Flower Phenology and Pollen Choice of Osmia Lignaria (Hymenoptera: Megachilidae) in Central Virginia

Interest in native bees as alternative pollinators of agricultural crops has greatly increased in recent years. These bees do not produce honey but are often excellent pollinators, not aggressive, and not subject to a multitude of pest and regulatory problems. Herein we report the results of a 2-yr study of the eastern subspecies of Osmia lignaria Say, a univoltine, early-spring, mason bee. Our objective was to determine pollen choice of a wild population of O. lignaria lignaria Say throughout the period of nest construction and relate this to the phenology of local floral resources. Artificial nesting sites were provided and pollen provisions were sampled from nest cells constructed over a 7-wk period. Pollen was identified and quantified with scanning electron microscopy. Approximately 20 types of pollen were found in bee nest provisions, selected from 80 flowering species. Pollen choice changed over time in accord with flower phenology and pollen availability. Eastern redbud (Cercis canadensis L.) pollen was the most abundant (28%) in nest provisions, and bloom was coincident with initial spring nest construction. Nest provisions had 11% oak (Quercus sp.), 10% boxelder (Acer negundo L.), 10% mustard (Brassicaceae), 8% willow (Salix sp.), 7% ash (Fraxinus sp.), 6% blackberry (Rubus sp.), 4% black gum (Nyssa sylvatica Marsh), and 4% poison ivy (Toxicodendron radicans L. Kuntze) pollen. Maximum nest cell construction coincided with apple bloom and continued for several additional weeks. Floral resources were identified that could be used by eastern orchardists to attract and enhance local populations of O. lignaria lignaria.