New research shows that bees get warmer when they carry more pollen. On summer days they may succumb to the heat. Scientists fear that global warming will increase this risk.
A bee in a field of flowers may seem soothing, but it is likely that the same animal experiences it differently. Every milligram of pollen carried by a bee raises its body temperature by 0.07°C. Bumblebees that collect a lot of pollen can be a couple of degrees warmer than bees that don’t have pollen. American researchers write this today Biology Letters.
On hot days, which are becoming more common due to climate change, bumblebees may need to adjust their behavior to avoid overheating. Researchers fear that the bees will be able to go out more or less time to collect pollen. This can lead to fewer plants pollinating and further reducing the number of bees. The problem of heat stress comes on top of other threats to bumblebees and other bee species, such as drought, pesticides, and poor food supplies.
Large bumblebees in particular are at risk of overheating. They naturally have a higher body temperature than young bees, because they generate more heat and lose less heat. In addition, they can collect more pollen than their smaller counterparts, which keeps them warmer.
The researchers, who work at North Carolina State University, caught 91 bees in a botanical garden. They measured each animal’s body temperature with a thermometer just 0.2 millimeters in diameter. Using toothpicks, they removed pollen from the hind legs of insects.
exposed for a longer period
The Americans did not investigate why bees would overheat if they were carrying more pollen. Packed bees may have to work harder to stay aloft. In addition, bumblebees that collect a lot of pollen may travel longer and thus be exposed to the sun’s heat for a longer period.
“It’s a fascinating study,” says ecologist and bee researcher Jeroen Schepper. He works at Wageningen University & Research (WUR) and is not involved in the new study.
Previous research has already shown that larger bees and bumblebee species decline faster than smaller bees and bumblebee species. “We always attributed it to a lack of food, because the young bees need less food,” Scheiber says. “But this research shows an interesting mechanism that also fits into the picture: Older bees are more susceptible to heat stress.”
At the same time, higher temperatures can also be beneficial to bees. “When it’s warmer, flowers can bloom longer and bees can collect more pollen and nectar,” explains Séverine Kotrschal, an evolutionary biologist and bee researcher at WUR, who was also not involved in the new study.
However, Cuttrshall emphasizes the findings of the current study. The bees are relatively large and have an insulating layer of hair. Therefore, high temperatures are more likely to threaten them than small insects. “Bumblebees may be able to adapt to higher temperatures, but this takes time and climate change is happening quickly,” Kotrschal says.
