Boosting fitness costs to sustain efficacy of Bt crops: the way forward

Fitness costs associated with resistance to Bt crops reduce the fitness of resistant individuals relative to susceptible individuals on non-Bt host plants. Costs select against resistance in refuges, and theory shows that they can delay, prevent, or reverse the evolution of resistance. We have shown in a recent review that costs are larger in pests that have evolved practical resistance to Bt crops than in pests that did not, indicating that costs have been delaying the evolution of resistance in the field. Because refuges planted by farmers are typically small, using refuge plants that can magnify costs could be useful for enhancing resistance management. We have shown in a recent review that the cost of resistance to Bt generally increases with a decline in host plant suitability. While this finding is encouraging, the effect of host plant suitability on costs is quite variable. A better understanding of how resistance mutations interact with host plant suitability to generate fitness costs will be useful for enhancing the refuge strategy and sustaining efficacy of Bt crops.