Aedes japonicus - Factsheet for experts
SPECIES NAME/CLASSIFICATION: Aedes japonicus japonicus (Theobald)
COMMON NAMES: East Asian bush or rock pool mosquito
SYNONYMS AND OTHER NAMES IN USE: Ochlerotatus japonicus japonicus , Hulecoeteomyia japonica japonica 
Hazard associated with mosquito species
Invasive species/Global dispersion
Aedes japonicus has become the third invasive mosquito species to be reported in Europe. Its geographical expansion has been facilitated by human activities such as the international trade in used tyres. It is now listed as one of the top 100 invasive species by the Invasive Species Specialist Group . Its distribution in central Europe is also expanding.
The success of the invasion of Ae. japonicus, particularly in the US, has been due to a number of factors including its ability to withstand long distance dispersal and winter temperatures in temperate regions, and its high tolerance to organic concentrations in a number of natural and artificial containers . Aedes japonicus has less specialised requirements for aquatic habitats, compared to Ae. albopictus, and this could facilitate furtherspread of this species .
Biting and disease risk
In Japan and Korea, its normal native range, Ae. japonicus is not considered an important disease vector . There is a concern however that this species may become a pest problem or be involved in the transmission of North American arboviruses such as West Nile virus . Aedes japonicus colonises urbanised environments  and females are active during the day , increasing the potential contact this species could have with humans which in turn may result in disease transmission. More recently, this species has shown vector competence for the transmission of dengue and chikungunya, both of which have been recently reported in Europe .
Aedes japonicus has been reported in Austria, Belgium, Canada, China, France, Germany, Korea, Japan, New Zealand, the Netherlands, Russia, Switzerland, Slovenia Taiwan and the US.
Brief history of spread and european distribution
Aedes japonicus is endemic to Korea, Japan, Taiwan, southern China and Russia  and has since spread to a number of other countries (see above). This spread has occurred since the 1990s and like other invasive mosquito species, Ae. japonicus has relocated to new geographical areas via the movement of infested tyres. It was first reported outside its native range in New Zealand, where it was introduced via the used tyre trade . Once introduced to the United States, the Standard-bred horse trade may have been contributed to expansion there, as early collection sites in New York and New Jersey were associated with trailers and Standard-bred horse breeding areas .
Timeline of initial movements
Aedes japonicus established in the United States in the 1990s  after which it rapidly spread throughout eastern and northern America and southern Canada . It was reported in New York state, New Jersey and Connecticut in 1998, Connecticut, Ohio and Pennsylvania in 1999, Maryland, Massachusetts and Virginia in 2000 and Quebec, Canada in 2000 . It has since spread to 31 states including Hawaii, Iowa, Wisconsin and Minnesota [2, 13, 14] . Its spread in the US may be due to multiple introductions and at least two abundant genetic forms are present [15, 16] . This species was intercepted on several occasions in ports of New Zealand (1993, 1998, and 1999) through the importation of used tyres from Japan [2, 17] .
Initial importations and spread in Europe
Aedes japonicus was first reported in Europe in 2000 when it was detected in Normandy (Orne) in northern France , where it was later eliminated . It was then reported in 2002 in Belgium at a tyre depot and presence as adults and larvae was confirmed in 2007 and 2008. It was most likely introduced through the trade of tyres and the population was thought to be established at the company site but does not appear to be spreading . It was detected in Switzerland in 2008 following reports of a biting nuisance and subsequent surveys revealed a 1,400km colonised zone including an area in Germany. This was the first detection of invasive mosquitospreading in central Europe . No obvious route of introduction was identified in this study but it is suspected that the species has been present here for some time. Adult Ae. japonicus were then found in Southern Germany during 2011, following intensified surveillance . This resulted in surveillance expanding to cover the entire federal state of Baden-Württemberg where a reduction in the colonised areas compared to 2010 was reported (possibly due to a dry spring during 2011). However, a large, newly infested area was also reported from the city of Stuttgart to the Swabian Mountains . Entomological surveys carried out during 2012 in North Rhine-Westphalia also revealed the presence of an established population in the west of the country . Aedes japonicus were then reported further north in southern Lower Saxony and northeastern North Rhine-Westphalia during spring 2013 . It was detected in 2012 and 2013 in Lelystad, the Netherlands (personal communication M. Braks).
Possible future expansion
It is suggested that Ae. japonicus may expand beyond its current geographical distribution  but there is still a lack of information available on this invasive mosquito species .
