Population genetics of the invasive Asian bush mosquito Aedes japonicus (Diptera, Culicidae) in Germany-a re-evaluation in a time period of separate populations merging.

The Asian bush mosquito Aedes japonicus, endemic to East Asia, is one of the most expansive mosquito species in the world and has as yet established in 15 countries of Europe. Within Germany, the species has been spreading tremendously during the last years, and its four once geographically isolated populations were on the verge of merging in 2017. To reveal relationships and carry-over ways between the various populations, and thus, migration and displacement routes, the genetic make-up of Ae. japonicus from ten different locations throughout its German distribution area was investigated. For this purpose, a part of the mitochondrial DNA (nad4 gene) of collected specimens was sequenced and seven loci of short tandem repeats (microsatellites) were genotyped. When related to similar genetic studies carried out between 2012 and 2015, the results suggest that admixtures had since occurred, but no complete genetic mixture of populations had taken place. At the time of sampling for the present study, the western collection sites were still uniform in their genetic make-up; however, a carry-over of individuals from the southeastern to the northern and southwestern German populations was determined. Further introductions from abroad are possible. In summary, the genetic diversity of Ae. japonicus in Germany had grown considerably, thus increasing ecological variability and adaptability of the species. At this point (10 years after the first detection), it is not possible anymore to draw conclusions on the origins of the populations.