Nesting and pollen preference of Osmia lignaria lignaria (Hymenoptera: Megachilidae) in Virginia and North Carolina orchards.

Cavity-nesting megachilid bees in the genus Osmia, found throughout the Palearctic and Nearctic regions, are good candidates for domestication. In North America, Osmia lignaria Say has been reported to be an excellent pollinator of tree fruit and is currently being developed for commercial use in orchards. This is largely because of research over several decades with the western subspecies of this bee, Osmia lignaria propinqua Cresson, in western orchards. The behavior of the eastern subspecies, O. lignaria lignaria Say, in eastern orchards has not previously been reported. This study evaluated the nesting activity and pollen preference of a population of the eastern subspecies in five orchards in the foothills and piedmont regions of North Carolina and Virginia over a 2-yr period. Apple was present in all orchards and all were bordered by hardwood forest. Shelters were placed both within orchards and the forest border. Emergence dates, nest construction, and orchard bloom were monitored weekly. Bee populations increased by 2-3 times annually at most orchards. Pollen species comprising nest provisions from 720 individual nest cells were identified and quantified using scanning electron microscopy. The greatest amount of pollen (46-82%) was that of a small understory tree, Eastern redbud (Cercis canadensis L.), at all orchard sites where these trees were present nearby. The quantity of orchard pollen was relatively low, <20% at full apple bloom, except for one orchard (53%) without nearby redbud. O. lignaria lignaria appears to prefer Eastern redbud pollen over orchard pollen.