First record and spreading of the invasive mosquito Aedes japonicus japonicus (Theobald, 1901) in Croatia

Aedes (Hulecoeteomyia) japonicus japonicus (Theobald, 1901) has recently established across North America and Central Europe. A 3‐year survey was conducted in northwestern Croatian regions from 2013 to 2015 using mosquito ovitraps at possible points of entry and house yards, occasionally complemented by larval collections from cemetery vases. In the first year, the survey investigated the county bordering Slovenia, where the first detection of Ae. j. japonicus had taken place on 28 August 2013. During the next 2 years, Ae. j. japonicus was detected in this area from early May until late October. In 2015, several counties further to the east were included in the survey, leading to the detection of Ae. j. japonicus approximately 100 km eastward from the initially surveyed region. Given a moderate continental climate and homogeneous climatic conditions in this part of Europe, the eastward spread of Ae. j. japonicus can be expected to continue.     

Unexpected Patterns of Admixture in German Populations of Aedes japonicus japonicus (Diptera: Culicidae) Underscore the Importance of Human Intervention

The mosquito Aedes japonicus japonicus, originally restricted to temperate East Asia, is now widespread in North America and more recently has become established in Europe. To ascertain the putative number of separate introductions to Europe and examine patterns of expansion we analyzed the genetic makeup of Ae. j. japonicus populations from five cemeteries in North Rhine-Westphalia and Rhineland-Palatinate, two western German federal states, as well as of specimens from populations in Belgium, Switzerland, and Austria/Slovenia. To do so, we genotyped individual specimens at seven pre-existing polymorphic microsatellite loci and sequenced part of the nad4 mitochondrial locus. We found evidence of two different genotypic signatures associated with different nad4 mitochondrial haplotypes, indicating at least two genetically differentiated populations of Ae. j. japonicus in Europe (i.e. two distinct genotypes). Belgian, Swiss, and Austrian/Slovenian populations all share the same genotypic signature although they have become differentiated since isolation. Contrary to expectations, the German Ae. j. japonicus are not closely related to those in Belgium which are geographically nearest but are also highly inbred. German populations have a unique genotype but also evidence of mixing between the two genotypes. Also unexpectedly, the populations closest to the center of the German infestation had the highest levels of admixture indicating that separate introductions did not expand and merge but instead their expansion was driven by punctuated human-mediated transport. Critically, the resulting admixed populations have higher genetic diversity and appear invasive as indicated by their increased abundance and recent spread across western Germany.     

Seasonal surveillance confirms the range expansion of Aedes japonicus japonicus (Theobald) (Diptera: Culicidae) to the Hawaiian Islands of Oahu and Kauai

The Asian bush mosquito, Aedes japonicus japonicus (Theobald) was not known to occur in the Hawaii archipelago until it was identified on the island of Hawaii in 2003. This mosquito species remained undetected on the neighboring islands for 8?years before it was discovered at the Honolulu International Airport on Oahu in 2012. By 2015, four Ae. j. japonicus mosquitoes were collected in the western mountains of Oahu and one was collected in the central mountains of Kauai. The collection of this invasive mosquito species across the neighboring Hawaiian Islands of Oahu and Kauai indicated the need for increased seasonal surveillance on these islands. Following nearly four years of surveillance, Ae. j. japonicus was also confirmed to occur in the eastern mountains of Oahu and in the central mountainous region of Kauai. To expand the knowledge of the spread of invasive mosquitoes species further surveillance is necessary to identify all possible areas where populations of Ae. j. japonicus and other invasive mosquito species occur in Hawaiian archipelago.     

The invasive mosquito Aedes japonicus in Central Europe

Complaints about a biting pest led to the recognition of invasive Aedes (Finlaya) japonicus japonicus (Theobald) (Diptera: Culicidae) in Central Europe. Larval collections from cemetery vases revealed a colonized area of approximately 1400 km² in northern Switzerland spreading into bordering Germany, suggesting that the mosquito has been established in this region for several years. Within this range, larvae of Ae. japonicus were recovered from more containers than the most common resident culicid species Culex pipiens. Possible introduction sites (used tyre yards and international airports) revealed few or no larvae, and the mode of introduction remains unclear. Given the vector potential of this species for arboviruses, implementation of surveillance and control measures should be considered.     

