Nilsa Bosque-Pérez, a UI entomologist, is on the trail of an invader that first surfaced in North America during the Revolutionary War. Found on Long Island in 1779, the Hessian fly was believed to originate in the straw bedding that accompanied German mercenaries to America.

Wheat growers have fought their own wars against the invader ever since. Now Bosque-PŽrez has launched the first systematic study of the fly in Idaho since its discovery here in the early 1990s by Nez Perce County extension educator Larry Smith.

Spring wheat and barley typically suffer the most damage from the flies' sap-sucking larvae, and plantings of both are increasing. In addition, conservation tillage practices, which are also becoming more widespread, leave crop residue on the soil surface over winter, providing a refuge for the fly pupae.

Wheat varieties susceptible to the flies can yield 45 percent less than resistant varieties when infestations are heavy.

With graduate student Dan Bullock, Bosque-Pérez studies the biotypes of Hessian fliesÑspecific genetic lines adapted to different resistant varietiesÑand their ecology in Idaho. Her work is essential to efforts by UI wheat breeder Ed Souza to develop resistant lines of wheat. Her findings might also suggest changes in farming practices.

A female Hessian fly looking to mate releases a sex pheromone from her extended abdomen. Photo by Dennis Schotzko.

Bosque-Pérez has also developed a breeding colony of the pest. The colony allows UI scientists for the first time to test wheat strains in the laboratory for resistance to the fly.

"In addition to screening the plants, we are extracting their DNA. Ed Souza uses the DNA samples to confirm resistance using molecular markers," Bosque-Pérez said.

She and graduate student Dan Cervantes also work with UI entomologist Sanford Eigenbrode to study how leaf waxes influence the flies' preferences for different wheat varieties. "We want to know if there are differences in wheat that will discourage the flies from laying eggs on the plants," Bosque-Pérez said.

"We're trying to play the game ahead of the fly."