- SPECIES NAME/CLASSIFICATION: Aedes japonicus japonicus (Theobald)
- COMMON NAMES: East Asian bush or rock pool mosquito
- SYNONYMS AND OTHER NAMES IN USE: Ochlerotatus japonicus japonicus , Hulecoeteomyia japonica japonica 
Morphological characters and similar species
Adults of Ae. japonicus are relatively large and show a black and white pattern due to the presence of white scale patches on a black background on the legs and other parts of the body. Some indigenous mosquitoes also show such contrasts (more brownish and yellowish) but in that case less obvious. However Ae. japonicus could be mixed up with other invasive (Ae. aegypti, Ae. albopictus, Ae. koreicus) or indigenous species (Ae. cretinus, restricted to Greece and Turkey), and the main diagnostic character is the presence of several lines of yellowish scales on a black background on the scutum (dorsal part of the thorax). The three other described subspecies differ in tibia ornamentation and are restricted to parts of South-eastern Asia . A DNA-based rapid assay has been developed in order to distinguish this species from other similar invasive species .
Larvae of Ae. japonicus appear brownish-yellow or darker, with a slender appearance and long siphon. The head capsule has no bright areas on the dorsal side. Eyes and mouthparts are not distinctly visible via the naked eye .
Life history (inc. details of overwintering stage)
Aedes japonicus can produce freeze and desiccation-resistant eggs  that can remain dormant over winter and hatch once environmental conditions become favourable. This allows for the species to be transported in infested containers . Larvae also overwinter in its native range, in New Jersey and North Carolina . During studies in Belgium in 2008, larval sampling during early spring confirmed that this species can overwinter as diapausing eggs in Northern Europe . In parts of Asia, Ae. japonicus overwinters as eggs such as in north eastern Japan but as larvae in other areas such as south western Japan . No larvae were found however during winter sampling in Belgium .
In North America, larvae and biting adults have been collected between May–November in Connecticut  and May–October in New York State . Larvae of Ae. japonicus have also been shown to be the dominant species within rock pools during the early to mid-summer months when temperatures are lower  and also during spring and fall collections in the United States . In Switzerland, eggs were found until October during field studies in 2008  and data from North American studies suggests Ae. japonicus remains active through early autumn in northern temperate zones .
Voltinism: (generations per season)
Reported to be multivoltine in Connecticut and southern Japan .
Host preferences (e.g. birds, mammals, humans)
This species preferentially feeds on mammalian hosts  . Studies inNew Yorkshowed Ae. japonicus fed solely on humans and mammals . Analysis of blood meals from specimens collected in Connecticut showed human, deer and eastern chipmunks as hosts . Analyses of blood meals from specimens collected in New Jersey also showed a preference for mammalian blood feeding; 52% were found to have fed on White tailed deer and 36% were found to have fed on humans. No samples were found positive for avian or reptilian blood , however there is evidence of bird biting under laboratory conditions .
Aedes japonicus can develop in a large range of both natural and artificial aquatic container habitats including rock pools, tyres, bird baths, milk cartons, buckets and tree holes . In North America their preference is for rock pools [2, 21] but those with relatively low summer temperatures  or shaded . Elsewhere in the United States and Japan, larvae have been found in various aquatic habitats with varying sunlight, elevation, detrital content, and within both urban and rural settings .The distribution of this species is reported to overlap with that of Ae. triseriatus in North America and an overlap in aquatic habitat use has been reported [10, 32] . An overlap in habitat use has also been reported for Ae. atropalpus, which like Ae. triseriatus, may actually be outcompeted by Ae. japonicus in the United States, particularly in tyre sites . The use of the same habitats as Ae. albopictus has also been reported, although highest abundances of each species differs seasonally . Sampling conducted across a wide area in northern Switzerland showed a preference for plastic vases in cemeteries, but fountains, rain water casks and catch basins were also colonised . Sampling in Germany revealed the presence of larvae in a variety of containers including flower vases, flower-pot saucers, watering cans and paddling pools .
In its native range, Ae. japonicus colonise tree-hole habitats but this has not often been reported for newly established areas in the United States or Europe .
Biting/resting habits (endo/exophily, endo/exophagy, biting periodicity)
Adults are often found in forested areas  being active during the daytime and crepuscular hours . This species is an aggressive biter and will readily bite humans outside and occasionally inside houses . Adult females were collected indoors whilst attempting to bite people in Germany during 2012 .
Environmental thresholds/constraints/development criteria
There is limited information on environmental thresholds constraining the distribution of Ae. japonicus. Although this species is said to be increasing in abundance in some areas of the US compared to native species, it was found that habitats with water temperature over 30 oC did not yield any Ae. japonicus . This could be a limiting factor for future spread in southern Europe. Although Ae. albopictus has been shown to be superior to Ae. japonicus in competing for food resources in larval habitats in the US (particularly in artificial container habitats), higher overwintering survival and earlier hatching means Ae. japonicus is able to exploit larval habitats before Ae. albopictus [25, 34] . Competition with larvae of other Aedes species may affect Ae. japonicus adult longevity, but exploitation of multiple aquatic habitats lessens the impact this may have on the success of Ae. japonicus in new habitats . It is also suggested that this species is outcompeting Ae. atropalpus in some areas of the United States due to shorter larval development periods .
