Combined exposure to heatwave and high humidity negatively impacts reproduction and survival of <em>Bombus impatiens</em> (Hymenoptera: Apidae)

Abiotic factors such as humidity can impact animal responses to temperature, but physiological and fitness consequences of their interaction has rarely been quantified. In this study, we investigated effects of a simulated heatwave and high humidity on <em>Bombus impatiens</em> individual and colony health.

Using a full factorial experimental design, we exposed queen-less microcolonies in laboratory conditions and queenright colonies in semi-field conditions to a five-day simulated heatwave (33°C) and high relative humidity (85%), and measured feeding, reproductive, and physiological traits relative to controls. We found that heatwave effects were highly dependent on humidity levels. Heatwaves increased pollen consumption, weight gains, and worker production in colonies, while high humidity led to lower worker and founder queen survival and slower drone developmental time.