VOA标准英语2008年-Study: Genetically-Engineered Cotton Protects N（在线收听）

According to a study published this week in "Science," genetically-engineered cotton planted near conventional crops may help protect the regular plants from bugs. The researchers say the finding could potentially protect a range of crops over millions of hectares. VOA's Jessica Berman reports.
　
Cotton field in Pakistan

The number one threat to cotton crops worldwide is the bollworm, a moth whose larvae feed on the plant's leaves.

Researchers responding to the threat 20 years ago genetically engineered a cotton plant that produces a toxic protein, called Bacillus thuriniegensis. The protein kills the moth larvae, but is engineered to be safe for humans and animals. Globally, an estimated 14 million hectares of so-called Bt cotton are grown today.

In a study reported this week in Science, researchers report that not only are bollworms destroyed by Bt cotton plants, but the plants appear to benefit unmodified crops that are nearby.

Chinese and American researchers monitored a number of different crops, including peanuts, soybeans, corn and vegetables, between 1992 and 2007 in six provinces in northern China (Hebei, Shandong, Jiangsu, Shanxi, Henan, and Anhui), which covered 38 million hectares of farmland.

Investigators found that three million hectares of Bt cotton planted among the other crops drove down populations of bollworm pests so much there were fewer moths to infest adjacent plants, according to Anthony Shelton an entomologist at Cornell University in Ithaca, New York and an advisor on the Science paper.

"So, basically what has happened is there has been a regional suppression of the cotton bollworm over a number of different provinces in China because this Bt cotton is acting like a sink and it is a dead end for them," he said.

While the bollworm is primarily a threat to cotton plants, there are lesser insect threats to it and surrounding crops.

Some experts, including the authors, have expressed concern that an over reliance on Bt technology has led to a reduction in the use of sprayed pesticides that are effective against a range of insects.

In particular, Shelton notes that mirids, which are leaf eating insects, are becoming a bigger problem in the Bt cotton.

"I do not want to downplay it, but at the same time when things are put into perspective, the benefits for overall pest population suppression of Bt cotton have been tremendous and the mirids are a much smaller player in the pest management program," he said.

There have been other concerns that the bollworm could become resistant to the toxin produced by Bt cotton. Shelton says that is something to watch out for.

But scientists say the success of Bt cotton in protecting unmodified crops could lead to other Bt crops such as rice.