Spikes of extreme heat caused by warming temperatures are a critical factor in the widespread die-off of wild bumblebees, according to a study published last week in the Science journal—even beyond the effects of pesticides.
“We are not saying pesticides are not a factor,” said Jeremy Kerr, a biologist at the University of Ottawa and the senior researcher on the study. “We are confirming positively that climate change is a factor.”
Bumblebees are different from honeybees. The former is a wild species, while the latter is cultivated for agricultural production.
Both are imperiled, but in different ways. Some 50 percent of 49 native bumblebee species in the US are declining, according to Leif Richardson, an ecologist at the University of Vermont and a bumblebee expert who did not work on this paper.
Some species’ populations, however, are growing. Wild bumblebees have been studied less than farm bees. The fate of honeybees is particularly well monitored by the government since they’re credited with fertilizing roughly $15 billion worth of crops yearly in the US alone, according to the Department of Agriculture.
Honeybees have been dying off at an alarming rate. Beekeepers across the United States lost 40.7 percent of their honeybee colonies from April 2018 to April 2019, according to the latest annual nationwide survey conducted by the University of Maryland-led nonprofit Bee Informed Partnership.
Recent research has linked farm bee die-offs to insecticide use.
But for this paper, contributors Peter Soroye, Tim Newbold and Kerr, looked at wild bumblebees, which scientists note also perform critical pollinating functions.
To evaluate climate impacts on wild bee sites, they developed records of bee occupancy at 550,000 locations across North America and Western Europe of 66 bumblebee species. They used a baseline period of 1901 to 1974 and compared it to 2000 to 2014.
They found declines of 17 percent in Europe and 46 percent in North America.
Controlling for other factors, they concluded that “climate change has driven stronger and more widespread bumblebee declines than have been reported previously.”
Richardson said the paper may actually underestimate the extent of the change.
“In the end,” he said, “lack of data, particularly in Northern climes, only allowed them to consider a small percentage of land mass.”
Kerr said that knowing about bumblebees’ sensitivity to heat spikes is helpful prevent their decline. “Just like we would plant a shade tree to help protect humans from heat, we could manage habitat to shield bees from extremes.”