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This is the VOA Special English Agriculture Report.
In 2008, scientists reported on a study of cotton grown in six provinces in northern China. The study involved bollworms, a major threat to cotton farmers. It also involved Bt cotton, a plant genetically engineered to resist that threat.
Bt cotton plants naturally kill bollworms. As a result, the study in China found that the cotton plants could also help protect nearby crops against damage by the insects.
Now, several researchers involved in that study have published another report in the same journal,Science. They studied the same farmlands again and confirmed the findings about bollworms.
But they also found something else. They say another kind of bug is now attacking the cotton and other crops.
The study reported on mirid populations between 1997 and 2008. The researchers also documented the use of insecticide chemicals by the Chinese farmers from 1992 to 2008.
Kongming Wu of the Chinese Academy of Agricultural Sciences in Beijing took part in both studies. He says mirids are destroying crops including cotton, apples, pears, peaches and vegetables. He says this is happening where mirids never before were a problem.
The report says the bugs invaded after farmers decreased their use of insecticides by planting Bt cotton. The scientists say their research shows that the Bt cotton has become a source of mirids. They say the population increases are related to drops in insecticide use on the cotton crop.
The genetically engineered cotton is designed to help farmers save money by decreasing the need for poisons. But the scientists say the Chinese farmers have now had to use more insecticides to fight the mirids.
Bt is a bacterium that was discovered in the early 20th century. Farmers started using it as a natural way to kill insects. Then scientists learned how to put a Bt gene into cotton plants.
Much of the cotton grown in northern China is a Bt variety made by Monsanto. Different companies produce Bt cotton. Around the world, farmers grow an estimated 16 million hectares of Bt cotton.
And that's the VOA Special English Agriculture Report, written by Jerilyn Watson. Tell us about a time when you have tried to solve one problem but unexpectedly produced another. Share your comments at voaspecialenglish.com. I'm Steve Ember.
bollworm: any of various moth caterpillars that destroy cotton bolls 棉鈴蟲
mirid: a variety of leaf bug 盲椿象
（來源：VOA 編輯：陳丹妮）
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