Photo: N. Henon/TIGER

Asian Tiger Mosquito

Currently three different invasive alien mosquito species have been identified in Switzerland: the Asian tiger mosquito (Aedes albopictus), the Japanese bush mosquito (Aedes japonicus) and the Korean bush mosquito (Aedes koreicus). From a medical point of view, the Asian tiger mosquito is of greater importance, because, apart from the fact that it is very annoying, it can also transmit pathogens such as dengue, chikungunya or Zika viruses.

On behalf of the Federal Office for the Environment (FOEN) and various cantonal authorities, Swiss TPH monitors tiger mosquito activity to inform targeted implementation measures for prevention and control. This includes processing suspected cases of tiger mosquitoes reported by the population. Swiss TPH is one of the four official FOEN reporting points for invasive mosquitoes in Switzerland.

In addition to monitoring tiger mosquitoes on behalf of the authorities, Swiss TPH researches various aspects of the biology of invasive mosquitoes to make their monitoring and control more efficient and better assess the risk of disease transmission under local conditions.

1. How do I recognize an Asian tiger mosquito?

The Asian tiger mosquito (Aedes albopictus) belongs to the family of mosquitoes (Culicidae) and is characterized by a contrasting black and white coloration of the abdomen and legs. With a size of 0.5 - 1 cm it is smaller than most native mosquitoes and are recognisable by the following characteristics:

1.      All legs have white scales, which appear as rings.

2.      The last segment of the hind legs are white.

3.      A white line runs from between the eyes to the back.

4.      The ends of the palps (olfactory receptors) are white.

The Asian tiger mosquito is often confused with other striped insects. Please check the above-mentioned characteristics closely and review the size ratios again. The tiger mosquito is very small! In the photo you can see the size in relation to a coin (Swiss five-centime piece).

 

2. How and where do I report an Asian tiger mosquito?

If you think you’ve seen an Asian tiger mosquito or possibly even been bitten by one at home or elsewhere, please take the following steps:

  1. Catch the mosquito without squashing it, e.g. with a glass and paper.
  2. Freeze the mosquito overnight in the freezer.
  3. Check whether it could be a tiger mosquito on the basis of the identifying characteristics listed in question 1 above. If the characteristics do not match your mosquito, it’s most likely not a tiger mosquito and can be discarded.
  4. Take a picture. The better the quality, the greater the chance for a successful determination! Make sure that you place the mosquito on a white background, e.g., on a white paper. Place a ruler or a 5-cent coin next to it so that its size can easily be estimated. Make sure that the insect is well lit and in focus before you take the photo.
  5. Submit your tiger mosquito find with photo to www.muecken-schweiz.ch and follow the instructions.
  6. Keep the mosquito for possible queries.
  7. If you cannot take a photo, put the mosquito in a small padded container (matchbox with cotton wool or similar) and send it to the following address, with your name and contact details, where the mosquito was found, and the date it was found:

    Tigermücken Meldestelle
    Schweizerisches Tropen- und Public Health-Institut
    Socinstrasse 57
    Postfach
    CH-4002 Basel

In 2019, Swiss TPH received almost 1300 mosquito reports and specimen by email and post.

3. Where has the tiger mosquito been found in Switzerland?

In Switzerland, the Asian tiger mosquito was first detected in the canton of Ticino in 2003. Following further individual findings, a stable, locally reproducing population was discovered for the first time in the Chiasso area in 2007. In the following years, the tiger mosquito spread further within the canton and established itself on a large scale.

Even north of the Alps, individual specimens are repeatedly introduced from the south by vehicles traveling along the main traffic routes - especially along the A2 motorway, and smaller tiger mosquito populations have been repeatedly detected in the cities of Basel and Zurich. Since the Asian tiger mosquito is only adapted to cooler climates to a certain extent - and thus its distribution is correspondingly limited - it is assumed that its distribution will increase with climate change.