Invasive Process and Repeated Cross-Sectional Surveys of the Mosquito Aedes japonicus japonicus Establishment in Belgium

When accidentally introduced in a new location, a species does not necessarily readily become invasive, but it usually needs several years to adapt to its new environment. In 2009, a national mosquito survey (MODIRISK) reported the introduction and possible establishment of an invasive mosquito species, Aedes j. japonicus, in Belgium. First collected in 2002 in the village of Natoye from a second-hand tire company, then sampled in 2003 and 2004, the presence of adults and larvae was confirmed in 2007 and 2008. A repeated cross-sectional survey of Ae. j. japonicus was then conducted in 2009 in Natoye to study the phenology of the species on two different sites using three kinds of traps: Mosquito Magnet Liberty Plus traps, BG sentinel traps and CDC Gravid traps. An analysis of the blood meals was done on females to assess the epidemiological risks. Five species of mosquitos were caught using the different kind of traps: Culex pipiens, Cx torrentium, Anopheles claviger, Aedes geniculatus and Ae. j. japonicus, Cx pipiens being the most abundant. The CDC gravid traps gave the best results. Surprisingly Ae. j. japonicus was only found on one site although both sites seem similar and are only distant of 2.5 km. Its population peak was reached in July. Most of the engorged mosquitoes tested acquired blood meals from humans (60%). No avian blood meals were unambiguously identified. Larvae were also collected, mostly from tires but also from buckets and from one tree hole. Only one larva was found in a puddle at 100 m of the tire storage. A first local treatment of Ae. j. japonicus larvae population was done in May 2012 using Bacillus thuringiensis subsp. israelensis (Bti) and was followed by preventive actions and public information. A monitoring is also presently implemented.     

Field evaluation of baited traps for surveillance of Aedes japonicus japonicus in Switzerland

The efficacy of Centers for Disease Control (CDC) miniature light traps and ovitraps was tested in the outskirts of the city of Zurich in Switzerland for their use in the surveillance of Aedes (Hulecoeteomyia) japonicus japonicus (Theobald) (Diptera: Culicidae), the invasive Asian bush mosquito. Sets of single CDC traps were run overnight (n = 18) in three different environments (forest, suburban and urban) in 3 × 3 Latin square experimental designs. Traps were baited with: (a) carbon dioxide (CO₂); (b) CO₂ plus light, or (c) CO₂ plus lure blend [Combi FRC 3003 (iGu^®)]. At the same locations, mosquito eggs were collected weekly using standard ovitraps baited with different infusions (oak, hay or tap water) and equipped with different oviposition substrates (a block of extruded polystyrene, a germination paper strip or a wooden stick). Data were analysed using Poisson and negative binomial general linear models. The use of light (P < 0.001) or lure (P < 0.001) significantly increased the attractiveness of CDC traps baited with CO₂. Oak and hay infusions did not increase the attractiveness of ovitraps compared with standing tap water (P > 0.05), and extruded polystyrene blocks were preferred as an oviposition substrate over wooden sticks (P < 0.05) and seed germination paper (P < 0.05). Carbon dioxide‐baited CDC miniature light traps complemented with light or iGu^® lure and ovitraps containing standing tap water and polystyrene oviposition blocks can be considered as efficient and simple tools for use in Ae. j. japonicus surveillance programmes.     

