Overusing rootworm-resistant corn is not ideal

WEST LAFAYETTE, Ind. — Farmers should be aware that overusing Bt corn can be problematic, according to an analysis of data covering 12 years and 10 U.S. Corn Belt states.

Farmers generally planted more Bt maize than the optimum across the Corn Belt, suggesting misconceptions of the costs and benefits.

This was especially true in eastern states, where crop rotation is more common and corn rootworm damage was lower in field trials.

“If you think of a Bt hybrid as a finite resource, like a declining debit card, every time you use it, you erode a little bit of susceptibility,” said Christian Krupke, entomology professor at Purdue University and coauthor of the report. “So, it’s a little less likely that it will work as well next time.”

“Overusing Bt may make sense for each individual, but all will eventually lose the technology sooner than might have been the case,” said study coauthor David Hennessy, the Cargill Professor in Economic Systems at Iowa State University.

“Essentially, each individual does not take account of the harm done to others due to the buildup of genetic resistance to the toxin.”

Historical Context

In 2003, scientists introduced the first genetically engineered corn hybrid trait lethal to corn rootworms and derived from the bacterium Bacillus thuringiensis. Since then, farmers have extensively used Bt corn hybrids.

Subsequently, multiple field studies have reported Bt resistance in rootworms since 2009, raising doubts about the long-term viability of the Bt traits.

Future Implications

The use of transgenic technologies such as Bt as a key pest-management tool is likely to continue, Krupke said. The technology is user-friendly for growers and reduces insecticide applications.

The report did, however, encourage a sustainable, responsible approach to using the technology.

Christina DiFonzo, a professor at Michigan State University, compared bundling seed traits to the packages formerly offered for cable TV. Consumers paid for hundreds of channels when they only wanted 10 or 15.

“Farmers would welcome a similar ‘pick list’ for the seed supply, and that would help insect-resistance management,” she said.

View the complete report at https://tinyurl.com/Bt-Maize.