Get the latest updates on western corn rootworm resistance. Michael Gray, professor of agricultural entomology, and his graduate student Preston Schrader will share considerations and recommendations for 2013 on Aug. 16. during the 56th annual Agronomy Day at the University of Illinois.

Research conducted at Iowa State in 2011 found evidence of evolving resistance in progeny of adult western corn rootworms that were collected from fields in which Bt hybrids (Cry3Bb1) had been planted for several consecutive years. Thus far, however, there is no evidence that field resistance has evolved for the European corn borer even though this species has been exposed to Bt proteins since 1996.

Gray thinks this is due to the use of hybrids that offer a high dose of Bt proteins for corn borers. “The refuge–20 percent historically–and high-dose events have worked in tandem very well for this once prominent pest,” he said.

However, the Bt hybrids that have been used for corn rootworm control are low- to moderate-dose events that leave survivors in every field. When enough heterozygotes (individuals with a resistant and susceptible allele) survive and mate, a Bt-resistant population can increase rapidly. The refuge structure that works well for the European corn borer is less effective for the western corn rootworm.

Even though some producers now use the refuge-in-a-bag (seed mixture) approach and pyramided hybrids (hybrids that express multiple Bt proteins against target insects), there is no guarantee that these recent developments will keep resistant corn rootworm populations in check.

“In August of 2011, I confirmed severe corn rootworm damage to a few producers’ fields in Henry and Whiteside counties in northwestern Illinois that were planted to Bt corn expressing the Cry3Bb1 protein,” Gray said. “In September 2011, I again observed significant damage and lodging to a Bt field, this time in LaSalle County.”

These fields, like the Iowa fields in which resistance had been documented, had been in continuous corn for many years, and the same Bt trait (Cry3Bb1) had been used for many consecutive growing seasons.

Western corn rootworm adults were collected from the Illinois fields in August 2011 and sent to Iowa state. The progeny from these adults will be subjected to bioassays to determine their susceptibility to the Cry3Bb1 protein. The result will be available toward the end of the summer of 2012.

Agronomy Day attracts more than 1,000 people each year to the Crop Sciences Research and Education Center in Urbana to find out the latest information on technology and techniques to improve food and fuel production. For more information on speakers and displays, like University of Illinois Agronomy Day on Facebook or go to http://agronomyday.cropsci.illinois.edu/.