Study of a recent invasion: distribution and population genetic analysis of the mosquito Aedes koreicus

Aedes koreicus is an invasive species of mosquito native of Far East Asia that has colonized Europe since 2008. The invasiveness success of this mosquito species is particularly evident in Italy where the populations of Ae. koreicus, after the first finding in Belluno in 2011, did not remain confined to small areas near- by the site of first introduction, a phenomenon that has instead been described in other European countries. However, despite the increasing number of reports of Ae. koreicus, no clear evidence of possible entry points were found, and poor investigations about dispersion pathways were made. The collection of updated information about species distribution in Northern Italy and population genetic analysis were performed in the present PhD thesis, with the purpose of making hypothesis about the invasive patterns and dispersal routes of Ae. koreicus in Italy, and possibly in other European countries. Monitoring activities were performed in North-Western Italy in summer and autumn 2021 and in summer 2022, confirming Ae. koreicus rapidly expanded in the area; these data also revealed that dispersal of the species is progressing, being Ae. koreicus found in districts that were negative in previous surveys. Occurrence data were then used to build a Species Distribution Model, which predicted areas highly suitable for further expansion both in Italy and in Europe. Specific microsatellite markers were subsequentially developed to perform population genetics of Ae. koreicus. Particularly, a panel of 11 microsatellites was identified in the present study, and a Multiplex PCR protocol was optimized for their amplification. Using this new tool, 14 populations of Ae. koreicus from Northern Italy, the neighboring Slovenia, and South Korea were studied. Invasive populations were mostly in equilibrium and genetically homogeneous, supporting a stable colonization of Northern Italy and Slovenia. Moreover, data suggested the presence of overwintering populations of Ae. koreicus in different areas of the Italian country. Population genetic and co-ancestry data also revealed that the population from South Korea here analyzed is not correlated to the individuals that have invaded Italy and Slovenia. On the contrary, the high relatedness of the invasive populations of the colonization of Italy and Slovenia suggested that it is a consequence of the expansion of the same population of Ae. koreicus. This hypothesis was evaluated thanks to preliminary demographic analysis. The relative results supported the expansion of the population firstly introduced in Italy toward the Western area of the country and in Slovenia. However, the occurrence of multiple introductions of Ae. koreicus in the Italian country cannot be excluded yet: co-ancestry analysis revealed that, beside a common origin, the individuals from North-Central Italy are differentially distributed among lineages when compared to other populations from North-Eastern and North- Western Italy, and from Slovenia. Further analyses are needed to make more robust conclusions. Additional native and European populations will be analyzed to allow the deduction of the putative origins of the individuals that invaded the Italian country. Monitoring activity should remain constant, to prevent the probable further expansion of the species.