A useful publication by entomologists Chris DiFonzo, Ph.D. (Michigan State University) and Eileen Cullen, Ph.D. (University of Wisconsin-Madison) has been updated. This fact sheet, Handy Bt Trait Table, provides a quick reference to the currently available Bt corn hybrid traits, their spectrum of control and refuge percentage and location requirements.
More corn hybrids contain multiple transgenic Bt insect traits, and cost of seed is steadily increasing — $300 or more per bag is not uncommon. Meanwhile, refuge requirements are changing for multi-trait corn. Some refuges remain at 20 percent and "structured," planted in a block or series of rows. Others are reduced to 5 percent "structured," or 5 percent or 10 percent "in the bag" mixed with the Bt seed. It is important that you are aware of the traits offered in different hybrids and their refuge requirements. This publication is free and available for download at http://www.entomology.wisc.edu/cullenlab/extension/ext_pubs.html