> The proventriculus is used to engulf pollen and other particles which contaminate the nectar carried into the crop. The four lips are closed and opened, pulled backwards and straightened by the external circular muscles and internal longitudinal muscles. Combs of filiform-hairs (70 pm in length) located on the margins of the lips ‘catch’ and filter particles from the fluid. By repeated filtering, opening and closing actions of the hairs and lips, particles are filtered and collected in pouches between the ventricular folds to form boluses and are eventually passed into the midgut. In the present experiment, particle sizes ranging from 0.5 to 100 pm in diameter, including dandelion pollen (Taraxucum officinale Web.), Torula yeast (Cundidu utilis Lodder et Kreger-Van Rij), bee disease spores of Nosema apis Zander and Bacillus larvae White, and man-made particles can be filtered by the hairs. Small particles (0.23 pm in diameter) filter through the hair and return back to the fluid. Large particles (100-200 pm in diameter) are caught between the stylets of the mouthparts and are not ingested. Torula yeast, which is often used as a pollen supplement for feeding adult honey bees (Peng et al., 1984), falls in the filtration size range of the proventricular hairs. It can be efficiently collected by the proventricular hairs during feeding, and therefore will not contaminate the honey.  

Physiological Entomology (1986) 11, 43-39
Filtering mechanism of the honey bee proventriculus
YING-SHIN PENG and JERRY M. MARSTON Department of Entomology,
University of California, Davis, U.S.A.

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