Scientists poring over a mass of studies into the response of pests to genetically-modified cotton say they have found the first confirmation that insects have developed resistance to transgenic crops.
They found evidence of genetic mutation among bollworms (Helicoverpa zea) in a dozen cotton fields sown in Mississippi and Arkansas between 2003 and 2006.
The mutation entails a slight change in the bollworm's DNA to help it resist a toxin that the cotton plant exudes thanks to a gene inserted by biotechnologists.
"This is the first documented case of field-evolved resistance to a Bt crop."
Green groups, who are fierce opponents of GM technology in agriculture, have long predicted that pests would become resistant to transgenic toxins, as happens frequently in the case of chemical insecticides.
"The resistance occurred in one particular pest in one part of the US," Tabashnik said.