Experimental heatwaves disrupt bumblebee foraging through direct heat effects and reduced nectar production

Heatwaves are an increasingly common extreme weather event across the globe and are projected to surge in frequency and severity in the coming decades. Plant-pollinator mutualisms are vulnerable due to interacting effects of extreme heat on insect pollinator foraging behaviour and their forage plants. We designed an experiment to parse the impact of extreme heat on bumblebee foraging mediated directly through air temperature and indirectly through changes in plant rewards. Temperatures simulating a moderate heatwave negatively impacted foraging bumblebees reducing the proportion of successful foraging bouts, foraging bout duration and plant and flower visitation and indirect stress through reduced nectar production that limited foraging bout duration. Our experimental results provide a mechanistic link between climate, plants and pollinators and suggest in situ conditions from heatwaves could have profound negative consequences for bumblebee colony persistence and maintenance of pollination services. Read the free Plain Language Summary for this article on the Journal blog.