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United States Department of Agriculture

Agricultural Research Service

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Butterflies and Bt corn
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Butterflies and Bt corn. Allowing Science to Guide Decisions.
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EPA approves Bt corn commercialization

The U.S. Environmental Protection Agency (EPA) regulates all pesticides and pest control agents to ensure that their use causes no unreasonable adverse effects on the environment or non-target organisms. This includes crop varieties genetically modified to express proteins that protect the plant from insects or other pests. Such “registration” is granted by EPA only after the agency has data to answer specific questions about safety.

Bt corn is enhanced through biotechnology to protect against insect pests. Its built-in insect protection comes from a naturally occurring microorganism called Bacillus thuringiensis or “Bt.” The protein produced by Bt corn selectively targets caterpillars within the order of Lepidoptera. This order includes several moth species harmful to corn, as well as other non-target butterfly species such as the monarch. The primary target is the European corn borer, a moth caterpillar that feeds on cornstalks and ears. Yield losses and the cost of controlling the European corn borer are staggering, estimated at more than $1 billion annually.

Prior to the registration of Bt corn, EPA examined risk assessment data to evaluate the potential effects on a wide range of organisms, including birds, aquatic invertebrates, honey bees, ladybird beetles, earthworms and other non-target organisms.

EPA concluded that “the Agency can foresee no unreasonable adverse effects” to non-target organisms, including butterflies (U.S. EPA, 1995).

This EPA conclusion – that non-target butterflies would not be adversely impacted – was based on knowledge that butterfly or caterpillar exposure to Bt corn in the environment would be low. Exposure would be limited to caterpillars developing on weeds within cornfields or very near to cornfields during pollen shed. The fact that pollen moves only a short distance away from cornfields also would limit exposure, as well as the low concentration of milkweeds typically found in cornfields.

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Entomologist Les Lewis (left) and technician Keith Bidne observe a group of newly emerged monarch butterflies.

“Although the EPA tested Bt corn or pollen on ‘representative organisms’ rather than all non-target organisms, we believe the EPA based its decision to register this product on sound science and well-reasoned assumptions.”

— Shelton & Sears, 2001

 

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Last Modified: 12/20/2014
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