industry news

March 23, 2001 - 00:00

Iowa researchers say Bt corn bugs butterflies; industry takes a closer look

The experts are up in arms about new research out of Iowa State University that further validates the lethal effects of Bt transgenic corn pollen on monarch butterfly larvae. Laura C. Hansen-Jesse and John J. Obrycki of the ISU Department of Entomology released a report in the Aug. 19 Internet journal Oecologia titled "Field deposition of Bt transgenic corn pollen: lethal effects on the monarch butterfly."


In the abstract, the researchers said, "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. epidoptera: Danaidae larvae." Further, Jesse and Obrycki say "the ecological effects of transgenic insecticidal crops need to be evaluated more fully before they are planted over extensive areas."


But how much of an impact does this have on monarch populations in natural fields of Bt corn? Prior research at Cornell University by John Losey (published in the May 1999 journal Nature) found a higher mortality rate among monarch larvae that ate milkweed leaves dusted with Bt corn pollen than among those that ate non-treated leaves. Critics said the study’s controlled environment made it difficult to draw conclusions about what would occur in a natural environment.


But in the Iowa study researchers attempted to simulate a natural field environment.


The industry is still debating whether there is significance to the 20 percent mortality rate Jesse and Obrycki found from larvae feeding for 48 hours on A. syriaca naturally dusted with pollen from Bt corn plants. This figure is compared to the 3 percent mortality rate of larvae that fed on leaves with no pollen or the zero percent of larvae feeding on leaves with non-Bt pollen. The scientists planted Bt corn and placed potted milkweed plants varying distances from the edge of the Bt corn field to capture the actual pollen dispersal. The milkweed leaves were taken into a lab and monarch butterfly larvae were applied to the leaves. Larvae were also placed on milkweed leaves that had been exposed to pollen from corn that had not been genetically altered.


The National Corn Growers Association disagrees with the study’s conclusions. "While the research may demonstrate an impact on monarch larvae under controlled conditions, the findings do not support the abstract’s final conclusion that ‘transgenic insecticidal crops’ need more evaluation before being planted over extensive areas," said NCGA Chairman Roger Pine, a Lawrence, Kan., corn grower. Pine is a member of the USDA Advisory Committee on Biotechnology that advises the Secretary of Agriculture on agricultural biotechnology issues.


According to Pine the scientific findings are nothing new. "The ecological effects are not unexpected, and are in line with other studies that have been conducted," he said. "Second, these findings were based on research using a single type of Bt, not all Bt traits. The Bt used in this study is already known to express the insecticide at the highest level in its pollen. Finally, corn hybrids incorporating this type of Bt trait are not widely planted."


The NCGA said it supports the U.S. Environmental Protection Agency’s investigation into Bt corn and Bt cotton.


On Aug. 9, the EPA published a Federal Register notice announcing that it is undertaking a comprehensive scientific and public review of the current registrations for genetically engineered corn and cotton. The EPA also extended the existing registrations of Bt cotton and Bt corn plant-pesticides until Sept. 30, 2001, in order to allow ample time for this comprehensive review.


Moreover, the EPA is using this comprehensive approach to ensure that decisions are based on the best available scientific analysis, and that opportunity is provided for an open dialogue with the public regarding Bt products.


The EPA is publishing a risk assessment for public comment and seeking scientific peer review of this assessment by the Scientific Advisory Panel. In addition to seeking advice from the panel, the EPA will receive recommendations from an administration-wide biotechnology review that is led jointly by the Council on Environmental Quality and the Office of Science and Technology Policy.


The Federal Register notice will enable the EPA to incorporate broad public input in the process of regulating Bt products. Additional information and documentation is available at www.epa.gov/pesticides/biopesticides and www.epa.gov/scipoly/sap. The Federal Register notice is available at www.epa.gov/fedrgstr/.

About The Author

Trisha Korioth is associate editor of GPN.

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