How climate change will impact the flight of the bumblebee

A bumblebee lands on a poppy flower on a field in Frankfurt, Germany, Friday, May 22, 2020. (AP Photo/Michael Probst)

TORONTO — Bumblebees' ability to fly for foraging and pollination is being impacted by extreme temperatures at both the high and low end.

Researchers at Imperial College London put bees to the test by measuring the motivation bumblebees had to fly at various temperatures ranging from 12 C to 30 C.

The scientists found that the bumblebees struggled flying further than a few hundred metres at the lower end of temperatures, after which their endurance increased with the temperature until 25 C – at which point the bee flight peaked, according to the study.

For most flying insects, body temperature influences flight activity, and air temperature impacts body temperature. Too cold, and the muscles needed for flight can't work quickly enough, too hot and they overheat, according to a press release.

The results, published in Functional Ecology on Wednesday, show that bumblebees living in more northern regions may stand to have improved flight performance from temperature increases, but those in already hot southern regions will suffer.

“Climate change is often thought of as being negative for bumblebee species, but depending on where in the world they are, our work suggests it is possible bumblebees will see benefits to aspects of an important behaviour," lead study author Daniel Kenna, said in the press release.

While this could be beneficial for some bumblebees, Kenna still cautions that the extreme fluctuations in temperatures could have a negative impact.

"More extreme weather events, such as cold snaps and the unprecedented heatwaves experienced in recent years, could consistently push temperatures beyond the comfortable flight range for certain species of bumblebees," he said.

This could prove to be disastrous for bumblebees and other pollinators who set up shop for the season, and forage around their nest site.

"These risks are particularly pertinent for ‘fixed colony’ pollinators like bumblebees, which cannot shift their position within a season if conditions become unfavourable, and potentially provide a further explanation as to why losses have been observed at species’ southern range limits," added Kenna.

In order to measure flight, the bumblebees were temporarily attached to 'flight mills'. Once attached they were able to fly in circles which allowed researchers to capture the distance and speed of flight, they used these results to create a thermal performance curve.

They found that at optimal temperatures, average bumblebee flight was around 3 kilometres. If temperatures rose to 35 C, flight distance would drop to 1 kilometre, and plummet even further, to just a few hundred metres at 10 C. At the colder temperatures, the researchers found that only the largest worker bees would fly.

"While we still need to understand how these findings translate to factors like foraging return to colonies and pollination provision, as well as applicability to other bumblebee species, the results can help us understand how smaller versus larger flying insects will respond to future climate change," Richard Gill, from the department of Life Sciences at Imperial College, said in a press release.

This could have far-reaching implications beyond pollinating insects, he added.

"It’s not just pollination: how different flying insects respond to warming temperatures could also affect the spread of insect-borne diseases and agricultural pest outbreaks that threaten food systems," said Gill. "Applying our experimental setup and findings to other species can help us to understand future insect trends important for managing service delivery or pest control methods.”