Diversity and associations of parasites, parasitoids, and nest-associated organisms of <i>Vespa mandarinia</i> (Hymenoptera: Vespidae) in South Korea

The northern giant hornet (<i>Vespa mandarinia</i> Smith, 1852) is a dominant eusocial wasp species in East Asia; however, knowledge of organisms associated with its colonies, including parasites and other nest-associated taxa, remains limited. To address this gap, this study investigated the diversity and ecological roles of organisms associated with <i>V. mandarinia</i> colonies and individuals in South Korea using a combination of morphological examination and DNA barcoding analyses. A total of seven associated species were identified: <i>Xenos moutoni</i> (du Buysson, 1903) (Strepsiptera: Xenidae); <i>Volucella suzukii</i> Matsumura, 1916 and <i>Vo</i>. <i>coreana</i> Shiraki, 1930 (Diptera: Syrphidae); <i>Pyralis regalis</i> (Denis & Schiffermüller, 1775) (Lepidoptera: Pyralidae); <i>Pheromermis vesparum</i> Kaiser, 1987 (Nematoda: Mermithidae); <i>Quedius pectinatus</i> (Sharp, 1874) (Coleoptera: Staphylinidae); and <i>Hermetia illucens</i> (Linnaeus, 1758) (Diptera: Stratiomyidae). These species exhibited distinct ecological associations with <i>V. mandarinia</i>. <i>X</i>. <i>moutoni</i> was confirmed as an obligate endoparasite that induces behavioral and reproductive alterations in its host. <i>Vo</i>. <i>suzukii</i>, <i>Q</i>. <i>pectinatus</i>, and <i>H</i>. <i>illucens</i> were primarily associated with nest-derived detritus beneath hornet nests and exhibited scavenger-like behavior, with no evidence of direct predation on host individuals, suggesting predominantly commensal associations. In contrast, <i>Vo. coreana</i> was consistently associated with the comb and nest cells, suggesting a more exploitative ecological strategy. <i>P</i>. <i>regalis</i> primarily consumed nest material and meconium and occupied an intermediate ecological position between a facultative predator and a nest-associated organism. <i>Ph</i>. <i>vesparum</i>, recorded for the first time in Korea and Asia, was detected in only a single <i>V. mandarinia</i> individual, suggesting a negligible impact on hornet populations under natural conditions. Overall, this study provides baseline taxonomic and ecological data on parasites and nest-associated organisms associated with <i>V. mandarinia</i> in Korea and highlights the ecological complexity of hornet nests as microhabitats that support diverse symbiotic assemblages. These findings serve as a foundation for future research on the life histories, host interactions, and potential functional roles of nest-associated organisms in hornet colony dynamics.