USDA Ends Bt Corn Debate

October 21, 2002

2 Min Read
USDA Ends Bt Corn Debate


USDA Ends Bt Corn Debate

WASHINGTON--Bt corn pollen does not pose a risk to the monarchbutterfly, according to Butterflies and Bt Corn: Allowing Science to GuideDecisions (www.ars.usda.gov/sites/monarch),which was released by the U.S. Department of Agriculture's (USDA) AgriculturalResearch Service (ARS) on Oct. 2. Soon after the controversy began in 1999, ARScoordinated a workshop that included representatives and researchers from thegovernment, environmental groups and industry to determine how best to learnwhether Bt corn was toxic to the butterflies. The workshop participants posedtwo questions: 1) What is the direct toxicity of Bt pollen for caterpillars; and2) What is the likelihood that caterpillars might be exposed to that muchpollen?

A group of researchers from several universities, as well as ARS, conducted aseries of studies to answer the questions from the workshop. In order todetermine whether Bt corn pollen was harmful to natural populations of monarchbutterflies, researchers exposed caterpillars to pollen on milkweed leaves forup to five days at doses ranging up to 1,000 pollen grains/cm2 without observingany effects in terms of weight gain or mortality. By measuring pollen levels onmilkweed leaves in cornfields during pollination, researchers learned levels donot commonly exceed 1,000 grains/cm2, with mean levels commonly ranging from 10grains/cm2 to 425 grains/cm2. Based on this, and the fact that there is limitedoverlap between the period that Bt corn sheds pollen and when caterpillars arepresent, researchers concluded Bt corn does not pose a risk to the monarchbutterfly. Based on this assertion, the Environmental Protection Agency (EPA)decided to renew the registration for Bt corn for an additional seven years.

The data from this research was combined into five papers that were publishedas a special group in the Proceedings of the National Academy of Sciences.The ARS report was compiled jointly by researchers from ARS, the University ofGuelph, the University of Maryland, Iowa State University, the University ofNebraska, Purdue University, Cornell University and Monarch Watch.

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