Bt is a naturally occurring soilborne bacterium that produces crystal-like proteins that selectively kill certain groups of insects. The protein crystals are insect stomach poisons that are activated by the insects digestive enzymes to form the toxin. Since the Bt is right in the corn plant, the only way insects are exposed to it, is eating the corn plant. Bt corn does not control feeding by most insects other than the European corn borer. Aphids, spider mites and grasshoppers will not be affected by Bt corn, although some cutworms may be suppressed.
Bt corn has little effect on beneficial insects.
There are many potential benefits to Bt Corn, the most obvious being control of the European corn borer. Other potential benefits include yield protection, reduced insecticide use, reduced control costs, proper timing of control, safety to wildlife and insect predators, reduced frequency of disease and reduced stalk lodging. There are also potential limitations to Bt corn. These include the unpredictability of corn borer densities, no guaranteed economic return, variable yield performance, marketing restrictions as a result of perceptions of transgenic crops and resistance of European corn borer to Bt. The European corn borer may have the potential to develop resistance to the Bt proteins found in Bt corn.