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United States Department of Agriculture

Agricultural Research Service

Title: Impact of Bt Corn Pollen on Monarch Butterfly Populations: a Risk Assessment

Authors
item Sears, Mark - UNIV OF GUELPH
item Hellmich, Richard
item Stanley-Horn, Diane - UNIV OF GUELPH
item Oberhauser, Karen - UNIV OF MINNESOTA
item Pleasants, John - ISU
item Mattila, Heather - UNIV OF GUELPH
item Siegfried, Blair - UNIV OF NEBRASKA
item Dively, Galen - UNIV OF MARYLAND

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 22, 2001
Publication Date: N/A

Interpretive Summary: A collaborative research effort by scientists in several states and in Canada has produced information to develop a formal risk assessment of the impact of Bacillus thuringiensis (Bt) corn pollen on monarch butterfly populations. Information was sought on the toxic effects of Bt corn pollen and the degree to which monarch larvae would be exposed to active amounts of Bt pollen on its host plant, the common milkweed found in and around cornfields. Expression of Bt proteins differed among hybrids, and especially so in the concentrations found in pollen of different events. In most commercial hybrids Bt expression in pollen is low and laboratory and field studies show no toxic effects at any pollen density that would be encountered in the field. Other factors mitigating exposure of larvae include the variable and limited overlap between pollen shed and larval activity periods, the fact that only a portion of the monarch population utilizes milkweed stands in and near cornfields, and the current adoption rate of Bt corn at 19% of North American corn-growing areas. This two-year study suggests that the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible. This information will be useful for all stakeholders interested in the potential nontarget effects of transgenic plants.

Technical Abstract: A collaborative research effort by scientists in several states and in Canada has produced information to develop a formal risk assessment of the impact of Bacillus thuringiensis (Bt) corn pollen on monarch butterfly populations. Information was sought on the toxic effects of Bt corn pollen and the degree to which monarch larvae would be exposed to active amounts of Bt pollen on its host plant, the common milkweed found in and around cornfields. Expression of Cry proteins, the active toxicant found in Bt corn tissues, differed among hybrids, and especially so in the concentrations found in pollen of different events. In most commercial hybrids Bt expression in pollen is low and laboratory and field studies show no toxic effects at any pollen density that would be encountered in the field. Other factors mitigating exposure of larvae include the variable and limited overlap between pollen shed and larval activity periods, the fact that only a portion of the monarch population utilizes milkweed stand in and near cornfields, and the current adoption rate of Bt corn at 19% of North American corn-growing areas. This two-year study suggests that the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible.

Last Modified: 4/20/2014
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