As temperatures rise, this phenomenon could threaten crops that rely on these pollinators
Increasingly common extreme temperatures are a rising threat to many around the world, but humans are not the only ones imperiled. In a study out today in the Proceedings of the Royal Society B, researchers show heat waves may severely jeopardize bumble bees’ ability to smell the flowers they feed on. The finding could foretell how climate change may affect the pollinators’ populations—and human industries that rely on them.
“The results are pretty clear: There is an effect of heat waves on bumble bee physiology,” says Coline Jaworski, a field ecologist at France’s National Institute for Agricultural, Food and Environmental Research who was not involved in the new study.
If these bees cannot find their food effectively, the impact on the crops they pollinate can be disastrous, she says.
“If pollinators are not coming for a few days … then there’s no pollination, no seeds, and no descendants—that’s it.”
Bumble bees pollinate crops that make up about one-third of our food supply – many vegetables, fruits, nuts, and legumes.
But bee populations have been declining for years/ Most researchers think the two main reasons are habitat loss and climate change.
Droughts can reduce flowers’ production of pollen and nectar that bees rely on to stay healthy. Extreme heat may also diminish flowers’ scent and nectar output., and both extreme heat and heavy rainfall can disrupt bees’ foraging patterns.
Sabine Nooten, an insect ecologist at the Julius Maximilians University of Würzburg, wanted to find out exactly how rising temperatures affect these pollinators’ physiology.
To investigate whether heat affected bumble bees’ smelling abilities, she and her team tested 190 insects from two species common in Europe: wild-caught Bombus pascuorum and B. terrestris from a commercial apiary.
The researchers placed each bumble bee in a 50-milliliter tube and simulated a heat wave by raising the temperature in the tube to 40°C for almost 3 hours. After exposing a bee to heat, they removed its antennae and inserted them into a tiny glass tube attached to an electrode to measure their electrical responses. (The antennae remain electrically active for some time after being removed.) They exposed the antennae to puffs of three fragrant compounds commonly found in flowers—ocimene, geraniol, and nonanal. Heat exposure reduced the antennal response significantly to all three scents.
In most instances, heat-exposed bumble bee antennae failed to recover their odor response, even if the researchers removed and tested them after the bees rested at cooler temperatures for 24 hours. That finding suggests the effects of heat waves on bumble bees could be long lasting, which is “quite alarming,” Nooten says.
The wild-sourced species, B. pascuorum, appeared to be less resilient to heat than B. terrestris in the new experiments. And for both species, female worker bees—which are responsible for collecting the colony’s food—seemed more susceptible to the heat than males.
Future studies should test for similar heat damage in other bee species and pollinators, such as hoverflies. Some of these “might be at higher risk” than bumble bees of harm from extreme heat, Jaworski says.
Bumble bees can regulate their temperature and live in colonies that store food; other pollinators such as the carpenter bee are solitary, so going a couple of days without food—either because they can’t effectively smell flowers or are simply foraging less to avoid the heat—could be devastating, she adds. “If they are not out to collect resources when they actually need it, then it’s over.”
Source: Science
