Pesticide resistance is on the rise in Iowa and the Midwest. Most corn and soybean farmers in the Corn Belt grow plants that have been genetically modified to express resistance to the herbicide glyphosate. In the case of corn, many hybrids have been genetically modified to express one or more Bt (Bacillus thuringiensis) proteins that are toxic to western corn rootworm, a major insect pest. The development of crops that are genetically modified to tolerate glyphosate has been tied to a substantial reduction in tillage, which has led to reduced soil erosion. The advent of Bt corn has been credited with a major reduction in the use of broad-spectrum insecticides. However, widespread and continuous use of these pest management technologies has led to selection pressure, or conditions that are conducive to the evolution of resistances to their modes of pesticide action.