FEBRUARY 9, 2008—Bollworms in cotton fields in Mississippi and Arkansas have genetically mutated to resist a toxin biotechnologists inserted into cotton crops, researchers at the University of Arizona found.

In a study of six pests in genetically modified cotton and corn in Australia, China, Spain and the United States, researchers discovered genetic adaptation in only the bollworms in a dozen fields in the United States.

The toxin inserted into the cotton plant is a common bacterium called Bacillus thuringiensis or Bt. The bollworms have become resistant to the Bt toxin strain Cry1Ac.

“What we’re seeing is evolution in action,” lead researcher Bruce Tabashnik told Terra Daily. “This is the first documented case of field-evolved resistance to a Bt crop.”

Published in the British journal Nature Biotechnology, the study found that the other five pests studied continue to be susceptible to Bt.

“The resistance occurred in one particular pest in one part of the U.S.,” Tabashnik told Terra Daily. “The other major pests attacking Bt crops have not evolved resistance. And even most bollworm populations have not evolved resistance.”

Bollworm evolution happened more rapidly in fields where there were few or no non-genetically modified plants nearby. Without non-resistant bollworms in the area, the opportunities for a resistant bollworms to mate with a non-resistant bollworms to create hybrid, non-resistant bollworms were diminished, thus speeding adaptation to the toxin among bollworms. In most pests, both parents must be resistant to the toxin in order for the offspring to inherit resistance.