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Some of the most popular products of biotechnology — corn and cotton plants that have been genetically modified to fend off insects — are no longer offering the same protection from those bugs. Scientists say that the problem results from farmers overusing the crops, and are pushing for new regulations.

These crops were the original genetically modified organisms, or GMOs. They weren't the first ones invented, but they were the first to be widely embraced by farmers, starting in the late 1990s.

They got their bug-resistant features from a kind of bacteria that lives in the soil, called Bacillus thuringiensis, or Bt, which is poisonous to the larval stage of some major insect pests, including the corn rootworm and cotton bollworm. Scientists inserted some of these bacterial genes into corn and cotton, and the plants themselves produced these insect-killing proteins.

Bt crops brought a two-fold benefit: Cotton and corn farmers didn't need to use so many chemicals to control the bollworm and related pests after they were released, starting in 1996. "Our insecticide sprays just plummeted, and there were guys who wouldn't have to treat at all," says David Kerns, an entomologist at Texas A&M University, speaking of cotton farmers.

This was also good news for the environment. The Bt proteins are toxic to a relatively small number of insects, and they're practically harmless to people and other animals. Unlike the insecticides that they replaced, they were not killing significant numbers of pollinators like bees and butterflies, or beneficial insects that prey on pests and help to keep them under control.

Farmers like Jonathan Evans in North Carolina liked Bt cotton because it made farming easier. "It's always better for the plant to protect itself, than for us to have to go out and spray for the worm," he says. "You can tend a lot more acres, with a lot less equipment."

Now all of those benefits are increasingly at risk. Bt crops are losing their power. New strains of bollworms, rootworms, and other pests have emerged that are able to feed on Bt plants without dying. David Kerns says some farmers are pretty angry about it. "There are words I can't use," he says, "but they want to know what the heck they're doing, paying for a technology and then they're still having to spray."