Female worker bees, which forage for the whole colony, struggle more to detect scents in the heat than males do, per the recent research
Elizabeth GamilloSeptember 23, 2024
Heat could be causing bees to lose their sense of smell, which can wreak havoc on their foraging behavior and affect both bees and crops, according to a recent study published in the Proceedings of the Royal Society B.
Bee populations have already taken a hit due to habitat loss and degradation. The study’s findings suggest the increasingly frequent and intense heat waves under climate change may exacerbate the problem.
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“The results are pretty clear: There is an effect of heat waves on bumblebee physiology,” says Coline Jaworski, a field ecologist at the National Institute for Agricultural, Food and Environmental Research in France who was not involved in the new study, to Science’s Rodrigo Pérez Ortega. And this effect might also harm flowers and crops: “If pollinators are not coming for a few days … then there’s no pollination, no seeds and no descendants—that’s it.”
Bumblebees are typically cold-adapted creatures. With traits such as their fuzzy, thick hair across their bodies, the insects can have difficulty adjusting to extreme heat. For the new study, researchers from the University of Würzburg in Germany wanted to see how heat impairs the bees’ ability to smell, which they rely on to find flowers for food.
The team observed 190 bumblebees commonly found in Europe that belonged to two species: Bombus pascuorum, which were caught from the wild, and Bombus terrestris, which were collected from a commercial apiary. The scientists simulated extreme summer temperatures by placing the bees inside tubes and raising the heat to 104 degrees Fahrenheit (40 degrees Celsius) for nearly three hours.
Then, the researchers snipped the bees’ antennae, which are used for smell and continue to be active for some time after removal, and attached electrodes to them. They measured the antennae’s responses to three floral scents—called ocimene, geraniol and nonanal—that are common in flowers and attract pollinators.
“The heat significantly impaired the bumblebees’ ability to detect floral scents,” says lead author Sabine Nooten, an insect ecologist at the University of Würzburg, in a statement.
The extreme temperature reduced the bees’ ability to smell by up to 80 percent in female workers and 50 percent in male bees. The antennae also had difficulty recovering from the heat exposure: Their scent responses were still abnormal after 24 hours of recovery in cooler temperatures. “That was surprising,” Nooten tells Science News’ Gennaro Tomma —the team had predicted the antennae would return to normal more quickly.
Notably, the experiment indicated wild bumblebees have more trouble adapting to heat than the commercially used bumblebees do. And female worker bees, which collect pollen and nectar for the colony, also appeared to struggle more than males. With about one-third of the global human food supply made up of crops that rely on bee pollinators, this could suggest a troubling trend. If heat waves persist or worsen, they may reduce the bees’ ability to pollinate essential crops.
Increasing record-breaking temperatures and heat that can last for days can spell trouble for pollinators. The paper is “an important first step to see really what is driving, potentially, these bee declines,” Sandra Rehan, a molecular ecologist not involved with the study, tells Science. She adds that the temperatures used in the experiment match what’s happening in nature under the present climate change scenarios. “Forty degrees [Celsius] is within the realm of what’s occurring currently, unfortunately.”
Future studies might examine how the bumble bees’ decreased ability to smell affects their foraging behavior—or how other bee species cope with heat exposure.
“If bumblebees suffer in this way, I think it’s probable that other bees would too,” Dave Goulson, a bumblebee ecologist from the University of Sussex in England who was not involved with the study, tells Science News. “But until someone looks, we won’t know for sure.”
