Population genetic structure of the Asian bush mosquito, Aedes japonicus (Diptera, Culicidae), in Belgium suggests multiple introductions.

BACKGROUND: Aedes japonicus japonicus has expanded beyond its native range and has established in multiple European countries, including Belgium. In addition to the population located at Natoye, Belgium, locally established since 2002, specimens were recently collected along the Belgian border. The first objective of this study was therefore to investigate the origin of these new introductions, which were assumed to be related to the expansion of the nearby population in western Germany. Also, an intensive elimination campaign was undertaken at Natoye between 2012 and 2015, after which the species was declared to be eradicated. This species was re-detected in 2017, and thus the second objective was to investigate if these specimens resulted from a new introduction event and/or from a few undetected specimens that escaped the elimination campaign. METHODS: Population genetic variation at nad4 and seven microsatellite loci was surveyed in 224 and 68 specimens collected in Belgium and Germany, respectively. German samples were included as reference to investigate putative introduction source(s). At Natoye, 52 and 135 specimens were collected before and after the elimination campaign, respectively, to investigate temporal changes in the genetic composition and diversity. RESULTS: At Natoye, the genotypic microsatellite make-up showed a clear difference before and after the elimination campaign. Also, the population after 2017 displayed an increased allelic richness and number of private alleles, indicative of new introduction(s). However, the Natoye population present before the elimination programme is believed to have survived at low density. At the Belgian border, clustering results suggest a relation with the western German population. Whether the introduction(s) occur via passive human-mediated ground transport or, alternatively, by natural spread cannot be determined yet from the dataset. CONCLUSION: Further introductions within Belgium are expected to occur in the near future, especially along the eastern Belgian border, which is at the front of the invasion of Ae. japonicus towards the west. Our results also point to the complexity of controlling invasive species, since 4 years of intense control measures were found to be not completely successful at eliminating this exotic at Natoye.

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.

Newly discovered population of Aedes japonicus japonicus (Diptera: Culicidae) in Upper Bavaria, Germany, and Salzburg, Austria, is closely related to the Austrian/Slovenian bush mosquito population.

BACKGROUND: The German mosquito surveillance instrument 'Mueckenatlas' requests the general public to collect and submit mosquito specimens. Among these, increasing numbers of individuals of invasive species have been registered. Specimens of the Asian bush mosquito Aedes japonicus japonicus submitted from German Upper Bavaria, where this species had not previously been recorded, triggered regional monitoring in mid-2015. METHODS: The search for Ae. j. japonicus breeding sites and developmental stages concentrated on cemeteries in the municipality of origin of the submitted specimens and, subsequently, in the whole region. A virtual grid consisting of 10 × 10 km(2) cells in which up to three cemeteries were checked, was laid over the region. A cell was considered positive as soon as Ae. j. japonicus larvae were detected, and regarded negative when no larvae could be found in any of the cemeteries inspected. All cells surrounding a positive cell were screened accordingly. A subset of collected Aedes j. japonicus specimens was subjected to microsatellite and nad4 sequence analyses, and obtained data were compared to individuals from previously discovered European populations. RESULTS: Based on the grid cells, an area of approximately 900 km(2) was populated by Ae. j. japonicus in Upper Bavaria and neighbouring Austria. Genetic analyses of microsatellites and nad4 gene sequences generated one genotype out of two previously described for Europe and three haplotypes, one of which had previously been found in Europe only in Ae. j. japonicus samples from a population in East Austria and Slovenia. The genetic analysis suggests the new population is closely related to the Austrian/Slovenian population. CONCLUSION: As Ae. j. japonicus is well adapted to temperate climates, it has a strong tendency to expand and to colonise new territories in Central Europe, which is facilitated by human-mediated, passive transportation. The new population in Upper Bavaria/Austria is the seventh separate population described in Europe. According to our data, it originated from a previously detected population in eastern Austria/Slovenia and not from an introduction event from abroad. The dispersal and population dynamics of Ae. j. japonicus should be thoroughly surveyed, as this species is a potential vector of disease agents.