Modeling the combined impacts of host plant resistance and biological control on the population dynamics of a major pest of wheat

BACKGROUND Single-tool approaches often fail to provide effective long-term suppression of pest populations, such that combining several tools into an integrated management strategy is critical. Yet studies that harness the power of population models to explore the relative efficacy of various management tools and their combinations remain rare. We constructed a Leslie matrix population model to evaluate the potential of crop resistance, acting alone or in combination with biological control, to reduce populations of the wheat stem sawfly,Cephus cinctusNorton, a major pest of wheat in North America. RESULTS Our model projections indicated that crop resistance reduced, but did not stop,C. cinctuspopulation growth, suggesting that implementing multiple management tools will be necessary for longer term control of this pest. The levels of parasitism needed to curtail population growth were much lower in model projections for resistant solid-stemmed compared with susceptible hollow-stemmed cultivars (22%versus86%). Furthermore, even when accounting for the reduced levels of parasitism observed in resistant cultivars, projected population growth rates forC. cinctuswere always lower in resistant compared with susceptible wheat cultivars. CONCLUSION Despite some empirical evidence for antagonistic interactions between resistance and biological control, our models suggest that combining these two approaches will always reduce population growth rates to lower levels than implementing either strategy alone. More work focused on integrating biological control into crop resistance breeding programs, and determining how these approaches affect performance of limiting life stages, will be important to optimize sustainable approaches to integrated pest management in this system and more broadly. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.