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 nad 4 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.

Abstract:In spring 2004, the mark-release-recapture study was conducted in the Osijek area, covering the total of 171 km 2 , to describe dispersal pattern of three floodwater mosquito species (Aedes vexans, Ochlerotatus sticticus and Oc. caspius). Forty CO2 baited Center for Disease Control and Prevention (CDC) traps were set at distances varying from 0.95 to 16.7 km from release site. Fifty thousand mosquitoes were released, and a total of 22 marked mosquitoes were recaptured in 12 traps, 82% of which were collected in the first six days after release. The maximum distance of recaptured mosquito (Oc. sticticus) was found at 11.68 km from the release site. During the study, the average dispersal rate per day for mosquitoes ranged from 0.96 km to 3.6 km in regard to different species.

This paper demonstrates the possibility of using geostatistics to monitor the dispersal of mosquitoes for mosquito control programs at the municipal level. The case study objective was to quantify the dispersal of floodwater mosquitoes from the natural marshland Kopacki rit into the city of Osijek, Croatia, and to analyze the main factors controlling it. Fifty thousand adult Aedes vexans, Ochlerotatus sticticus, and Ochlerotatus caspius mosquitoes were marked with a powdered fluorescent pigment and released from the southern part of Kopacki rit on April 28, 2004. Forty CO2-baited Centers for Disease Control and Prevention traps were set in the area of the municipality of Osijek (171 km2) and were monitored for 10 days. A total of 582,471 mosquitoes were captured and examined in the laboratory. The mosquito counts from different sites were then interpolated using ordinary kriging and visualized dynamically to detect the dominant migrational directions. Mosquito dispersal and frequency were greatly influenced by wind speed (r = 0.82). The marked mosquitoes were found at 12 sites located from 1 km to 11.7 km away from the release point. The recapture rate was 0.044% (54% Oc. sticticus, 32% Ae. vexans, and 14% Oc. caspius). Based on the Lincoln index, the estimated total population size for floodwater mosquitoes in the study area ranged from 875 million to 2.0 billion mosquitoes. Limitations of the approach, recommendations for the improvement of the monitoring network, and spatial predictions are further discussed.

Summary Lowland riverine floodplains are among the most dynamic and heterogeneous of ecosystems, but many have been extensively modified. Their provision of important habitats provides a key motivation for restoring natural flow regimes (in terms of magnitude, frequency, duration, timing and rate of change of hydrological conditions). Despite general recognition that aquatic insects respond to changes in water availability, there is little agreement about the influence of flow regime components on community structure in floodplains. We analysed a 6‐year (2005 and 2007–2011) data set of aquatic insects (Heteroptera and Coleoptera) in a large Danubian floodplain characterised by pronounced hydrological variability. We hypothesised that abundance and assemblage structure would depend on flow regime components. In particular, we predicted that high‐flow events in the mainstream and concurrent high‐magnitude floods of prolonged duration would have a positive effect on diversity and abundance and that insect assemblages would differ between phases of hydrological connectivity. In addition, we assessed whether the survival of two threatened aquatic insects, Graphoderus bilineatus and Berosus geminus, depends on hydrological connectivity. Abundance and species richness of Heteroptera and Coleoptera increased during years with frequent extremely high flood pulses and prolonged flooding. Multivariate ordination showed subtle relationships between hydrological conditions, hydrological connectivity and insect assemblages with number of days in flood providing the best fit. Spring floods had a more pronounced effect on the assemblages than autumn floods. The time lag between flood occurrence and its apparent effect on aquatic insects was 17–31 days, reflecting insect life cycles. The abundance of G. bilineatus (Coleoptera: Dytiscidae) was affected by mean water level during the month preceding sampling, whereas the abundance of B. geminus (Coleoptera: Hydrophilidae) was related to the occurrence of prolonged high‐magnitude floods. The current water regime of the Danube River favours generalist species with high dispersal capacities and broad niches and food resources. Changes in flow management practices could remove the positive influence of floods on aquatic insect communities and lead to losses of threatened species that depend on these river–floodplain habitats. Our results contribute to the understanding necessary for appropriate evaluation and prioritisation of international floodplain conservation efforts.

Improvement of morphological and molecular identification methods allows the detection of new species of mosquitoes. The mosquito fauna of Croatia currently includes 52 species, belonging to eight genera, including Anopheles (12 species), Aedes (24 species), Coquillettidia (one species), Culex (seven species), Culiseta (six species), Orthopodomyia (one species), and Uranotaenia (one species). This is an updated checklist, which includes five new species found in Croatian mosquito fauna. Two of these are invasive mosquito species, Aedes albopictus (Skuse, 1895) and Aedes japonicus (Theobald 1901), which are spreading across Europe and Croatia. The other three species, Culex laticinctus (Edwards 1913), Culex torrentium (Martini 1925), and Anopheles daciae (Linton, Nicolescu & Harbach 2004) are autochthonous species which haven't been recorded so far. Since there are several more invasive species spreading across Europe, we assume that this is not the final list.