Repellent efficacy of wood vinegar against Culex pipiens pallens and Aedes togoi (Diptera: Culicidae) under laboratory and semi-field conditions

The repellent efficacy of wood vinegar was assessed against mosquitoes under laboratory conditions at 1, 5, 10, 20, 40, 60 and 80% concentrations. The study evaluated whether wood vinegar is able to repel Culex pipiens pallens Coquillet and Aedes togoi (Theobald) from the human body and if so at what concentrations. The tests were conducted using the arm-in-cage method in 80 × 40 × 40 cm screened mosquito cages. The data were analyzed and compared with those of N,N-Diethyl-3-methylbenzamide (deet) at 10.3% concentration. The results showed that wood vinegar provided mosquito repellence of varying degree depending on the concentration used. The observed repellence averaged from as low as 39.6% at 5.0% concentration to as high as 100% at 80% concentration against Ae. togoi. Repellence against Cx. pipiens pallens was high being 90.3% at 20% concentration, 92.2% at 40% concentration, 93.9% at 60% concentration and 100% at 80% concentration. The duration of protection time tests showed that the 40% and 60% concentrations of the wood vinegar give protection from landing of Ae. togoi for a period of up to 7 h, though the lower concentration gave lower protection after the first five hours. The results indicated that wood vinegar has mosquito repellent characteristics that tend to vary with the concentration used and the species of mosquitoes. Wood vinegar in this case was very effective in repelling Cx. pipiens pallens, even at lower concentrations while higher concentrations were required to repel Ae. togoi.     

Modelling the ecology of the coastal mosquitoes Aedes vigilax and Aedes camptorhynchus at Port Pirie,South Australia

Abstract Two mosquito species, Aedes camptorhynchus (Thomson) and Aedes vigilax (Skuse) (Diptera: Culicidae) are responsible for significant nuisance biting and disease transmission in southern coastal Australia. Mosquito abundance, tide height, temperature and rainfall data were collected over three summer seasons (2002, 2003, 2004) at Port Pirie, South Australia and subjected to statistical analysis to develop ecological models for predicting problem mosquito outbreaks. A logistic regression model for Ae. camptorhynchus gave a predictive R² of 0.30 using mean air temperature, whereas, for Ae. vigilax, tide height, mean air temperature and day length yielded a regression with an R² of 0.68. These models identify significant environmental drivers for both species and may be useful in the prediction of future outbreaks, particularly of Ae. vigilax.     

State‐wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Aedes aegypti and Aedes albopictus are invasive mosquito species with geographic ranges that have oscillated within Florida since their presence was first documented. Local transmission of dengue, chikungunya, and Zika viruses serves as evidence of the public health importance of these two species. It is important to have detailed knowledge of their distribution to aid in mosquito control efforts and understand the risk of arbovirus transmission to humans. Through a partnership involving the University of Florida Institute of Food and Agricultural Sciences Cooperative Extension Service and the Florida Medical Entomology Laboratory; the Florida Department of Health; and mosquito control agencies throughout Florida, a container mosquito surveillance program involving all life stages was launched in the summer of 2016 to detect the presence of Ae. aegypti and Ae. albopictus. Results from this survey were mapped to provide a picture of the current known distribution of Ae. aegypti and Ae. albopictus in Florida. Aedes aegypti and/or Ae. albopictus were detected in the 56 counties that were part of the survey. Only Aedes albopictus was detected in 26 counties, primarily in the panhandle region of Florida. The results of this work underscore the importance of maintaining container mosquito surveillance in a state where chikungunya, dengue, and Zika viruses are present and where there is continued risk for exotic arbovirus introductions.     

Fine‐scale spatial and temporal population genetics of Aedes japonicus,a new US mosquito,reveal multiple introductions

The newly introduced mosquito Aedes japonicus has expanded from its original range in Northeastern Asia to 29 US states (including Hawaii) plus Canada and northern Europe. Our objectives were to test an earlier hypothesis of multiple introductions of this species to the Northeastern US and evaluate putative temporal changes in genetic makeup. Using a panel of seven microsatellite loci, we confirmed the existence of two abundant genetic forms in specimens originally collected in 1999–2000 (F_ST value based on microsatellite data = 0.26) that matches the disjunctive distribution of mitochondrial haplotypes. To examine the distribution of the two genetic ‘types’ across Pennsylvania we created a fine‐scale genetic map of Ae. japonicus using 439 specimens collected from 54 Pennsylvania counties in 2002–2003. We also made direct comparisons between collections in 1999–2000 and new collections made in 2004–2005 obtained from the same areas in the northeastern US. We observed that the strong association between mtDNA haplotype and microsatellite signature seen in 1999–2000 had weakened significantly by 2002 across Pennsylvania, a trend continued to some extent in 2004–2005 in PA, NJ, and NY, indicating that once easily distinguishable separate introductions are merging. The two expanding genetic forms create a complex correlation between spatial and genetic distances. The existence of multiple introductions would be obscured without sampling early and across time with highly polymorphic molecular markers. Our results provide a high‐resolution analysis of the spatial and temporal dynamics of a newly introduced disease vector and argue that successive introductions may be a common pattern for invasive mosquitoes.     