Introduction of the tiger mosquito: Frequency of ovitraps with tiger mosquito eggs 2013-2019. The circles each represent a location, while the colour tone indicates how often this location was positive between 2013 and 2019. Map sources: Federal Office of Topography swisstopo and Federal Statistical Office (BFS), GEOSTAT.

4. Where does the tiger mosquito come from?

The tiger mosquito originally comes from Southeast Asia, where it broods as a forest dweller, especially in tree hollows. With the increased distribution of the tiger mosquito, caused by the replacement of forest areas by settlements, they have penetrated further into urban areas and adapted to those conditions. Small stagnant bodies of water are prevalent and diverse in urban areas offering the tiger mosquito ideal conditions to breed and reproduce.  In addition, humans are ideal hosts for females, which are dependent on blood for egg production. From there, the Asian tiger mosquito has spread worldwide through global trade and international travel. The eggs of the Asian tiger mosquito are very resistant to drought and can therefore be easily transported between continents, for example with scrap tyres. Regionally, the Asian tiger mosquito spreads mainly along main traffic routes, as mosquitoes often follow people into vehicles.

In 1979 the tiger mosquito was discovered for the first time in Europe (Albania). Most likely, it was introduced with deliveries of used tires containing eggs. However, it is assumed that the tiger mosquitoes in Europe are mainly derived from populations in Italy. At the beginning of the 1990s, Asian tiger mosquitoes were introduced from the USA, which were already well adapted to a rather moderate climate and from there spread along the transport routes throughout the Mediterranean region and to Switzerland.

The Asian tiger mosquito likes to lay its eggs in small stagnant pools of water such as rain barrels, flowerpots and trays, flower vases, animal drinking basins, blocked drains, rain gutters, unused watering cans and similar vessels.

5. Can tiger mosquitoes transmit the coronavirus?

There is no evidence that COVID-19 can be transmitted by mosquitoes. The new coronavirus is a respiratory virus that is primarily transmitted via droplets from infected people that are produced when they cough or sneeze, or by droplets of saliva or nasal fluid.

6. Does the tiger mosquito transmit diseases in Switzerland?

The Asian tiger mosquito has been shown to transmit numerous infectious diseases, in particular Chikungunya and Dengue fever, as well as Zika viral diseases. Theoretically, it would also be possible that these diseases could be transmitted in Switzerland, where the Asian tiger mosquito occurs. For example, it would be possible that if a person returned from an area where these viruses circulate and became infected with them there, could be bitten by an Asian tiger mosquito here and thus spread the virus locally. That such local transmission cannot be ruled out in Europe either is demonstrated by the numerous cases of disease transmission in Europe due to infected travellers returning home and locally resident Asian tiger mosquitoes. However, no such transmission has yet been documented in Switzerland.

The risk of transmission depends on many factors such as mosquito density, ambient temperature or human behaviour. In order to keep the risk of transmission as low as possible, authorities are making various efforts to limit the spread of the Asian tiger mosquito by means of preventive measures and, where necessary, to combat it in a targeted manner.

7. How can I protect myself from mosquito bites?

In contrast to most native mosquitoes, the Asian tiger mosquito is predominantly day-active and perceived as very aggressive. Wearing light-coloured, long, non-tight clothing is recommend. In addition, mosquito repellents can help to keep the pests away. It is important to distinguish between products that are applied to the skin and those for clothing. You can find more information on this in our information sheet "Mosquito repellents".

8. What can I do against the Asian tiger mosquito?

The Asian tiger mosquito likes to lay its eggs in small stagnant pools of water such as rain barrels, flowerpots and trays, flower vases, animal drinking basins, blocked drains, rain gutters, unused watering cans and similar vessels. It is, therefore, worth checking your garden or balcony regularly for such breeding sites and, if possible, removing them so that the mosquito cannot reproduce. Pay particular attention to the following points:

  • Avoid standing water in flowerpot trays or exchange at least once a week
  • Do not pour stale water into the gully, but tilt it directly onto the ground or pavement
  • Empty watering cans, buckets etc., after use and store upside down
  • Remove leaves from gutters
  • Regularly clean all water containers such as drinking troughs
  • Regularly renew water in paddling pools and remove from toys
  • Seal rain barrels with mosquito nets
  • Prevent water accumulation on tarpaulins etc.

