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Bt branches out

In the old days of the biotechnology revolution, pests other than European corn borer (ECB) could rest easy. Insects such as black cutworm likely cackled as ECB larvae failed to slay Bacillus thuringiensis (Bt) corn.

The laughing's over.

Pioneer Hi-Bred International and Dow AgroSciences LLC are working on a transgenic Bt event, TC1507, which contains Cry1F protein. Like other Bt events, TC1507 protects corn against ECB. But its Cry1F protein also gives the event very good to excellent control of black cutworm, southwestern corn borer and fall armyworm.

“We think that the ability of products like the Cry1F to expand into the spectrum of black cutworm is a significant advantage,” says Paula Davis, entomology technology manager for Pioneer. “The Cry1F protein can obtain 75 to 80% control of black cutworm, which is higher than the level of protection planting-time insecticides give.”

TC1507 is nontoxic to humans and mammals and breaks down within seconds in the insect's digestion process. Because it is specific to Lepidoptera species such as ECB and black cutworm, Cry1F poses low risk to nontarget insects such as ladybugs.

Corn rootworm control. Pioneer and Dow scientists also are working to establish a Bt product for corn rootworm. Proteins from the Bt strain 149B1 give a high level of root protection from the western corn rootworm and the northern corn rootworm. Unlike Cry1F, 149B1 does not control other root/seed-feeding insects or adult corn rootworm beetles.

Although farmers normally use soil insecticides to control corn rootworm, the event could curtail larvae with no chemical use. “We expect it to provide as good or better protection against corn rootworm as insecticides,” Davis says.

These events are consistent with the biotechnology industry's effort to expand Bt application. For example, Monsanto plans to bring its corn rootworm-resistant Bt MaxGard hybrids to market in 2002 (see January issue, page 30). “Products in the second phase of ECB control contain proteins with a broader spectrum than in the initial phase,” says Randy Krotz, director of industry affairs for Monsanto.

The paper trail. This year Pioneer and Dow scientists will focus on event selection and characterization, regulatory submissions and breeding for the 149B1 corn rootworm event. If approval goes as expected, the firms plan to market the event commercially in 2003.

The companies also have filed approvals for the Cry1F Bt event with the USDA, FDA and EPA. Approval is expected this year.

However, it will be 2002 or 2003 by the time Pioneer and Dow market the event commercially. Davis says the firms are first seeking approvals from major corn export markets. “We will commercialize it only after we receive approval for food and feed use,” Davis says.

To prevent any potential mix-up in food channels, company officials are developing appropriate detection and reference technologies, such as ELISA test kits.

Refuge required. Growers also must commit to a resistance-monitoring program, Davis says. In northern regions, farmers will follow an industry-approved Integrated Resistance Management (IRM) plan. To grow the event, farmers will have to commit to a 20% refuge in which they treat corn with non-Bt insecticides. Growers must plant the refuge within one-half to one-quarter mile of each Cry1F field. In limited regions where growers routinely treat non-Bt corn with foliar insecticides, the refuge must be within one-quarter of a mile.

“Every person who buys the product will need to sign a contract for the 20% refuge requirement,” Davis says. “We are serious about educating growers about the refuge requirement.”

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