Millions of acres of corn are being planted around the state, and many of those acres will be planted with Bt corn, genetically modified corn that can kill insects that otherwise could have reduced corn yields.

But a University of Illinois scientist is worried that not enough farmers are following environmental guidelines that come with planting such corn.

Entomologist Mike Gray polled farmers at meetings held around the state earlier this year and found about 90 percent will plant Bt corn, and about 20 percent of those will not comply with the refuge requirements. Gray also found 5 percent to 10 percent of farmers would not plant any refuge acres.

The U.S. Environmental Protection Agency requires that farmers devote 20 percent of their corn acres to be so-called refuge acres, planted with non-Bt corn. If a farmer plants 100 acres of corn, 20 of those acres should be non-Bt corn. Non-Bt corn can be planted on the perimeter of a field, in strips or blocks near the Bt corn, Gray said.

"Those refuges are mandated by the EPA for the purpose of making sure there are enough surviving insects out there so any resistant individual that would emerge from Bt corn would be overwhelmed by other insects," Gray said.

That would "hopefully" delay any resistance to Bt that might be developing, he said.

The first Bt corn hybrids, which are genetically modified with the insect-killing protein Bacillus thuringiensis, debuted commercially in 1996. Insects like corn borers, which as larvae bore into corn and interrupt the plant's development, die after ingesting part of the Bt corn plant.

Over the years, more farmers have planted Bt corn to protect their fields. As a result, the populations of corn borers have declined in recent years.

"We're fortunate not to have had any field develop resistance to Bt in the Corn Belt. That's a real success story," Gray said.

A growing concern, however, has been declining refuge compliance among farmers, "and if producers aren't putting in that refuge, it increases the selection pressure that resistance could develop," Gray said.

The findings uncovered at the UI meetings from earlier this year were similar to results issued by the Center for Science in the Public Interest in a 2009 report. That organization found that although 10 percent of corn farmers were noncompliant between 2003 and 2005, the number increased to 25 percent by 2008.

Among the reasons given for noncompliance: Some viewed it as an added hassle, some viewed it as possibly sacrificing yield, while others believed since the "refuge in a bag" option is just around the corner, they'll wait to follow the refuge requirements, Gray said.

Seed companies have started selling bags of seed called "refuge in a bag" in which the Bt seeds come with non-Bt corn, such as 10 percent non-Bt corn. That way, farmers aren't slowed down when planting, Gray said.

As for when resistance can develop, a number of factors, including genetics, overall use of Bt corn and percentage of compliance with planting refuges, come into play, according to Gray. Some computer models have suggested resistance may begin to show up in a 15- to 20-year time span, he said.

"We're always looking for odd situations that may develop in a field," he said, such as when a farmer planted Bt corn but has discovered some insect-damaged corn.

Gray expects to continue monitoring the situation throughout the growing season and will be sharing information on the UI's pest bulletin at http://bulletin.ipm.illinois.edu.