Haelewaters D, De Wint FC, Gorczak M, Hessmann D, Jensen AB, Francis F, Luangsa-ard J, Pawłowska J, Ruszkiewicz-Michalska M, Tischer M, Verbeken A, Ben Fekih I. 2026. Ecology and management perspectives in arthropod–fungal associations. https://doi.org/10.22541/au.177032832.23372849/v1 [preprint]
Fungal interactions with arthropods remain underexplored despite their abundance and ecological importance. Arthropod-associated fungal parasites and pathogens span a wide range of strategies in their interactions with hosts. At one end of the spectrum are obligate ectobionts and ectoparasites, such as the Laboulbeniales, which depend entirely on living hosts to complete their life cycle. At the other end, highly specialized entomopathogenic fungi, including
Ophiocordyceps unilateralis and
Pandora neoaphidis, kill their hosts to reproduce and disperse. Others, such as
Beauveria bassiana and
Metarhizium brunneum, are more facultative and generalist, capable of infecting a broad range of hosts while also persisting as saprotrophs or endophytes in the absence of suitable hosts. These associations influence arthropod population dynamics, community structure, and ecosystem processes, while also offering opportunities for applied biological control. This chapter reviews current knowledge on fungal parasites and pathogens of arthropods. We discuss host dependence, specificity, and behavioral manipulation, and abiotic drivers shaping infection dynamics and fungal persistence. We also identify key research challenges, from clarifying lifestyle transitions to assessing community-level impacts, and propose interdisciplinary approaches to advance understanding. Together, these insights underscore the ecological and applied significance of arthropod–fungal associations. We hope that this review will encourage more researchers to engage with the rich and largely untapped diversity of arthropod–fungal associations.
Keywords: Arthropod-associated fungi; Biological control; Host range; Parasites; Pathogens
Cazabonne J, Martin TE, Matthews TJ, Quandt CA, Wayman JP, Haelewaters D. 2025. Knowledge gaps explored for Laboulbeniomycetes, a clade of understudied microfungi, including a new shortfall related to a lack of taxonomic expertise. Authorea. https://doi.org/10.22541/au.173956895.54632274/v2 [preprint]
Scientists ought to apply universally accepted definitions to technical terms to enable precise communication and discussion. Throughout history, many definitions have shifted, such as those of important terms in evolutionary biology, modes of life, and the nature of interactions. Conversely, throughout history, important terms have been used without proper definition. Two such terms are parasites and pathogens. An extensive body of literature considers parasites and pathogens to be categorically negative, which has resulted in definitions that lack objectivity and limit a full understanding of the biology of these organisms. Different interpretations have resulted in shifting definitions, in turn causing confusion. Here, we present the remarkable history of both definitions, an overview of alternative definitions put forward throughout history, and a working definition for both terms. We find that the line between what is a parasite or a pathogen is often blurry, and is additionally complicated due to the multi-modal nature of interactions.
Keywords: Complex Interactions; Definition; Parasites; Pathogens
Kaishian P, Lubbers M, Ben Fekih I, de Groot MD, Schilthuizen M, Haelewaters D. 2024. Definitions of parasites and pathogens through time. Authorea. https://doi.org/10.22541/au.165712662.22738369/v2 [preprint]
Despite escalating efforts to document and understand biodiversity, gaps in knowledge persist due to the inherent complexity of biological systems and the sheer scale of global biodiversity. Such knowledge shortfalls have been identified, described, and discussed for several well-studied organismal groups, leading to significant advancements in research and conservation. However, less-studied organismal groups (including most fungi) continue to suffer from pronounced knowledge gaps. Recently, Laboulbeniomycetes (phylum Ascomycota), a class of minute fungi obligately associated with arthropods either for dispersal or as epibionts, has been proposed as a model system to illustrate the extent of biodiversity and conservation shortfalls in poorly known organismal groups. Here, we explore biodiversity knowledge shortfalls for the Laboulbeniomycetes, examining gaps in species diversity (Linnean), distribution (Wallacean), populations (Prestonian), evolution (Darwinian), functional traits and ecological functions (Raunkiaeran), abiotic tolerance (Hutchinsonian), ecological interactions (Eltonian), natural history knowledge (Parkerian), persistence (Latimerian), conservation assessment (Scottian), and applied conservation, legal policies, fundings, and public awareness (Ostromian). Additionally, we introduce the Thaxterian shortfall, named after Roland Thaxter (1858–1932), professor at Harvard University and leading expert of Laboulbeniales, that quantifies the lack of taxonomic expertise in a given organismal group. We also discuss the implications of these shortfalls for conservation and future research avenues. We hope this chapter will serve as a catalyst for further discussion on biodiversity shortfalls in other taxa and pave the way towards a global momentum for the integration of poorly known organisms into conservation frameworks.
