A stochastic, spatially-explicit computer model has been developed to simulate the evolution of resistance in cotton bollworm to Bt cotton in an agroecosystem that includes Bt and non-Bt corn. The model incorporates important aspects of insect biology and behavior, of agronomy and of agricultural operations. The model has been used to examine the effects of altering values for the parameters for which we have insufficient field data or which are inherently variable in nature.

Sensitivity analyses of the proportion of both corn and cotton fields that are planted to Bt, the initial frequency of resistance alleles, the functional dominance of resistance alleles, the fitness of susceptible larvae on Bt plants, the ratio of corn to cotton fields, and the spatial distribution of Bt crop deployment, among others, play a key role in determining the rate of evolution of resistance to Bt crops. Field determination of the mean values for these parameters, and the natural variation in these values, is crucial before predictions can be made of resistance evolution. In reducing risk, insect resistance management plans should pay heed to the consequences of uncertainty revealed by this model.