Predation on the invasive mosquito Aedes japonicus (Diptera: Culicidae) by native copepod species in Germany

Some limnic copepod species are predators of mosquito larvae. Seven species belonging to the order Cyclopoida, family Cyclopidae, were collected in the field in Germany and tested for the first time in laboratory bioassays for their potential to serve as biological control agents of the invasive Asian bush mosquito Aedes japonicus (Theobald), a vector of various pathogens causing disease. Females of Diacyclops bicuspidatus (Claus) did not attack 1^st instar larvae of Ae. japonicus, but Macrocyclops distinctus (Richard), Cyclops divergens Lindberg, and C. heberti Einsle predated a mean of 14, 18, or 19 1^st instar larvae, respectively. Acanthocyclops einslei Mirabdullayev and Defaye killed 30 larvae, and high predation rates with a mean of 39 or 46 larvae, respectively, were obtained by Megacyclops viridis (Jurine) and M. gigas (Claus). In regression analyses, predation rates by M. viridis correlated with body size, with specimens of 1.8 mm length being more effective than smaller or bigger ones. Based on the presented data, the two Megacyclops species seem to be promising candidates for use in field studies on the biological control of Ae. japonicus.     

The hitchhiker's guide to becoming invasive: exotic mosquitoes spread across a US state by human transport not autonomous flight

Not all exotic species establish and expand aggressively (i.e. become invasive). As potential vectors of disease agents, invasive mosquitoes can have considerable impact on public health, livestock and wildlife; therefore, understanding the species characteristics and ecological circumstances promoting their invasiveness is important. The mosquito Aedes japonicus japonicus, originally from north‐east Asia, was introduced at least two separate times to the north‐eastern USA, as surmised from the initial existence of two populations with distinct nuclear and mitochondrial genetic signatures that later intermixed. Since these original introductions in the late 1990s, Ae. j. japonicus has expanded across 31 US states, two Canadian provinces and five European countries. Although some of the expanded range was due to other independent introductions, to understand what drove the postintroduction expansion of Ae. j. japonicus within the north‐eastern USA, we performed a high‐resolution landscape genetic analysis of 461 specimens collected across Virginia, a state south of the original introductions. All specimens were genotyped at seven pre‐optimized microsatellite loci, and a subsample was sequenced at one mitochondrial locus. We concluded that throughout Virginia this species has primarily expanded in association with humans: genetic distance and distance along roads remained correlated after controlling for geographic distance, and proximity to I‐95, a major interstate highway, strongly predicted nuclear ancestry. In contrast, there was very limited evidence of diffusion even at distances potentially suitable for autonomous mosquito flight. This implies that its association with humans (rather than innate species characteristics) is the single most important determinant of invasiveness in this mosquito.     

Spatial and temporal patterns of abundance of Aedes aegypti L. (Stegomyia aegypti) and Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] in southern Florida

Invasion by mosquito vectors of disease may impact the distribution of resident mosquitoes, resulting in novel patterns of vectors and concomitant risk for disease. One example of such an impact is the invasion by Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] (Diptera: Culicidae) of North America and this species' interaction with Aedes aegypti L. (Stegomyia aegypti L). We hypothesized that Ae. aegypti would be found in urban, coastal areas that experience hotter and drier conditions, whereas Ae. albopictus would be more commonly found in suburban and rural areas that are cooler and wetter. In addition, we hypothesized that Ae. aegypti would be more abundant early in the wet season, whereas Ae. albopictus would be more abundant later in the wet season. Urban areas were drier, hotter and contained more Ae. aegypti than suburban or rural areas. Aedes aegypti was relatively more abundant early in the wet season, whereas Ae. albopictus was more abundant in both the late wet season and the dry season. The spatial patterns of inter‐ and intraspecific encounters between these species were also described. The distribution of these mosquitoes is correlated with abiotic conditions, and with temperature, humidity and the relative availability of rain‐filled containers. Understanding the ecological determinants of species distribution can provide insight into the biology of these vectors and important information for their appropriate control.     

