Invasive Mosquitoes

In Switzerland, three  invasive mosquito species have been reported: Aedes albopictus (the Asian tiger mosquito), Aedes japonicus (the East Asian bush mosquito) and Aedes koreicus. All three mosquito  species are similar in that they have a black-and-white body coloration, in particular on the hind legs. They breed in small water containers present in urban areas. However, they differ in terms of the level of biting nuisance, potential in transmitting diseases and their geographical distribution in Switzerland.

If you find an invasive mosquito, please do report them to us.

Aedes albopictus – the Asian Tiger Mosquito

R. Eritja

The Asian tiger mosquito is considered one of the most invasive species globally. Originally from Southeast Asia, the mosquito has colonised the world in just a few decades thanks to human activities, such as the passive transport by vehicles and the trade of used tyres, and its marked ecological
adaptability. It is currently present throughout southern Europe and is advancing north (see European Distribution Map).

In addition to Asian tiger mosquito’s biting nuisance, the mosquito is of public health concern as it can potentially transmit infectious diseases such as dengue and chikungunya from a travellers returning from endemic areas to other people even in Switzerland.

Although it is virtually impossible to prevent the mosquito’s expansion, the aim is to keep population densities as low as possible through a coordinated effort by the authorities and with the public alike.

Citizens, therefore, take noteof the simple measures to be taken to limit its presence and send us your reports of suspicious cases.


Morphology

The Asian tiger mosquito resembles the other mosquito species both in shape and size, yet it has a black coloration with clearly visible white patterns on the body and the legs. It has also a clear white stripe running across the back.


Biology

Knowing the tiger mosquito will help to control it:

Life Cycle. After mating, the female mosquito needs a blood meal to complete the development of its eggs. Aquatic phase. The tiger mosquito attaches its eggs on a solid surface just above the water surface line. Once the water level raises the eggs will hatch. Before the newly hatched larvae reach the pupal stage they undergo four larval stages and one pupal stage. From the pupa new adults emerge and the aerial phase begins again. During summer the aquatic phase usually lasts one week. The adults, resting in the shade on the vegetation, live about a month and may deposit eggs multiple times. All mosquitoes need still water. Rivers are therefore not places of mosquito production.

Nuisance. The female bites during the day and may take repeatedly a blood meal from both humans and animals.

The Asian Tiger Mosquito Colonises  Small Amounts of Water. Various containers (e.g. saucepans, drums, catch basins, holes in the walls, etc.; see information leaflet) that contain water for over a week can produce tiger mosquitoes. The species does not like large quantities of water in open spaces, so it is not found in ponds, flooded roofs or unattended pools, while it may colonise underground cisterns or shady pools.

The Mosquito’s Strategy to Overwinter. Eggs can survive dry conditions for longer periods of
time. Eggs laid in late summer can easily withstand winter temperatures and then hatch in the following spring. Another strategy to overcome the winter, as frequently observed in the Canton of Ticino, are quiescent adults inside homes.

Exponential Growth. A female lays about 60 eggs, half of which will produce females. Without prompt intervention a single female may produce thousands if not millions offspring during one summer. At our latitudes, the first mosquitoes appear mid-April while the highest densities are reached in mid-August and towards the end of September before the mosquitoes become inactive, either as dormant eggs or quiescent adults. Depending on the weather conditions, mosquitoes might still be active seasonally until November.

Urban. At our latitudes, the Asian tiger mosquito resides almost exclusively urban areas, where it finds abundant sites of reproduction.

Short Flight Ranges. The adult mosquito is assumed to fly only a few meters from the breeding site. Therefore, the breeding sites are usually near the place where you are bitten.

Potential Disease Vector. As a female takes multiple blood meals it may transmit pathogens from an infected to a non-infected person. Even though not all mosquitoes can transmit diseases, the Asian tiger is known to be competent to transmit dengue, chikungunya and Zika viruses, and dirofilaria (heartworm). The above viral diseases are all notifiable and closely monitored in Switzerland.


