Monsanto Co. (MON) and other seed makers reported a threefold increase last year in U.S. farmers caught violating requirements designed to stop insects from developing resistance to genetically modified corn.

The data relates to farmers planting seeds modified to produce a toxin derived from Bacillus thuringiensis, or Bt, a natural insecticide. The Environmental Protection Agency requires growers to also plant an adjacent area -- a so-called refuge -- of non-Bt corn so that bugs don’t become immune.

About 41 percent of 3,053 farmers inspected in 2011 failed to fully comply with the refuge requirement, according to data from the Agricultural Biotechnology Stewardship Technical Committee, which Monsanto provided today in an e-mail.

Seed companies are trying to get farmers to plant refuges amid concern that resistance among bugs to modified crops may be increasing. In July, Iowa State University found some rootworms have evolved resistance to Cry3Bb1, the Bt gene engineered into Monsanto corn. Entomologists in Illinois and other Midwestern states are studying possible resistance in fields where the insects devour roots of Monsanto’s Bt corn.

An increase in the proportion of farmers found not planting refuges was expected because of a new industry initiative that uses sales data, the National Corn Growers Association said today in a statement on its website. Seed companies used the data to identify farmers who may not have purchased enough seed for a refuge, said Nick Storer, global science policy leader for Dow Chemical Co. (DOW) and the company’s representative on the ABSTC.

“What’s new is that every grower had some sort of scrutiny this year,” Storer said in a telephone interview. “The whole purpose of doing that was to try to increase the frequency with which we identify non-compliant growers.”

The ABSTC, whose members include St. Louis-based Monsanto, Dow, DuPont Co. (DD) and Syngenta AG (SYNN), files compliance reports with the EPA each January. The industry found about 15 percent of growers weren’t complying in 2010.

Farmers who violate the requirements are now revisited at least twice over five years, Joanne Carden, who is stewardship strategy lead at Monsanto and represents the company on the ABSTC, said in an interview. Farmers who fail the follow-up inspection lose access to the technology, she said.

To contact the reporter on this story: Jack Kaskey in Houston at jkaskey@bloomberg.net

(Blomberg)