BEIJING (AP) - Rapidly evolving insect populations could render the most widely used type of bioengineered bug-resistant cotton ineffective in as little as two years, a Chinese scientist affiliated with the environmental group Greenpeace warned Monday.

Xue Dayuan, a researcher at the Nanjing Institute of Environmental Sciences, based his warning on experiments he said had been done at four state-run Chinese laboratories. Xue is a science adviser for Greenpeace, which opposes biotech crops.

Xue said Chinese researchers found it took about five years for bollworms, a cotton-munching caterpillar, to develop resistance to toxins produced by genetically modified cotton plants.

The experiments involved "Bt" cotton, which has become the most widely used genetically altered cotton since it was introduced by U.S.-based Monsanto Co. in 1996.

Xue said five years in a laboratory translates into eight-to-10 years in actual cotton fields.

"We expect similar bugs to begin appearing in the fields in two-three years," Xue told The Associated Press. "What's only a small experiment in scientists' labs now will become a huge threat to agriculture."

Chinese researchers also found the use of Bt cotton, which is designed to target bollworms, was leading to larger populations of other cotton-eating pests, he said. Xue said this could cause unpredictable disruptions to the environment.

A spokesman for Monsanto, which began selling Bt cotton in China four years ago, said the Chinese findings contradicted previous research.

"Throughout the world, there has been no evidence to date of resistance in the six years of this cotton's use," said Lee Quarles, a spokesman at the company's headquarters in St. Louis.

Bt cotton is also produced by other companies, including some in China.

It is genetically engineered to produce its own pesticide, reducing the need for chemical pesticides. In China, Bt cotton accounts for more than a third of the nation's annual 1.5 million-hectare (3.7 million-acre) cotton crop.

Xue's findings will be issued Tuesday in a report by Greenpeace.

"Scientists in China have actually found ill effects, unlike what industry has been saying," said Lo Sze Ping, a Greenpeace spokesman in China.

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