Experimental heat waves disrupt bumble bee foraging through direct heat effects and reduced nectar production

Heat waves are an increasingly common extreme weather event across the globe and are projected to increase in frequency and severity in the coming decades. Plant-pollinator mutualisms are vulnerable due to interacting effects of extreme heat on ectothermic insect pollinator foraging behavior and their forage plants. We designed an experiment to parse the impact of extreme heat on bumble bee foraging mediated directly through air temperature and indirectly through changes in plant rewards. Temperatures simulating a moderately severe heat wave negatively impacted foraging bumble bees 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 heat waves could have profound negative consequences for bumble bee colony persistence and maintenance of pollination services.