An assessment of Osmia rufa (syn. bicornis) as a pollinator of the sour cherry (Prunus cerasus) cv. Stevnsbaer in eastern Denmark

The sour cherry (Prunus cerasus) cv. Stevnsbaer is self-fertile but it is recommended that bees are placed in the orchards during flowering. The solitary bee Osmia rufa can be managed, and has previously been suggested as an alternative pollinator to Apis mellifera, so consequently, this study investigates the activity and food preferences of this species during flowering of sour cherry (P. cerasus cv. Stevnsbaer). Female O. rufa provisioned a mean of 2.96 +/- 1.44 cells each with 6.24 +/- 1.46 pollen types during the receptive period of flowering. In all 17 different pollen types were collected of which the most dominant were Salix (41.4% +/- 9.34%) and Acer (33.24% +/- 8.81%), followed by Betula (8.16% +/- 5.08%), P. cerasus (8.16% +/- 1.79%) and Fagus (3.56% +/- 1.96%). P. cerasus was present in all samples. Nine pollen types were from anemophilous plants and represented 87.94% of the pollen collected. The remaining 8 pollen types were from entomophilous plants. Based on the results it is estimated that a mean of 220,000 O. rufa cocoons would be needed per hectare if the species were to be an effective, supplementary pollinator of P. cerasus cv. Stevnsbaer. Practical, economic and environmental considerations suggest that the use of O. rufa as an alternative pollinator to A. mellifera in this instance is not realistic.