Integrating management tactics to mitigate Spodoptera frugiperda resistance in Bt corn: refuge proportions, natural parasitoids, and selective insecticide application

Different approaches have been adopted to manage Spodoptera frugiperda resistance to Bt toxins. However, studying the synergism among these practices applied directly in crop fields is a major challenge. We used a computational model to investigate how the proportion of refuge strips [crop area occupied by non-Bt corn (maize): 5%, 10%, 15%, or 20%] and the presence of naturally occurring parasitoid, affected or not by a pesticide with different selectivities applied in the field, could influence the dynamics of the resistance allele (R) in a S. frugiperda population. Our model showed that proportions of 15% and 20% of non-Bt corn, together with parasitism, led to a reduction in the initial frequency of the R allele. However, the efficiency of the parasitoid depended on the selectivity of the insecticide. Simulations with 5% non-Bt corn and 50% selectivity, or without selectivity (0%), resulted in elimination of the parasitoid. In the absence of selection pressure, S. frugiperda larvae carrying at least one copy of the R allele showed higher susceptibility to parasitization. Our findings suggest that parasitoids can potentially reduce the need for refuge zones, because they offset the reduction of non-Bt crops. Nevertheless, preservation of these benefical insects hinges upon the implementation of appropriate management practices by producers. Further investigations are warranted to corroborate these results, including the study of additional natural enemies. © 2024 Society of Chemical Industry.