[Identification of Culex quinquefasciatus Highlights the Need for Strengthened Vector Mosquito Surveillance in the Republic of Korea].

OBJECTIVES: We investigated the presence of subtropical mosquito vectors that may become established in the Republic of Korea (ROK) owing to climate change. Comprehensive surveillance was conducted on Jeju Island, a region with a subtropical climate with active external entry routes, where the risk of subtropical mosquito introduction and establishment is increasing. METHODS: In July 2025, adult mosquitoes were collected from 47 sites across Jeju Island using BG-Sentinel traps baited with carbon dioxide, in collaboration with Honam Regional Center for Disease Control, the Jeju Institute of Health and Environment, Jeju National University, and Cheju Halla University. A total of 147 mosquitoes, morphologically classified as belonging to the Culex pipiens complex, were subjected to genetic analyses for species identification. The collected specimens were screened for major mosquito-borne viruses, including the Japanese encephalitis, West Nile, Zika, Dengue, Chikungunya, and Yellow fever viruses. RESULTS: Cx. quinquefasciatus is morphologically very similar to the Cx. pipiens complex, making it difficult to distinguish based on external characteristics. In addition, the cytochrome c oxidase subunit I marker alone was insufficient for clear species differentiation. Therefore, through multiplex molecular analyses incorporating nuclear gene markers such as acetylcholinesterase-2, a total of 11 Cx. quinquefasciatus individuals were identified from five collection sites. Furthermore, all specimens tested negative for six major mosquito-borne viruses. CONCLUSIONS: This study provides the first official report confirming the presence of subtropical mosquitoes on Jeju Island, ROK. These findings highlight the need to strengthen vector surveillance systems and refine public health strategies to address the potential establishment and northward expansion of subtropical mosquito species due to ongoing climate change and reveal an increased risk of exotic species introduction.