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Bumblebee populations in North America and Europe have plummeted thanks to temperature extremes, according to a study published Thursday in the journal Science.

The number of areas populated by bumblebees has fallen 46% in North America and 17% in Europe, and the new research found that regions seeing sharp bee declines also experienced strong variations in climate, and especially higher temperatures and worse heat waves.

It's yet another piece of bad news for bee populations. Declining colonies of commercial honeybees have been blamed on a strange phenomenon called Colony Collapse Disorder but also probably stem from a bevy of other causes. Now, the new research suggests bumblebees in the wild are suffering, too.

"Where temperatures are getting more extreme, bees tend to be disappearing more often," said Peter Soroye, a researcher at the University of Ottawa and one of the study's authors.

The loss of bumblebee populations is alarming because they play a central role in pollinating many plants, including key crops such as tomatoes and cranberries.

"Unlike honeybees in North America, which have been brought over from Europe and kept in these colonies, bumblebees are native and evolved with these plants," Soroye said. "So when it comes to these natural landscapes, bumblebees are pretty irreplaceable."

The study, which Soroye conducted with colleagues from the University of Ottawa and University College London, compared the observed locations for 66 species of bumblebees between 1901 and 1974 with places where they could be found between 2000 and 2014.

They found that nearly half of all regions in North America where bumblebees had been recorded in the earlier period no longer registered bees in the later period.

It's unclear whether the bees might recover. Franklin's bumblebee is a species once found in a narrow region where California and Oregon meet. The U.S. Fish and Wildlife Service recently proposed an endangered-species listing for the bee but noted that the listing may not actually happen because it's not clear there are any bees left to protect.

"Based on the lack of observations of Franklin's over the last 13 years it is possible that the species is extinct," the agency wrote.

The study combined observations of bumblebees, such as Franklin's, with a map of changing temperatures and precipitation extremes over the same periods. And it found a strong link between the regions where bumblebees had declined or disappeared and those experiencing worsening heat waves or other types of weather extremes.

"Basically it was measuring how these extremes have pushed species beyond what they had to tolerate before," Soroye said.

But in a comment on the new study, bee expert Sydney Cameron of the University of Illinois at Urbana-Champaign said there is a lot more work to do. Cameron argued that the data is "Western-centric" since it's only focused on North American and Europe, and that beyond the large-scale correlations shown in the study between temperature and species declines, researchers need more-detailed studies of precisely what's happening to bumblebees.

"I have no doubt that climate change is a likely factor in biodiversity decline in general, but this needs to be tested with experiments in both field and lab," Cameron said.

Unlike many other insects, bumblebees are especially sensitive to temperature. Their large, hair-covered bodies give them an ability to internally heat up by flapping their wings at different speeds. But that also makes them vulnerable in hot weather.

SundayMonday on 02/09/2020

Print Headline: Climate cited in bees' demise

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