Worm Now Thrives in GMO Corn Designed to Kill It, Study Says

Scientists have confirmed that corn-destroying rootworms have evolved to be resistant to the Bt corn engineered to kill them Jim Young/Reuters

One of industrial agriculture’s biggest GMO crops may have just backfired. Scientists have confirmed that corn-destroying rootworms have evolved to be resistant to the Bt corn engineered to kill them.

Bt stands for Bacillus thuringiensis, the name of the genetically modified corn’s “donor” organism. Bacillus thuringiensis is a naturally occurring soil bacterium that produces protein crystals that bind to certain receptors in the rootworm’s intestine, killing it. For years, farmers have planted Bt corn as an alternative to spraying insecticides. Bt corn accounted for three-quarters of all corn planting in 2013. That may have to change.

After finding a cornfield in Iowa in 2011 that was decimated by rootworm despite being planted with the Bt corn, Iowa State University entomologist Aaron Gassmann and his team began to study the pests’ interactions with the genetically modified organism (or GMO) corn in a lab. Their study, published Monday in the Proceedings of the National Academy of Sciences, describes the western corn rootworm’s rapid evolution after feeding on the engineered crop.

But Bt corn is still capable of warding off other pests, so farmers will likely keep planting it. Except now they’ll need to use pesticides to protect their crop from rootworms. As entomologists warned the Environmental Protection Agency in 2012, rootworm resistance means that the environmental advantage of Bt corn—that it could be raised pesticide-free—may disappear.  

“Unless management practices change, it’s only going to get worse,” Gassmann told Wired. “There needs to be a fundamental change in how the technology is used.”

Scientists have predicted for years that this could happen, but warnings were repeatedly ignored by regulators and farmers. It takes millions of dollars to develop seeds like Bt, so engineering an alternative is not an attractive option. Instead, the authors of another study on rootworm Bt resistance, which focuses on Nebraska, take a biodiversity approach.

“Crop rotation is the best tool,” University of Nebraska-Lincoln entomologist Lance Meinke told Farm & Ranch Guide. "Generally, one year of soybeans in a field with resistant western corn rootworms wipes out that population. The beetles will lay eggs that hatch, but when larvae try to feed on soybean plants, they dont find the nutrients they need and they die.

Crop rotation can suppress rootworm populations over time, reducing the threat posed by their new Bt resistance.

But as entomologist Elson Shields of Cornell University told Wired, rootworm is just one symptom of a systemwide problem that will likely come back to bite the GMO seed industry’s focus on short-term profit. The next engineered seed trait “will fall under the same pressure,” said Shields, “and the insect will win.”

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