Hidden in Plain Sight: iNaturalist Observations of Harmonia axyridis Reveal New Records of its Fungal Ectoparasite Hesperomyces harmoniae in Québec, Canada

Citizen scientists are being increasingly leveraged to document the diversity of fungi and advance fungal conservation. Previous work indicated that the interaction between Harmonia axyridis (Harlequin Ladybird; Coleoptera, Coccinellidae) and the fungal ectoparasite Hesperomyces harmoniae (Ascomycota, Laboulbeniales) is a well-suited host–parasite system for citizen science initiatives. Because the formal description of H. harmoniae and the introduction of this model on citizen science platforms are recent, we hypothesize that records of H. harmoniae may be hidden among the host's observations. Focusing on the province of Québec, Canada, we manually screened all available observations of the Harlequin Ladybird on iNaturalist for the presence of H. harmoniae. We found 318 new records of H. harmoniae on a total of 4658 observations of the Harlequin Ladybird. In addition to previous observations of H. harmoniae (n = 43), our work brings the total number of records of this fungal parasite to 361 for Québec, an 8.4-fold increase. Our study suggests that more records of H. harmoniae may be hidden within observations of its natural host on iNaturalist. We believe such work on a broader scale could help fill existing knowledge gaps about this host–parasite interaction, and potentially other ones, as well as pose a promising avenue to engage citizen scientists with fungi and poorly known organisms.