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre‐imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.     

Aquatic thermal conditions predict the presence of native and invasive rock pool Aedes (Diptera: Culicidae) in the southern Appalachians,U.S.A.

The native rock pool mosquito, Aedes atropalpus (Coquillett), and the invasive Aedes japonicus (Theobald) have been found in many types of artificial and natural containers throughout North America. Little is known about the ecology of these two species in habitats where they co‐occur, although multiple investigators have reported the decline of the native species concurrent with the introduction and spread of the invasive species. Here we report the results of riverine rock pool collections (n=503) in the southern Appalachian Mountains between 2009‐2015. Surface water temperatures strongly predicted the presence of each species across a broad range of observed temperatures (11‐39.8° C). For every unit of increase in temperature (°C) the odds of collecting Ae. atropalpus larvae increased by 0.34 while the odds of collecting Ae. japonicus larvae decreased by 0.28. No Ae. japonicus larvae or pupae were collected at temperatures greater than 36° C; however, immature Ae. atropalpus were found in rock pools with temperatures up to 39.8° C. In contrast, Ae. japonicus were highly abundant in cooler rock pools (<17° C) where Ae. atropalpus were infrequent or absent. Our findings suggest that in spite of the successful invasion by Ae. japonicus, Ae. atropalpus remains well established in the southern Appalachian Mountains. Given the strong correlation of temperature with the presence of the two species and the contrasting absence of each species at observed temperature extremes, the role of thermal conditions should be carefully explored in the context of other ecological factors likely influencing the range and abundance of these mosquitoes.     

Horizontal distribution affects the vertical distribution of native and invasive container‐inhabiting Aedes mosquitoes within an urban landscape

The vertical dimension constitutes an important niche axis along which mosquitoes may adjust their distribution. Here, we evaluated whether the vertical distribution of container‐inhabiting Aedes mosquitoes differs along a gradient of anthropogenic land‐use intensity within an urban landscape. Using a pulley system, we hung oviposition cups at three heights (ground level, 4.5, and 9 m) and in three habitats: forest, park, and a built environment. We hypothesized that mosquito abundance and diversity would be highest in the least disturbed forest habitat, decrease in the park, and be lowest at the UNC‐Greensboro campus. We also expected Aedes albopictus (Skuse) and Ae. triseriatus (Say) to mainly oviposit at ground level and Ae. hendersoni (Cockerell) at canopy height. Aedes albopictus was the most common species (68.8%) collected in all three habitat types and was the only species found in the built environment. In that habitat, Ae. albopictus exhibited a bimodal distribution with the lowest activity at the intermediate height (4.5 m). Aedes triseriatus (28.9%) did not differ in egg abundance between the forest and park habitats but did exhibit diverse vertical habitat use while avoiding the canopy in the park habitat. Aedes hendersoni (2.3%) was the most sylvatic species and oviposited only at ground level. Our results indicate that the vertical distribution of mosquitoes is affected by the type of habitat in which they occur, and that this variation could be driven via local‐scale modification of microclimatic factors.     

