The gene, known as Bt, codes for a toxin that kills corn-munching caterpillars, including European corn borer and corn earworm.

The findings suggest measures are needed to reduce pollen spread from Bt corn to corn fields that should be Bt-free, according to the researchers.

The discovery is important because planting non-Bt corn, which is susceptible to insect attack, near Bt corn delays pest resistance to the Bt toxin. Such fields of non-Bt corn are called refuges.

However, this research indicates a need to revise the current Environmental Protection Agency guidelines for interspersing non-Bt corn with Bt, or transgenic, corn. The gene is from the bacterium called Bt--short for Bacillus thuringiensis.

"It's the first documentation of gene flow from a transgenic crop into a refuge," said Bruce E. Tabashnik, head of the entomology department at the University of Arizona in Tucson and co-author on the research paper. "This will almost certainly cause a revision of some of the regulations," adding, "I think it's a problem that once observed, recognized and accepted can be readily overcome."

Tabashnik, who works on the evolution of resistance in insects, was involved in devising the refuge guidelines. Using such biotech crops can reduce the need for chemical insecticides, he said.

"If Bt crops were grown wall-to-wall, everyone would expect resistance in insects to evolve overnight," he said. "The EPA rules say that if you grow Bt corn, you must plant a refuge of non-Bt corn for at least 20 percent of your crop."

Caterpillars that can survive on Bt corn are rare at first, and only a few resistant adult moths emerge from Bt corn fields. But refuges of non-Bt corn produce oodles of susceptible moths. The idea is that the uncommon resistant moths
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10-May-2004