Corn rootworms, responsible for roughly $2 billion in annual crop losses, are evolving resistance that weakens even the latest biotechnology controls, according to a new study published in the Proceedings of the National Academy of Sciences.
University of Arizona entomologists analyzed decades of field data collected across the Corn Belt, which extends from western Ohio to eastern Nebraska and northeastern Kansas. Their research evaluated millions of rootworms from 12 previous studies.
"The results consistently show that in fields where resistance to Bt has evolved, the combination of Bt and RNA interference provides less protection from rootworm damage," said Bruce Tabashnik, lead author and head of the U of A Department of Entomology.
Corn rootworms earned their nickname "billion-dollar bugs" because they cause approximately $2 billion in yearly yield losses while farmers spend another billion dollars annually trying to control them.
Bt corn, which produces proteins from soil bacteria that kill pests but aren't toxic to humans or wildlife, was first introduced against rootworms in 2003. It initially provided effective control, but resistance soon emerged as many farmers planted it year after year.
Seed companies responded by combining two different Bt proteins, a strategy called "pyramiding," but rootworms eventually developed resistance to both types.
In 2022, companies commercialized RNA interference (RNAi) technology, which works by silencing specific genes the pest needs to survive. This technology was always intended to work alongside Bt, not replace it.
"It was never meant to stand on its own. It was intended to be a one-two punch with Bt," Tabashnik explained. "But by the time the RNAi was actually commercialized, the effectiveness of Bt plus RNAi was already undermined because of the pre-existing resistance to Bt."
The researchers recommend farmers use integrated pest management strategies, including crop rotation and planting conventional corn "refuges" alongside transgenic crops.
"It's a reminder that there's no silver bullet. Evolution doesn't stop," Tabashnik said.
