Towards a real-time tracking of an expanding alien bee species in Southeast Europe through citizen science and floral host monitoring

Abstract

Citizen science, a practice of public participation in scientific projects, is popular in Western countries, however, it is still a relatively novel approach in Southeast Europe. In this region, citizen science can be a useful tool for increasing the understanding of alien species. One such species is the sculptured resin bee, Megachile sculpturalis, a putatively invasive alien pollinator native to East Asia. It was introduced to France in 2008, from where it quickly spread across West and Central Europe. However, our knowledge of its eastern distribution is scarce since it is based mostly on isolated findings. We combined citizen science and data extraction from online sources (e.g., naturalist's databases and social media) covering 6 years, and 3 years of targeted floral resource monitoring in the search for M. sculpturalis across regions of southeastern Europe. We collected presence data and information on M. sculpturalis abundances across an urban-rural gradient from eight countries: Hungary, Slovenia, Croatia, Serbia, Bosnia and Herzegovina, Montenegro, Romania, Bulgaria, and the region of the Crimean Peninsula. We present the first country records for Romania, Bulgaria, and Montenegro, identify the dynamic expansion front in southern Serbia and provide new southernmost occurrences in Southeast Europe. We also collected data on species ecology (e.g., phenology, pollen/nectar sources, nest characteristics) and gathered evidence of reproducing populations of this species across the studied region. Citizen science data provided a five times larger spatial coverage, including recordings from remote locations, than the data collected by expert field surveys and provided critical additional data about the species biology, thanks to exceptionally engaged participants. We emphasize the importance of close collaboration between regional scientist teams and citizen participants and the benefits of this approach for monitoring a species with a continent-wide spread potential.