Gut microbiome of Vespa orientalis: functional insights and potential honey bee pathogen dynamics.

Vespa orientalis, the oriental hornet, is an emerging predator of honey bees whose ecological impact and microbial ecology remain poorly understood. Here, we present the first detailed characterisation of its gut microbiota by integrating 16S rRNA gene sequencing, predicted microbial function, pathogen screening, and a three-year beekeeper survey across urban and rural sites in Malta. Hornets were sampled from four locations and classified by observed foraging behaviour, either predation on honey bees or scavenging on cat food.Survey data confirmed consistent V. orientalis sightings and seasonal colony losses, particularly during peak foraging months. Microbiome analysis revealed a conserved core community dominated by Spiroplasma, Arsenophonus, and Rosenbergiella, with overall diversity stable across sites and diets. However, specific taxa varied with foraging behaviour. For example, Arsenophonus was enriched in bee-predating hornets, while Enterobacter and Serratia were more common in scavenging individuals, suggesting environmental and dietary influences on microbiota composition. Predicted functional profiles remained broadly conserved, reflecting robust nutrient metabolism and potential detoxification capabilities, with some variations related to the diet behaviour.Pathogen screening detected Nosema ceranae and Crithidia bombi in a substantial proportion of hornets, including those not observed feeding on bees. Although our findings do not demonstrate pathogen transmission, they support the hypothesis that V. orientalis may act as a transient carrier, potentially contributing to pathogen persistence via environmental exposure.Together, these results reveal the dietary flexibility and microbial flexibility within the gut microbiome of V. orientalis, and highlight its potential involvement in pollinator pathogen dynamics.