Getz, M. P.; Best, L. R.; Melathopoulus, A. P.; Warren, T. L.

Mason bees, subgenus Osmia Panzer (Hymenoptera: Megachilidae), are economically and ecologically significant pollinators. In eastern North America, the rapid spread of two non-native species from Asia, O. cornifrons Radoszkowski and O. taurus Smith, has coincided with declines in native Osmia populations, raising concern about the effects of further exotic invasions. Here we investigate the recent establishment in British Columbia, Canada of the European orchard bee, O. cornuta Latreille, previously thought to be limited to Europe and its periphery. We document O. cornuta records ranging over 170 km, including sightings of live adults and the discovery of a multigenerational nest with hundreds of cocoons. We tested whether these O. cornuta cocoons could be discriminated from other Osmia species by training a machine learning classifier on features extracted from images. The best performing model could not reliably discriminate cocoons by species, raising the possibility O. cornuta could be inadvertently intermingled in future commercial shipments. Spatially isolated records of O. cornifrons and O. taurus further suggest ongoing anthropogenic dispersal of these species. To determine environmentally suitable regions for O. cornuta to spread in North America, we estimated its climate niche using native-range occurrence data. This analysis indicated broad regions of the Pacific Northwest and eastern North America contain potentially suitable habitat. Together, our findings document the establishment of O. cornuta in North America and the potential for it to spread broadly. Our study demonstrates the utility of accessible biodiversity data archives and public observation programs in tracking biological invasions and highlights the need for future monitoring of exotic Osmia.