We used computer simulations to examine the effect of action thresholds and landscape diversity on the evolution of resistance to the insect growth regulator pyriproxyfen by the sweetpotato whitefly, Bemisia tabaci (Gennadius), biotype B (=Bemisia argentifolii [Bellows & Perring]). Lower action thresholds for using pyriproxyfen slowed the evolution of resistance, as population densities in treated fields decreased compared to densities in refuges when action thresholds were decreased. However, lower action thresholds for using pyriproxyfen resulted in more insecticide applications per year. Resistance evolved slowest in regions in which multiple crops were grown throughout the year, followed by regions with spring crops and then cotton. Resistance evolved fastest in cotton-intensive regions. These results show that non-biological factors may contribute to evolution of resistance to pyriproxyfen.