Migration of the Army Cutworm, Chorizagrotis auxiliaries (Lepidoptera: Noctuidae). I. Evidence for a Migration1

Indirect evidence is presented to support the conclusion that the army cutworm, Chorizagrotis auxiliaris (Grote), migrates from the Great Plains to the Rocky Mountains during the spring and the same individuals return to the Plains in the fall. Spring activity occurs progressively later from east to west, the delay being greater than that caused by emergence but commensurate with flight potential of the moth. Flight is predominately from east to west and a constant turnover of moths occurs at all locations on the Plains. Seasonal occurrence in the mountains coincides with the period of inactivity on the Plains, during which fat reserves increase. Summer survival is unlikely on the Plains and little or no reproduction occurs in the mountains. Fall populations on the Plains are correlated with oversummering populations in the mountains but not with populations at any location on the Plains the preceding spring.