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Pollinating Bumblebees

Study: Floral Vibrations by Buzz-Pollinating Bumblebees More Powerful Than Their Flight or Defensive Buzzes

Buzzing by buff-tailed bumblebee (Bombus terrestris audax) workers during pollen foraging is much more powerful than that used for defense or flight, according to new research from the University of Stirling.

The buff-tailed bumblebee (Bombus terrestris). Image credit: Marta Boroń / CC BY 2.0.

The buff-tailed bumblebee (Bombus terrestris). Image credit: Marta Boroń / CC BY 2.0.

“Buzz-pollinated flowers represent some of the most important economic crops, such as potatoes, tomatoes, aubergines and blueberries,” said Dr. David Pritchard, a researcher in the Department of Biological and Environmental Sciences at the University of Stirling.

“We found that flower buzzes were much more powerful than those used for defense or flight — suggesting that, rather than being due to drag, bumblebees might have evolved different types of buzzes for different tasks.”

Previous studies have identified variations between flight buzzing and defensive buzzing.

During flight buzzing, bumblebees’ wings flap, however, during defensive buzzing they do not — therefore, it was not clear whether buzzing variations were caused by flapping wings, or not.

To further understand the issue, Dr. Pritchard and his colleague, Dr. Mario Vallejo-Marin from the Department of Biological and Environmental Sciences at the University of Stirling, looked at flower buzzing, during which the bumblebees’ wings do not flap.

Flower buzzing occurs when bumblebee vibrate flowers to shake pollen onto their bodies.

“We know that bees use their distinctive buzzing vibrations for lots of different tasks and, for this study, we wanted to understand whether buzzes differed by task — or if variations in buzzing were caused by drag on the wings,” Dr. Pritchard said.

During the experiment, buff-tailed bumblebees foraged on a buzz-pollinated flower, performed a tethered flight, or were encouraged to perform a defensive buzz through a gentle stroke of their body.

The scientists used a laser to scan a reflective tag on the bees’ bodies to measure the speed of movement 10,000 times per second, with the data analyzed by computer.

They found that flower buzzing produced forces of more than 50G — five times that experienced by fighter jet pilots.

“We found that flower buzzes were much more powerful than buzzes used for defense or for flight — suggesting that, rather than being due to drag on the wings, bumblebees might have evolved different types of buzzes for different tasks,”

“Flower buzzing is important to understand because not all bees can buzz flowers.”

“For example, we still do not understand why honeybees do not buzz flowers.”

“By better understanding how flower buzzes appear and differ from the other vibrations bees produce, it may shed light on the reasons why some bees buzz flowers and some do not.”

The research was published in the Journal of Experimental Biology.

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David J. Pritchard Mario Vallejo-Marín. 2020. Floral vibrations by buzz-pollinating bees achieve higher frequency, velocity and acceleration than flight and defence vibrations. Journal of Experimental Biology 223: jeb220541; doi: 10.1242/jeb.220541

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