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

Jonathan Cazabonne^1,*, Michiel D. de Groot^2,3, and Danny Haelewaters^2,4,5

¹Institut de recherche sur les forêts, Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, QC J9X 5E4, Canada. ²Research Group Mycology, Department of Biology, Ghent University, 9000 Ghent, Belgium. ³Research Institute for Nature and Forest (INBO), 1000 Brussels, Belgium. ⁴Biology Centre of the Czech Academy of Sciences, Institute of Entomology, 370 05 České Budějovice, Czechia. ⁵Department of Zoology, Faculty of Science, University of South Bohemia, 370 05 České Budějovice, Czechia. *Corresponding author.

Northeastern Naturalist, Volume 33, Issue 2 (2026): 141–159

First published early online: 4 May 2026

Abstract
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.

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