When the honeybee hives arrived in Ireland, their size and activity changed.
When people bring their honeybees to the floral feast, local bumblebees may face competition even in the face of vast fields of flowers. When beekeepers truck their hives to a mass-blossoming event in upland Ireland to forage for nectar, local wild bees end up smaller than usual and focus on foraging for their young, researchers report December 10 in Proceedings of the Royal Society B: Biological Sciences.
This could indicate that the human-bred bees have run them over, stressing an essential pollinator. The late-summer bloom of heather in the Wicklow Mountains of Ireland coats the range in lovely purple flowers. For the occasion, beekeepers typically relocate their hives to the heathlands. The farmers' honeybees (Apis mellifera) descend on the local nectar supplies in the same way that tourist buses do in Times Square.
Unlike honeybees, which live all year round, the local wild bumblebee colonies are typically smaller and more seasonal. During the heather bloom, bumbling workers gather nectar to feed themselves and pollen to feed their young, a few of which will grow into queens that will overwinter, while the rest of the colony dies. The heather is key to this strategy. Dave Goulson, an entomologist at the University of Sussex in England who was not a part of the study, says, "So suddenly, having lots of competitors arriving on the back of a lorry is not ideal." Dara Stanley, an ecologist at University College Dublin, and her colleagues wondered how the temporary bee boom might affect local bumblebees.
They gently caught and measured members of six local bumblebee species—including the white-tailed bumblebee, Bombus lucorum, and the small heath bumblebee, Bombus jonellus—as well as honeybees from nearby hives as they strode through fields of blooming heather. The number of bumblebees in the area was unaffected by the honeybee hordes. But bumblebees the scientists measured in honeybee-heavy areas were smaller than those elsewhere. Larger bumblebees could be going to areas with fewer honeybees for better nectar opportunities, leaving small bees to forage in crowded areas, Stanley says. Or the bumblebee colonies could be having trouble taking in enough food, sending out more workers to forage — resulting in smaller bumblebees doing the grocery run.
The researchers also observed the behavior of local bees by following them, and they discovered that smaller bumblebees were more likely to forage for pollen rather than nectar. Pollen is nutrition for bee young, Stanley says, so “when a colony is under stress, it might prioritize reproduction or pollen collection for larva.”
It’s a subtle change in behavior, but the information could help guide beekeepers toward more ecological hive placement, Goulson says. While moving bees to flowers might be fine in more agricultural areas, findings like this and others suggest that honeybees shouldn’t be buzzing around nature reserves in the heathlands.
“We do know that wild pollinators have been in decline for quite some time,” he says. “Anything that contributes to their woes is something we should pay attention to.”
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