Granular Behavior of the Honey Bee Pollen Pellet and Associated Removal Mechanics

Abstract

Honey bees collect and store pollen in the form of a pellet by packing the pollen grains together with regurgitated nectar. This research has indicated that the pollen pellet is a granulated suspension, i.e. a fluid that behaves largely as a solid due to capillary stresses on the surface of the granule. By alleviating these stresses, the granule can be melted (return to behaving as a liquid). Experiments that were performed involved melting the pollen pellet by bringing it into contact with the liquid from the suspension. It was found that the melting of the pellet is dependent on what type of pollen it consisted of. Pellets made from light yellow pollen melt when in contact with approximately 0.5 µL of 55% by mass sugar solution, while pellets made from dark yellow pollen do not melt with any amount of fluid contact, as determined from experimentation and imaging with a Scanning Electron Microscope (SEM). This phenomenon could be due to a differing amount of pollenkitt1 (an adhesive substance secreted by pollen producing flowers) between the two types of pellets, or possibly due to the size difference between different pollen grains. Additionally, the mechanism by which honey bees remove pollen pellets depends on the speed of removal along with factors including the size, composition, and mass of the pellet. Pellets removed at the higher speed of 4.8 mm/s had an average peak force magnitude of 51 ± 33 mN, \ an average time for removal of 4.8 ± 2.2 sec, average peak energy of 0.16 ± 0.1 mJ, and average peak power of 0.78 ± 0.8 mW. Pellets tested at the lower speed of 1.0 mm/s had an average peak force magnitude of 24 ± 9.9 mN, an average time for removal of 3.6 ± 3.6 sec, average peak energy of 0.078 ± 0.03 mJ, and average peak power of 0.28 ± 0.5 mW. Future work will involve determining mechanisms of pollen pellet granulation through melting experiments and the creation of artificial pellets along with further collection of pollen pellet removal force measurements.