Scientists reveal "major" new factor in bumblebee decline

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Scientists have revealed a "major" new factor in the decline of bumblebee populations across the world.

Bumblebee populations have declined by 90 percent in the past 20 years, according to Environment America. There are many different factors contributing to their decline, including the use of pesticides and urban development. However, climate change is perhaps the biggest factor.

The decline of the bumblebees is highly concerning as they are vital for ecosystems. They pollinate flowers and crops. If populations were to continue to decline, crops would not be able to produce fruits and vegetables. Despite being small, they are crucial to nature's delicate balance.

And now, a new Frontiers in Bee Science study has found that the rising heat caused by global warming might be a reason for the decrease in numbers across the globe.

"The decline in populations and ranges of several species of bumblebees may be explained by issues of overheating of the nests and the brood," Peter Kevan of the University of Guelph in Canada and lead author of the study said in a statement. "The constraints on the survival of the bumblebee brood indicate that heat is likely a major factor, with heating of the nest above about 35 degrees Celsius being lethal, despite the remarkable capacity of bumblebees to thermoregulate."

A stock photo shows a bumblebee in a flower. A new study has found a new factor in the species decline across the world. Sazonoff/Getty

Kevan and colleagues decided to take a closer look at factors relating to bumblebee populations across the world. Although it is clear that many populations are in trouble, a definitive factor for all species has not really been identified.

They looked at 180 years of literature on the species and found one common factor across all bumblebee species that they can survive in temperatures up to 36 degrees Celsius (96.8F), but the ideal temperature for nests is between 28 to 32 degrees Celsius (82.4 to 89.6F).

But they are unlikely to be able to thermoregulate to the extent that rising temperatures due to climate change require, the study reports. While individual bees may be able to deal with increased heat better than others, the study notes that if a nest is too hot, the colony will not thrive.

"Excessively high temperatures are more harmful to most animals and plants than cool temperatures. When conditions are cool, organisms that do not metabolically regulate their body temperatures simply slow down, but when temperatures get too high metabolic processes start to break down and cease," Kevan said. "Death ensues quickly."

The study notes that a bumblebee colony "acts as a superorganism," which relies on collective survival.

The temperature thresholds appear to be similar in many bumblebee species. The study authors are concerned that this has limited their ability to adapt over time, meaning rising temperatures are more of a threat.

"The effect of high nest temperatures has not been studied very much, which is surprising," Kevan said in the statement. "We can surmise that nest temperatures above the mid-30s Celsius would likely be highly detrimental and that above about 35 Celsius death would occur, probably quite quickly."

Similar studies have been done on honeybees, another threatened yet highly important species, which shows high nest temperatures threatening the health of the queen bee. This suggests further that heat stress is a major factor in bees' overall decline.

More research needs to be done, however, so that scientists can understand more.

"We hope that future scientists may take the ideas we present and apply them to their own research on bumblebee health and conversation," Kevan said.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about bumblebees? Let us know via science@newsweek.com.

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