Pollen preference and nesting of a native bee, Osmia lignaria, in Eastern orchards

A native bee, Osmia lignaria Say, was established at five orchard locations in western Virginia and North Carolina using artificial nest shelters.  Bee populations were monitored and nest provisions were sampled over multiple years.  Bee populations increased by at least 2x in most years.  However, about half of all pollen from nest provisions came from Eastern redbud, Cercis canadensis L., a common understory tree in Eastern hardwood forests.  Pollen from oak, willow, and ash was also common.  Orchard pollen accounted for less than 10% of total pollen except in one orchard where redbud was not present nearby.  However, in this case bee nest establishment was low.  This bee does not appear a good choice as an alternative pollinator for orchards located near eastern hardwood forests.