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Pest resistance feared as farmers flout rules

(Tuesday, July 15, 2003 -- CropChoice news) -- Tom Clarke, Nature, 07/10/03: Nearly one-fifth of farmers in the US midwest are ignoring federal rules about how much transgenic maize (corn) they can plant, according to government figures. Experts fear that this non-compliance could encourage insects to develop resistance to the insecticide produced by the crop.

Some transgenic maize contains a gene from the bacterium Bacillus thuringiensis (Bt), which allows the corn to produce a natural insecticide. Under rules laid down by the Environmental Protection Agency, farmers who plant Bt maize must devote 20% of their acreage to non-Bt varieties. These 'refuge' areas should prevent pests from developing resistance to the insecticide, as resistant insects will breed with susceptible insects living in the refuge and dilute the trait.

But a study released last month by the Center for Science in the Public Interest (CSPI), a Washington-based pressure group, reveals that this rule is being ignored. The report describes data from the US Department of Agriculture showing that last year 19% of all Bt maize-growing farms in Iowa, Minnesota and Nebraska failed to plant the necessary refuges. No refuge at all was planted on 13% of the farms.

Most farms that broke the rule were small, planting less than 80 hectares (200 acres) of Bt maize. Farms of this size are not monitored by the Agricultural Biotechnology Stewardship Technical Committee, the industry body that monitors growing practices.

"It's just a matter of time before resistance develops," warns the report's author Gregory Jaffe, director of biotechnology projects at the CSPI. Bt maize will be rendered useless, adds Jaffe, if pests such as the European corn borer, the chief target of transgenic maize, develop resistance.

But transgenic-crop firms disagree. "This won't jeopardize the long-term effectiveness of the technology," says Eric Sachs, director of scientific affairs at biotechnology company Monsanto, based in St Louis, Missouri. Those ignoring the rules grow just 5% of Bt maize planted in the three states, he says.

Only 25% of maize grown in the midwest contains Bt, and the likelihood that non-compliance from a fraction of these farms will lead to resistance is small, agrees insect ecologist Bruce Tabashnik at the University of Arizona in Tucson. "It's unlikely that there is sufficient pressure on the insects," he says. In seven years of academic field surveys, insects resistant to Bt maize have not been documented in the United States, Tabashnik adds.

But this could change. New Bt maize, developed by Monsanto and designed to control a root pest, the maize rootworm, is due to be sown next year, and is expected to be adopted far more widely than existing Bt varieties. "Although non-compliance may not be an immediate hazard, it could lead to a serious problem in the future," says Tabashnik.

The transgenic-crop developers maintain that small farms won't pose a major problem - but they are concerned. "It's not clear that we have a problem of biological significance," says Val Giddings, vice-president for food and agriculture with the US Biotechnology Industry Organization, "but we do have a problem of regulatory significance."