Pollen availability for the Horned mason bee (Osmia cornuta) in regions of different land use and landscape structures

1. Osmia cornuta is a generalist regarding its habitat requirements and is used for pollination in orchards. The species collects pollen from different plant taxa, but pollen richness and pollen quantity in a nest may be affected by land use and landscape structures. 2. The availability of pollen resources for O. cornuta was studied across different land use types (one urban, village-structured, agricultural, and viticultural region each) by pollen analysis in the context of landscape structures. 3. In total, 16 pollen types were identified in 1180 brood cells of O. cornuta. On average (± SD), the highest pollen richness per region (n = 4) was found in the viticultural region (4.75 ± 0.96) and the lowest in the agricultural region (1 ± 2). Osmia cornuta collected predominantly pollen from the Sorbus-pollen group, which includes Prunus species. Salix was primarily collected in the village-structured and agricultural regions, and Quercus was frequently found in samples from the viticulture region. The highest mean (± SD) number of brood cells per region (n = 4) was found in the viticulture region (136.35 ± 57.45) and the lowest in the agricultural region (20.25 ± 40.5). Increasing proportions of green areas in urban and village-structured regions affected the pollen richness positively, whereas agricultural areas had a negative impact on pollen richness and the number of brood cells. 4. It was concluded that the polylectic O. cornuta uses a wide range of flowering plants dependent on their availability. The maintenance of fruit trees as well as willow and oak trees enhances floral resources qualitatively and quantitatively for O.cornuta specifically in intensively farmed agricultural areas.