Heather nectar extracts reduce within-colony epidemics of the bumblebee parasite Crithidia bombi

Disease and habitat loss are significant causes of pollinator declines, and evidence indicates the two are linked. In Britain, lowland heath is an important bee habitat, but over 80% has been lost since the 1800s. This deprives wild bees of a rich food resource, but also the health benefits of an antimicrobial metabolite from Calluna vulgaris nectar, callunene, which reduces infection by the gut parasite Crithidia bombi in individual bumblebees. Here, we test whether these individual impacts can control epidemics in social colonies. We inoculated workers in early-stage Bombus terrestris colonies with Cr. bombi and randomly assigned colonies to the following treatments: (i) heather extract, (ii) callunene, and (iii) a sugar-water control. Colony infection rates were measured weekly. Colonies that were exposed to heather metabolites or callunene had a lower prevalence of Cr. bombi, especially the flagellated, infectious form, when compared to controls. Consequently, we conclude that these antimicrobial metabolites can control epidemics in social bumblebees. This suggests that lowland heaths may act not just as an important food source but as an essential natural pharmacy for pollinators.