Like most bees, bumble bees are having a tough time. Pesticides, habitat loss, light pollution, and parasites have caused steep declines in their populations, upward of 75% in the few places researchers have tracked the insects for long periods of time.
Now, scientists have identified a new way global warming may be taking a toll on some of these key pollinators.
Rising temperatures are forcing some bees to take shallow, rapid breaths—essentially hyperventilating—which burns more energy and makes them less likely to survive, according to research presented here last week at the annual meeting of the Society for Integrative and Comparative Biology.
The study “showed pretty nicely that different [bumble bee] species have different vulnerabilities to climate change,” says John Hranitz, an ecological geneticist who studies bees at Bloomsburg University but who was not involved with the work.
About half of the 45 bumble bee species in the United States seem to be in trouble. The reasons are unclear, but climate change appears to be at least somewhat responsible.
“The big concern is that the bumble bees that are decreasing tend to be the more specialized ones with longer tongues,” says Avery Russell, an evolutionary biologist at Missouri State University who was not involved with the new study. If these particular bees disappear, the flowers that rely on these pollinator 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 rely on bumble bees 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 bumble bee (Bombus auricomus), a species in decline, and the common eastern bumble bee (B. impatiens), which is doing just fine. The researchers gathered the females as they emerged from their winter’s rest to mate and build nests, and in the lab kept them in conditions that the queens would experience outdoors, mimicking soil as well as 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 at the edges of what the insects normally experience.
In this way, Riddell’s group studied the many ways warming might affect a bee’s physiology, something that has rarely, if ever, been done before, says Rylee Vigil, an undergraduate at Samford University who spent last summer studying bees in Greece with Hranitz.
At 18°C—a mild spring day—the queens of both species took about one breath an hour, the team found. When the researchers cranked up the thermostat, breathing in the black and gold bumble bee queen “completely changed,” Riddell told conference attendees. The common eastern bumble bee’s breathing sped up a little, to one breath every 10 minutes, but black and gold bumble bees began breathing 10 times faster, once a minute. “It’s almost like hyperventilating,” Riddell said.
Bees – a solution to human-elephant conflict
After 3 days, 25% of the eastern bumble bees had died, whereas twice as many of the black and gold bees perished, the team reported. The increased breathing in certain bee species could explain why some bees are declining and may continue to decline as the climate warms, Riddell suggested.
“It’s a superinteresting finding,” says Ellen Keaveny, a graduate student at the University of Wyoming who studies temperature effects on bees but was not involved with the work.
Still, it’s unclear whether 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 a few other species.”
Riddell is doing just that. This past summer his team collected seven more bumble bee species common in the United States. Those that are declining in number all start to hyperventilate at warm temperatures, he and colleagues have found.
It is extremely challenging and time consuming to measure declines in bees on a continental scale, Riddell noted. This work “potentially provides a litmus test” for at least assessing which ones should be monitored.
