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Worker size and body region infuence infection dynamics of Aegeritella fungi in red wood ant

par Van Engeland, Aurélie;Dekoninck, Wouter;Rigaut, Blandine;Billen, Johan;Wybouw, Nicky;Parmentier, Thomas
Référence Myrmecological News, 36, page (145-159)
Publication Publié, 2026-06-01

Article révisé par les pairs

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Résumé :

Social insects are among the ecologically most dominant organisms. Yet, the densely populated colonies of social insects foster conditions where pathogens and parasites can thrive. Despite considerable attention to ant-fungus interactions, numerous fungal pathogens and parasites of ants remain scarcely studied. One such example is the fungal genus Aegeritella, which forms abnormal growths, or bulbils, on the cuticle of Formica ants. To unravel spread and infection on a local level, we focused on a single study site of 100 hectares with 41 red wood ant (Formica rufa group) colonies, assessing over 1 200 workers for the presence of bulbils. To determine host specificity, we investigated whether the fungus could infect related Formica species co-occurring at the site as well as unrelated arthropods (myrmecophiles) found inside the nest mounds of four heavily Aegeritella-infected red wood ant colonies. Surprisingly, Aegeritella infection was exceptionally widespread at our study site. Among the surveyed red wood ant colonies, 38 of the 41 contained infected workers. Across these infected colonies, the mean percentage of infected workers was 40%. Colonies of other Formica species also carried Aegeritella, although infection rates were lower than in red wood ants (10%). None of the over 3 400 surveyed nest-associated arthropods displayed bulbils, suggesting a narrow host range. Red wood ant nests infected by Aegeritella showed spatial autocorrelation, but infection appeared independent of nest size. Red wood ant worker size strongly influenced infection dynamics as smaller individuals were more frequently and more heavily infected with bulbils. Bulbils were concentrated towards the rear of the body, being most abundant on the mesosoma, gaster, and third leg pair. Histology and scanning electron microscopy confirmed that Aegeritella fungi do not penetrate the ant cuticle. Overall, this study underscores the importance of high-resolution sampling in localized areas to fully uncover how fungal parasites spread through social insect colonies.