Modeling the dynamics of resistance evolution of Spodoptera frugiperda in Bt corn: Simulating off-season and spatial heterogeneity

Computational modeling has been widely used by entomologists to study the dynamics of insects in agricultural landscapes. In this context, we used an individual-based model with cellular automata approach (CA) to investigate how an intercropping system composed by of transgenic crops (Bacillus thuringiensis), refuge zones (non-Bt), and grasses could influence the evolution of resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae),  one of the main agricultural pests and presents populations resistant to Bt crops. Our hypothetical crop area was composed of Bt and non-Bt corn and a common grass, Cynodon nlemfuensis Vanderyst, in the system. We designed the Bt and non-Bt plants in two different arrangements: a) a seed mixture and b) alternate rows, adding grasses in adjacent areas of the field. We added the temporal planting dynamics (crop season and off-season) so that we were able to evaluate six different agricultural scenarios. We followed a crop calendar from the United States to bring our simulations close to agricultural practice. The results showed that the frequency of resistance allele is strongly related to landscape arrangements and its their dynamics. Periods of the off-season, i.e., after corn harvest, can delay the evolution of resistance in S. frugiperda. Due to insect mobility in the field, seed mixture treatment increased the frequency of resistance allele followed by alternate rows, especially when corn harvest did not occur. Spontaneous grasses can contribute to the resistance management of S. frugiperda in the field.