A corn farmer's nightmare may be taking place across the Midwest -- genetically-modified corn in four states has been found damaged by rootworm.

Rootworms Evolve

Monsanto's rootworm-resistant corn seeds were introduced in 2003. The seeds were genetically engineered to kill rootworms using Bacillus thuringiensis, or Bt. The Bt gene was inserted into the seeds, and effectively killed the worm who feasted on the plants. For awhile.

This summer, an Iowa State University study found some plants had fallen prey to the rootworm -- the bug had evolved and now resisted the pesticide Bt that is found in Monsanto's genetically-modified corn seeds.

Four states total have found rootworm damage to their corn crops -- Nebraska, Iowa, Illinois and Minnesota.

EPA Dissatisfied With Monsanto

The Environmental Protection Agency took notice, and in a Nov. 22 memo told Monsanto the company wasn't doing enough to monitor resistance.

Some suggestions from Monsanto were to rotate crops, or use another genetically-modified seed that uses two types of Bt, SmartStax Corn.

The EPA is concerned SmartStax Corn will breed more problems. For now, they are asking Monsanto to monitor their seeds better.

Read More:

• Monsanto Corn May Be Failing to Kill Bugs In 4 States, EPA Says (Bloomberg BusinessWeek)
• EPA Warns Monsanto About Bugs (Wall Street Journal)
• Insects Find Crack In Biotech Corn's Armor (NPR)