Casey Kuhn/KJZZ

Cotton crops in Arizona.

Arizona cotton growers use a crop that’s been genetically modified to kill potentially devastating pests, called the pink bollworm. 

In a perfect example of evolution, second generations of cotton-eating insects are now completely resistant to the added gene. That gene was introduced in 1996 and makes a protein in the plant to mimic a bacteria that kills bugs.

University of Arizona's Bruce Tabashnik heads the entomology department and analyzed decades of data on these crops and pest responses. He found that resistant pests are overwhelming bio-engineered crops in places like India.

Not so in Arizona.

“When people follow resistance management strategies, then it’s been possible to delay resistance even up to two decades as we’ve done here in the state of Arizona,” he said.

Those strategies include planting traditional cottonseeds, along with the genetically modified ones, to keep the pests' resistant gene at bay.

Tabashnik says the first decade of using the GM cotton showed only three cases of resistant bugs.

“In the second decade, there were 13 cases," he said. "So the total number of cases surged from 3 to 16, more than a fivefold increase in the last ten years.”

Arizona growers have practically eliminated the pink bollworm by using other resistant  management strategies like releasing sterile moths.