9. How is the tiger mosquito monitored in Switzerland?

In Switzerland, there are various programmes for monitoring the tiger mosquito, both at national and cantonal level. These programmes usually consist of monitoring, prevention and control measures. "Active" and "passive" monitoring are used to collect information on the spread of the tiger mosquito. In active monitoring, mosquito traps are set up and regularly checked at potential introduction sites (e.g., motorway service areas, goods transfer points or port facilities) and in possible, or already populated areas in settlements (e.g., cemeteries, leisure gardens). The capture of mosquitoes is supplemented by sampling of possible breeding sites (larvae sampling).

Since it is not possible to set traps everywhere in Switzerland, the programmes are dependent on the support of the population. Therefore, we encourage you to become a mosquito hunter yourself and report suspicious mosquitoes to us! Preventive measures, such as avoiding breeding sites and the selective use of parricides, are intended to stem the spread of the tiger mosquito. Here, too, we are dependent on your help to prevent the formation of breeding sites in your own environment and make the life of the tiger mosquito difficult!

Swiss TPH is involved in several projects to monitor the tiger mosquito in Switzerland, both on a national and cantonal level. Furthermore, we are involved in several research projects related to the tiger mosquito and at any given time, we employ several PhD students who deal with different aspects of this topic and publish their data in international journals. The Vector Control group at Swiss TPH includes people with various expertise allowing us to cover many aspect related to the tiger mosquito problem.

TIGER Interreg V

TIGER (Tri-national Initiative Group of Entomology in the Upper Rhine valley) is an EU-funded INTERREG-V project with the purpose of supporting institutions responsible for public health in relation to the Asian tiger mosquito and improving communication within the tri-border region. The focus of the project group is on supporting public institutions with competent scientific and technical information. TIGER is instrumental in ensuring that access to important data related to alien mosquitoes and risk assessment is always available. More information and details about TIGER can be found here: https://tiger-platform.eu/.

National tiger mosquito monitoring programme

The tiger mosquito has been monitored in Switzerland since 2013 at national level. At the beginning of each summer, traps are set up and monitored along the motorways and in various places with a high potential for introduction, such as ports, airports and railway stations. Swiss TPH has been involved in this project from the beginning - we helped to define the trap network and are responsible for setting up and controlling the traps in the whole of Northeastern and Western Switzerland. The latest reports of the national tiger mosquito surveillance programme are available here:

Cantonal monitoring programmes (Basel-City, Basel-Country, Solothurn)

The Swiss TPH team supports several cantons in monitoring and controlling the tiger mosquito. Trap locations are identified, monitoring networks installed and regular inspection visits carried out. The data are then processed at regular intervals and sent to the cantonal authorities so that measures can be taken as quickly as possible. Our team is constantly working to make the collection, combination and evaluation of data even more effective and to review the latest strategies for controlling alien mosquitoes and adapt them to Switzerland.  

Mark-release-recapture studies

So-called mark-release recapture experiments are used to determine the population density of mosquitoes, their distribution patterns, flight distance and lifespan. These factors are important for estimating the disease transmission potential of tiger mosquitoes in a given area and for taking appropriate measures. For this purpose, mosquitoes are marked with a dye and released. A trap network is established to catch as many of these mosquitoes as possible. Based on the generated data, conclusions can be drawn about movement patterns and mosquito density. 

Population genetic research

Population genetics is the branch of genetics that deals, not with an individual, but with the genetic processes within a population. The transmission of genetic information from one generation to the next plays a central role in this. Population genetics determines the relative frequency of certain genes within a population and investigates their alteration under the influence of mutations, selections, random genetic drifts, the separation of subpopulations and the gene flow between different populations.

