Stylopization by Xenos spp. (Xenidae, Strepsiptera) in invasive alien hornet, Vespa velutina, in South Korea.

The invasive hornet Vespa velutina Lepeletier, which first invaded South Korea in 2003, has spread throughout the country, significantly affecting apiaries, ecosystems, and human health. Xenos spp. (Xenidae, Strepsiptera) are primarily parasitic to social wasps, with V. analis being the only known host in Korea. Until recently, no parasites or parasitoids on V. velutina had been discovered. In 2020, strepsipteran parasites were discovered on 11 hornet workers in Andong City, South Korea. These parasites, comprising four larvae and seven pupae, were all male, except for one individual of an undetermined sex. Molecular analysis and morphological examination identified the parasites as Xenos moutoni (du Buysson, 1903) and X. oxyodontes Nakase & Kato, 2013. This marks the first recorded instance of strepsipteran parasites on V. velutina in regions invaded by this hornet. Although the exact infection rate of these parasites could not be determined, it appears that native strepsipteran parasites have adapted to a non-native Vespa species. Stylopization, the condition caused by these parasites, is known to negatively affect hornet colonies: infected workers do not contribute to nest activities, hindering nest development, and infected reproductive individuals (males and new queens) do not mate, which impedes the establishment of new colonies. However, due to the hornet's high reproductive rate and compensatory mechanisms, the overall control effect of the parasites is likely to be minor.