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Bt Corn Poses “No Significant Risk” to Monarchs

A consortium of federal, university and industry scientists led by the Agricultural Research Service has completed two years of research to answer the question: Does Bt corn pose a threat to monarch butterflies? The answer, supported by science, is that there is no significant risk.

The results are discussed at length in a feature story that appears in the February issue of Agricultural Research magazine. ARS, the U.S. Department of Agriculture’s primary scientific research agency, also has a web site about the Bt corn-monarch butterfly issue at:

www.ars.usda.gov/is/br/btcorn

Bt corn is corn to which genes from the bacterium Bacillus thuringiensis have been added so the plant naturally produces proteins that protect it from insect pests such as the European corn borer.

The research found that Bt corn pollen levels usually had to be more than 1,000 grains per square centimeter to have any negative impact on monarch caterpillars, let alone mortality. Scientists have concluded that less than 1 percent of the time are monarch caterpillars in the environment exposed to levels that even come close to that magnitude.

ARS entomologist Richard Hellmich is already planning the next round of investigations. He hopes to extend the consortium’s work this summer with new collaborative studies, especially field studies, to look at whether there are any effects on monarch caterpillars from long-term or chronic exposure to Bt corn pollen.

While the data already accumulated show Bt corn pollen does not pose a threat to monarch populations, these new studies should indicate if any minor effects are possible and the nature of those effects if they occur.

ARS entomologist Leslie C. Lewis is planning to extend the work to look at whether Bt corn has any impact on non-target ground insects such as beetles. Hellmich and Lewis are both with the ARS Corn Insects and Crop Genetics Laboratory in Ames, Iowa.

You can read more about this in the February issue of Agricultural Research magazine, available on the World Wide Web.