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Recently Published Information About Bt Corn and Monarch Butterflies

October 5, 2001
Recently published scientific studies have revealed that Bt corn presents a low risk to monarch butterflies. These studies refute most of the negative statements that have been generated in the press as a result of two previously published articles:

Losey, J. E., Rayor, L. S., and M. E. Carter. 1999. Transgenic pollen harms monarch larvae. Nature 399: 214.

Jesse, L. C. H., and J. J. Orbycki. 2001. Field deposition of Bt transgenic corn pollen: Lethal effects on the monarch butterfly. Oecologia 125: 241­248.

More recently, Obrycki et al. published an article that interpreted many of the ecological issues related to Bt corn:

Obrycki, J. J., J. E. Losey, O. R. Taylor, and L. C. H. Jesse. 2001. Transgenic insecticidal corn: Beyond insecticidal toxicity to ecological complexity. BioScience 51: 353­361.

Obrycki et al. published their article, which highlights the potential negative aspects of Bt corn, before the more recent studies were published in the Proceedings of the National Academy of Sciences (PNAS).

The studies to which I am referring comprise the results of collaborative research conducted by scientists from universities and research institutions in the United States and Canada. The studies were designed to investigate the potential for any adverse effects of Bacillus thuringiensis (Bt) corn on the monarch butterfly, Danaus plexippus. Each study addressed a specific research area, and the collective results address the potential risk of Bt corn to monarchs under natural field conditions. Ecological risk is determined when both toxic effects and exposure are jointly assessed. These studies provided quantitative data from laboratory studies with different Bt proteins from different sources and from fields in which Bt corn hybrids were grown, with a variety of exposure scenarios.

Most of the research was supported by a pooled grant provided by the United States Department of Agriculture (USDA), Agricultural Research Service and the Agricultural Biotechnology Stewardship Technical Committee, and funding from the Canadian Food Inspection Agency, Environment Canada, the Ontario Ministry of Agriculture, Food and Rural Affairs, the Ontario Corn Growers Association, the Maryland Agricultural Experiment Station, and the Leopold Center for Sustainable Agriculture (Ames, Iowa).

In a nutshell, the studies provide science-based evidence that potential risks of Bt corn to monarchs are low. The explanation for this rather simple conclusion is too lengthy for this article, so I invite you to read the articles for yourself. The papers are available on-line using the following link: http://www.pnas.org/papbyrecent.shtml. Because articles are added to this site weekly, you'll need to scroll to the bottom to get to the articles that were posted on September 14, 2001. The PNAS "Early Edition" contains papers published online before they are printed. When the papers appear in print, they are removed from this feature and grouped with other papers in an issue. The publication date appears below each title, followed by the article's unique Digital Object Identifier (DOI). So, if you want to review the articles, you'll need to do it soon before they no longer are available on the Web.

Following are the authors and titles of six related articles:

Hellmich, R. L., B. D. Siegfried, M. K. Sears, D. E. Stanley-Horn, M. J. Daniels, H. R. Mattila, T. Spencer, K. G. Bidne, and L. C. Lewis. 2001. "Monarch larvae sensitivity to Bacillus thuringiensispurified proteins and pollen."

Oberhauser, K. S., M. D. Prysby, H. R. Mattila, D. E. Stanley-Horn, M. K. Sears, G. Dively, E. Olson, J. M. Pleasants, W. F. Lam, and R. L. Hellmich. 2001. "Temporal and spatial overlap between monarch larvae and corn pollen."

Pleasants, J. M., R. L. Hellmich, G. P. Dively, M. K. Sears, D. E. Stanley-Horn, H. R. Mattila, J. E. Foster, T. L. Clark, and G. D. Jones. 2001. "Corn pollen deposition on milkweeds in and near cornfields."

Sears, M. K., R. L. Hellmich, D. E. Stanley-Horn, K. S. Oberhauser, J. M. Pleasants, H. R. Mattila, B. D. Siegfried, and G. P. Dively. 2001. "Impact of Bt corn pollen on monarch butterfly populations: A risk assessment."

Stanley-Horn, D. E., G. P. Dively, R. L. Hellmich, H. R. Mattila, M. K. Sears, R. Rose, L. C. H. Jesse, J. E. Losey, J. J. Obrycki, and L. Lewis. 2001. "Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies."

Zangerl, A. R., D. McKenna, C. L. Wraight, M. Carroll, P. Ficarello, R. Warner, and M. R. Berenbaum. "Effects of exposure to event 176 Bacillus thuringiensis corn pollen on monarch and black swallowtail caterpillars under field conditions."

So, you can judge for yourself. In my opinion, these studies allay most, if not all, of the fears that have been associated with the potential negative impact of Bt corn pollen on monarch butterflies, at least for now. This is not to say that additional studies are not necessary. Nor am I suggesting that the broader ecological consequences of growing transgenic crops should be ignored. Rather, I am suggesting that reporting of issues associated with transgenic crops should be responsible and as objective as possible. Sensationalism usually does not lead to a balanced presentation of controversial issues.--Kevin Steffey

Author: Kevin Steffey


The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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