Managing pesticide resistance by changing the applied dose: a modeling analysis incorporating pesticide persistence and including low-dose mixtures

Dose change is one of the main levers of pesticide resistance management. Various arguments have been made about the consequences of changing the applied dose, especially arguing against decreasing dose below the full dose because it increases the dominance of monogenic resistance and increases the speed, level, and/or likelihood of polygenic resistance. Here, using simulations and analytics of a model that explicitly incorporates pesticide persistence, the effects of changing the applied dose on resistance evolution for solo and mixture strategies are described and explained. A methodological breakthrough allows the simulations and analytics to powerfully show that decreasing dose should generally be expected to delay the evolution of pesticide resistance. While decreasing dose can increase dominance and change the level of polygenic tolerance, the critical effect of decreasing the applied dose on the evolution of resistance is the decrease in pesticide efficacy. Consequently, efficient dose mixtures, which have lower than full doses of each pesticide but have the same efficacy when mixed, are most often the winning strategy in 51% of simulations. Analytical techniques show that decreasing dose tends to delay resistance because of the incorporation of pesticide persistence across plausible scenarios involving low susceptible migration, high target efficacy, and high resistance factors. The methodological breakthrough opens the scope for incorporating the critical effects of pesticide persistence into the analysis of other resistance-management questions.