Pollen Preferences of Seven Osmia Species (Hymenoptera: Megachilidae)

Pollen foraging as determined from nest provision analysis of seven Osmia species from one area for 2 yr indicated two specialist and five generalist species. Osmia coloradensis Cresson and O. californica Cresson were Asteraceae specialists. Osmia generalists showed significant pollen preferences. Osmia bakeri Cresson, O. indeprensa Sandhouse, O. kincaidii Cresson, and O. lignaria Say preferred Hydrophillaceae ( Phacelia ) pollen. Osmia pikei Cresson preferred Saxifragaceae ( Ribes ) and Ericaceae ( Arctostaphylos ) pollen. For aging parameters of flowering species collected, dominant pollen, number of cells with 100% one pollen, and niche breadths were not significantly different between specialists and generalists. The wide use of Asteraceae genera by the specialists and the preferences shown by the generalists reduced the foraging differences between the groups.