Enrih Merdić

The arbovirus vector Culex torrentium is more prevalent than Culex pipiens in northern and central Europe

Two species of arbovirus vector, Culex torrentium and Culex pipiens (Diptera: Culicidae), occur in several European countries, but difficulties in their accurate identification and discrimination have hampered both detailed and large‐scale distribution and abundance studies. Using a molecular identification method, we identified to species 2559 larvae of Cx. pipiens/torrentium collected from 138 sites in 13 European countries ranging from Scandinavia to the Mediterranean coast. In addition, samples of 1712 males of Cx. pipiens/torrentium collected at several sites in the Czech Republic were identified to species based on the morphology of their hypopygia. We found that the two species occur together in large areas of Europe, and that Cx. torrentium dominates in northern Europe and Cx. pipiens dominates south of the Alps. The transition in dominance occurs in central Europe, where both species are roughly equally common. There was a strong correlation between the length of the growing season at different sites and occurrences of the two species. As the growing season increases, the proportion and detection of Cx. torrentium decrease, whereas those of Cx. pipiens increase. The present findings have important consequences for the interpretation of the results of studies on major enzootic and link‐vectors of mosquito‐borne bird‐associated viruses (i.e. Sindbis, West Nile and Usutu viruses), especially in central Europe and Scandinavia.

Spatiotemporal monitoring of floodwater mosquito dispersal in Osijek, Croatia.

ABSTRACT 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 Kopački 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 Kopački 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.

Recently discovered Aedes japonicus japonicus (Diptera: Culicidae) populations in The Netherlands and northern Germany resulted from a new introduction event and from a split from an existing population

BackgroundOriginally native to East Asia, Aedes japonicus japonicus, a potential vector of several arboviruses, has become one of the most invasive mosquito species in the world. After having established in the USA, it is now spreading in Europe, with new populations emerging. In contrast to the USA, the introduction pathways and modes of dispersal in Europe are largely obscure.MethodsTo find out if two recently detected populations of Ae. j. japonicus in The Netherlands and northern Germany go back to new importations or to movements within Europe, the genetic makeup of mosquito specimens from all known European populations was compared. For this purpose, seven microsatellite loci from a representative number of mosquito specimens were genotyped and part of their mitochondrial nad4 gene sequenced.ResultsA novel nad4 haplotype found in the newly discovered Dutch population of Ae. j. japonicus suggests that this population is not closely related to the other European populations but has emanated from a further introduction event. With five nad4 haplotypes, the Dutch population also shows a very high genetic diversity indicating that either the founder population was very large or multiple introductions took place. By contrast, the recently detected North German population could be clearly assigned to one of the two previously determined European Ae. j. japonicus microsatellite genotypes and shows nad4 haplotypes that are known from West Germany.ConclusionAs the European populations of Ae. j. japonicus are geographically separated but genetically mixed, their establishment must be attributed to passive transportation. In addition to intercontinental shipment, it can be assumed that human activities are also responsible for medium- and short-distance overland spread. A better understanding of the processes underlying the introduction and spread of this invasive species will help to increase public awareness of the human-mediated displacement of mosquitoes and to find strategies to avoid it.

Seasonal dynamics of mosquitoes (Diptera: Culicidae) in Osijek (Croatia) for the period 1995-2004.

The ten year research (1995–2004) of adult mosquitoes in the area of Osijek by dry ice baited CDC traps has provided significant information on mosquito species, species prevalence, their dynamics and seasonal activity. A total of 207,136 adult mosquitoes comprising twenty species belonging to the following genera: Anopheles, Ochlerotatus, Aedes, Culex, Coquillettidia, Culiseta and Uranotaenia were collected. The seven most common species collected during this study were: Aedes vexans (75.6%), Ochlerotatus sticticus (13.3%), Culex pipiens complex (5.9%), Anopheles maculipennis complex (1.9%), Oc. cantans (0.9%), Oc. caspius (0.6%) and Oc. excrucians (0.6%). The temporal changes in the relative abundance of the twenty mosquito species in the Osijek area were reflected in three peaks: in May, July and September. Seasonal population dynamics differed between years and between mosquito species in relation to wetland, urban and forest habitats and was influenced by water level of the Drava and the Danube rivers.

The flight distances of floodwater mosquitoes (Aedes vexans, Ochlerotatus sticticus and Ochlerotatus caspius) in Osijek, Eastern Croatia

In spring 2004, the mark-release-recapture study was conducted in the Osijek area, covering the total of 171 km2, 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.

Structure of aquatic assemblages of Coleoptera and Heteroptera in relation to habitat type and flood dynamic structure

