The surprising importance of modeling abundance when assessing PIP durability

Models of pesticide resistance evolution have commonly employed either a frequency-based or abundance-based approach. Particularly for a structured-refuge IRM strategy, as commonly used with PIP crops, the two approaches can deliver dramatically different assessments of the time to resistance. Drawing on general theory of source-sink evolution, we demonstrate analyitically that abundance can be necessary to describe phenomena early in the process resistance evolution, particularly for high-dose transgenic events. We then use the RAMAS IRM modeling tool to compare the behavior of abundance-based models with the dynamics of resistance predicted by a frequency-based model to explore the magnitude and meaning of their dissimilarities under block refuge and blended refuge strategies.