Pest munches up China fields after GM crop sprays halt

HONG KONG, May 14 (Reuters) - A once minor pest has ravaged fruit orchards and cotton fields in China after farmers stopped spraying insecticide in crops of a genetically-modified type of cotton resistant to bollworms, experts said.

China started growing Bacillus thuringiensis (Bt) cotton in 1997 because it gave better yields and stood up to bollworms, but a key fallout has been a thriving population of mirid bugs, which were earlier just an insignificant pest.

“Entire swathes of agricultural land that never had any problem with this pest are facing a major problem,” said Kongming Wu at the State Key Laboratory for Biology of Plant Diseases and Insect Pests in Beijing.

The bug had infested plantations of apples, strawberries, pears, peaches and vegetables, Wu told Reuters by telephone, adding that the problem emerged after regular insecticide spraying had been halted.

“Bollworms love to go to cotton fields in June,” he said. “So when we were cultivating normal cotton in the past, we would spray insecticides every June. That meant every June, other pests were also eradicated.

“After we started cultivating Bt cotton, we no longer needed to spray insecticides. That’s why other pests like the mirid bug are thriving in cotton fields and have become a major pest.”

In a paper published in the journal Science on Friday, Wu and his colleagues said they began monitoring cotton fields and fruit orchards in six major cotton-growing provinces in northern China -- Anhui, Henan, Hebei, Jiangsu, Shandong and Shanxi -- in 1997.

The study covered 3 million hectares of cotton and 26 million hectares of other crops grown by more than 10 million farmers.

As mirid bugs eat a wide variety of plants, the researchers warned the pest was emerging as a threat to other crops for the first time.

“Before 1997, it was never a problem. It couldn’t even be seen and we needn’t guard against it. Now we have to spray insecticide every year to fight it,” Wu said.

“In fact, from 2000, the problem was already seen in cotton fields, and from 2005 was seen in other cultivated land.”

The findings show how controlling one pest can trigger the spread of others, the scientists said, urging the need to study such scenarios before adopting large-scale farming strategies.

“We have to develop a centralised system to control it,” Wu said. “We have to study the whole ecosystem.” (Editing by Chris Lewis and Clarence Fernandez)