A prominent hypothesis about insecticide resistance is that genesof major effect play a key role in field-evolved resistance because theintensity of selection is extremely high in the field. A corollaryhypothesis is that the lower intensity of selection in laboratoryselection experiments favors polygenic control of insecticideresistance. Contrary to these hypotheses, a literature review revealedthat the intensity of selection for insecticide resistance in the fieldvaries widely and overlaps broadly with selection intensities in thelaboratory. Also contrary to these hypotheses, results from simulationsof population genetic models suggest that selection intensities typicalof laboratory selection experiments favor resistance that is conferredby major genes. Major genes dominated responses to selection forresistance across a wide range of simulated selection intensities, withand without fitness costs and refuges. The simulation results alsosuggest that the intensity of selection, rather than the number of lociconferring resistance, is central in determining rates of resistanceevolution and effectiveness of refuges.