Keywords: Biodiversity gaps; Biological conservation; Fungi; Habitat; Host–interaction network; Parasite; Taxonomic expertise
Luo C, Haelewaters D, Krings M. 2023. Fossils of parasitic fungi. Authorea. https://doi.org/10.22541/au.166696714.49994889/v2 [preprint]
Parasitic fungi occur in virtually every ecosystem, where they can significantly affect the functions of other organisms. Fungal parasites were probably also widespread in the geologic past. However, evidence of fossil fungi and their ecological roles is relatively rare. Here we demonstrate a spectrum of (putative) parasitic relationships in ancient continental ecosystems, using fossil examples of Chytridiomycota, zygomycetous fungi, Basidiomycota, and Ascomycota, along with several fungal fossils whose affinities remain unknown, from different periods of the Phanerozoic. Although many of the hosts no longer exist, the fungi involved mostly appear morphologically very similar to extant forms.
Keywords: Amber; Chert; Coal Ball; Host Response; Interaction; Preservation
Bermúdez-Cova MA, Haelewaters D, de Bekker C, Piepenbring M, Schoutteten N, Quandt CA. 2023. Hyperparasitic fungi—definitions, diversity, ecology, and research. Authorea. https://doi.org/10.22541/au.168787020.07281183/v2 [preprint]
Even parasites have parasites. By definition, a hyperparasite is an organism capable of parasitizing another parasite. Hyperparasitism caused by fungi is a common phenomenon in nature, but it has been poorly studied. This life history strategy evolved several times in the fungal tree of life, and is crucial in the maintenance of ecosystems as well as in the mediation of parasite–host interactions. Although the interest for hyperparasitic fungi is growing in the context of biological control, hyperparasitism is not ecologically and evolutionarily understood. This chapter summarizes the most relevant aspects of the terminology, diversity, and ecology of hyperparasitic fungi on both fungal and non-fungal hosts. We also discuss the problems related to molecular research on hyperparasitic fungi. As they represent a hidden source of diversity, it is necessary to increase sampling efforts and to undertake further morphological, molecular, and ecological studies to understand these fungi and their potential biotechnological and pharmaceutical uses.
Keywords: Ampelomyces quiqualis; Biological Control; Host; Hyperparasite; Trichoderma; Trophic Interactions
Haelewaters D, Gorczak M, Kaishian P, De Kesel A, Blackwell M. 2021. Laboulbeniomycetes, Enigmatic Fungi With a Turbulent Taxonomic History. pp. 263-283. In: Zaragoza Ó, Casadevall A (eds.) Encyclopedia of Mycology, Volume 1. Elsevier, Oxford. https://doi.org/10.1016/B978-0-12-819990-9.00049-4 [pdf]
Phylogenetic studies of Laboulbeniomycetes support recognition of three orders (Herpomycetales, Laboulbeniales, Pyxidiophorales) and two unnamed clades containing conidial, arthropod-associated fungi and a poorly known perithecial genus,
Subbaromyces. Herpomycetales and Laboulbeniales include obligate arthropod-associated biotrophs characterized by a parenchymatous thallus of several thousand cells. Pyxidiophorales are hyphal mycoparasites with an unusual three-morph life cycle. The two-celled ascospore with a distinctive apparatus for attachment to arthropods ties together all Laboulbeniomycetes. The complex morphologies and life histories of these fungi are described as a background for research directions that will rely heavily on molecular methods, including phylogenomics, with emphasis on host–parasite relations.
