Biopesticides

About 8 percent of land covered by genetically modified crops is planted with insect-resistant crops. Although insect-resistant crops have not been employed as widely as disease-resistant crops, there are some notable examples. These include Hessian fly resistance in wheat and European corn borer resistance in corn. Resistance to corn borers has been provided by using a naturally occurring toxin produced by Bacillus thuringiensis (BT). This bacterium has traditionally been applied to corn and other crops. Genetic engineering has allowed the toxin to be manufactured by the corn plant itself.

The most serious problem with the use of BT toxin genes has been with STARLINK corn. This variety of genetically modified corn was approved for use only as animal feed, not as human food. STARLINK corn nevertheless found its way into the food-processing industry when farmers did not keep their STARLINK corn separate from corn to be used as human food. Some grain elevator operators as well did not keep the STARLINK corn separated. The STARLINK mix-up cost the United States an estimated $5 billion of processed food that had to be destroyed because of the BT toxin restriction.

Plants that have been genetically modified to make BT toxin produce it in every cell. BT corn pollen may harm nontarget moths and butterflies, like Monarch butterflies. Milkweed leaves dusted with drifting BT corn pollen are toxic to Monarch butterfly larvae, but some corn does not naturally pollinate at the same time of the year as butterflies are in their larval stage, so the effects may not be great. The full extent to which natural populations of butterflies are affected by BT corn is not known.