Mosquito Control

Everyone is encouraged to take care of their own property, while the cantons take care of the public areas. The tiger mosquito can be effectively controlled in your surrounding through the prevention of larval breeding by removing standing water and by treating those containers that cannot be removed (see leaflet).


Distribution in Switzerland

The tiger mosquito has first been established along the valley bottoms in the canton of Ticino and the Italian part of the Canton of Grisons, while an initial population might also be present in Basel-Stadt, Basel-Landschaft, Zurich, Geneva and Valais. In addition, the mosquito is regularly found in several service areas along Swiss motorways, especially along the Chiasso-Basel road.

Aedes japonicus –The Asian Bush Mosquito

F. Schaffner

The Asian bush mosquito is another invasive species. Aedes japonicus, endemic to Japan and Korea, has reached North America and Europe through the trade of used tyres. The mosquito has rapidly colonised large areas of central Europe (see European Distribution Map) both through passive transport (vehicles, used tyres trade), and through active dispersal. The species prefers colder temperatures as compared to the tiger mosquito. The bush mosquito mainly bites in close proximity to woodlands. So far no disease cases have been associated to this species in Europe. In urban areas, the measures taken against the tiger mosquito are effective against the Asian bush mosquito as well.


Morphology

The species is often confused with the tiger mosquito due to the visible white and-black patterns on the legs and body. Usually, the Asian bush mosquito is slightly larger in size than the tiger mosquito and does not have a clear white line that runs across the back, instead it is characterised by five, five slightly yellowish lines.


Biology

The life Cycle of Aedes japonicus is similar to that of the tiger mosquito (Aedes albopictus). The Asian bush mosquito prefers also small water containers, produces eggs that are resistant to dessiccation and cold winters, and bites mainly during the day. However, adults are more active in cooler areas such as the edges of forests. It seems that adults move quickly along green corridors, allowing this species to colonise large regions within few years.
Aedes japonicus is not considered an important disease vector. Together with other species, it is regarded as vector of the West Nile virus in the United States and its competence for dengue and chikungunya transmission has been demonstrated in the laboratory.


Mosquito Control

In urban areas the same prevention measures adopted against the tiger mosquito work against Aedes japonicus.


Distribution in Switzerland

Aedes japonicus was first found in the Canton of Aargau in 2008. Since then it has rapidly spread into  Germany and neighboring cantons. Since 2012 the Asian bush mosquito is also found south the Alps and continues to actively spread in all directions.

Aedes koreicus

R. Eritja

Originally from Korea and as suggested by its name, Aedes koreicus is also an invasive species that has managed to reach Europe through human activities (probably the trade of used tyres). The species is not yet widespread in Europe, but has been reported from northern Italy, Switzerland, Belgium and Russia (see European Distribution Map). Like the Asian bush mosquito, Aedes koreicus prefers more temperate climates but prefers more urban habitats, much like the Asian tiger mosquito. So far, Aedes  koreicus has not been implicated as a carrier of human diseases.


Mosquito Control

In urban areas, control measures taken against the tiger mosquito may also work against Aedes koreicus.


Morphology

Aedes koreicus is often confused with the Asian tiger mosquito due to the visible white and-black patterns on the legs and on the body. Its size corresponds to that of the tiger mosquito, but it does not have a clear white line that runs through the thorax.


Biology

The life Cycle of Aedes koreicus is similar to that of the Asian tiger mosquito (Aedes albopictus) in that  this species also prefers small water containers for breeding, produces desiccation resistant eggs, may also survive cold winters and the females bite during the day.

Aedes koreicus is not considered a vector of human diseases.


Distribution in Switzerland

Aedes koreicus has been found for the first time in the Canton of Ticino in 2012, in the Italian speaking part of Grisons in 2017 and along the Swiss motorways in 2016. In Switzerland, this mosquito species is currently present only at low densities in urban environments.