Adult flies begin to emerge from the pupae in late June or early July. Emergence may continue for about six weeks. The midge may exist at low population levels for several years before it becomes a significant problem. But if conditions become favourable, populations can reach epidemic proportions quickly. Producers often mistake the symptoms of an infestation and report that frost or drought has reduced wheat yields or grain quality.
Crop damage occurs during the larval stage.
After hatching, the midge larva feeds on the developing wheat kernel, causing it to shrivel, crack and become deformed. The damage to the crop is not readily apparent because there are no visible changes in colour, size, or shape of the affected wheat head. Damage can only be detected by inspecting the developing seed itself. Damage to wheat kernels will vary within a single head. A few kernels may be aborted entirely.