DvSnf7 dsRNA is an unusual insecticide. You don’t spray it on crops. Instead, you encode instructions for manufacturing it in the DNA of the crop itself. If a pesky western corn rootworm comes munching, the plant’s self-made DvSnf7 dsRNA disrupts a critical rootworm gene and kills the pest.
This last step is called RNA interference, or RNAi, and the Environmental Protection Agency last week approved the first insecticide relying on it. Just a few years ago, RNAi was the hot, new biotechnology generating both hype and controversy. But its first approval as an insecticide has been surprisingly low-key. The EPA’s decision attracted little attention from the press or even from environmental groups that reliably come out against new genetically modified crops.
The first product DvSnf7 dsRNA will show up in is SmartStax Pro, a line of genetically modified corn seeds made in collaboration between two agricultural giants, Monsanto and Dow. The RNAi part comes from Monsanto, which has its eye on a number of RNAi applications. Monsanto expects corn seed with RNAi to be on the market by the end of this decade.
For some corn farmers, this can’t come soon enough. The western corn rootworm is known as the “billion dollar pest” because of the damage it wreaks on cornfields. And it keeps becoming resistant to the toxins farmers throw against it. First it was spray-on pesticides; then it was corn genetically modified to make the Bt toxin, a technology also commercialized by Monsanto. “When I go out and I talk to farmers,” says Joseph Spencer, an entomologist at University of Illinois at Urbana-Champaign, “you talk about Bt resistance and invariably the moment will come where they say, ‘We’ll have the RNAi soon and that’ll take care it.'” To cover all the bases, SmartStax Pro will contain both Bt and DvSnf7 dsRNA.
RNAi is useful because it can be highly specific: It’s supposed to, in theory, turn off one specific gene in one specific species while leaving others unharmed. Plants and animals naturally use this process to “silence” their own genes. And scientists have previously harnessed RNAi to create genetically modified crops, like apples and potatoes that don’t brown because their browning gene is silenced. With Monsanto and Dow’s genetically modified corn, however, the DvSnf7 dsRNA is actually silencing a gene in another living organism, the western corn rootworm. Rather than modifying itself, it modifies its environment.
The Center for Food Safety, along with other groups, vocally opposed the apples and potatoes modified through RNAi. Bill Freese, CFS’s science policy analyst, admits they were caught a bit off guard by the EPA’s decision with RNAi in corn. The EPA only allowed for 15 days of public comment, and the agency did not post its proposed decision in the Federal Register. It’s not the first time the EPA has approved pesticides quietly like this, but Freese argues the unprecedented use of RNAi as insecticide should have merited more public scrutiny.
The EPA was the last of three agencies-along with the FDA and USDA-that signed off on the safety of DvSnf7 dsRNA. Critics often point to a 2011 paper to question the safety of tinkering with RNAi. In that study, Chinese scientists found naturally occurring RNA molecules from rice circulating in the bloodstream of people eating it. That paper has gotten a lot of criticism, and scientists have had trouble replicating its findings.
The real problem, says Freese, goes beyond RNAi itself. “There’s faddish interest in the latest technology,” says Freese. “It often neglects the basic issues of the unhealthy practices used in planting corn.” Rotating crops, for example, rather than planting corn multiple years in a row in the same field can cut down on the western corn rootworm problem.
Spencer, the entomologist in Illinois, also stresses the importance of rotating crops and planting refuges of non-genetically modified corn. He’s seen what happened to Bt, when overplanting of Bt corn led to resistance.With RNAi, farmers get a new tool and a fresh start. “We need to treat these things carefully because we really can’t just afford to throw them away,” he says. (Spencer has received funding from Monsanto for his research into western corn rootworms.)
Western corn rootworm is just the beginning of Monsanto’s ambitions for RNAi. Robb Fraley, the company’s chief technology office, ticked off the other RNAi products in the pipeline: a soybean whose oil contains less saturated fat and an insecticide that kills mites harming honeybees.* “I would put RNA in the suite of really advanced, next-generation technologies that are adding to the excitement from a research perspective,” he says.
In recent years, CRISPR has displaced RNAi as the newest darling of genetic engineering. (Monsanto has licensed CRISPR, too.) Getting technology from the lab into the field takes time. SmartStax Pro, when it is on the market in a few years, will finally be RNAi pest-control technology’s entry into the real world, and it could just be the beginning.
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