Pollen release during buzz pollination depends on vibration amplitude and floral vibration transmission, but not on spectral composition

Bees use vibrations across behavioural contexts, including a specialised foraging routine in which they vibrate flowers to release pollen (floral vibrations). Floral vibrations often have complex spectral properties, combining fundamental frequencies and their harmonics, yet their functional consequences remain unknown. We experimentally replicated bee buzzes with identical fundamental frequency (300 Hz) but different harmonic content (0, 2, or 4 harmonics) to determine their effect on pollen release, a key functional outcome for both the bee and the flower. We normalised signals to the same average power by holding root mean squared (RMS) acceleration constant and applied three RMS levels to test for interactions between power and spectral composition. We applied vibrations to flowers and quantified both the input signal (at the shaker) and the vibration transmitted at a distal anther, and measured pollen release. Harmonic content did not explain pollen release at any RMS level. In contrast, RMS acceleration strongly predicted pollen removal. The RMS measured at the distal anther was only weakly correlated with the input RMS, suggesting that the flower strongly modifies the vibration signal. Both input RMS and distal anther RMS explained pollen release, irrespective of spectral composition. Our results suggest that pollen release is determined by vibration amplitude (RMS acceleration) rather than spectral composition and is jointly governed by the bee-generated input and the mechanical filtering properties of the flower.