Evaluation of collection methods for Culex quinquefasciatus,Aedes aegypti,and Aedes simpsoni in northeastern Tanzania

In East Africa, significant morbidity and mortality are caused by infections spread by Culex quinquefasciatus and Aedes aegypti. Sticky traps have been shown to be effective tools for sampling populations of Aedes mosquitoes and have been found to catch Cx. quinquefasciatus. Thus, they could potentially be used to sample populations of this species. This study compared Sticky ovitraps (SO) and MosquiTraps (MQT) with the CDC Gravid trap (CDC‐GT) for collection of Culex and Aedes mosquito populations in Tanzania. A follow‐up experiment was carried out using traps set for a 24‐h period to accommodate the oviposition habits of Aedes aegypti and Ae. simpsoni s.l. mosquitoes. The results showed that the CDC‐GT caught significantly more Cx. quinquefasciatus and Ae. aegypti than the SO or MQT, but there was no significant difference in the number of mosquitoes caught between the two sticky traps or of Ae. simpsoni s.l. caught among the three trap types. The results suggest that CDC‐GTs are the most appropriate in sampling of Cx. quinquefasciatus. Although CDC‐GTs collected more Ae. aegypti than the sticky traps, the simplicity and cost benefit of sticky traps facilitates large scale studies. All three trap types should be considered for monitoring Aedes mosquitoes.     

Evaluating the competence of the primary vector,Culex tritaeniorhynchus,and the invasive mosquito species,Aedes japonicus japonicus,in transmitting three Japanese encephalitis virus genotypes

Japanese encephalitis virus (JEV) is maintained in an enzootic cycle between swine, water birds, and mosquitoes. JEV has circulated indigenously in Asia, with Culex tritaeniorhynchus as the primary vector. In some areas where the primary vector is scarce or absent, sporadic cases of Japanese encephalitis have been reported, with Aedes japonicus japonicus presumed to have the potential as a secondary vector. As one of the world’s most invasive culicid species, Ae. j. japonicus carries a considerable health risk for spreading diseases to wider areas, including Europe and North America. Thus, evaluation of its competency as a JEV vector, particularly in a native population, will be essential in preventing potential disease spread. In this study, the two mosquito species’ vector competence in transmitting three JEV genotypes (I, III, and V) was assessed, with Cx. tritaeniorhynchus serving as a point of reference. The mosquitoes were virus-fed and the infection rate (IR), dissemination rate (DR), and transmission rate (TR) evaluated individually by either RT-qPCR or focus forming assay. Results showed striking differences between the two species, with IR of 95% (261/274) and 9% (16/177) in Cx. tritaeniorhynchus and Ae. j. japonicus, respectively. Both mosquitoes were susceptible to all three JEV genotypes with significant differences in IR and mean viral titer. Results confirm the primary vector’s competence, but the fact that JEV was able to establish in Ae. j. japonicus is of public health significance, and with 2%–16% transmission rate it has the potential to successfully transmit JEV to the next host. This may explain the human cases and infrequent detection in primary vector-free areas. Importantly, Ae. j. japonicus could be a relevant vector spreading the disease into new areas, indicating the need for security measures in areas where the mosquito is distributed or where it may be introduced.     

Sterilization of Hulecoeteomyia japonica japonica (= Aedes japonicus japonicus) (Theobald, 1901) by high‐energy photon irradiation: implications for a sterile insect technique approach in Europe

Hulecoeteomyia japonica japonica (= Aedes japonicus japonicus) (Diptera: Culicidae) (Theobald 1901), a container‐breeding invasive species in North America and Europe, is attracting particular attention for its high local abundances and possible roles in the transmission of human and animal pathogens. The preferential habitats of this species are forested and bushy areas, which renders control measures extremely inefficient. Use of the sterile insect technique (SIT) may contribute to the implementation of area‐wide integrated pest management strategies, as has been successfully proven with other aedine mosquito species. The present study investigates the effects of irradiation at a dose of 40 Gy on fitness parameters in H. j. japonica. Irradiation was performed on 16–24‐h‐old pupae from a colonized strain (PA) using a TrueBeam linear accelerator. Males from the PA strain were crossed with females of the same colony or with field‐collected females. Irradiation induced a slight increase in mortality in male pupae, but did not alter the survival and mating abilities of emerging adult males. Rates of blood feeding and fertility were lower when PA strain males were kept with field‐collected females rather than PA females. Irradiated males induced reductions in fertility (residual fertility: 2.6%) and fecundity in mated females. The data indicate that the SIT is a suitable technique to enhance the control of this species.