(With videos). A pilot experiment was carried out in Prades-le-Lez (Hérault) this summer, the encouraging results of which were revealed on Tuesday. For the first time in France, scientists have shown that groups of male tiger mosquitoes can be sterilized so that they have no offspring and spread them 50 meters above the ground. There are still some pitfalls to overcome before validating and using this fruitful method.
Sterilize the tiger mosquito, the idea will produce babies. From here “five years”, perhaps, as mentioned by the participants, the time to mobilize elected officials, to convince the populations of the harmlessness of the method, to raise a necessarily substantial budget, the tiger mosquito, an invasive species – 64 departments are infested to date , including Aine, north of Paris – arrived in Menton in 2004 in tires imported from Asia, and in Hérault in 2011, and now present in a large part of France, could be better fought.
“Wound” everyday, one of the most invasive species
Dreaded to mark the skin with a hot iron and convey serious diseases, aedes albopictus, present from May to November in our regions, and perhaps much longer in the future, because of the warming, is this mosquito, “A plague” of everyday life, one of the hundred most invasive in the world, which follows us. He lives with us and invariably lays in every drop of water in his garden, balcony, etc. Its lifespan is only one month on average but it continuously ensures its offspring without any predator being able to block its way. Especially since we have very few weapons at our disposal, if not a single product, the BTI, bacillus thuringiensis israelensis, usable only on larvae. He reveled in advance of global warming and our suburban areas where he found lodgings and shelter in abundance.
40,000 mosquitoes dropped by drone 50 meters from the ground
It is precisely there, a stone’s throw from Montpellier, in two districts of Prades-le-Lez, including that of Nouau, that the scientists carried out an innovative experiment: the sterile insect technique (TIS) then carried out releases of these tiger mosquitoes, rendered sterile, by drones 50 meters above the ground! The tests were carried out between June and August 2021. Some 40,000 insects were thus “spread” in an area of ten hectares. “We also had exceptional authorizations for this”, said Remi Cluset, technical director of EID.
Ten cases imported into the region each year
Banned by Europe for its harmful effects on ecosystems, the insecticides of yesteryear are only used in emergencies, to “clean” the home (mainly with deltamethrin), and its surroundings, assumed to be a carrier of chikungunya, dengue or zika that the “tiger” will have transmitted to him on his return from an infested country. And that a “local” mosquito must not be transported elsewhere. There are around ten imported cases in our region each year (1).
An experience with “promising” results
Good news, therefore: scientists have already taken a step and validated the technique and process of sterilization and dispersal of its sterile tigers. Either way, it will only be one more weapon in our meager wrestling arsenal. “We will never be able to eradicate this insect” given the countless number of lodges ”, underlined for his part Charles Jannin, entomologist at EID, Interdepartmental mosquito control agreement, a public operator specializing in mosquito control.
However, scientists from EID and Cirad (Center for International Cooperation in Agricultural Research for Development), partners in this experience, wore a broad smile this Tuesday morning, in Prades-le-Lez, north of Montpellier (Hérault) opposite “With promising results” of their experience. Hear: a majority of “tigers” survived until they were dropped; the drones were effective, a good recapture rate “Huge, from 2% to 10%”, using 40 sentinel traps, 32,547 adult mosquitoes collected, a slight drop in laying …
Study real conditions in a small area
This pilot study, which is part of a larger project funded to the tune of € 150,000 by Europe, Mosquarel, tends to show that there is a possible path with this method. Emanating from a larger project, ERC Revolinc, funded by the European Research Council and led by CIRAD, aims to study in real conditions, but in a limited space, the feasibility of mosquito releases in Valence, Spain, Reunion Island and the Montpellier region.
“Other, larger trials will be essential”, underlines Rémi Cluset. There are many pitfalls to overcome in order to one day consider using this weapon, the sole purpose of which is to reduce, not eradicate, populations of tiger mosquitoes on our terraces and in our gardens. We have to find the funds to build a gamma-ray or x-ray factory; convince communities and populations of the harmlessness of this technique and of its value. As for the costs, which we imagine pharaonic, they are rather low cost in China, one of the rare countries to use this method. “To produce these sterile mosquitoes, China says it costs them € 1,100 for every million of these insects”, revealed Claire Garros, a CIRAD entomologist placed in the public. We can already doubt it … In Italy, the cost would be € 100 to € 200 per hectare and per year, but the “tigers” are dispersed on the ground.
It takes… ten times more sterile males than savages!
“It is the role of a community like ours to participate in this experience and in the general interest”, testified the mayor of Prades-le-Lez. Florence Brau even wondered: “Isn’t this method more useful in problematic areas in terms of health…? In any case, I don’t think it is to simply improve the comfort of the inhabitants tomorrow morning or in the very long term…? ” Director General of EID, Bruno Tourre intervened to recall important things: “This sterilization and these releases only work because the mosquitoes only do one mating and you have to release about ten times more sterile males than there are wild mosquitoes…”
Delivered to Montpellier in isothermal packages by plane!
The mosquitoes, from which a strain was selected, were mass-reared and bombarded with gamma rays, for sterilization, at the CAA (Centro Agricoltura Giorgio Nicole) in Crevalcore, near Bologna, Italy. They were delivered by plane to Montpellier in 14 hours in isothermal packages at a temperature below 10 degrees to keep them asleep! Before releasing, these males were marked with a fluorescent powder, to better recognize them, once a part was recaptured, and passed under an ultraviolet light lamp. More detailed analyzes will still be necessary; “Knowing that the objective of the experiment was not so much to demonstrate the real effectiveness of these sterile mosquitoes as of the feasibility of the process”, we point out to the EID.
The EID did a lot of work to reassure the volunteer families who took part in the experience… ”
“Technically, we know how to sterilize mosquitoes in France”, added Marlène Dupraz from CIRAD. But you have to find the money to build a factory to sterilize mosquitoes by the millions, on a large scale; convince the public authorities to dedicate this beautiful budget envelope to achieve this equipment and “Take into account social acceptance.”
The population must accept for a few days an artificial, massive arrival of additional insects in their neighborhood … Even if they are only males – sterile – and who, unlike females, never bite. “The EID did a lot of work to reassure the volunteer families who took part in the experience, highlighted the mayor of Prades-le-Lez. To tell them that there will be no disease resulting from it, for example… ”
Other control solutions are being studied
This feasibility test is a first in France. Tests took place in Brazil in 2018 and in Réunion this year “A pioneer, Reunion had certainly taken ten years in advance”, as Marlène Dupraz, from CIRAD, pointed out, but it had taken five years to convince local elected officials of the value of this method. “We are working on other control solutions, such as traps, the effectiveness of which has yet to be demonstrated”, added Remi Cluset, technical director of EID.
In Polynesia, as explained to you HERE Dis-Leur, a group of researchers are working on infested atols, in particular that of Marlon Brando, Tétiaora, with a bacterium, volbakia, which gives excellent results : it makes the females sterile there. The future is not a single method but a bunch of solutions. There is also the sterile transgenic mosquito. This does not pose ethical problems in India or Brazil …
Olivier SCHLAMA
- Diseases. Dengue fever was 3.34 million cases in 2016 in 128 high-risk countries; chikungunya, it is 1.2 million cases reported in 2015 and zika, it is 1.5 million cases estimated in 2016.
