Previous studies have identified variations between flight buzzing and defensive buzzing. During flight buzzing, bees’ 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 – working with Stirling colleague Dr Mario Vallejo-Marin – looked at flower buzzing, during which the bees’ wings do not flap. Flower buzzing occurs when bees vibrate flowers to shake pollen onto their bodies.
During the experiment, bees 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 team 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 analysed by computer.
“We wanted to understand whether defensive buzzing and flower buzzing were similar – and if buzzing variation could be attributed to wing flapping or if bees adapt depending on the task in hand,” Dr Pritchard said. “We found that flower buzzes were much more powerful than buzzes used for defence or for flight – suggesting that, rather than being due to drag on the wings, bees might have evolved different types of buzzes for different tasks.”
He added: “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 study is part of a wider project funded by a Leverhulme Trust grant awarded to Dr Vallejo-Marin and Dr Gema Martin Ordas, from the division of Psychology at Stirling, and Professor Fernando Montealegre-Zapata, of the University of Lincoln.
The paper, Floral vibrations by buzz-pollinating bees achieve higher frequency, velocity and acceleration than flight and defence vibrations, is published in the Journal of Experimental Biology.