Monsanto Co.'s corn, genetically modified to resist insects, may be susceptible to rootworms, according to ongoing research.

The corn has been toppling in northwestern Illinois fields, leading one scientist to believe that rootworms outside of Iowa may have developed a resistance to the crop. “Whatever is the cause, it is generating a lot of concern,” said Michael Gray, an agricultural entomologist at the University of Illinois in Urbana. “I wouldn’t say at this point it’s just an isolated field here or there. It's very, very significant damage.”


Growers in other states are currently on the lookout for evidence that the bug has affected their crops.