Abstract
Approximately 10% of flowering plant species conceal their pollen within tube-like poricidal anthers. Bees extract pollen from poricidal anthers via floral buzzing, a behavior during which they apply cyclic forces by biting the anther and rapidly contracting their flight muscles. Vibration dislodges pollen from the interior anther locule walls and causes pollen grains to exit the anther pores. The success of pollen extraction during floral buzzing relies on the direction and magnitude of the forces applied by the bees, yet these forces have not been previously quantified. In this work, we developed an experiment to simultaneously measure the directional forces and thorax kinematics produced by carpenter bees (Xylocopa californica) during defensive buzzing, a behavior regulated by similar physiological mechanisms as floral buzzing. We found that the buzzing frequencies averaged about 130 Hz and were highly variable within individuals. Force amplitudes were on average 170 mN, but at times reached nearly 500 mN. These force amplitudes were 30 to 80 times greater than the weight of the bees tested. The two greatest forces occurred within a plane formed by the bees' flight muscles. Force amplitudes were moderately correlated with thorax displacement, velocity and acceleration amplitudes but only weakly correlated with buzzing frequency. Linear models developed through this work provide a mechanism to estimate forces produced during non-flight behaviors based on thorax kinematic measurements in carpenter bees. Based on our results, we hypothesize that carpenter bees leverage vibration amplification to increase the motion of poricidal anthers, and hence the amount of pollen ejected.
Competing Interest Statement
The authors have declared no competing interest.
