Imagine this scene: The larva of a Hessian fly bites into the tender leaf of a wheat plant. In its saliva are substances poisonous to the plant, causing stunted growth and even death. But this time, endowed with unique resistance genes that act like an alarm system, the wheat is able to detect the intruder and deploy a fighting response.

Scientists with the Agricultural Research Service and Kansas State University (KSU) aim to give wheat this defensive edge by understanding its enemy's offensive arsenal. For the first time, ARS entomologist Ming-Shun Chen and KSU colleague Xuming Liu have identified several genes from the Hessian fly's salivary glands that may be responsible for triggering release of the plant-altering compounds.

What makes the Hessian fly such a troubling pest is its ability to reinvent itself — literally. The Hessian fly, which has plagued U.S. wheat farmers since at least the Revolutionary War, has countless biotypes. In other words, the insect is capable of mutating to produce races that can overcome the resistant wheat plants put out by scientists and breeders.

Engaged in a vicious cycle, plant breeders must have new wheat varieties ready to fend off the resilient Hessian fly, which typically makes a comeback in six to 10 years. And as the pool of fly genes with counter-resistance grows, the task of creating hardy wheat plants becomes increasingly more difficult.

Hoping to find a more stable solution, Chen and Liu have gone to the source of the unique Hessian fly-wheat interaction: the fly's salivary glands. There the potent molecules are synthesized and directed into the wheat plant. These compounds appear to help create a favorable environment for the developing Hessian fly larva.

Chen's next step is to determine if the recently found fly genes and gene products are associated with the virulence, or counter-resistance, of the different fly biotypes.

The Hessian fly has been known to cause up to $100 million worth of damage and crop losses in a single year.