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Background: Invasive mosquito species (IMS) of the genus Aedes are a cause of increasing concern in Europe owing to their ability to vector important human viral diseases. Entomological surveillance to early detect alien mosquito and flavivirus circulation in Liguria, northwest Italy, has been carried out since 2011. Results: The invasive species Aedes koreicus was first detected in Genoa in September 2015, when a male specimen was caught near the international airport; species identity was confirmed by genetic analysis. Over the next three years, 86 more adult specimens were trapped at sites throughout the city, accounting for 0.50% of all mosquitoes and 1.04% of Aedes sp. mosquitoes trapped in Genova in the four-year period 2015–2018. So far, no other monitored sites in Liguria have revealed the presence of this species. Ovitraps at two sites became positive for the species in July–August 2017. All female Ae. koreicus pools analysed were negative in biomolecular assays for Flavivirus. Conclusions: Our findings of Ae. koreicus in Genoa constitute, to the best of our knowledge, the first report of the species in northwest Italy and in a Mediterranean port city. The species appears to be established; trapping and climatic data support survival of Ae. koreicus in the area through three consecutive winters. Monitoring of adult mosquitoes detected the species two years before its discovery with ovitraps; trapping for adult specimens appears to be a more effective tool for the early detection of IMS. The airport (located near the commercial port area) and the flower market are the most probable sites of introduction; however, the exact time and place of arrival of this IMS in Liguria remain unknown. Based on morphological and genetic data, a common origin for most of the Ae. koreicus populations established in Europe is suspected. So far, no control measures have been adopted in Genoa and the species will probably colonize an even wider area in the next few years. [ABSTRACT FROM AUTHOR]