In the Inland Northwest, extensive field surveys by Pike have shown that Hessian fly infestations have been largely restricted to the irrigated Columbia Basin fields and dryland wheat fields located close to irrigated areas. Occasionally, he has found Hessian fly infestations in dryland wheat in extreme eastern areas receiving about 20 or more inches of annual precipitation. The adult mosquito-like fly lives only about 4 days, laying eggs on the leaves. They prefer to lay eggs on newly emerged and very young wheat plants in preference to older wheat plants and alternate hosts. Larva hatch from the eggs within 3 to 10 days and migrate down the leaf to the crown of the seedling or to the node in jointed wheat.
Adults emerge a short time later, depending on the weather and the time of year.
The second generation typically emerges between May and June. The main fall emergence normally takes place between late August and mid-October. Adults lay eggs on volunteer and seeded wheat in the fall, or other alternate hosts, if wheat is not available. Larval activity generally ceases about mid October with the onset of cold weather. Pike points out that no single generation of Hessian fly ever completes its development uniformly, with the emergence of at least some of each generation delayed.