Native bees serve a vital role in pollination services, and in recent years there has been increased attention on native bee decline. Previous work has sought to identify flowering plants that best support native bees, generally using microscopy or direct observation of bee behavior. The blue orchard mason bee, Osmia lignaria Say, is a native solitary bee in the western U.S. that forages over relatively short distances, and over a short time period in early spring. Due to this limited spatial and temporal foraging window, O. lignaria is sensitive to changes in landscape composition and climate. Consequently, it serves as an ideal model system for understanding native bee health. We placed O. lignaria and nesting materials at 12-24 sites across diverse landscapes in western Washington in 2018 and 2019, and over two distinct foraging periods. The first foraging period (mid April-mid May) best reflected the natural emergence of O. lignaria adults, while the second foraging period (mid May-mid June) reflected potential asynchrony with host plants. Pollen samples taken from each period were sequenced using Next Generation Sequencing (NGS) to identify flower visitation. Plant composition data at study sites was also measured for ground-truthing results from NGS.
Results/Conclusions
Genetic analyses of pollen data revealed that O. lignaria visited up to 39 plant genera in the first foraging period, and up to 38 plant genera in the late foraging period, including Salix, Rubus, Cercis, and Philadelphus. During the first foraging period, O. lignaria highly preferred Salix spp., while during the late foraging period when Salix spp. were not available, it preferred Rubus spp. In sites where species from these two genera were not available, pollen samples were more likely to be comprised of a greater diversity of plant species. Osmia lignaria preferred Salix spp. and Rubus spp. even when the foraging distance was greater than it was for other available flowering plants. Plant composition data taken from study sites reflected the results from NGS. The findings from this research reinforce hypothesized behavior of native bees to seek higher diversity of food sources in areas where highly preferred pollen is not available, and reveals the applicability and success of NGS to decipher O. lignaria foraging behavior. A better understanding of O. lignaria foraging behavior, as well as the foraging behavior of other native bees, greatly enhances our ability to develop improved pollinator conservation management strategies.