Preliminary study on pollen digestibility by Osmia cornuta Latr. (Hymenoptera Megachilidae)

Osmia cornuta L. food habits were studied in Pisa in April-May, 1995. Pollen grains were collected from Osmia deposits and were studied microscopically either to ascertain the botanical species collected or to compare the substances removed from the grain during digestion. Osmia females collected pollen grains covered with pollenkitt, carried them to the nest and placed them in storage areas. The grains were either monospecific or composed of no more than three species. Pollen grains stored by Osmia may contain starch as a polysaccharide reserve. In most botanical species, pollen protoplast and DNA are digested. Depending on the plant species, the starch may be totally digested by larvae. Exine sporopollenin may also be partially digested. In many cases, after ingestion a reduction in the intine wall in the region of the apertures was observed. This facilitates penetration of digestive enzymes and subsequent aggression and absorption of cytoplasm.