A harvester works through a field of corn near Santa Rosa, Calif. This corn has been genetically modified, and contains bacterial genes that kill certain insects, but the genes have become less effective.
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.”
The current situation is complicated by the fact that biotech companies have deployed close to a dozen slightly different Bt genes, targeting a variety of insects. In many cases, the bugs have evolved resistance to some Bt proteins, but not others, and the prevalence of Bt-resistant insects varies from place to place. “The impact can be patchy, but when it’s there, it’s big,” says Julie Peterson, an entomologist at the University of Nebraska. “If you’re the farmer who ends up with all of their corn laying down on the ground because the roots have been completely fed on by rootworm beetles, that’s a huge impact to you.”
Scientists have long warned about this risk. They’ve been engaged in a long-running argument with the companies selling Bt crops, such as Monsanto, which has been acquired by Bayer.
Even before Monsanto started selling the first Bt crops, independent scientists pushed the Environmental Protection Agency to limit the amount of land that farmers could devote to Bt crops. If these crops were planted everywhere, the scientists argued, it would create a situation in which, if a few rare insects happened to be genetically capable of surviving Bt proteins, they would be the sole survivors, quickly mate with each other, and produce a new strain of resistant insects. Biologists call this “selection pressure.”
The solution, they said, was a requirement that farmers devote some of their land to non-Bt crops. This would allow plenty of non-resistant insects to survive, and make it less likely that the rare resistant insects would mate with each other.
The EPA adopted this strategy, but independent scientists and biotech companies have disagreed over the years about how big these refuges need to be. In the case of some Bt crops, such as corn hybrids with genes targeting the corn rootworm, scientists have urged the EPA to require that farmers to devote at least half of their fields to non-Bt corn. The companies balked at that, since it would have limited sales of their products. They convinced the EPA that such large refuges weren’t necessary.
The warnings, however, turned out to be well-founded. Over the past decade, insects like the corn rootworm, the cotton bollworm, and the Western bean cutworm have become resistant to one Bt gene after the other.
Now scientists, once again, are pushing for tighter government rules. “We are at an important point, where we’ve seen what can happen, and definitely do need to make some changes,” Julie Peterson says.
The biggest proposed changes are intended to preserve one particular Bt gene, called called Vip3A, which has been incorporated into both corn and cotton plants.
Vip3A came on the market a little later, and it is slightly different from other Bt genes, “so it still is effective against a lot of insects, and it’s sort of carrying a lot of the weight right now,” Peterson says. The company Syngenta sells it under the trade name Agrisure Viptera.
Scientists are worried that it will soon break under the weight of overuse, especially in cotton-growing areas of the South. There, the Vip3A gene is currently deployed in both corn and cotton to fight off an insect known both as the cotton bollworm and the corn earworm. Kerns says that he and his colleagues have found a recessive genetic trait for Vip3A resistance in this insect population. If Vip3A is widely used, insects carrying this resistance trait will be more likely to survive, mate, and produce fully resistant offspring.
Two years ago, a group of the EPA’s outside scientific advisors recommended unanimously that the agency prohibit the use of Vip3A in corn in the South. This would preserve its effectiveness in cotton, they said, where it’s much more valuable.
The company that owns the Vip3A gene — Syngenta — argued that such a prohibition wasn’t necessary or fair. In its latest draft document on the issue, the EPA backed away from the idea. Instead, the agency proposed a variety of other measures. They include a requirement that companies plant and monitor “sentinel plots” of Bt crops that could provide early warning of insect resistance, and also that companies force farmers to abide by existing requirements to plant non-Bt refuges. Studies have found many farmers ignoring these rules.
Peterson says that if current farming practices don’t change, it’s possible that all of the Bt genes currently on the market will stop working reliably within a decade.
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