Abstract
The Asian bush mosquito, Aedes japonicus japonicus (Theobald, 1901), a potential vector of several pathogens, has recently established in North America and Central Europe. In 2013, it was found on the Slovenian-Croatian border, and during the following years, it emerged in more and more counties of northwestern Croatia. Surveillance of Ae. j. japonicus and other invasive mosquito species was subsequently extended both spatially and temporally in Croatia and neighbouring Bosnia and Herzegovina and Serbia. Mosquito collections were conducted in 2017 and 2018, based on adult trapping through dry ice-baited CDC traps and BG-Lure-baited BG-Sentinel traps, larval sampling through dippers and nets, and ovitrapping. Aedes j. japonicus specimens from collected samples were subjected to population genetic analysis by comparing microsatellite signatures and nad4 DNA sequences between sampled locations and with data previously obtained from more western European distribution areas. Aedes j. japonicus immature stages were found at 19 sites in Croatia, two sites in Bosnia and Herzegovina and one site in Serbia. In Croatia, four new counties were found colonised, two in the east and two in the south of the previously known distribution area. A spread of 250 km could thus be documented within five years. The findings in Bosnia and Herzegovina and Serbia represent the first records of Ae. j. japonicus in these countries. Genetic analysis suggests at least two introduction events into the surveyed area. Among the locations analysed, Orahovica can be considered a genetic border. The individuals collected west of this point were found to be similar to samples previously collected in the border regions of Southeast Germany/Austria and Austria/Slovenia, while the specimens from more eastern Croatian localities, together with those from Bosnia and Herzegovina and Serbia, were genetically different and could not be assigned to a probable origin. Thus, introduction from Central Europe, possibly by vehicular traffic, into the study area is likely, but other origins, transportation routes and modes of entry appear to contribute. Further dispersal of Ae. j. japonicus to other parts of southeastern Europe is anticipated.
Highlights
The invasive Asian bush or rock pool mosquito Aedes (Hulecoeteomyia) japonicus japonicus (Theobald, 1901) originates from East Asia and the Far East, where it is widespread and even colonises regions with harsh winters [1]
Ae. j. japonicus has become widely distributed in North America and Central Europe where it can be found from lowlands to mountainous areas higher than 1,000 m a.s.l. [5, 6]
In Bosnia and Herzegovina, Ae. j. japonicus eggs were found at two locations close to the Croatian border, Odzak (7 July 2017) and Brčko (9 August 2017), once each (Fig 1 and S1 Table)
Summary
The invasive Asian bush or rock pool mosquito Aedes (Hulecoeteomyia) japonicus japonicus (Theobald, 1901) originates from East Asia and the Far East, where it is widespread and even colonises regions with harsh winters [1]. The species has a preference for forested and bushy areas, where it is essentially a rock pool breeder [1]. In invaded areas of North America and Europe, larvae develop in rock pools and tree-holes, too, but more frequently and more to find, they use artificial containers such as used tyres, rain-water barrels, catch basins, tin cans, bird-baths, roof gutters, flower vases, buckets, etc. The developmental stages can withstand a wide range of water temperatures but are absent from warm water constantly exposed to sunlight [3, 4]. These facts explain the geographical and altitudinal distribution of the species in its invaded territories, which are usually characterised by moderate climates. The species is usually absent from areas with temperatures regularly exceeding 30–35 ̊C [7], it has succeeded in establishing on Hawaii and in Florida [8, 9]
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