Beetlehangers.org: harmonizing host–parasite records of Harmonia axyridis and Hesperomyces harmoniae

Citizen science is an increasingly powerful tool to gather large quantities of biological data and to engage the public. The number of citizen science initiatives has rapidly increased in the last 15 years. Invasive alien species such as the harlequin ladybird, Harmonia axyridis (Coleoptera, Coccinellidae), provide a particularly good opportunity for broad-scale use of such initiatives. Harmonia axyridis is parasitized by a fungus, Hesperomyces harmoniae (Ascomycota, Laboulbeniales), that can be found throughout the range of its host. Here we present Beetlehangers.org, a website and data repository where we combine observations of He. harmoniae from literature, online databases, and citizen science initiatives, including new records of both Ha. axyridis and He. harmoniae. Whereas Ha. axyridis is now present in 86 countries across six continents (including seven new country records), the distribution of its parasite He. harmoniae comprises 33 countries in five continents (including two new country records since its description in 2022). We explore spatiotemporal trends of He. harmoniae in light of these records. Finally, we discuss challenges and new opportunities for citizen science in relation to species interactions such as these and provide future perspectives for the website as a home for future Laboulbeniales research and outreach.