Honeybee hive density has consequences for foraging bumblebees in Irish heathlands

Abstract

Heathlands provide vital foraging resources for wild bumblebees, as well as managed honeybees that are brought to heathlands in late summer for heather honey production. With this increased honeybee activity, there is potential for competition for floral resources between honeybees and bumblebees. We studied how increasing number of honeybee hives in Irish upland heathlands, influenced honeybee abundance, nectar availability and bumblebee abundance, size and activity at two distances from the honeybee hives. In general, an increasing number of hives resulted in elevated honeybee abundance, and - while we observed no change in nectar volumes - an increase in flower-visitation activity (flowers/minute) by individual bumblebee workers. Furthermore, bumblebee worker size declined with hive density, suggesting that larger workers - which have a longer foraging range - may have foraged further from the hives, or possibly that smaller workers may have been forced participate in foraging to compensate for smaller rewards. This highlights the need to consider interactions between wild and managed bees for floral resources in land management and conservation to ensure the protection of wild bumblebee populations and the continued productive management of honeybee populations for profitable honey production.