Why the tiger mosquito finds “a favorable context” for its development around Toulouse

It has already been rotting our warm evenings for a decade, and we track it down on a daily basis. In this summer of 2022, we are celebrating a funny anniversary: ​​the ten years of the discovery of the first tiger mosquito at Toulouse. The pest has indeed shown its credentials for the first time in the Pink City in 2012, eight years after its first appearance in metropolitan France, near Menton (Alpes-Maritimes). Since then, in addition to the South, it has colonized almost all of France: “After Morbihan last year, the hot weather in Brittany this summer should push it to Finistère”, already warns Jean-Sebastien Dehecq, medical entomologist and sanitary engineer at ARS Occitanie. With a key booster shot: once it’s there, it stays there.

“In the Top 5 of the most painful in the world”

“We tried to fight against it, but it is one of the most invasive mosquito species in the world”, supports Gregory L’Ambert, medical entomologist at the EID (Interdepartmental agreement for mosquito control) Méditerranée.

“Out of 3,500 species of mosquitoes, it is in the Top 5 of the most troublesome”.

In Toulouse as elsewhere, the pattern of implantation of the tiger mosquito is the same: after its introduction, its presence “increases in power, until it reaches a plateau. Since they are parasites, it is not a species that will regulate itself. If you put 500 buckets of water in the garden, you will probably have larvae in the 500s, and you will then have created a giant insectarium”, warns Grégory L’Ambert, who also gives advice on how to fight against its proliferation.

“A Toulouse context favorable to nuisance”

“For the tiger mosquito to establish itself and develop, it needs heat and humidity”, summarizes Grégory L’Ambert. “And we know that in Toulouse, it is developing well, it is proliferating”.

“With a conjunction of heat and humidity, there is a Toulouse context quite favorable to nuisance, in residential areas”.

“We give him room and board”

“The mosquito obviously does not know if it is in Nice, Lyon, Marseille or Toulouse. But what he will need are regular water points, reasonable heat and humidity”.

“There are quite humid areas around this city and this can clearly contribute to the fact that we are annoyed more often (by the tiger mosquito, editor’s note) in Toulouse than in Montpellier”.

In the Pink City and its outskirts there is therefore the perfect combo between “presence of heat, vegetation”, and above all “water brought by man…” Because for Grégory L’Ambert, “we give him room and board”.

According to the ARS, “302 municipalities are officially colonized by the tiger mosquito in Haute-Garonne, representing 92% of the population: i.e. the entire agglomeration of Toulousebut also low wall, Saint-Gaudens…” Only Haut-Comminges really resists, until when?

Fewer mosquitoes in the hypercentre than in outlying districts

If the hypercentre of Toulouse is a priori less affected by the phenomenon than the outlying districts and neighboring municipalities, it would not be so much because of the pollution, as because of the urban density: In more mineralized areas, where the habitat is more collective, there are fewer breeding grounds for mosquitoes, which prefer suburban habitat,” judge Grégory L’Ambert.

But other more unsuspected places, where humans regularly bring humidity, also make good days for mosquitoes: “In cemeteries, for example, there are many”. The water from the flowers and the cups left in front of the tombs are indeed their daily bread…

“The tiger mosquito will especially find its happiness in the garden of the houses, he continues. “If the water persists for at least a week, the larvae will fully develop and give rise to adults”. And from there, the intruder and his (large) family of intruders settle in your home… for life!

“A tiger mosquito moves very little”

As summarized by Grégory L’Ambert, the female mosquito lives to the rhythm of a hell of a vicious circle: “She bites to take blood, and be able to lay eggs behind”. If she does lives “only two to three weeks”, she can lay eggs in her (short) existence up to 800 to 900 eggs… And bad luck, if the mosquito is greedy, it is also quite lazy:

“A tiger mosquito moves very little: it only travels 50 to 100 meters in its entire life. In short, it only moves a house or two. So if you are invaded by mosquitoes, you must first look in his garden or around his house”.

Where it gets complicated is that the fight against the tiger mosquito also relies on the goodwill of the neighborhood, as Grégory L’Ambert points out: “If you are very careful in your garden, but next door, the inhabitants have placed 200 cans of water in their garden, it’s lost in advance… You have to try to lead a collective struggle and encourage its neighbors to do the same”.

