The armyworm, Pseudaletia unipuncta (Haw.), has been an important pest of grasses in North America for many years, largely in the eastern half of the Continent, from the more southerly regions of Canada to the southern United States. The larvae skeletonize rhe surface of the leaf blades or rhe inner surface of the sheaths during the early instars, and later feed from the margins of the leaves, consuming all the tissues. The inflorescence is seldom damaged unless leaf foliage is scarce but in some grasses, notably timothy, the green heads are often readily consumed by the older larvae even when foliage is abundant. Normally, populations of the armyworm are small, attracting little attention, but at irregular intervals of five to 20 years widespread outbreaks have occured simultaneously in Canada and the united States; eight such outbreaks have been recorded since 1860. In some of the intervening years smaller and more localized outbreaks have occurred. During the outbreak, damage to forage grasses and cereal crops has been so severe that the armyworm constitutes one of the most important insects attacking these crops. The latest great outbreak occurred on the North American Continent in 1954; this was preceded by a smaller but severe attack in 1953, largely in the central United States east of the Mississippi River. In Canada, in 1954, all the provinces from eastern Saskatchewan to Newfoundland were involved.