One of the nation's most widely planted crops - a genetically engineered corn plant that makes its own insecticide - may be losing its ability to kill a major pest.

Scientists fear potentially risky farming practices are spurring the rise of insects immune to the sophisticated weaponry in so-called Bt corn.

When it was introduced in 2003, the corn seemed like the answer to farmers' dreams because it would allow growers to bring in bountiful harvests using fewer chemicals. It now accounts for 65% of all U.S. corn acres. The grain ends up in thousands of everyday foods such as cereal, sweeteners and cooking oil.

But over the last few summers, rootworms have feasted on the roots of Bt corn in parts of 4 states. That suggests some of the insects are becoming resistant.