Overuse makes Bt corn less effective

Widespread planting of corn hybrids designed to combat corn rootworm, the crop’s most damaging pest in the Corn Belt, is reducing both the technology’s effectiveness and some farmers’ profits.

The findings come from a new analysis of 12 years of field trials and seed usage data across 10 Midwestern corn-growing states, including Iowa.

The study, recently published in Science, shows rootworms are increasingly resistant to the built-in protection of corn that is genetically engineered to produce insecticidal proteins derived from a bacterium called Bacillus thuringiensis (Bt).

The title of the Science article, “Too much of a good thing: lessons from compromised rootworm Bt maize in the U.S. Corn Belt,” captures the study’s main thrust, said Aaron Gassmann, professor of plant pathology, entomology and microbiology at Iowa State University.

“‘Too much of a good thing’ is really the key message,” Gassmann, one of three Iowa State faculty among the study’s 20 co-authors, said in a university news release. “Overplanting Bt corn causes farmers to lose some of its benefits for suppressing rootworm populations and preserving yields.”