci conferring resi stance, is central in determining rates of resistance evolution and effecti veness of refuges.