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EPA's Regulation of Bacillus thuringiensis (Bt) Crops

May 2002

What is Bacillus thuringiensis (Bt)?

Bacillus thuringiensis, or simply Bt, is a naturally occurring soil bacterium that, when sprayed on plants, is toxic to certain pest insects. For years, farmers and home gardeners have used Bt as a microbial spray pesticide to control caterpillars, certain types of beetles, as well as mosquitoes and black flies.

More recently, scientists have developed techniques by which traits from the Bt bacterium, including its ability to resist pests, can be introduced into a plant. Specifically, scientists have identified the gene that produces the toxin in Bt and, through the use of biotechnology, have incorporated it into the genetic material of several plants. These Bt plants, which include corn, cotton, and potatoes, now synthesize their own bacterial protein to kill pests. Thus, farmers need not rely on external spraying. For example, use of conventional pesticides recommended for control of the European corn borer has dropped by about one-third since Bt corn was introduced.

Registering Bt Products

In 1995, EPA registered the first Bt plant-incorporated protectants for use in the United States. Since then, EPA has registered 11 Bt plant-incorporated protectants, although 5 of these registrations are no longer active. In October 2001, EPA extended the registration of Bt corn for an additional 7 years and the registration of Bt cotton for an additional 5 years, while leaving the registration decision for Bt potato unchange

EPA decided to extend the registrations for Bt corn and cotton after completing a comprehensive reassessment of all Bt products. Before reaching any decisions, EPA consulted with scientific advisory groups, requested outside peer review, and solicited public comment. To further ensure that we based our registration decisions on the most current health and environmental data, the Agency adhered to a review process that emphasized up-to-date scientific data and methodologies. After a nearly 2-year long review process, EPA concluded that Bt products will not pose unreasonable risks to human health or the environment. For more information on the Bt reassessment, including related documents, please visit the Bt Crops Reassessment web page.

Insect Resistance Management

The potential for insects to develop resistance to the Bt protein poses a threat to the future use of Bt plant-incorporated protectants. Because plant-incorporated protectants are recognized as a safe method of pest control, EPA has imposed management requirements on registered plant-incorporated protectants that will prevent insects from developing resistance to Bt proteins. Insect resistance management (IRM) is the term used to describe such practices. As a condition of EPA's approval of the renewed registrations of Bt corn and cotton, EPA included numerous provisions to strengthen insect resistance management. These provisions include the following items:

Planting Refuges

Another key component of IRM is the planting of refuges. An example of a refuge is a block of non-Bt corn planted near a Bt corn field. EPA requires all farmers who use Bt crops to plant a portion of their crop with such a refuge. The aim of this strategy is to provide an ample supply of insects that remain susceptible to the Bt toxin. The non-Bt refuge will greatly decrease the odds that a resistant insect can emerge from a Bt field and choose another resistant insect as a mate. The likelihood that two insects with a resistant gene will find each other and mate is greatly decreased. By preventing the pairing of resistant genes, these refuges help ensure that susceptibility is passed on to offspring.

Assessing Risk of Harm to the Monarch Butterfly

University scientists have conducted several laboratory studies during the last 2 years that raise questions about the potential risk that Bt corn pollen poses to monarch butterfly larvae and other butterfly species. Like any corn pollen, Bt pollen can blow onto milkweed leaves, which are the exclusive diet of monarch caterpillars.

While the Agency was aware of the toxicity of Bt to some species of moths and butterflies, data from other, prior studies did not suggest that Bt crops would threaten nontarget butterflies because they do not tend to inhabit areas where corn is planted. Further, because corn pollen is heavy and not easily carried long distances by the wind, EPA believed that the risk to monarchs and other nontarget butterflies was low.

After learning of the newer laboratory data, EPA required companies to conduct field studies to verify the actual risk to the butterflies. The results of these studies were published in September 2001 by the Proceedings of the National Academy of Sciences. Our scientists reviewed the monarch research and other data and have since confirmed the safety of Bt for nontarget insect species.

Monitoring StarLink Corn

Another issue raised with the introduction of Bt products came from StarLink, which is the trade name for corn genetically modified to produce a protein, Cry9C. Cry9C acts as a pesticide, protecting the plant from pests such as the European Corn Borer. Sold by Aventis CropSciences, StarLink corn was registered for use in animal feed only. EPA did not register the product for human consumption due to unresolved questions concerning StarLink's potential allergenicity.

In September 2000, some nongovernmental organizations tested taco shells and found traces of StarLink corn DNA. Confirmed by the FDA, this detection of StarLink caused a number of food companies to implement a voluntary recall of taco shells and other products manufactured with yellow corn meal.

Upon discovery of StarLink corn in processed food, the Federal Government took several steps to ensure the diversion of StarLink from the human food supply. USDA, FDA, and EPA worked to test corn grain for the presence of StarLink and to remove any potentially contaminated corn seeds from the market. Aventis CropSciences has since voluntarily withdrawn its registration for Starlink, and EPA will no longer issue such split registrations for pesticide products.

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