Premise of research. Bees rely on pollen for growth and reproduction and have evolved a variety of behaviors to remove pollen from plants with diverse floral morphologies. Notably, some bees use vibrations generated by their thoracic muscles to remove pollen from flowers. These floral buzzes can effectively remove pollen from species with poricidal flowers (e.g., anthers that open through small apical pores). However, little is known about the effectiveness of floral buzzes in removing pollen from nonporicidal flowers. Here, we compare pollen release in species and with (Solanum rostratum, Solanum dulcamara, and Solanum lycopersicum; Solanaceae) and without (Sinapis alba and Raphanus caudatus; Brassicaceae) poricidal anthers.
Methodology. We used a shaker and a laser vibrometer (for calibration) to apply controlled mechanical vibrations of different magnitudes (amplitude velocity) to flowers and used a particle counter to estimate the relative and absolute number of pollen grains removed. Pollen release under different vibration amplitude velocities was analyzed using a linear mixed effects model.
Pivotal results. Floral buzzes removed, proportionally, more pollen in nonporicidal than in poricidal flowers. Yet because poricidal flowers contain significantly more pollen grains per flower, buzzing poricidal flowers result in more pollen grains removed per buzz. As expected, pollen release increased with amplitude velocity of the applied vibrations.
Conclusions. Our results show that floral buzzing is an effective behavior for removing pollen from different types of floral morphologies, and we suggest that the less frequent buzzing of nonporicidal flowers may be explained by the potentially high energetic costs of producing thoracic vibrations when pollen can be gathered by less expensive means.