Rootworms, the most costly pest affecting the U.S. Corn Belt, are showing signs of resistance to Syngenta AG’s genetically modified corn just as they do with crops developed by Monsanto Co., researchers said at a conference.
Switzerland’s Syngenta, the world’s largest producer of crop chemicals, and St. Louis-based Monsanto compete to supply farmers with corn containing a genetic trait that enables it to produce its own pesticide. Rootworm resistance, first documented last year in Iowa and suspected in Illinois, Minnesota and Nebraska, is forcing farmers to spray crops with the kind of chemical pesticides the modified corn was supposed to avoid.
Laboratory experiments show Syngenta’s Agrisure corn may have “cross-resistance” with Monsanto’s YieldGard corn, meaning the crop is vulnerable to the same rootworms that are no longer killed by Monsanto’s toxin, said Sarah N. Zukoff, a doctoral candidate at the University of Missouri, and Bruce E. Hibbard, a research entomologist with the U.S. Department of Agriculture. They spoke yesterday in a presentation at the annual meeting of the Entomological Society of America in Knoxville, Tennessee.
Cross-resistance may already be showing up in Nebraska cornfields, said Lance Meinke, an entomology professor at the University of Nebraska in Lincoln. Meinke presented preliminary data showing rootworms collected this year in Wayne County have “low-level” resistance to Monsanto engineered corn, probably because farmers over-used the technology.
Syngenta corn had similarly poor performance even though it had never before been planted in the experimental field, Meinke said.
Rootworm can cause $1 billion of damage annually, making it the most costly corn pest, according to the USDA. There’s “mounting evidence” that resistance is developing in multiple states, the U.S. Environmental Protection Agency said in August.
“This has been the most difficult insect to control in the Corn Belt in my lifetime,” Dirk Benson, Syngenta’s head of trait projects, said by phone yesterday. “We are very concerned about trait performance.”
Seeds accounted for $3.19 billion of Basel-based Syngenta’s 2011 sales, or 24 percent of total revenue, according to data compiled by Bloomberg.
Monsanto, the world’s biggest seed company, sold enough of its rootworm-killing corn last year to cover 37 million acres (15 million hectares), with 75,000 acres showing “unexpected damage” from the pest, William J. Moar, the company’s corn insect-resistance management technical lead, said yesterday in a presentation at the conference. That figure dropped to 45,000 acres this year, said Kelly J. Klauss, a company spokeswoman.
Monsanto’s YieldGard corn is engineered to produce the Cry3Bb1 protein derived from Bacillus thuringiensis, or Bt, a natural insecticide. Syngenta’s Agrisure produces a similar insecticidal protein known as mCry3a.
Rootworms known to be resistant to Cry3Bb1 survived feeding on Syngenta’s corn and caused root damage at higher-than-expected rates, said Zukoff, the University of Missouri researcher.
“This does suggest the possibility of cross-resistance between these proteins,” she said in the presentation.
Zukoff’s study is preliminary and some of it doesn’t support the possibility of cross-resistance, Syngenta’s Benson said.
“They have an indication of concern,” Benson said. “More study is needed.”
Benson also disagreed with Meinke’s suggestion that rootworms in Nebraska may be resistant to Syngenta corn. The more likely explanation for the unexpected damage was high bug concentrations feeding on young plants in an unusually early spring, Benson said.
Monsanto says farms with suspected resistance are rare. Growers can avoid problems by rotating to non-corn crops or switching to a product such as SmartStax, which includes a second trait that kills rootworms, and following planting recommendations, Klauss said in an e-mail.
“In 2012, corn-rootworm protected products containing the Cry3Bb1 protein provided exceptional value to growers on greater than 99.8% of the acres where the technology was planted,” she said.
Monsanto’s SmartStax combines the company’s technology with Herculex, a Bt corn developed by DuPont Co. and Dow Chemical Co. Herculex didn’t exhibit cross-resistance in Zukoff’s experiment. That trait is coming under increased rootworm pressure as growers switch from Monsanto’s YieldGard in the hope of keeping resistant insects at bay, the USDA’s Hibbard said.
SmartStax may be vulnerable in areas where rootworms have already overcome the Monsanto trait, Hibbard said. Resistant varieties of rootworm have been developed in laboratories for every type of Bt crop, so field resistance is “almost certainly possible for every Bt product that is out there,” he said.
DuPont plans to add the Syngenta trait to its Herculex corn varieties next year because adding the second toxin should deter resistance, Marlin E. Rice, a senior research scientist with the company’s Pioneer seed unit, said today in a presentation. He declined to say whether the company’s field trials of the new combination have found cross-resistance to the Syngenta technology.