The Invasion of Tiger Mosquitoes: Mayor’s Fight Against an Invasive Species in Lebbeke

He only came into contact with it by chance, Jan Vanderstraeten (32), mayor of the East Flemish municipality of Lebbeke on behalf of the Christian Democrats. Until last year he had never heard of the beast. Logically. As a rule, a mayor is not concerned with the detection and control of an invasive species. But now he is an expert. Does he know how they ended up in his municipality, how they reproduce, and how they are fought.

It was an observant resident of Lebbeke who managed to take a picture of a black mosquito with white stripes last year and uploaded it to the website muggensurveillance.be, a platform where citizens can report an invasive animal species since 2021. After examination by experts, it turned out to be the species that was already feared because it appears in more places every year; the tiger mosquito, or aedes albopictus, which actually belongs in warm, damp Asia, but is increasingly able to maintain and spread in northern Europe due to climate change, among other things. Lebbeke was not the only Flemish municipality where the tiger mosquito was found. Alarm bells also went off in Wilrijk, not far from Antwerp. Because close to where that one tiger mosquito was found, it was teeming with them.

The Flemish Agency for Nature and Forest immediately started fighting mosquitoes, says Mayor Vanderstraeten at his office just outside the center of Lebbeke. “The nice thing about this mosquito species is that it can’t fly that far; maximum of about two hundred metres. In a radius of five hundred meters around the first site, we no longer found them. So you map them quite easily. Larvicide has been sprayed in the hope that this will stop reproduction. And we have placed traps, which we now, a year later, check every two weeks.”

Standing water is an attractive breeding ground for tiger mosquitoes
Photo Nick Somers Mayor Jan Vanderstraeten is on his way to a breeding ground for tiger mosquitoes.
Photo Nick Somers Mayor Jan Vanderstraeten of Lebbeke now knows everything about tiger mosquitoes: how they reproduce, but also where they like to breed – in stagnant water.
Foto’s Nick Somers

Car tires

It is not the first time that the tiger mosquito appears in Belgium. Already in 2018, the insect was detected in five different places, mainly in parking lots along the motorway in Wallonia. They probably first reached Europe via the transport of car tires from Asia. Tiger mosquitoes lay eggs just above the surface of standing water. In the tires, which are often outside, there is a perfect layer of rainwater where the eggs can be laid. If the eggs are then submerged in water, they can hatch. The Asian tiger mosquito also came to Europe via batches of bamboo stems. The first specimens appeared in Italy in the 1990s.

Researchers at the Institute of Tropical Medicine (ITM) in Antwerp estimated five years ago that the mosquito can travel about a hundred kilometers a year via France, where established populations were found as early as 2004. Five years later, it seems to have come true. Tiger mosquito eggs are resistant to fairly extreme weather conditions and the larva and mosquito thrive best in warm conditions. If it gets too cold, they die. But due to climate change, the tiger mosquito survives the milder winters in Europe.

The European Center for Disease Prevention and Control maintains mosquito maps on behalf of the European Union. A look at the map that accompanies the tiger mosquito shows that the creature has already established itself in some areas north of Paris. This means that populations of the tiger mosquito overwinter and can expand. On the same map, large parts of Belgium (except for Brussels) and the Netherlands – with the exception of the northern provinces and the Wadden Islands – are colored orange, because this means that the tiger mosquito has already been introduced there, but in all probability has not yet hibernated. That is, says Isra Deblauw, an entomologist at ITM, a matter of time. “The tiger mosquito will settle in Belgium,” she says. “But it is better to postpone that as long as possible. We need all European governments to do that. They must continue to put money into combating this species.”

Read also ‘It is not a question of if, but when the tiger mosquito settles in the Netherlands’

Why is clear; the sting of the tiger mosquito in itself is not such a problem, although this species, unlike many other mosquito species, is also active during the day – and quite aggressive, so a nuisance. But the dangerous thing about the tiger mosquito is that it spreads tropical viruses that do not originate in Europe. This mainly concerns the dengue virus (or dengue fever), chikungunya and the Zika virus. Deblauw: “These are viruses against which there is no vaccine on the market yet, although promising research has recently been done into dengue. Healthy people can become seriously ill from these infectious diseases, but they will not die. But for pregnant women, children and the elderly, they can lead to problems. We would rather not see those viruses here.”

The diseases mentioned are not transmitted directly from person to person. You need a tiger mosquito for that. It sucks up the blood of an infected person, allows the virus to multiply in it, and infects the next person with a sting. As long as the tiger mosquitoes in Europe do not carry a tropical virus and do not come into contact with travelers who bring dengue or Zika from South American or African countries, there is little danger, says Deblauw. “But if the mosquitoes are there and you have travelers who return to Europe infected, you have a chance of an outbreak.”

