Using refuge plants to manage resistance evolution and crop yield in agricultural fields

The evolution of pesticide resistance in herbivores poses a significant challenge in agriculture. A refuge strategy, where farmers plant non-toxin-treated plants to promote growth of susceptible herbivore individuals near treated plants and facilitate gene exchange between susceptible and resistant individuals, has been used in resistance management. However, we know very little about the effect of spatiotemporal fluctuations in selection pressure on resistance management. Furthermore, pests show oviposition preference and habitat mating preference behaviours. However, both aspects have rarely been considered when designing resistance management strategies. Using a stochastic eco-evolutionary plant-herbivore model, we show that over a wide range of population parameters, directional changes in toxicity level and refuge frequency that reduce selection pressure for the resistance allele in the initial pest generations are much more effective for resistance management than exposing pests to a constant toxicity level and refuge frequency across pest generations. However, the exact magnitude of the effect of changing toxicity and refuge frequency relative to keeping them constant across pest generations is sensitive to underlying population parameter values. Our results show that the refuge strategy is most effective when niche choice can evolve, but habitat mating preference shows both negative and positive effects in resistance management. Thus, our results reveal a potential mechanism underlying the refuge strategy's successes in the field. We show how resistance allele dominance and resistance costs influence our observations, and discuss our results in the context of partial protection from directional selection and field resistance management.