Comparative analysis of pollen viability across hair types on Osmia cornifrons (Hymenoptera: Megachilidae)

The Japanese horn-faced bee, Osmia cornifrons (Hymenoptera: Megachilidae), is a solitary, cavity-dwelling mason bee. Native to Japan, O.cornifrons was introduced to North America in 1977 to enhance apple orchard pollination. As a solitary bee, O.cornifrons females construct individual nests and gather pollen to provision offspring, necessitating extensive flower visits and promoting cross-pollination. Once collected, pollen is stacked in unbranched scopa hairs on the bee’s ventral abdomen, allowing the bee to transport the pollen to her nest. As different hair type holds onto the pollen differently, we hypothesized that the pollen viability would differ among hair types. We collected female O.cornifrons returning to their nests with pollen, then sampled pollen from each body part/hair type using a tapping method to avoid damaging the pollen grains. The pollen was cultured in a modified Brewmaker and Kwack liquid growth medium at 25°C and 70% RH. Using microscopy imaging, we assessed the number of pollen grains and pollen tubes produced. Electron microscopic analysis showed pollen grains on various hair types—branched, chisel-tip, and enlarged tip— located at distinct locations on the body of O.cornifrons. We also found variations in pollen viability between different body parts and among hair types. These findings suggest that certain hair types might be better suited for transporting viable pollen, which could help determine factors influencing pollination success when taken in conjunction with bee physiology and behavior. This underscores the potential of O.cornifrons as a valuable alternative pollinator and highlights aspects that may be utilized in developing tools for artificial pollination.