Source region and abundance of the army cutworm moth (Euxoa auxiliaris)

After migrating from the Great Plains to the Rocky Mountains in early summer, the army cutworm moth (Euxoa auxiliaris) occupies the talus-covered peaks of the region and forages for nectar in adjacent alpine vegetation to increase its lipid reserves. Grizzly bears (Ursus arctos horribilis) of the Greater Yellowstone Ecosystem consume these ephemeral visitors in vast quantities, relying increasingly on this moth as climate change continues to alter the availability of other food sources. However, despite the importance of the army cutworm moth in the grizzly bear’s diet, very little is known about the moth’s specific migration patterne at these alpine sites, making it difficult to inform management practices for both species. Therefore, to establish likely region of origin for moths collected on peaks throughout the Greater Yellowstone Ecosystem, we conducted isotopic analysis on known-origin samples collected throughout the moth’s source region. We statistically analyzed these data to create a base “isoscape,” and moths collected on peaks were referenced against the isoscape to establish region of likely origin. Our findings provide for a better understanding of the moth’s ecology and facilitate more comprehensive conservation management of the grizzly bear.