Alfalfa blotch leafminer

Identification and Life Cycle. The alfalfa blotch leafminer may go through 3-4 generations/year in the upper Midwest. The adult is a black, approximately 1/8-inch long hump-backed fly. The maggots are small and pale yellow. Females will lay 1-3 eggs/leaf. When the maggots hatch, they feed between the leaf surfaces in a mining fashion. When development is complete, larvae will leave the leaf and drop to the ground to pupate.
Damage. Larval mines can usually be diagnosed through their comma-like appearance. Twenty five to fifty percent of the leaflets may be mined during heavy infestations and this could result in loss of quality. Yield loss is not expected unless significant leaf drop occurs. Adults feed by puncturing tiny "pinholes" in the leaf. This type of damage is usually not considered a plant health problem.