(2nd Place) Effects of heat waves and high humidity on colony and individual fitness in bumble bees

Bumble bees are experiencing population declines that have been associated with several stressors including climate change that increases the frequency, intensity, and duration of extreme weather events patterns such as heat waves, floodings, and droughts. While these can have detrimental effects on their own, high ambient temperatures experienced during heat waves can have magnified effects in high humidity since it reduces the evaporative cooling ability of organisms. Despite the known correlation of temperature and humidity, the effects of this interaction have been poorly investigated. In this study, we investigated whether heat waves in combination with high humidity affects Bombus impatiens colony and individual fitness. We exposed queen-less microcolonies in the lab to a realistic five-day simulated heat wave (33°C) and to constant high humidity (85%) and measured reproductive outputs, behavior, and survival. We found that both high temperature and humidity differentially impact individual and colony impact. We discuss the implications of these results for bumble bee survival under these extreme weather events.