AUSTIN—Like most bees, bumblebees are having a tough time. Pesticides, habitat loss, light pollution, and parasites have led to sharp declines in their populations, more than 75% in the few places where researchers have tracked the insects for long periods of time. Now, scientists have identified a new way that global warming may be affecting some of these key pollinators.
Rising temperatures are forcing some bees to breathe shallowly and rapidly, essentially hyperventilating, which burns more energy and makes them less likely to survive, according to research presented here last week at the Society for Integrative Biology annual meeting. and Compared.
The study “showed very well that different [bumble bee] species have different vulnerabilities to climate change,” says John Hranitz, an ecological geneticist who studies bees at Bloomsburg University but was not involved in the work.
About half of the 45 bumblebee species in the United States appear to be in trouble. The reasons are unclear, but climate change appears to be at least somewhat responsible.
“The big concern is that the bumblebees that are declining tend to be the more specialized ones with longer tongues,” says Avery Russell, an evolutionary biologist at Missouri State University who was not involved in the new study. If these particular bees disappear, the flowers that depend on these pollinating specialists will be in trouble. The disappearance of those species could make spring meadows less colorful and, more importantly, could lead to the disruption of entire ecosystems. People also depend on bumblebees to pollinate crops.
Eric Riddell set out to understand why climate change might affect some bees but not others. A global change biologist at Iowa State University, he and his colleagues collected and studied local queens belonging to the black and gold bumblebee (auricomus bombus), a declining species, and the common eastern bumblebee (B. impatience), which is working fine. The researchers rounded up the females as they came out of their winter rest to mate and build nests, and in the lab kept them in conditions that queens would experience outdoors, mimicking soil and air temperatures.
To test the queens’ response to temperature, the team placed them in glass tubes and tracked how fast they breathed and how much water they lost at 18°C and 30°C, temperatures on the border of what queens normally experience. insects.
In this way, Riddell’s group studied the many ways that heating could affect a bee’s physiology, something that has rarely been done before, says Rylee Vigil, a Samford University student who spent last summer studying bees. in Greece with Hranitz.
At 18°C, a mild spring day, the queens of both species breathed about once an hour, the team found. When the researchers turned up the thermostat, the black-and-gold queen bumblebee’s breathing “completely changed,” Riddell told conference attendees. The common eastern bumblebee’s respiration sped up a bit, to one breath every 10 minutes, but the black and gold bumblebees began to breathe 10 times faster, once a minute. “It’s almost like hyperventilating,” Riddell said.
After 3 days, 25% of the eastern bumblebees had died, while twice as many black and gold bees perished, the team reported. Increased respiration in certain bee species could explain why some bees are declining and may continue to decline as the climate warms, Riddell suggested.
“This is a super interesting finding,” says Ellen Keaveny, a graduate student at the University of Wyoming who studies the effects of temperature on bees but was not involved in the work.
Still, it’s not clear if the findings will apply to other types of bees in different regions, Russell says. “It’s hard to know if there’s a general pattern,” he says. “It would be nice to include some other species.”
Riddell is doing just that. Last summer, his team collected seven more species of common bumblebees in the United States. Those that are declining in number begin to hyperventilate in warm temperatures, he and his colleagues have found.
It’s extremely challenging and time consuming to measure bee declines on a continental scale, Riddell noted. This work “potentially provides a litmus test” to at least assess which ones should be monitored.