Effects of Operational and Environmental Factors on Evolution of Resistance to Pyriproxyfen in the Sweetpotato Whitefly (Hemiptera: Aleyrodidae)

Pyriproxyfen has been an important insecticide used as part of an integrated pest management (IPM) program for the sweetpotato whitefly, Bemisia tabaci (Gennadius) (B biotype), in Arizona cotton. We used a simulation model to examine the effects of pyriproxyfen concentration, insecticide action thresholds, crop diversity, planting date, and pyriproxyfen decay on evolution of resistance to pyriproxyfen in B. tabaci. In the model, pyriproxyfen use was restricted to cotton with a limit of one application per season. Other model parameters were based on data from laboratory and field experiments. Whitefly population densities and the number of insecticide applications per year increased as resistance evolved. Resistance evolved slowest with a low pyriproxyfen concentration. Lower action thresholds for pyriproxyfen and higher action thresholds for insecticides other than pyriproxyfen also slowed the evolution of resistance. However, lower action thresholds for pyriproxyfen resulted in more insecticide sprays per year with a high pyriproxyfen concentration. Resistance to pyriproxyfen evolved fastest in cotton-intensive regions and slowest in multicrop regions. In regions with noncotton crops, increasing immigration to cotton slowed resistance. Resistance evolved faster with earlier planting dates, although fewer insecticide sprays were needed compared with fields planted later in the year. Faster rates of pyriproxyfen decay slowed resistance. In some cases, strategies that delayed resistance were effective from an IPM perspective. However, some strategies that delayed resistance resulted in higher population densities. Results suggest that modification of operational and environmental factors, which can be controlled by growers, could prolong the efficacy of pyriproxyfen.