Farmers in two Illinois counties are reporting that the Western corn rootworm, a potentially devastating pest, is showing up in their fields despite rotating fields and planting Monsanto Co's insecticidal corn.
On Monday, two University of Illinois entomologists were called to Livingston and Kankakee counties, where they spotted severe damage from the corn rootworm in two fields that were newly planted with corn this year.
In certain parts of the Corn Belt, including the northern two-thirds of Illinois, corn rootworm is not entirely controlled by rotating fields between corn and soy, or is "rotation-resistant." In these regions, farmers rely on the Monsanto-developed corn, which produces an insecticidal protein that kills the rootworm.
The corn, launched in 2003 and grown on some 37 million acres in 2011, is engineered to produce the fatal protein derived from a bacterium, Bacillus thurigiensis, or Bt.
But the product, referred to as "Bt corn" or a "Bt hybrid," is now showing evidence that it isn't as effective anymore.
"This really represents the loss of a very important tool for growers in this region," said Joe Spencer, one of the entomologists who visited the fields earlier this week and is an insect behaviorist with the university's Illinois Natural History Survey.
Spencer and Michael Gray, the other entomologist, will now run tests to confirm that these rotation-resistant rootworms are also resistant to the protein expressed by the corn.
In a report this week, Gray said that producers across a wide swath of the state will face a "formidable insect foe" capable of overcoming both crop rotation and the protein.
He and Spencer collected corn rootworm not just in the damaged corn but in adjacent soybean fields. "The density of the western corn rootworm adults in both crops was additional evidence that the Bt hybrids had failed to offer the necessary root protection," Gray said in a statement.
The Western corn rootworm costs American growers an estimated $1 billion a year in crop losses and preventative products.
"The corn rootworm is one of the most devastating pests to the U.S. corn yield," said Luke Samuel, who's in charge of corn insect traits for Creve Coeur, Mo.-based Monsanto, in an email response Wednesday. "Similar to years past, we've seen pockets of heavy corn rootworm pressure in isolated areas of Illinois and have been closely working with those farmers to address those issues through a series of best management practices."
Spencer and Gray say that rotation-resistant rootworm is found not just in Illinois, but also in parts of Indiana, Michigan, Ohio and Iowa. That might mean farmers in a larger area could see similar problems in years to come.
"This is a pretty new situation," Spencer said. "We won't know how big this area is."
Gray and Spencer say that growers will have to switch to a product that has "multiple modes of action" against corn rootworm — such as Monsanto's Genuity SmartStax line, which kills the worms with an additional protein.
Those growers who don't plant the product with the additional protein may have to use soil insecticides — the very practice that the Bt hybrids were intended to curb.
In a study issued last year, Washington State University researcher Charles Benbrook reported that Bt crops have reduced insecticide use by 123 million pounds, or 28 percent, since their introduction.