Population genetics helps us to better understand where the various tiger mosquito populations in Switzerland originally come from and how they spread within the country. It can also tell us whether a local population is already established and hibernates, or whether it is introduced each year. Such findings are important to elucidate the distribution patterns of the Asian tiger mosquito and to take effective measures against the further spread of this invasive species.

Pie Müller, PD, PhD, heads the Vector Control Group at Swiss TPH. He is a medical entomologist working on the biology of disease vectors, insecticide resistance, insect monitoring and the development of new strategies and products for effective disease vector control.

Pie Müller has extensive experience in the development of new molecular biological methods for monitoring mosquito populations, especially malaria-carrying mosquitoes. Currently, his work focused on the development of new methods for monitoring and control, and the biology of invasive mosquitoes in Europe.

Martin Gschwind, MSc, is a scientific assistant and member of the Vector Control Group. His main activity is the monitoring of the tiger mosquito in Switzerland. This includes the concrete planning and implementation of cantonal and national monitoring, the cooperation with the different authorities, other institutes, universities and the population of the affected areas, the determination of the mosquitoes and eggs with morphological and mass spectrometric methods and the co-development of new determination methods.

In addition, he identifies the mosquitoes reported by the population, searches for mosquito larvae with his team and supports and advises the cantonal authorities in raising public awareness and combating the tiger mosquito.

Other activities include testing insecticides and repellents against mosquitoes at the mosquito test centre and developing new test methods.

Tobias Suter, PhD, is a research associate and a member of the Vector Control Group. Within his PhD thesis, he worked on the distribution, biology and surveillance of the Asian tiger mosquito near the Swiss-Italian border and helped to establish a national surveillance network for invasive mosquitoes in Switzerland.

Tobias Suter has extensive experience in monitoring mosquitoes in the field and conducting experiments to identify resistance to insecticides. At the Swiss TPH, he is also responsible for the mosquito testing centre, where insecticide products, repellents and other methods of mosquito repellence are tested.

Müller P et al. Surveillance of invasive Aedes mosquitoes along Swiss traffic axes reveals different dispersal modes for Aedes albopictus and Ae. japonicus. PLoS Negl Trop Dis. 2020;14(9):e0008705. DOI: 10.1371/journal.pntd.0008705

Wipf N.C, Guidi V, Tonolla M, Ruinelli M, Müller P, Engler O. Evaluation of honey-baited FTA cards in combination with different mosquito traps in an area of low arbovirus prevalence. Parasit Vectors. 2019;12:554. DOI: 10.1186/s13071-019-3798-8

Roiz D et al. Integrated Aedes management for the control of Aedes-borne diseases. PLoS Negl Trop Dis. 2018;12(12):e0006845. DOI: 10.1371/journal.pntd.0006845

Suter T et al. Insecticide susceptibility of Aedes albopictus and Ae. aegypti from Brazil and the Swiss-Italian border region. Parasit Vectors. 2017;10:431. DOI: 10.1186/s13071-017-2364-5

Flacio E, Engeler L, Tonolla M, Müller P. Spread and establishment of Aedes albopictus in southern Switzerland between 2003 and 2014: an analysis of oviposition data and weather conditions. Parasit Vectors. 2016;9:304. DOI: 10.1186/s13071-016-1577-3

Suter T.T et al. Surveillance and control of Aedes albopictus in the Swiss-Italian border region: differences in egg densities between intervention and non-intervention areas. PLoS Negl Trop Dis. 2016;10(1):e0004315. DOI: 10.1371/journal.pntd.0004315

Suter T, Flacio E, Farina B.F, Engeler L, Tonolla M, Müller P. First report of the invasive mosquito species Aedes koreicus in the Swiss-Italian border region. Parasit Vectors. 2015;8:402. DOI: 10.1186/s13071-015-1010-3.