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Corn Rootworm Transgenic Hybrids: More Questions Than Answers for 2003

December 6, 2002
Much uncertainty surrounds the potential availability of transgenic corn rootworm hybrids for the 2003 growing season. We continue to wait for a decision from the U.S. Environmental Protection Agency (US EPA) that would allow Monsanto Company to commercialize the first transgenic hybrids for corn rootworm management. A Scientific Advisory Panel was held in Arlington, Virginia, during August 28 to 29, 2002, to offer advice and counsel to the US EPA as part of the registration process as outlined by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The panel offered several recommendations to US EPA. Some of the key recommendations follow:

· "It was the consensus of the Panel that large-scale studies on male movement and fitness from beetles produced from both MON 863 (Monsanto's transgenic corn rootworm event) and isolines are of particular importance."

· "The Panel did not recommend developing a demarcation line between low and moderate dose. Instead it concluded that determining the impact of each transgenic event on selection intensity is important for determining appropriate refuge size."

· "The Panel concluded that the use of SS (homozygous susceptible) survival rates was sufficient to demonstrate that MON 863 is not high dose, because SS survival is so much higher than that expected at 25H the LC99 (lethal concentration to 99% of a population)."

· "The Panel differed on what percent refuge would be appropriate, conservative, and workable. The majority of the Panel members concluded that an appropriate, conservative, approach for an insect resistance management plan (IRM) plan would involve a refuge size of approximately 50%. Because important data are lacking and because grower adoption rates are likely to be low initially, these members viewed the 20% refuge as premature."

· "Other Panel members differed with the majority. A few Panel members were supportive of a 20% refuge. Their justification for supporting this figure was that it was compatible with the current refuge recommendation for Bt corn resistant to European corn borer, the 20% refuge amount would set the stage for IRM recommendations that would be compatible for both ECB and western corn rootworm, and it was noted that a simpler IRM strategy would be less confusing to growers, and ultimately would increase compliance."

· "It was the consensus of the Panel that there was not sufficient data to support in-field strips over immediately adjacent blocks or vice versa to delay resistance during a three-year period."

Other interesting portions of the Scientific Advisory Panel Meeting minutes include the following observations:

· "Overall, the majority of the Panel felt that even though there are limitations with the IRM plan, the experiments to address these questions should be conducted after commercialization. It was also pointed out that some of these experiments are already underway by members of NCR-46 (technical research committee on corn rootworms) and their associates."

· "The reason for commercializing MON 863 before conducting the above experiments is that significant benefits of the MON 863 technology over currently available options for growers would be lost if MON 863 were not commercialized. These benefits include:

1. Equivalent to or better than soil insecticides in terms of plant damage.

2. Reduced applicator, handler, and farm worker exposure to insecticides.

3. A narrow spectrum of activity could possibly eliminate or greatly reduce the environmental concerns generated by broader spectrum insecticides.

4. The technology is easy to use and does not delay planting.

5. The technology does not require special application equipment, the need for calibration, or the dispoal/return of containers.

6. Performance consistency is improved since each plant is protected and this protection is relatively unaffected by weather."

Regarding the use of soil insecticides and seed treatments, the panel offered the following suggestions:

· "It was the consensus of the Panel that soil insecticides and seed treatments targeted toward corn rootworms could be used in the refuge if significant numbers of adult beetles are still produced. This is the case with currently registered soil insecticides. However, if a highly efficacious insecticide that prevented significant adult emergence were to be used, this could have a major detrimental effect on IRM."

For additional information on the Scientific Advisory Panel recommendations regarding the use of transgenic hybrids for corn rootworms, please visit the following Web site:

Just recently, the Illinois Farm Bureau offered the following position statement with respect to the use of corn varieties that are not approved by the European Union and other "major markets" (

"The U.S. production and marketing system has had challenges meeting certain purity requirements for segregated commodities. At the same time, companies introducing new varieties have not been able to achieve approval in all of our major markets. Given the significant economic importance to Illinois agriculture of the European corn gluten market, the Illinois Farm Bureau opposes the planting of corn varieties that are not approved in the European Union and other major markets."

So as stated at the beginning of this article, more questions than answers remain concerning the potential commercialization of transgenic corn rootworm hybrids for the 2003 growing season. Because so many producers have made or will soon make their seed selections, they are most likely moving ahead and not waiting for the US EPA. Consequently, soil insecticide use will remain very high on continuous and rotated corn acres in many areas of the Corn Belt. With crop rotation not performing adequately as a pest management tool for western corn rootworms in the eastern Corn Belt and resistance to methyl-parathion and carbaryl confirmed in Nebraska, producers are eager to use a new pest management tool for this significant insect pest. However, even if the US EPA approves a conditional registration for transgenic corn for rootworm control for the 2003 growing season, producers in Illinois may not benefit from its availability right away.--Mike Gray and Kevin Steffey

Author: Kevin Steffey Mike Gray

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

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