Nearly two dozen insect experts have signed a letter to the EPA urging action on an emerging threat to corn crops.
Iowa State University field tests released last summer showed a major corn pest has developed resistance to a widely used variety of genetically modified corn sold by Monsanto.
There are also reports of multiple areas, including southern Minnesota, in which the corn is not effective at controlling the western corn rootworm.
Monsanto has not accepted the Iowa State findings, and says only that it is reviewing performance issues with its corn. The letter says high corn prices may give farmers an incentive to ignore simple steps that prevent resistance.
The group asks the EPA to respond with "a sense of some urgency," saying rootworm resistance could hurt corn production for a long period of time if it spreads.