Documenting the behaviour of pollinators on flowers is key to understanding the ecology and evolution of plant-pollinator interactions. In particular, the physical coupling between plant and pollinator can affect how pollen is collected by pollinators and moved between flowers. Buzz-pollination is a unique interaction between bees and flowers with special tubular morphologies. In buzz-pollinated flowers, pollen is locked away inside the anthers, the male reproductive structures. The key to accessing this pollen is through vibrations, which the bee produces with the muscles in its thorax. These muscles are used for many other functions, including flight, defence, and communication. The vibrations produced by these muscles must be transmitted to the flower from the bee's body for pollen to be released, but little is known about how precisely these vibrations are transferred.
In a new study published in the journal Current Biology, the authors demonstrate that an efficient way for bees to transmit vibrations is through the head. As the thorax vibrates, the head moves back and forth with up to three times more movement than the thorax. The bee then bites the anther to deliver this enhanced head vibration to the flower, causing the motion of the anther to double. The study also demonstrates that the specific angle at which the bee bites the flower can affect this vibration transfer, and that flowers may have evolved different morphologies to limit the ways that bees can hold the anthers during buzz-pollination.
This study has come from an ongoing HFSP-supported collaboration between Noah Jafferis, University of Massachusetts Lowell, USA, and Mario Vallejo-Marín (Uppsala University, Sweden), which aims to recreate a bee's buzz through the use of micro-robotics. This project seeks not to replace bees with robots, but to use robots to understand how the morphology and biomechanics of different bees and flowers translate into diverse buzz pollination functions, for the broader benefits of informing conservation and bio-inspiration.
Now that the team understands how these bees transmit their vibrations to flowers, they are incorporating head vibrations into the following stages of their micro-robotic designs to move closer to a better understanding of this unique interaction between bees and flowers.