She says that 65 local cases of dengue were diagnosed in the south of France last year. “Those people had not traveled. So they are most likely infected by a tiger mosquito. This is also the case in municipalities such as Lebbeke. It only takes one person to return from abroad with dengue and be bitten by a tiger mosquito, and you have a problem. Although that chance is still very small at the moment.” In Lebbeke, GPs have now been instructed to sound the alarm if there is a suspicion of an infection with dengue. That is normally not mandatory.

A trap for tiger mosquitoes: a block of Styrofoam floats in the bucket filled with water, on which the mosquito lays an egg. But the Styrofoam prevents the egg from being submerged and hatching as a larva.
Photo Nick Somers Mayor Jan Vanderstraten of Lebbeke
Photo Nick Somers A trap for tiger mosquitoes: a block of Styrofoam floats in the bucket filled with water, on which the mosquito lays an egg. But the Styrofoam prevents the egg from being submerged and hatching as a larva.
Foto’s Nick Somers

Traps

In France, pesticides are used in a circle of two hundred meters from the places where the tiger mosquito is found and people are trying to find out how the insect could have got there. Ditto in the Netherlands; when the tiger mosquito appeared on a business park in Weert at the beginning of July, the Dutch Food and Consumer Product Safety Authority immediately removed all breeding grounds and used pesticides.

In Lebbeke they are currently using less aggressive methods, says mayor Jan Vanderstraeten. There they set up about thirty traps within the area where the mosquito appeared earlier. They first want to see how big the problem is, before Nature and Forest starts fighting again. No mosquitoes were found in an earlier round of control in April. “It was probably still too cold then,” says Jan Vanderstraeten.

The mayor, the third youngest in Belgium at 32, wears shorts and a T-shirt and leads his speed pedelec through the village to show how the mosquito traps work. After a trip through the modest center of Lebbeke, he stops at an industrial estate. Anyone who does not know that there is a mosquito trap will not notice anything.

Vanderstraeten says that there are two types of traps; one that catches the mosquito itself, and one that causes the mosquitoes to lay eggs. The latter is an ordinary black bucket filled with water on which a block of Styrofoam floats. The mosquito lays an egg on that block, which should eventually hatch into a larva when the eggs are submerged. But that prevents the styrofoam, so the larva will not hatch. The cubes are collected every two weeks by the municipality and sent to the federal public health research center Sciensano for screening.

On the other side of the street, the municipality of Lebbeke bought a piece of land a few years ago to create allotment gardens. There are now about a hundred people who grow vegetables and flowers. Next to a gypsy wagon are rain barrels full of stagnant water. Exactly a place where the tiger mosquito feels comfortable. Nets should have been stretched over that, but “the urgency is not yet the same for everyone, although people did their best last year,” says the mayor.

Employees of Lebbeke’s technical service place traps for tiger mosquitoes near waste and stagnant water.
Photo Nick Somers Employees of Lebbeke’s technical service inspect a trap for tiger mosquitoes.
Photo Nick Somers Employees of the technical service of the municipality place a trap and inspect a trap for tiger mosquitoes.
Foto’s Nick Somers

He continues into the fields, where another mosquito trap has been set up not far from the railway line. It is sweltering hot this June day. The mercury is approaching thirty degrees, exactly what the tiger mosquito likes. A little further on, Ruben Meert (46), a teacher from Lebbeke and founder of a study group on insects, is mowing grass. He says that last year he checked “all rain barrels” that he found around his site for the tiger mosquito. “I have looked at thousands of larvae. None of the tiger mosquitoes were included. So for the time being, his advance seems to be limited.”

But that’s only a matter of time. And the tiger mosquito is not the only invasive exotic that is advancing in Europe, partly due to climate change. In France, northern Spain and also in Belgium, an increase in the number of Asian hornets has been observed for a few years now. This is an aggressive wasp species that preys on bee colonies and can therefore potentially have major consequences for food security. “We also suffer from this in Lebbeke,” says the mayor. “Employees of our control service have to wear special suits there, because they sting right through the suits we use when we work with normal wasps.”

The heat does not only cause doom and gloom – at least for bird lovers. According to experts, during the heat wave at the end of June there was a real ‘raptor tsunami’ in the Netherlands and Belgium. Species that normally never occur here, such as the griffon vulture, floated here on thermals, but also left again as soon as the temperature dropped. This phenomenon is expected to become more frequent in the coming years.

About this series Afraid of Summer

The European summer is changing. The season of sun and holidays is increasingly becoming the season of drought, heat and other problems. In this series, correspondents report on the summer consequences of climate change in their country.

A version of this article also appeared in the newspaper on August 2, 2023.
2023-08-01 10:51:27
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