Elevation and mean winter temperatures differentially impact the distribution of two non-native mason bee species (genus Osmia) across the Commonwealth of Virginia

In recent years, concern for the decline in bee populations has increased. With potentially tremendous negative impacts on our ecosystem, the decline in bee population is of legitimate concern, not simply some trendy social media hashtag. The mason bees (genus Osmia) are a prevalent group of cavity-nesting bees in the Mid-Atlantic United States. In the last decade, exotic mason bees have been proliferating throughout the Mid-Atlantic while some native mason bees have been experiencing declines. These exotic mason bees are Osmia cornifrons and Osmia taurus, both from Japan. Based on observations in their native range of Japan, we hypothesized that these two exotic mason bees would exhibit different distributions across Virginia based on winter climate (30-yr averaged wintertime temperature) and elevation. With the help of citizen scientists in 2017, we provided wooden nesting blocks to 100 locations to capture mason bees. After collection of nests, we identified the sex and species of each mason bee inside every nest. Our observations from this data set indicate there is a significant difference in exotic mason bee distributions: O. taurus is found nearly everywhere throughout Virginia, but O. cornifrons is only found in areas at higher elevations with lower mean wintertime temperatures. This finding mirrors the patterns of their native range in Japan. We are unsure at this time as to how far O. taurus could spread beyond Virginia, but projecting its spread in the United States is a crucial next step.