Wheat midge are small, orange, fragile-looking flies that attack members of the grass family including barley, couch grass, wheat grass, triticale, and spring rye, though their preferred host is wheat.
Adults emerge from mid-June through mid-July and typically coincide with wheat head development and flowering. Wheat midge remain in the humid crop canopy throughout the day and emerge on calm, warm evenings to mate and lay eggs. Eggs are laid singly or in groups of three to five on wheat kernels prior to flowering.
Upon hatching, larvae crawl to developing kernels and feed for two to three weeks. Larval feeding damage results in shriveled, misshapen, cracked, or distorted kernels. Kernels must be inspected within the glume, as damage may not be readily apparent at a glance. Lost or damaged kernels from feeding result in lower crop yield and quality. The Canadian Grain Commission allows midge damage between two and five percent prior to impacting the assigned grade.
After feeding, larvae remain inside the heads until rain or a moisture event occurs, at which point they drop to the soil, bury themselves, and form a cocoon to overwinter. In the spring, if moisture and temperature requirements are met, larvae leave their cocoons and return to the soil surface, pupating for a period of two weeks.
Wheat fields should be inspected for wheat midge in late June and early July, as wheat heads emerge, and females are laying eggs on the developing heads. Scouting should occur in the evening (after 8:30 PM) on calm, warm (15 °C) evenings. The number of adults should be counted on four to five wheat heads in three or four locations. Insecticide applications should be considered if economic thresholds are met. To maintain optimum grain grade, the economic threshold is one adult wheat midge per eight to ten heads during susceptible stages (wheat head emergence up until flowering). To prevent yield loss, the economic threshold is one adult wheat midge per four to five heads.
Varieties of midge-tolerant wheat are available to help manage this pest! More information on these can be found at www.midgetolerantwheat.ca.