The biology and control of Penthaleus major as a pest of small grains were studied. Wheat, oats, and barley are favored hosts, but it also feeds on many other grasses, weeds, and vegetables. The summer is spent as aestivating eggs on field debris. Cool, moist conditions in the fall are necessary for hatching and development, and damage occurs throughout the winter. Damage is of 2 types[long dash]reduced amount of forage throughout the winter and reduced yields of grain in the spring and summer. Where winter grazing is practiced the former is of greater importance, because farmers rely on small grains for fall and winter pasture for livestock. Fields continuously in small grains are most heavily damaged. Crop rotation greatly reduces or eliminates damage. Satisfactory control was obtained with sprays of parathion, TEPP, Systox, Metacide, and malathion at relatively low dosages. Parathion, TEPP, or malathion at 0.25 pound per acre are recommended.