Increasing temperatures affect thoracic muscle performance in Arctic bumblebees.

Increasing temperature beyond a species' optimum is a major threat to insect biodiversity, particularly in rapidly warming regions such as the Arctic. For cold-adapted pollinators, high temperatures can disrupt physiology and ecosystem services, threatening pollinator populations and plant reproduction. In bumblebees, increased temperature disrupts the physiology of the indirect flight muscles. However, these muscles, which generate the bee's charismatic buzz, also facilitate key non-flight behaviours including communication, defence, and buzz-pollination, where temperature effects remain unexplored. Here, we assess the thermal performance of non-flight muscle function across 15 Arctic bumblebee species by measuring thorax vibrations during defensive buzzing behaviour. Thorax acceleration is found to peak at an air temperature of 25 °C, declining after this peak as a potential strategy to prevent overheating. Conversely, vibration frequency continues to increase with temperature, and is better explained by thorax temperature than air temperature. Surprisingly, there are no differences in thermal response across species, castes, or temperature habitat specialisations, indicating that non-flight vibrations are similarly susceptible to unfavourable temperatures across bumblebee species. If such findings translate to non-flight buzzing in other contexts, such as buzz-pollination, changes in buzzes have the potential to disrupt key plant-pollinator interactions.