Providing evidence to improve practice

Individual study: San Rafael Desert bee Osmia sanrafaelae numbers increase four-fold in one year when reared in a cage; field studies near Clarkston, Utah, USA

Published source details

Parker F.D. (1985) A candidate legume pollinator, Osmia sanrafaelae Parker (Hymenoptera: Megachilidae). Journal of Apicultural Research, 24, 132-136


Some leafcutter bee species (family Megachilidae) are declining or threatened, and captive rearing may be one strategy to augment or re-establish populations. Osmia sanrafaelae is known only from the deserts of southern Utah. This study reared O. sanrafaelae in a cage on an alfalfa field near Clarkston, Utah, USA, to see if populations could be managed or augmented.


On 7 July 1983, 50 male and 50 female adult O. sanrafaelae bees were released in a 6 x 6 x 2 m cage made of saran cloth, erected over a crop of alfalfa Medicago sativa before flowering. Several potted evening primrose plants Oenothera hookeri were put in the cage for nesting material. An unspecified number of pine nest boxes were attached to a board and placed near the top of the cage on the west side, facing east. Boxes were 15 cm3, each with 49 9-mm holes drilled and lined with waxed paper drinking straws.

On 29 July and 6 and 11 August 1983, straws with completed nests (plugged at the end) were removed and replaced with new straws. These nests were kept at 25° C until 8 November, then at 4°C. In late November, nests were cut open and the number of bees or parasites inside each was counted.
Nests of O. sanrafaelae from identical nest boxes without a cage, treated in a similar way in a 1982 study in the San Rafael Desert, were used for comparison. 


83 nests were built in the cage, containing 1,148 cells in total. Each female bee in the cage produced an average of 23.1 cells and 1.6 nests.

The average and range in number of cells/nest did not differ between caged and uncaged nest boxes (average 12.1 and 13.8 cells/nest, in natural and caged nest boxes respectively, range 1-22).
47% of bees in nests in the cage died for unknown reasons, with higher mortality in the late larval and pupal stages, compared with 9.2% of bees in nest boxes without a cage. 3.6% of cells in the cage had predators, parasites or diseases, compared to 35.8% of cells in nest boxes outside a cage.
The surviving new adult population in the cage was four times higher than the original population (exact number not given), with a male:female ratio of 2.2:1.
Note: If using or referring to this published study, please read and quote the original paper, which is available through the International Bee Research Association