A Structural Model of US Corn Farmers’ Pest Control Decisions: Rootworm Resistance in US Corn Fields

In 2009, corn farmers planting rootworm resistant (Bt-CRW) seeds experienced unexpectedly severe yield losses throughout the U.S. Corn Belt. By 2011, resistance had been reported in Illinois, Iowa, Minnesota, Nebraska, and South Dakota. In 2012, a group of twenty-two entomologists suggested that the EPA take urgent, immediate action (Porter et. al, 2012). Though the EPA held a scientific advisory panel meeting to discuss rootworm resistance in 2013, the agency did not find strong evidence of resistance. As of 2015, the agency has not taken remedial regulatory action. This study assesses the evidence that rootworms are adapting to Bt toxins. First, a novel, two-stage, damage abatement model is used to derive a non-linear, soil insecticide demand function. This demand function is estimated using repeated cross sections of data from the USDA’s Agricultural Resource Management Survey. Finally, the model’s results are used to determine whether the effectiveness of Bt-CRW seeds decreased over the course of the study period. If rootworms developed resistance, then the effectiveness of the seeds should be lowest on fields where selective pressure is the highest (i.e. on fields where Bt-CRW seeds have been planted in continuous rotations)