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[BEIJING] Chinese scientists say genetically modified (GM) cotton can not only protect the crop from a particular pest, but also fend off the pest's threat to neighbouring crops.

Wu Kongming, a professor at the Chinese Academy of Agricultural Science in Beijing, and colleagues analysed levels of cotton bollworm — a major pest to the crop — in six Chinese provinces between 1992 and 2007.

They analysed over 38 million hectares of farmland, three million hectares of which was cotton and 22 million hectares was other crops, such as corn, peanuts, soybeans and vegetables.

The researchers found that the population density of bollworm was drastically reduced after the 1997 introduction of Bt cotton — a GM crop containing an insecticide gene from a bacterium that affects pests such as bollworm.

At a news briefing in Beijing last week (17 September) ,Wu said that cotton is usually the main host for bollworm moths to lay eggsin and acts as the source for subsequent generations of the moth that infect other crops. Bt cotton decreased moth density, thus leading to reduced populations of bollworm, not only on cotton but on other host crops too.

The scientists ruled out the contribution of other factors like temperature and rainfall.

Chinese farmers often grow multiple crops together because of the limited cultivated area. So Bt cotton can be utilised in China's rural area to control diseases and pests, say the researchers.

"This work points out some very, very important issues," says Wei Wei, an associate professor at the Institute of Botany, the Chinese Academy of Sciences. "However, further work should be done to prove that cotton is the main spawning ground of the insect."

However, Wu warns that "the [cotton bollworm] may selectively evolve to seek new genes to suppress this highly toxic Bt cotton".

And while insecticide use has decreased since the introduction of Bt cotton, a new insect — mirid — has gradually replaced bollworm to become the main cotton pest.

Wu says, future research should look into mirid resistance and search for another transgenic crop to kill the pest.

Link to the full paper in Science