Army cutworm moth migration and grizzly bear conservation in the greater Yellowstone ecosystem

Migrating insects play a crucial role in connecting ecoregions and influencing plant and animal abundance and diversity. The army cutworm (Euxoa auxiliaris) is an agricultural pest in its natal Great Plains region, but it is a valuable food source for the federally protected grizzly bear (Ursus arctos horribilis) in the Rocky Mountains after migrating there as an adult and congregating in large numbers at moth-aggregation sites. Accurate predictions of migrating army cutworm moth abundance is critical to understand summer food-source availability for grizzly bears. 

Two portable radar units were deployed in Wyoming along the front range of the Greater Yellowstone Ecosystem (GYE) from 20 June 2023 to 11 August 2023 to identify and monitor migrations of the army cutworm moths. Preliminary results indicate that independent of radar location, army cutworm moths migrated in large numbers during the first week in July. Moths flew toward directions consistent with some of the most active grizzly bear moth foraging sites within the GYE. To support target attribution from radar data, we conducted a laboratory-based study to determine the wing beat frequency of army cutworm moths under various pressure (550 hPA, 700 hPA, 850 hPA) and temperature (7℃, 13℃, 24℃) combinations. Results indicate that pressure had no significant effect on wing beat frequency of army cutworm moths, but wing beat frequency increased with increasing temperature. The mean wing beat frequency of army cutworm moths was 37.8 Hz (wing beats/second), consistent with radar-derived wing beat frequency data.