Each year since 1911 the pale western cutworm, Agrotis orthogonia Morr., has taken a toll of the grain crops in some part of the Canadian prairies. The extent of the outbreak has varied from small, isolated areas of infestation to gcneral outbreaks covering over 150,000 square miles. Until 1936 the only practical method of controlling this cutworm was the use of definite cultural practices designed to prevent the moths from ovipositing in certain fields during August and early September.