Buzz pollination: investigations of pollen expulsion using the discrete element method

Abstract

Buzz pollination is a specialized mechanism by which bees extract pollen from flowers using vibrational energy. This process is essential for the reproduction of many plant species, including economically important crops such as tomatoes and blueberries. Despite its ecological and agricultural significance, the mechanical factors governing pollen expulsion remain incompletely understood. While previous experimental studies have examined how vibration frequency and amplitude influence pollen release, they often lack the ability to resolve the detailed interactions between pollen grains. This study addresses this gap by using the Discrete Element Method (DEM) to simulate pollen expulsion under vibratory excitation, providing a computational approach to analyzing pollen motion at a granular level. Two primary simulations were conducted to model pollen expulsion: translating anther motion, in which the entire anther oscillates as a rigid body, and deforming anther motion, which accounts for structural vibrations that more closely resemble natural conditions. In the translating anther simulations, pollen-pollen interactions played a critical role in directing grains toward the anther pore, challenging prior assumptions that grains move independently. Initial analyses of total pollen expulsion over long time periods showed little variation across different vibration settings. However, by examining earlier time steps, trends emerged that revealed higher displacement amplitudes and frequencies led to more rapid pollen release. To quantify this effect, expulsion rates were measured based on the time required to eject half of the initial pollen grains. These results were further analyzed using a parameter called jerk, which describes how rapidly acceleration changes over time. Jerk was found to be a strong predictor of pollen expulsion rates, effectively collapsing the parameter space into a single governing variable. Simulations of deforming anthers introduced additional complexity, as the shape and motion of the anther influenced the efficiency of pollen release. The findings suggest that vibratory forces are distributed differently in deforming anthers compared to rigidly translating ones, leading to differences in expulsion behavior. This study advances the understanding of vibratory pollen expulsion mechanics and provides a foundation for future research into artificial pollination technologies and pollination efficiency in natural ecosystems.