Microsatellite typing of Aedes albopictus (Diptera: Culicidae) populations from Germany suggests regular introductions.

The global spread of the Asian tiger mosquito Aedes albopictus is of concern, as this mosquito species constitutes an important vector of a number of emerging pathogens including dengue virus, chikungunya virus and Zika virus. Since its first appearance in Albania (1979) and Italy (1990), the species has been reported from more than twenty-five European countries. However, the dispersion process in Europe is largely unknown, as information on population genetic structure is lacking, which is relevant to understand the observed spread. In order to determine whether the ten Ae. albopictus populations detected in Germany until 2017 originate from a single introduction event or from independent importations, genetic analyses with a set of sixteen microsatellite markers were performed. The samples included specimens from three locations with potentially overwintering populations, collected in three consecutive years. The results indicate a heterogeneous population structure consisting of two clusters with significant substructuring, suggesting regular, independent introductions instead of a continuous spread across Germany originating from one or few sites. Moreover, the analyses provide further evidence for Ae. albopictus overwintering in Germany as samples from identical locations collected in three consecutive years had a relatively high genetic similarity. However, the population structure is probably influenced by local mosquito control activities. The results presented provide further evidence for regular introductions of Ae. albopictus specimens into Germany, probably leading to local establishment north of the Alps. This highlights the need for constant surveillance and control of Ae. albopictus not only in southern, but also in Central Europe.

First mass development of Aedes albopictus (Diptera: Culicidae)-its surveillance and control in Germany.

The Asian tiger mosquito Aedes albopictus has undergone a dramatic expansion of its range in the last few decades. Since its first detection in 2007 in Germany at the motorway A5 coming from Italy via Switzerland to Germany, it has been continuously introduced by vehicles, most probably from Italy. After a hint from an alert gardener in an allotment garden area in Freiburg, Southwest Germany, in 2015, a surveillance programme was started focusing on the garden area and adjacent areas as well as most of the cemeteries as potential infestation areas. The surveillance programme confirmed a high infestation of the allotment garden. The container index (CI) exceeded almost 30% in August 2015. In lethal gravid Aedes traps (GATs) and BG-Sentinel traps, 4038 adults were caught. It could be proven that the Aedes population is more or less still spatially restricted to the allotment garden area which is adjacent to a train station where trucks from Novara, Italy, arrive loaded on trains. Outside the garden area, only a few breeding sites with developmental stages and adults were found within a radius of approximately 600 m from the highly infested garden area. It is most likely that Ae. albopictus females are constantly introduced as 'blind passengers' to Freiburg via trucks from Italy to Freiburg, Germany. After the first detection of the mass development of Ae. albopictus immediate and comprehensive control measures were initiated to reduce or even eliminate the Aedes population. Citizen awareness, especially of the gardeners, was increased by providing thorough information about the biology and control of Ae. albopictus. Beside environmental management, tablets based on Bacillus thuringiensis israelensis (Bti) were applied. The success of the control activities by the gardeners is reflected by the data gained during monthly inspection of the garden plots. The number of gardens without any container increased from 17% in July to 22% in August and 35% in September, 2015, resulting in a successful reduction of the Ae. albopictus population. The study underlines the importance of a comprehensive surveillance programme to assess the population density of Ae. albopictus as a basis for integrated control activities.

Successful overwintering of Aedes albopictus in Germany.

The Asian tiger mosquito (Aedes albopictus) is of great concern to public health authorities due to its vector competence and rapid spread across the globe. In 2015, two large local breeding populations of Ae. albopictus were discovered in southwest Germany. In spring 2016, we were able to demonstrate the first evidence of a successful overwintering in Germany of this originally tropical mosquito species in different research projects. Particularly noteworthy is the successful hatching of diapause eggs of an Italian strain (Calabria), which overwintered successfully in the field in St. Georgen im Schwarzwald (Baden-Wuerttemberg) at 820 m above sea level. Furthermore, within the scope of a larvae monitoring, the first larvae that hatched in the field were detected on the April 09, 2016 in a rain barrel within the Heidelberg population. Our first results show that self-extinction due to an unsuccessful overwintering cannot be assumed for populations of the Asian tiger mosquito which settled in Germany in previous years. The evidence of a successful overwintering of a large number of diapause eggs and the hatching of the first larvae in field conditions opens the control year against Ae. albopictus in southwest Germany.