A bumblebee gathers pollen from a purple coneflower plant in a bed in D.C.’s Georgetown Waterfront Park on July, 12, 2019. Bill O’Leary/The Washington Post file
Warming temperatures could be responsible for a worldwide bumblebee decline, a new analysis finds – and the damage may rise as temperatures soar because of climate change.
Published in Frontiers in Bee Science, the study looked at heat stress in bumblebees, reviewing 180 years’ worth of literature to determine the optimal temperature of bumblebees’ brood nests. The hundreds of species of bumblebee function best when their brood nest remains between 82.4° and 89.6° Fahrenheit, scientists conclude – a range that, though narrow, has “remarkable uniformity.”
While there have been numerous studies of honeybee hives, the researchers write that bumblebee nests – which are usually hidden underground – have been neglected. Nest temperatures are regulated by factors including the soil around them and the bumblebees themselves. When things get too hot, bumblebees use their wings as fans. They can also fly from the nest in large numbers and defecate en masse to cool themselves.
But the insects’ best attempts to cool off could fail as air and soil temperatures rise, the researchers write, warning that “heat stress may be lethal even if slightly elevated above optimum.”
Such stress could already be playing a role in bumblebees’ decline, they posit. Bumblebee populations have fallen globally for years, with bumblebees disappearing from nearly half of their former habitat in North America alone.
More research is needed to fill out the picture as global temperatures rise, the researchers write.
“The effect of high nest temperatures has not been studied very much, which is surprising,” Peter Kevan, an emeritus professor in the School of Environmental Sciences at Canada’s University of Guelph and lead author of the article, said in a news release.
Nor is it clear whether bumblebees will develop effective ways to adapt to rising heat.
The researchers recommend more studies on bumblebee nests, which, they say, could help scientists understand how soaring temperatures might affect other social insects such as ants and termites.
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