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Scientist Says Worm Has Evolved to Eat Killer Crop
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A bollworm caterpillar eats an immature cotton boll. USDA
Betsy Blaney
Bollworms seems to have evolved the ability to survive while feeding on cotton that's been genetically engineered to poison them. AP
Alex Yelich
Scientist Bruce Tabashnik says he found evidence that the bollworm is becoming resistant to the Bt toxin. University of Arizona
Day to Day, February 12, 2008 ? Evolution may be more powerful than genetic engineering.
A type of insect has developed the ability to survive while feeding on corn or cotton that's been genetically engineered to poison it, says scientist Bruce Tabashnik of the University of Arizona.
Many cotton farmers and corn growers in the United States have come to rely on Bt crops ? plants that have been spliced with a special gene, extracted from an insect-killing microbe called Bacillus thuringiensis. The result is that they produce a toxin that kills certain caterpillars but does not harm other animals or people ? an appealing combination of results.
Scientists who study insects, however, predicted that the crops wouldn't work for long, because insects eventually would evolve to resist the Bt toxin, just as they resist other insecticides.
Tabashnik was among the most pessimistic about the crops' long-term prospects.
"I thought we might see resistance to Bt crops in five years or less," he says.
That didn't happen. But recently, Tabashnik says, he found evidence that one type of insect is becoming resistant to the Bt toxin.
By examining a series of studies conducted by University of Arkansas researchers, Tabashnik found that cotton bollworms ? a worm that feeds on cotton plants and corn before growing wings and turning into a moth ? are surviving much higher doses of Bt poison now than they were several years ago. His findings, which he says are clear evidence of "evolution in action," were published in the current issue of Nature Biotechnology. This could mean that Bt will cease to be an effective form of insecticide.
Not everyone is convinced, however. In an odd twist, the scientists who collected and tested the bollworms disagree with Tabashnik's conclusions. Randall Luttrell from the University of Arkansas says the data may not present a completely accurate picture of what is happening in cotton fields. He suspects that the hardy bollworms may have been living in cotton fields all along, but he simply did not happen to find them until recently.
In any case, if more bollworms are surviving on Bt cotton, farmers haven't noticed. That may be because they are killed by additional chemical sprays and a new generation of Bt crops with a slightly different version of the gene ? too new to have been overcome by evolution.