Epidemiology and transmission of pathogens
Known Vector Status (In Field, Experimental Transmission)
This mosquito has been found positive for West Nile virus on a number of occasions in the US [6, 26] and laboratory studies show it is a competent vector of West Nile virus . Laboratory studies have also shown Ae. japonicus to be a competent carrier of Japanese encephalitis virus , La Crosse virus  and a moderately effective vector of Saint Louis encephalitis virus , Eastern equine encephalitis virus , Chikungunya virus and Dengue virus  and Rift Valley fever  .
Role as Enzootic or Bridge Vector
In North America this mosquito feeds on white-tailed deer, which are known reservoir hosts for a number of pathogens including Jamestown Canyon virus, Cache Valley virus and Potosi virus . Aedes japonicus may also act as a possible bridge vector of Eastern equine encephalitis virus, La Crosse virus, and West Nile virus, with field-collected Ae. japonicus being frequently found in the United States . Dunphy et al.  suggests that it is a likely bridge vector for La Crosse virus given that (a) its established range coincides with regions where the primary vector is also present and hence the virus amplification will be occurring, and (b) laboratory studies have shown it to be competent. La Crosse virus has also been isolated from field collected Ae. japonicus. One pool of Ae. japonicus collected in Eastern Tennessee during 2010 tested positive by PCR . This represents the first report of natural infection in this mosquito species. Further studies are required to assess host preferences of this mosquito within the endemic area . Aedes japonicus have also been shown to be competent vectors of both chikungunya virus and dengue, both of which have been recently reported in Europe .
Its role in the transmission of the above mentioned viruses in natural conditions is unclear . The propensity of this mosquito to feed on humans, as demonstrated in a recent study using human landing catches in Belgium , highlights the importance of establishing the role(s) Ae. japonicus might play in disease transmission. However, as of yet, there are limited reports of this species being a nuisance, especially when compared to Ae. albopictus .
Public health (control/ interventions)
Specific surveillance programmes in Europe have been associated with Ae. japonicus. Firstly a survey of used tyres importers in France and Belgium led to the discovery of this species in both countries, and appears a useful method of determining the introduction and presence in the country. Then in Belgium, a ‘nationwide’ survey (MODIRISK) has completed the knowledge of it distribution and relative abundance. In 2012, a surveillance study at import sites (EXOSURV), including the infested area, provided updated information on the local spread of the species in Belgium. Finally an extensive specific study in Switzerland has mapped the distribution and spread throughout and around the colonised region.
In 2013, a control campaign was funded in Belgium to eliminate the species seen its limited distribution around the initial import site, actions were taken between April–October 2013.
Appropriate Sampling Strategy (aquatic larval sampling, adult traps)
Various techniques have been used. For example, Versteirt et al  used CO2 baited traps, CDC gravid traps and human landing catches to collect adult specimens in Belgium, with human landing catches at sunset the most successful way of collecting blood-seeking females. Nets, sieves and small dippers were used for larval collection.
Light traps, grass infusion baited gravid traps, CO2 CDC traps and encephalitis virus surveillance traps were used to collect specimens in New Jersey  and ovitraps have also been widely used . Andreadis et al  found that grass-infused gravid traps and CO2 light traps were the most successful, with little success with ovitraps. Dunphy et al  also found gravid traps to be successful for collecting Ae. japonicus and these were also used by Falco et al.,  in New York. Anderson et al.  used CDC miniature light traps baited with CO2 plus TrapTech Mosquito Lure as an effective method to collect Ae. japonicus under field conditons.
Species Specific Control Methods e.g. insecticide, public health education etc
There is no specific guidance on control of this mosquito species, although much of the guidance for other container breeding species, like Ae. albopictus would be equally applicable. As in the case of source reduction at cemeteries, specific guidance can be provided on a case-by-case basis.
Current Nuisance Biting/Vector Issues in Europe
A biting nuisance reported in Switzerland led to the identification of this mosquito species here in 2008 .
Existing Public Health Awareness and Education Materials
Key areas of uncertainty
- Not a well studied invasive mosquito species compared to other species such as Ae. albopictus .
- Host feeding preferences in the wild are unknown , only a few blood meals were analysed so far . Host feeding preferences in areas where this mosquito could act as a vector for West Nile virus (and other arboviruses) need to be researched.
- Need to establish if this mosquito feeds on birds in the field since birds are viewed as the principle reservoir for West Nile virus. Shown to feed on White-tailed deer in New Jersey and deer in New Jersey have been found serologically positive for West Nile virus infection but it is not known if they sustain high enough viral titre to pass the virus on .
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