Spread of Aedes japonicus japonicus (Theobald, 1901) in Austria, 2011-2015, and first records of the subspecies for Hungary, 2012, and the principality of Liechtenstein, 2015

Background: The Asian bush mosquito, Aedes (Hulecoeteomyia) japonicus japonicus (Theobald, 1901) (Diptera: Culicidae), was first identified in Austria in August 2011 in the federal state of Styria at the border to Slovenia. Methods: Between 2011 and 2015 the spread of Ae. j. japonicus was monitored in southern, eastern and western Austrian provinces as well as in neighbouring countries by checking natural and man-made container habitats for the aquatic stages. The search concentrated around the most recent occurrence of Ae. j. japonicus and extended up to several kilometres until the subspecies could not be found anymore. Results: Between May and July 2012 the distribution area of Ae. j. japonicus was found to be extended westwards into Carinthia, and eastwards towards the federal state of Burgenland. In August 2012, the subspecies was found in Hungary, representing the first record of an invasive mosquito species in this country. In 2013 its expansion was confirmed at several sites in Austria. Additionally, between April and July 2015, the subspecies was detected in all districts of the westernmost Austrian state Vorarlberg reaching the alpine Montafon valley at the end of October 2015, at all three examined sites in southern Bavaria bordering Vorarlberg, and in the adjacent Principality of Liechtenstein, for which it also represents the first record of an invasive mosquito species. One remarkable finding of the subspecies was located close to the city of Kufstein in the lower Inn valley of the Tyrol in September 2015, which is an isolated occurrence without spatial connection to any known established population. Conclusions: Our findings demonstrate the ongoing spread of Ae. j. japonicus towards all directions within Austria and beyond. Together with the absence of supposed natural barriers, e.g. high mountain chains, at the borders of the current subspecies' distribution area in south-eastern Austria, these findings suggest a further spread to the Austrian capital Vienna and the Hungarian tourist region of Lake Balaton within the upcoming few years. The observed intrusions in western Austria represent most probably extensions of the population established and spreading in eastern Switzerland and southern Germany. The putative role of the subspecies in pathogen transmission together with its rapid spread observed argues for the implementation of comprehensive nation-wide surveillance and response preparedness.