Global warming and urbanization are threatening bee populations across the country. One factor in that threat is heat. At high temperatures, bees become unable to reproduce, fly or even walk.
So researchers from North Carolina State University recently set out to see just how much heat local wild bees could handle.
Steve Frank, associate professor of entomology at NC State University, tested 15 species of the most common wild bee species that exist in Southern cities to identify the highest temperatures each could withstand. Frank said the study focused on urban areas because the infrastructure in cities causes them to be a few degrees hotter than surrounding rural areas.
Researchers first tested how much heat wild species could tolerate inside a test tube.
“At their maximum temperatures, bees become incapacitated. They’re near death,” Frank said.
After lab testing, researchers compared the bees' tolerance to how often they could be found in urban backyards. The scientists counted bee species in 18 backyards in Wake County during spring and summer months for two years.
As predicted, bee species that are less tolerant to heat were less prevalent in hotter, urban locations. These so-called heat islands are simply urban areas surrounded by asphalt roads, concrete and less grass and tree shade.
BEES NECESSARY FOR NORTH CAROLINA AGRICULTURE
Frank said some bees were more vulnerable to heat, with a heat tolerance about 10 degrees lower than other species. Those bees may be likely to move out of a region as it becomes closer to their maximum heat tolerance. As temperatures rise, that could be bad for Southern farmers.
"Some crops can only be pollinated by bumblebees, for instance, because they rely on the specific way a bumblebee buzzes, or vibrates when it reaches a flower, is what shakes out the pollen, and other bees just can't do that, " Frank said.
Frank said the results should be especially concerning in North Carolina.
"North Carolina is one of the most rapidly urbanizing states in the country," he said. "It also relies heavily on agriculture for its economy. And so if we lose pollinators, that could negatively affect our economy."
Bumblebees were among the least heat tolerant species in North Carolina. The bees become incapacitated at about 110 degrees Fahrenheit. Bumblebees were also the first bee to be named an endangered species in the United States.
BEES THAT CAN'T STAND THE HEAT LEAVE
Frank said the study’s results mean bumblebees and other vulnerable species could disappear from the South as temperatures rise from global warning.
"The geographic area of some bumblebees is contracting as the climate warms, which means those species are moving North. As the climate warms, we can lose species, not just because they die, but because they leave," he said.