Keywords: Arthropod dispersal; Ascomycota; Biotrophic; Chantransiopsis; Coreomycetopsis; Herpomycetales; Laboulbeniales; Laboulbeniopsis; Perithecial Fungi; Pyxidiophorales; Subbaromyces; Systematics; Tetromeronycha; Thaxteriola
Quandt CA, Haelewaters D. 2021. Phylogenetic Advances in Leotiomycetes, an Understudied Clade of Taxonomically and Ecologically Diverse Fungi. pp. 284-294. In: Zaragoza Ó, Casadevall A (eds.) Encyclopedia of Mycology, Volume 1. Elsevier, Oxford. https://doi.org/10.1016/B978-0-12-819990-9.00052-4 [pdf]
The class Leotiomycetes encompasses many fungi that were historically classified as inoperculate discomycetes. Molecular phylogenetics has changed our perception of the diversity of higher taxonomic lineages and morphologies in the class as well as our understanding of how these clades are related to one another. Leotiomycetes are found in all environments where researchers have explored and have myriad ecological strategies – including economically important pathogens (e.g., powdery mildews on various plants and the causal agent of the white-nose syndrome of bats), endophytes, saprobes, and mycorrhizae. In this article, we provide a summary of the morphological and ecological diversity of Leotiomycetes, and an overview of the taxonomic diversity and systematics. Major challenges in studying this group include historical biases in sampling outside of temperate Europe and North America and a lack of sequence data for many taxa especially in the sprawling mega-order Helotiales. With the help of environmental sequencing and genomic-scale data, researchers are beginning to reveal new perspectives on Leotiomycetes ecology, evolution, and systematics.
Keywords: Ascomycota; Discomycetes; Erysiphaceae; Helotiales; Leotiales; Phacidiales; Rhytismatales; Sampling Bias; Systematics; Thelebolales
Haelewaters D, Dick CW, Cocherán Pittí KP, Dittmar K, Patterson BD. 2021. Chapter 21. Bats, Bat Flies, and Fungi: Exploring Uncharted Waters. pp. 349-371. In: Lim BK, Fenton MB, Brigham RM, Mistry S, Kurta A, Gillam EH, Russell A, Ortega J (eds.) 50 Years of Bat Research. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-54727-1_21 [pdf]
Bats serve as hosts to many lineages of arthropods, of which the blood-sucking bat flies (Nycteribiidae and Streblidae) are the most conspicuous. Bat flies can in turn be parasitized by Laboulbeniales fungi, which are biotrophs of arthropods. This is a second level of parasitism, hyperparasitism, a severely understudied phenomenon. Four genera of Laboulbeniales are known to occur on bat flies,
Arthrorhynchus on Nycteribiidae in the Eastern Hemisphere,
Dimeromyces on Old World Streblidae,
Gloeandromyces on New World Streblidae, and
Nycteromyces on Streblidae in both hemispheres. In this chapter, we introduce the different partners of the tripartite interaction and discuss their species diversity, ecology, and patterns of specificity. We cover parasite prevalence of Laboulbeniales fungi on bat flies, climatic effects on parasitism of bat flies, and coevolutionary patterns. One of the most important questions in this tripartite system is whether habitat has an influence on parasitism of bat flies by Laboulbeniales fungi. We hypothesize that habitat disturbance causes parasite prevalence to increase, in line with the “dilution effect.” This can only be resolved based on large, non-biased datasets. To obtain these, we stress the importance of multitrophic field expeditions and international collaborations.
Keywords: Ectoparasitic Fungi; Fieldwork; Hippoboscoidea; Hyperparasites; Multitrophic Interactions; Parasitism
