Buzz pollination—a process in which bees extract pollen by vibrating flowers—occurs in over 20,000 plant species. Among the most specialized examples are the wildflowers of the Pedicularis genus (Orobanchaceae), whose curved "elephant-nose" petals rely exclusively on bumblebee vibrations for pollination. Despite the simultaneous blooming of multiple Pedicularis species and their shared reliance on bumblebee pollinators, hybridization between co-occurring species is exceptionally rare. Now, a research team has uncovered the biomechanical mechanisms behind this phenomenon.

Published in Science China Life Sciences, the study—led by researchers from the Kunming Institute of Botany of the Chinese Academy of Sciences, reveals how floral vibrations and pollinator size mediate these interactions.

In the Himalayan-Hengduan Mountains of southwestern China, hundreds of lousewort (Pedicularis) wildflower species produce unique "elephant-nose" flowers, characterized by a long nose-like beak. Bumblebees, their sole pollinators, must vibrate these structures to release pollen. Yet, observations show that bees consistently bite the same region of the flower, regardless of species.

To investigate, the researchers developed a three-dimensional (3D) finite element model of Pedicularis flowers, incorporating structural and material properties derived from micro-CT scans and atomic force microscopy. Their analyses identified an "optimal biting point" at the base of the floral beak, where vibrations most efficiently dislodge pollen. However, the effectiveness of this mechanism depends on a precise match: the bumblebee’s body length must align with the distance from the biting point to the flower’s tip.

The study further revealed that Pedicularis species vary in beak length, curvature, and coiling, each requiring a specific pollinator size for successful pollen transfer. Notably, bumblebee workers within a single colony exhibit size variation across seasons, meaning different individuals may specialize on different flower species.

An individual-level pollination network analysis confirmed strong "size matching" between bumblebee body length and floral beak dimensions, explaining why hybridization is rare: bees of differing sizes inadvertently isolate Pedicularis species by preferentially visiting flowers that match their morphology.

"The serious challenge is to integrate biomechanics with pollination ecology, as buzz pollination involves complex vibrational coupling," said PhD student XU Yuanqing, first author of the study. "We established a multidimensional research framework that combines vibrational mechanics, insect behavior, and ecological networks."

The findings highlight the vibrational coupling mechanism in buzz pollination and emphasize the critical role of floral biomechanics in shaping plant-pollinator interactions. This study offers new insights into the co-evolution of plants and pollinators, as well as the development of floral diversity in wild communities over time.

Bumblebees always bite at the base of the flower’s beak and then buzz it. (Image by KIB)