Are there times when it stings the most?

And if the inhabitants have the feeling of being bitten more at the end of the afternoon, it is (partly) true, according to the specialist of the EID: “The tiger mosquito has a peak of activity shortly after sunrise, then at the end of the afternoon and shortly before sunset “. Or roughly speaking, “when the humidity rises and when the temperature drops a little”. But when the temperature rises, he remains sheltered…

If “the notion of nuisance is very subjective”, Jean-Sébastien Dehecq even considers that “the high temperatures that we experienced from the month of June maybe weakened populations “. Because if “the heat wave in itself is not necessarily negative for mosquitoes, which will always be able to find a little freshness, they suffer mainly from the lack of water, since they cannot lay eggs”.

The town hall has “multiplied awareness campaigns”

“There is no miracle solution” to eliminate the sworn enemy of lovers of summer aperitifs, argues Jean-Sébastien Dehecq. The authorities are especially striving to call on the inhabitants to be vigilant, to dry up the slightest source which allows the multiplication of the harmful. The town hall of Toulouse points out that since the arrival of the tiger mosquito in 2012, it has “multiplied awareness campaigns residents at the elimination of stagnant water, to prevent the proliferation of this insect when it encounters favorable conditions (water, prey, caches of greenery)”.

“All municipal and metropolitan services are also mobilized and trained to fight against their proliferation in public spaces and to guide and inform residents who request it”.

Despite the passing years, in mid-July, according to the municipality, Hello Toulouse had still been requested 71 times since the beginning of the year, compared to 127 in 2021 and 160 in 2020, to “report the presence of tiger mosquitoes and the nuisance they constitute”.

When is there mass mosquito control?

The campaigns of mosquito control massive – based on insecticides – are now very exceptional, and the vast majority are no longer authorized except for health reasons, when cases of dengue fever or chikungunya, or even zika, appear, since “the tiger mosquito can transmit a hundred viruses in this way,” says Jean-Sébastien Dehecq.

A situation was however the subject of an exception in Occitania, at the beginning of July 2022 on the Mediterranean coast, where an unprecedented proliferation was run away from the tourists in droves: “Le Grau-du-Roi (Gard) was the subject of a derogation, after validation by all the administrative authorities, because the invasion of mosquitoes threatened the entire local economy”, according to Grégory L’Ambert.

A single mosquito control campaign in Toulouse in 2022

After an imported case of disease has been reported, the health authority has 72 hours to perform mosquito control. In Toulouse, according to the municipality, one campaign was conducted this year, last June. The ARS corroborates the facts: “A mosquito control campaign was carried out on June 23, on two sites in Toulouse, two days after the report of an imported case of dengue”. The two sites were frequented by the same resident of the Pink City, who was returning from a stay in Indonesia: Purpan Hospital, where he was admitted, and the Empalot district, where mosquito control was carried out “within a radius of 150 meters around his place of residence”.

Very few cases of dengue fever or chikungunya this year

As of July 20, this Toulouse man who returned from Indonesia with dengue is according to the ARS “the only imported case of disease linked to the tiger mosquito in 2022″. A figure in sharp decline, since last spring, in the month of May 2021 alone, there were already five…

Unlike previous years, there are also few cases of dengue fever and chikungunya this year elsewhere in the region, “because there is no major epidemic in the West Indies or in Reunion”, observes Jean-Sébastien Dehecq, who however wants to be cautious: “We know that the peak will arrive at the beginning of August, with tourists returning from Overseas, Indonesia or Africa”.

“Each year, there are on average forty cases of diseases imported into Haute-Garonne, especially dengue fever, and mainly in August and September, when there are the greatest flows of returns from vacation”.

By domino effect, there were therefore far fewer forced mosquito control campaigns in the districts of Toulouse in 2022 than in recent years… “The best solution to fight against the tiger mosquito is still to avoid being stung”, maintains Grégory L’Ambert, who calls for “fight against breeding sites”, and tackle the problem at the source: no water, no mosquitoes.

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