The abundance and taxonomic composition of the aquatic insect fauna were investigated, with focus on adult water bugs, water beetles and water scavenger beetles (Heteroptera: Nepomorpha and Gerromorpha, and Coleoptera: Hydradephaga and Hydrophilidae) in two different freshwater habitats: (1) a periodically flooded area of the Special Zoological Reserve in Kopački rit Nature Park, Croatia; and (2) melioration canals in the wider area of the Nature Park during 2005. Aquatic insects are generally abundant in various water systems, including floodplains that are exposed to water level fluctuations. Our aims were (1) to determine abundance and species richness in relation to habitat type; (2) to determine the influence of high flood peaks and oscillations during high water levels on the diversity of aquatic Coleoptera and Heteroptera in the flooded area; and (3) to identify characteristic species associated with each habitat type. We collected 71 species; 41 were captured at canals and 64 at the flooded area. Diversity of the two habitat types varied depending on the months but there were remarkable differences in species pool and their abundance. Both high and low water levels as well as oscillations during high water levels had major influence on species assemblages at the flooded area. Diversity of aquatic Coleoptera and Heteroptera was higher when the water level decreased after high water level peaks. A total of 11 species fulfilled the criteria for specificity and were sufficiently abundant to be suitable species characteristic for these two habitats. A higher proportion of significant characteristic species was present in the flooded area than in the canals. The presence of two Red List species of water beetles (Graphoderus bilineatus De Geer, 1774 and Berosus geminus Reiche et Saulcy, 1856) and nine significant characteristic species at the flooded area clearly indicates that the contribution of floodplains in maintaining freshwater biodiversity is not only important regionally but also at the international level. Also, our results suggest that the power of high water levels is an important factor that can be used in analyses on aquatic Coleoptera and Heteroptera assemblages, showing the uniqueness of large floodplain areas.

Seasonal and Spatial Oviposition Activity of Aedes albopictus (Diptera: Culicidae) in Adriatic Croatia

ABSTRACT Seasonal and spatial ovipositional activity of Aedes albopictus (Skuse, 1894) was investigated in Split, South Croatia. During 2009 and 2010, 35 oviposition traps were used in this research. For studying oviposition behavior, mean egg density and Lloyds mean crowding were used to define the dispersion of eggs into ovitraps and, together with Taylors power law, to show aggregation degree. To show monthly distribution of egg density, Kriging interpolation was used. Oviposition activity started in April (week 13) and was completed at the beginning December (week 48). Mean egg density reaches the highest values from June to early September (week 25–35). Slope of regressions (mean crowding on mean density and log variance and log mean density) indicated a clumped distribution of eggs. Sampling sites were divided in four groups based on quartiles of median and maximum of mean density. There was no significant difference in measured abiotic factors (temperature, humidity, and rainfall) and measured mean egg density, total amount of eggs, and percentage of positive ovitraps between investigated years, except in mean egg density in some localities.

Efficacy of mosquito attractants in various habitats of a floodplain

Efficacy of different mosquito attractants was invesigated at four sites in three plant communities (Galio-Salicetum albae, Populetum nigro-albae, Genisto elatae-Quercetum roboris) of flooded and forest habitats in Kopački rit Nature Park, Croatia. The attractants were: dry ice, horse urine, horse urine + acetone, acetone, 1-octen-3-ol and ammonium hydroxide baited CDC traps. A total of 11,441 mosquito specimens of 12 species were collected. Aedes vexans (91.43%) was the most numerous species. A statistically significant difference between the efficacy of dry ice and the other attractants was shown, whereas there was no difference between the other attractants. A greater number of specimens and species number were noted in the flooded plant communities (Populetum nigro-albae). The response of Ae. vexans to dry ice was higher in flooded sites, and it was significantly lower in forest habitat (Genisto elatae-Quercetum roboris) according to fuzzy c-means cluster analysis. The same analysis shows a higher efficacy of other attractants (horse urine, horse urine + acetone, acetone, octenol and ammonium hydroxide) in forest habitat when compared to the flooded area habitats.

An overview of mosquitoes and emerging arboviral infections in the Zagreb area, Croatia

Mosquito control in the Zagreb area has been conducted for many years, whereas the fauna has only been investigated in the last 20 years. So far 30 mosquito species have been detected in the city area. Culex pipiens form molestus is the dominant mosquito species in indoor breeding sites. In forested areas and areas exposed to flooding, the active period is early spring and the dominant species are Ochlerotatus sticticus, Ochlerotatus cantans, Ochlerotatus geniculatus and Aedes vexans. The eudominant mosquito species found in the artificial breeding sites are Culex pipiens and the Asian tiger mosquito, Aedes albopictus. Invasive Ae. albopictus, present in the Zagreb area since 2004, has expanded to a larger area of the city during the last three years. The recent emergence of the human West Nile virus and Usutu virus neuroinvasive disease in Zagreb and its surroundings highlighted the role of mosquitoes as vectors of emerging arboviruses. The paper focuses on mosquito species and arboviral infections detected in humans and animals in the Zagreb area, Croatia.

Maximum radius of carbon dioxide baited trap impact in woodland: implications for host-finding by mosquitoes

CDC traps were used to determine the maximum radius of carbon dioxide attraction within forest habitat (a forest plant community with Carpino betuli-Quercetum roburis). A central CDC trap with dry ice (CO2) was set as the source of attractant (Ck). Around Ck trap two circles (A and B) of CDC traps without attractants were placed. Circle A was constituted of 6 CDC traps and Circles B with 12 CDC traps. Radius from Circle A and B to the Ck trap were used to determine CO2 maximum range. During the experiment, the average emissions of CO2 were 0.08 to 0.1 g s−1. Regarding the data, optimal radius attraction where CO2 was affected on mosquitoes was between 55 and 70 m from the source. Results propose that the distance between traps should be greater than 140 m, to ensure the absence of bias by each of the traps. Changes in CO2 maximum concentration and wind velocity directly affected the catch of different species. The number of Ochlerotatus sticticus collected was positively correlated with wind speed.