CHAMPAIGN, Ill. A new study answers a question that has baffled researchers for more than 15 years: How does the western corn rootworm an insect that thrives on corn but dies on soybeans persist in fields that alternate between corn and soybeans? The answer, researchers say, has to do with enzyme production in the rootworm gut.
Their findings are described in a paper in Ecology and Evolution.
Crop rotation declined in the middle of the 20th century as the use of insecticides and fertilizers expanded in the U.S. Then in the 1950s and '60s, when some insecticides began to fail, growers again turned to crop rotation to kill off the rootworms that fed on corn. The method was effective for decades, but by 1995 some growers started seeing rootworm damage even in rotated fields. Today rotation-resistant rootworms are widespread in the Midwest cornbelt, where corn and soybeans dominate the landscape.
Crop rotation in East Central Illinois imposed intense selection pressure on rootworms, a key to the emergence of insect resistance to crop rotation, said University of Illinois crop sciences professor Manfredo Seufferheld, who led the new study.
"In Champaign County, Illinois, where you see a lot of rotation-resistant rootworms, 84 percent of the total land area is corn or soybeans," he said. "But as you go to Missouri, which has only wild-type (non-resistant) rootworms, almost 50 percent of the land area is not corn or soy."
Rootworm larvae live on the roots of corn plants, so it makes no sense for a rootworm beetle to deposit its eggs in a soybean field, Seufferheld said. "But with crop rotation, we're making special conditions that allow those crazy insects to survive."
Previous studies focused primarily on the behavioral changes that led rootworm beetles into soybean
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign