Many of the genes that allow wheat to ward off Hessian flies are no longer effective in the Southeastern United States, and care should be taken to ensure that resistance genes that so far haven't been utilized in commercial wheat lines are used prudently, according to U.S. Department of Agriculture and Purdue University scientists.

An analysis of wheat lines carrying resistance genes from dozens of locations throughout the Southeast showed that some give little or no resistance to the Hessian fly, a major pest of wheat that can cause millions of dollars in damage to wheat crops each year. Others, even those considered the most effective, are allowing wheat to become susceptible to the fly larvae, which feed on and kill the plants.

Wheat resistance genes recognize avirulent Hessian flies and activate a defense response that kills the fly larvae attacking the plant. However, this leads to strains of the fly that can overcome resistant wheat, much like insects becoming resistant to pesticides.

"The number of genes available to protect wheat is limited. There really aren't that many," said Richard Shukle, a research scientist with the USDA Agricultural Research Service Crop Production and Pest Control Research Unit and Purdue adjunct associate professor of entomology. "In the Southeast, having multiple generations of Hessian fly each year enhances the ability of these flies to overcome wheat's resistance."