when planting bt corn, farmers must plant an area of refuge corn. a refuge area is an area of crops that do not contain the insecticidal genes. this refuge area is necessary is to prevent the european corn borer and other pests from developing resistance to the bt gene. insects who feed on the non-bt crops will not develop resistance, but will continue to mate with any moths that survive after eating the genetically-modified corn. it is rare for an insect to survive after eating bt corn, but when these resistant individuals mate with moths from the refuge area, the offspring they produce will still be susceptible to the toxin. studies on the dispersal of european corn borers found that planting refuge corn within a half-mile of bt crops prevents resistance.