When Bt corn was first engineered, it was hailed as the perfect weapon to fight off one of the most troublesome crop-devouring pests around: the corn rootworm. And since 1996, when it was first planted, Bt corn has helped US farmers kill rootworms and prevent billions of dollars in damages. Over the years, however, researchers have expressed concerns that the rootworm could become resistant to Bt corn. Unfortunately, those warnings were widely ignored by farmers and regulators and, as Wired reports, the ravenous rootworm is once again causing devastation.

The toxin breaks down the rootworm's gut lining

Bt corn currently makes up 75 percent of US corn. Once highly effective, it's supposed to kill rootworms thanks to a protein that targets the insect's gut. This protein, called Bt delta endotoxin, breaks down the rootworm's gut lining hours after it ingests the plant — a process that allows the worm's gut bacteria to invade the body cavity and cause a lethal infection. But according to a study published yesterday in Proceedings of the National Academy of Sciences, some rootworm populations are handling this protein just fine.

The study explains that Bt toxin resistance arises because some plants produce smaller amounts of the poison. This low dose still manages to kill some insects, but not all, which means that the hardier ones go on to reproduce. So, a few insect generations later, you end up with fully-resistant populations.

many farmers fail to plant refuges

But that should not be a problem on its own, because farmers are required to maintain areas called "refuges" — land that still contains non-Bt corn crops. These refuges are essential because they ensure that the rootworms in those areas are still susceptible to the toxin. So, when these populations mate with hardier ones, they keep full-blown resistance at bay. But, as Wired reports, many farmers fail to plant refuges because they yield little revenue, and the companies that buy the corn do little to enforce these rules.

Despite the increase in resistant populations, Bt corn is bound to stick around, as the genetically-modified plant continues to be effective against other types of insects. But, as the Wired article notes, a widespread increase in resistance will undoubtedly cause farmers to use more insecticides. And, unfortunately, going back to a more chemical-focused approach to pest-control will do more than increase farming costs — it'll harm the environment as well.