Flying bumblebees trade off fighter-jet-like maneuverability for jumbo-jet-like stability when they shift their load from nectar to pollen, researchers have found.
The findings, published this week in the Proceedings of the National Academy of Sciences, are among the first to show how nectar and pollen affects the flight dynamics of bumblebees.
"The literature shows bumblebees can carry just about over half their body mass in pollen or close to their body mass in nectar," says Dr Sridhar Ravi of aerospace engineering at RMIT University.
While nectar is carried in an insect's abdomen, pollen is carried on its legs. Ravi and colleagues figured that these different load positions would affect how the insect flew.
They hypothesised that when an insect was carrying pollen instead of nectar it would have added stability because, like a tightrope walker, it had balancing weights at a distance from its body.
But these weights would also slow down the insect's turning process and make it harder for it to maneuver quickly to escape a predator or to land on a moving flower.
By contrast, when an insect was carrying nectar, the researchers thought it would have added maneuverability because its weight was focused near its center of gravity.
Ravi and colleagues carried out a set of experiments in a wind tunnel with a robotic flower, which looked at the flight performance of 14 bees under different conditions.
They put markers on the bees and then using high speed video measured their speed, acceleration and orientation over time.
If a bee had to land on a stationary flower in turbulent wind conditions, it flew with greater stability and efficiency when it was loaded with pollen than when it was loaded with nectar.
When a bee had to track a moving robotic flower in steady wind conditions, by contrast, a nectar load enabled the bee to maneuver more deftly.
In a final experiment where the bee had to track a moving flower in turbulent wind conditions, there was no advantage to carrying pollen or nectar, says Ravi.
"Such a test has never been done," he says. "It shows there's a trade off between stability and maneuverability."
"So if something is stable it's not going to be maneuverable and if something is maneuverable it's probably not going to be stable.
Ravi likens the difference that pollen and nectar loads make to a bee to the difference between a jumbo passenger aircraft that is very stable but unable to perform rapid, quick maneuvers, and a fighter jet that performs rapid maneuvers, but is not stable.
While honey bees have dedicated foragers for pollen or for nectar, bumblebees are generalists and will carry either pollen or nectar depending on what the hive requires.
The latest findings provide insight into the cost different loads impose on flying bumblebees, says Ravi.
It also suggests that on windy or rainy days they might prefer to collect pollen, an idea that he and colleagues are now looking into.