Establishment and spread of the invasive ladybird Harmonia axyridis (Coleoptera: Coccinellidae) in Greece: based on contributions from citizen scientists

Harmonia axyridis (Pallas, 1773), also known as the harlequin ladybird, is an invasive alien species intentionally introduced to many countries as a biological control agent of agricultural pests. In Greece, H. axyridis was first introduced as a biological control agent in 1994, with releases taking place between 1994 and 2000. For many years there was no evidence to indicate that H. axyridis had established self-sustaining populations. Following introduction to Greece in 2008, a recording scheme was launched but unfortunately failed to yield results and was discontinued meanwhile several online platforms have become available. Our study examines records from iΝaturalist and other databases, such as Alientoma and social media demonstrating that H. axyridis has been established in Greece since 2010. The distribution, phenology and presence of H. axyridis in different habitat types and protected areas are investigated, using both citizen science data and literature records. H. axyridis is present in 13 administrative districts of Greece, most of them in considerable distance from the initial release sites, and mainly inhabits urban and agricultural habitats as well as 17 NATURA 2000 sites. The adverse socioeconomic and environmental impacts of H. axyridis are briefly discussed alongside suggestions for action. Based on our findings, we propose the establishment of a national monitoring scheme for H. axyridis and native ladybirds, encouraging public participation in recording ladybird observations that will provide information on the distribution, spread and impact of this invasive alien species.