Pollinators in a warming world: the impact of heatwaves on the physiology and behaviour of bees

Climate change is considered one of the major threats to biodiversity and is associated with an increase in the frequency and intensity of heatwave events. Heatwaves create stressful conditions that can affect the survival, physiology, and behaviour of pollinators, such as bees. The first three projects of this thesis, conducted in controlled laboratory settings, focus on assessing the impact of simulated heatwaves on the British subspecies Bombus terrestris audax, while the fourth project uses citizen science to evaluate bee responses amidst natural heatwaves. Laboratory-based experiments revealed that bumblebee workers exhibit high heat tolerance, but their ability to acclimate to heatwaves is limited. I also observed important effects on colony performance during heatwaves, with mild heatwaves leading to increased offspring production compared to extreme heatwaves and controls. Brood-care behaviours were significantly impacted, with increased wing fanning observed at higher temperatures. In the third study, I found that workers were unable to maintain optimal brood temperatures during heatwaves and their exposure during the pupal stage affected adult male responses to visual stimuli. These results improve our understanding of the effects of heatwaves on bumblebee workers and males at both individual and colony levels. Given the importance of complementing laboratory experiments with field-based studies, the final project focused on investigating the responses of bees to natural heatwaves using citizen science. I found that bee abundance was higher before heatwaves compared to after and that temperature significantly influenced bee activity. During the study period, bees showed a preference for nectar over pollen collection, and we identified the plant species they frequented for resources at different temperatures. This project highlights the role of citizen science as a valuable tool in climate change studies. These studies can foster public awareness on the importance of pollinators and contribute to the development of pollinator conservation strategies in a rapidly changing world.