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Here We Go Again: Bt Corn and Monarch Butterflies

August 25, 2000
CBS Evening News aired yet another story about Bt corn and monarch butterflies on Monday, August 21. By Tuesday and Wednesday of that week, the Web was filled with related stories, including points and counterpoints, punches and counterpunches, pros and cons. The furor this time was generated from an article published electronically for the journal Oecologia by Laura C. Hansen Jesse and John J. Obrycki at Iowa State University. The title of the article is "Field Deposition of Bt Transgenic Corn Pollen: Lethal Effects on the Monarch Butterfly," and you can find it on the Web at Click on "Article in HTML" to get the complete article, with tables, figures, and references in separate windows. Following is the abstract of the paper:

"We present the first evidence that transgenic Bacillus thuringiensis (Bt) corn pollen naturally deposited on Asclepias syriaca; common milkweed, in a corn field causes significant mortality of Danaus plexippus L. (Lepidoptera: Danaidae) larvae. Larvae feeding for 48 h on A. syriaca plants naturally dusted with pollen from Bt corn plants suffered significantly higher rates of mortality at 48 h (20±3%) compared to larvae feeding on leaves with no pollen (3±3%), or feeding on leaves with non-Bt pollen (0%). Mortality at 120 h of D. plexippus larvae exposed to 135 pollen grains/cm2 of transgenic pollen for 48 h ranged from 37 to 70%. We found no sub-lethal effects on D. plexippus adults reared from larvae that survived a 48-h exposure to three concentrations of Bt pollen. Based on our quantification of the wind dispersal of this pollen beyond the edges of agricultural fields, we predict that the effects of transgenic pollen on D. plexippus may be observed at least 10 m from transgenic field borders. However, the highest larval mortality will likely occur on A. syriaca plants in corn fields or within 3 m of the edge of a transgenic corn field. We conclude that the ecological effects of transgenic insecticidal crops need to be evaluated more fully before they are planted over extensive areas."

Dr. Val Giddings, Vice President for Food and Agriculture of the Biotechnology Industry Organization (BIO), issued the following statement in response:

"Dr. Obrycki's research stands in the shadow of more than 20 independent studies by widely recognized scientific experts who have found that Bacillus thuringiensis (Bt) corn does not pose a significant risk to the monarch butterfly. This report considers only one small area of this complex topic and the conclusions put forward by the authors stand in stark contrast to those of the broader scientific community's research. The Oecologia paper is not truly 'field research' inasmuch as much of what it reports is based on analyses taking place in laboratory manipulations rather than field conditions. Furthermore, the paper clearly shows that larval mortality was not correlated with the number of pollen grains on the plant or the plant location within or at the edge of the field, surprises in search of an explanation. Both the United States Environmental Protection Agency and the Department of Agriculture have studied Bt corn for many years. Just last week the EPA extended the registrations of these products through the 2001 growing season. And in April, the EPA dismissed a Greenpeace lawsuit challenging the Bt plant registrations on a lack of merit, and stated '. . . available scientific data and information indicates that the cultivation of Bt crops has a positive ecological effect, when compared to the most likely alternatives.' To imply that Bt corn has a negative effect on monarch butterflies flies in the face of the fact that last year, more than 28 million acres were planted with Bt corn, an increase of approximately 40% over the previous year. In the same time period, the monarch butterfly population flourished and increased by about 30%, according to Monarch Watch."

There you have it, point and counterpoint.

I read the Oecologia article carefully, and the study reported was most definitely not what I would consider a field study. I fact, I've read that it has been referred to as a "modified field study." Although the corn and milkweed plants initially were grown outside in relatively small plots, the mortality information generated was from first-instar monarch caterpillars feeding on milkweed leaf disks (with different amounts of Bt and non-Bt corn pollen) in the laboratory. Another critical point is that although pollen deposition was measured from two types of Bt corn (from event 176 and event Bt11), mortality of monarch caterpillars exposed to field-deposited pollen was measured only for event 176 Bt corn. Less Bt toxin is expressed in event Bt11 pollen than in event 176 pollen. In addition, most of the Bt corn grown in the United States is from event MON810, an event very similar to event Bt11. The comparative amounts of Bt toxin in events 176 and MON810 are 7.1 micrograms and 0.9 micrograms Bt toxin/g fresh weight of pollen, respectively. Furthermore, the contrived density of 135 pollen grains/cm2 was considerably higher than the mean densities of pollen grains measured on milkweed plants 0.2, 1, 3, 5, and 10 meters from the edge of the Bt corn.

Quite frankly, I'm getting tired of the press making an issue out of scientific findings that don't describe the real world very well. I also am dismayed by some of the sweeping conclusions the authors of the Oecologia article made in reference to the potential effects of Bt corn pollen on monarch butterflies in the real world. I will not argue with the assertion that potential limitations of Bt corn and other transgenic crops need to be studied. However, I am disgusted with the misrepresentation of some scientific findings and the accompanying hyperbole engendered by some of the media. If scientific evidence reveals negative impacts of transgenic crops, then let the chips fall where they may. But let's be very careful about interpretations of scientific studies.--Kevin Steffey

Author: Kevin Steffey

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

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