Culture-based survey of fungi from decaying Vespa orientalis colonies reveals Beauveria varroae as a virulent and horizontally transmissible entomopathogen

Culture-based survey of fungi from decaying Vespa orientalis colonies reveals Beauveria varroae as a virulent and horizontally transmissible entomopathogen Ernesto Ragusa1, Karen Power2*, Livio Torta1, Marika Lamendola1, Giovanni Jesu3 , Giovanna De Leva3, Alessandro Scavuzzo1, Laura Bortolotti4, Andrea Becchimanzi3,5* 1 Department of Agricultural, Food and Forest Sciences, University of Palermo, Palermo, Italy 2 Department of Biology, University of Napoli “Federico II”, Naples, Italy 3 Department of Agricultural Sciences, University of Napoli “Federico II”, Napoli, Italy 4 Council for agricultural research and economics, Research Centre for Agriculture and Environment, Bologna, Italy 5 BAT Center - Interuniversity Center for Studies On Bioinspired Agro-Environmental Technology, University of Napoli “Federico II”, Napoli, Italy * To whom correspondence may be addressed. Email: [email protected], [email protected] AbstractThe oriental hornet (Vespa orientalis) is increasingly recognized as a significant pest of honey bees in southern Europe and other dry sub-humid regions, where it causes colony losses, disrupts foraging activity, and may contribute to pathogen circulation among apiaries. Current control measures, based mainly on trapping and nest destruction, are labor-intensive and raise concerns for non-target organisms, highlighting the need for sustainable alternatives. Entomopathogenic fungi represent promising candidates due to their insecticidal activity and potential for horizontal transmission within social groups. Here we characterized the fungal community associated with decaying V. orientalis nests and identified Beauveria varroae as a naturally occurring entomopathogen. The nest-associated strain was compared with a commercial Beauveria bassiana strain (ATCC 74040; Naturalis®) in laboratory bioassays on adult hornets using contact, ingestion, and indirect transmission routes. Survival analyses revealed significant route-dependent mortality for both strains. Histological observations confirmed fungal penetration and systemic colonization, particularly of fat body tissues, and indicated host immune responses at lower inoculum levels. Indirect transmission assays demonstrated the capacity of infected individuals to disseminate conidia to conspecifics. These findings identify B. varroae as a virulent pathogen of V. orientalis and support the feasibility of exploiting nest-level horizontal transmission (“Trojan horse” strategy) for...