The effects of temperature and barometric pressure on the wingbeat frequency of the seasonal migrant, <i>Euxoa auxiliaris</i> (Lepidoptera: Noctuidae)

The annual westward migration of army cutworm moths, Euxoa auxiliaris (Grote), to the Rocky Mountains plays a crucial role in the diet of grizzly bears, Ursus arctos horribilis (L.), which face considerable variability in food availability throughout the year. During the bears' hyperphagia period, when they must consume an excess of calories to prepare for hibernation, these migrating moths provide a vital and reliable energy source. Seasonal dispersal of E. auxiliaris has been primarily documented through ground observations. However, advancements in radar technology now offer new opportunities to track high-altitude migrations including direction, speed, and wingbeat frequency (WBF) of flying insects. Atmospheric conditions such as temperature and pressure can influence insect flight dynamics, yet their effects on E. auxiliaris remain poorly understood. Therefore, we characterized the WBF of lab-reared E. auxiliaris under 9 combinations of air temperature (7, 13, 24 °C) and pressure (550, 700, 850 hPa). Using a pressure-controlled altitude chamber, individual moths were systematically subjected to combinations of these conditions, and their WBFs were recorded. Our results show that temperature significantly affected WBF, but barometric pressure did not. These findings provide critical baseline data for understanding the flight dynamics of E. auxiliaris and highlight the importance of integrating biological data into radar-based studies of migration. These results enhance the interpretation and utility of radar-derived datasets and contribute to the development of more accurate monitoring tools, particularly for the study of insect migration.