The pollen-collecting activities of some andrenid bees

Information about the pollen-collecting activities of bees is usually based on field observations. From such records it cannot be inferred whether pollen was actually collected, as bees, especially the males, also may visit flowers to suck honey or to rest. One may expect more exact data from an analysis of the pollen actually carried by the bees. This paper deals with a study on bees of the genus Andrena. Some species of this genus are supposed to be oligolectic. Pollen loads were taken from preserved collection specimens and the pollen was prepared following the usual methods for the study of recent pollen. In the greater part of the samples taken one type of pollen proved to be dominant. Apparently a bee tends to visit only one species of flower per flight. Whether a species of bee always collects from the same flower species remains to be seen. A large number of specimens should be examined before conclusions can be drawn. Also the bees should be collected at different sites so as to eliminate the influence of the local flora. We also have to take into account the floral succession throughout the season. Early flying species are restricted in their choice of supplier of pollen (e.g. Salix) but as the season advances other plants come into flower and may be preferred. When a sample contained less than 5% of a different kind of pollen this was considered a contamination, either due to the preparing technique, or to unintentional addition to the normal pollen load when the bee rested on or came into contact with other plants. The results have been compared with flower records from Van der Vecht (1928) and Stöckhert (1933). A. florea is supposed to visit Bryonia only. This was confirmed by analysis