Hiding in plain sight: Uncovering the hidden diversity of Culicoides spp. (Diptera: Ceratopogonidae) in the Republic of Korea using DNA barcoding data.

Culicoides spp. (Diptera: Ceratopogonidae) are vectors of livestock diseases, including bluetongue, Akabane, and African horse sickness. Accurate species identification is a crucial first step in effective vector management. However, morphological identification of the genus Culicoides is challenging due to their small size (<2.5 mm) and considerable intraspecific morphological variability. Additionally, there is a notable lack of molecular studies to support the identification process. This study aimed to use DNA barcoding data (Cytochrome c oxidase subunit 1) to accurately identify Culicoides species in the Republic of Korea (ROK) and to elucidate intra- and interspecies relationships. Samples were collected from livestock farms across various regions of the ROK between 2022 and 2024. DNA barcoding sequences were analysed, and species delimitation was conducted using split methods (ABGD, ASAP, bPTP, GMYC) to investigate the potential presence of cryptic species. A total of 24 morphospecies were identified, among which five (Culicoides circumbasalis, Culicoides circumscriptus, Culicoides erairai, Culicoides kibunensis, and Culicoides sumatrae) formed two or more molecular operational taxonomic units, suggesting the potential existence of cryptic species. In addition to compiling existing literature, we updated the checklist of Culicoides species in the ROK, identifying three species (C. circumbasalis, C. thurmanae, and C. verbosus) that had not been previously documented in the ROK. The findings of this study provide a foundation for the precise identification of Culicoides species in East Asia and contribute to the development of effective control programs aimed at managing livestock disease outbreaks.