Connecting ecoregions: Migration of the army cutworm moth

The army cutworm moth, Euxoa auxiliaris (Grote; Lepidoptera: Noctuidae), is a migratory noctuid with a range spanning the Great Plains to the Rocky Mountains. Upon emergence as an adult, it migrates west following the spring bloom to the Rocky Mountains, spending summer months in high-alpine environments feeding nocturnally on nectar and aggregating in interstitial talus during the day. These annual aggregations are a valuable summer food source for the grizzly bear, Ursus arctos horribilis, particularly in the Greater Yellowstone Ecosystem (GYE), due to their caloric concentration and convenient availability during hyperphagia.

Although the agricultural significance of the army cutworm moth is relatively well understood, little is understood about the phenomenon of their migration. Therefore, my study assesses factors that influence migratory behavior and phenology and the abundances of migrating moths.

My objectives are primarily addressed through radar observation of migration supported by laboratory-based wingbeat frequency (WBF) recordings of army cutworm moths. Preliminary results from radar observations suggest 5 million moths were detected during the sampling period June-July. Direction of flight was consistent with moth movements towards known aggregation sites in the GYE. At low altitudes (<750 m above ground level), WBF were consistent with mean WBF recordings of army cutworm moths in a laboratory. 

Results will provide evidence and insight into army cutworm moth abundance, biomass, and calorie influx into the GYE, which is critical information for understanding the long-term potential of this food source for grizzly bears and for better informing management plans for bear populations in the GYE.