Navigating a warming world: heatwave exposure during development affects responses to UV light in male bumble bees

Abstract

Heatwaves can create adverse conditions that impact physiological and behavioural traits in insects. Although the ability to tolerate extreme temperatures is species-specific, it also depends on factors such as life stage. Exposure to extreme temperatures during a sensitive developmental stage can have long-lasting effects in adulthood. Bumble bees are important pollinators found primarily in temperate regions. Most bumblebee species grow their colonies over the summer, when extreme heat events are most common. In this study, we investigated the effects of simulated heatwaves of two different magnitudes (32–34 °C and 36–38 °C) on microcolonies of Bombus terrestris audax. We investigated whether bumblebee workers were able to successfully thermoregulate the brood during heatwaves and assessed whether exposure to elevated temperatures during larval and pupal development affects responses to sensory stimuli of adult males. We found that workers were unable to maintain the brood temperatures within the optimal range during heatwave exposure. Our behavioural tests indicated that exposure to short-term heatwaves of 36–38 °C during the pupal stage affects the initial responses of adult males to visual ultraviolet stimulus, but we were unable to detect effects to olfactory, gustatory or mechanosensory stimuli. Finally, we did not find an effect of heatwave exposure on the body size of adult males when exposed to heatwaves as either larvae or pupae. Our results indicate that exposure to short-term heatwaves at a developmental stage closer to adulthood may cause detrimental effects on the behaviour of male bumble bees. Given the importance of males for colony foundation, additional work is strongly encouraged to understand their vulnerability in the face of climate change.