Aggressive tiger mosquitoes, capable of spreading tropical diseases like dengue and Zika, are spreading across Europe , but scientists hope it will be possible to control these biting pests, with a form of insect birth control and with drones. .
The Asian tiger mosquito bite may be little more than a pin prick, but it causes tens of thousands of deaths worldwide each year.
Named for its striped appearance, this aggressive little insect carries a number of viruses that cause diseases such as yellow fever, dengue fever, chikungunya, Zika, and Japanese encephalitis . While these are largely viewed as tropical diseases, the spread of the mosquitoes that carry them has raised fears that the viruses could also be more common in Europe.
The European Centers for Disease Control (ECDC) predicted ten years ago that tiger mosquitoes would spread across Europe and climate change now threatens to make their spread more likely . “Even the southern part of Sweden is potentially climate-friendly for this mosquito, although it has not yet gotten there,” said Professor Jan Semenza, who heads a section of the ECDC that assesses infectious disease threats.
The striped pest, which is also known as Aedes albopictus , is native to Southeast Asia , but arrived in Albania in the 1970s before landing in Italy in the 1990s. Initially it colonized the Mediterranean coast, then spread northward. and it is now found in much of France, Greece, Bosnia, parts of Spain, southern Portugal, and Germany . It has even been found in greenhouses in the Netherlands. During the summer, mosquitoes have become a nuisance in certain places.
And with mosquitoes can come disease. So far, the outbreaks have been relatively contained and in low numbers, but there have been cases of dengue in Croatia, France and Spain . In Italy, hundreds of people became ill with chikungunya in 2017. In 2019, two cases of Zika were detected in the south of France.
The diseases can be brought to Europe by people infected with the virus who travel from countries in South America and Asia where they are endemic. Brazil, for example, has been a hot spot this year for dengue fever. If these people are bitten by a tiger mosquito in Europe, the insect can then transmit the virus to other people it bites.
“We have seen an increase in vector capacity due to climate change,” warns Prof. Semenza, with warmer temperatures allowing biting insects to survive through winter. “Dengue has a huge burden of disease around the world. It can become a life-threatening condition, so we are concerned about it entering Europe. “
Dengue was endemic in Greece in the early 20th century, but it was eliminated. “We do not want this type of disease to be repeated in Europe,” added Professor Semenza. But the growing number of mosquitoes capable of carrying the disease makes it more likely that these viruses will re-establish themselves on the old continent . Another disease-carrying insect – Aedes aegypti , also known as the yellow fever mosquito – also threatens to return to Europe after being eradicated there in the 20th century. Originally from Africa, it is present today near the Black Sea, on the Portuguese island of Madeira and in northeastern Turkey. But with many insecticides, now banned in Europe due to their toxicity and the broader damage they cause to the environment, there are fewer options for controlling mosquitoes.
Insect birth control
Dr Jérémy Bouyer, a biologist and mosquito expert at the Center for Agricultural Research for International Development (CIRAD) in Montpellier, predicts that Europe could face an uncontrolled dengue epidemic in the next five to ten years unless more is done. to control mosquito populations.
“Aedes tiger mosquitoes are very difficult to control,” said Dr. Bouyer. The insects tend to breed in relatively small sites, making it difficult to attack them, he said. “Instead of ponds or lakes, they like man-made habitats.”
But we may not be totally defenseless against these mosquito pests. Dr. Bouyer is developing a new approach to fighting mosquitoes as part of a research project called REVOLINC. In the coming years, it will release tens of thousands of sterile male yellow fever mosquitoes on Reunion Island , a French territory in the Indian Ocean.
When released, males must mate with wild females and produce sterile eggs , thus suppressing the number of mosquito larvae. However, the males will also be covered in a secret weapon, a biopesticide called pyriproxyphene, which mimics the hormones of insects and restricts their growth . Males transfer this biopesticide to the female when they try to mate with them, and she contaminates their eggs and larval habitat. This means that the eggs fertilized by the unsterilized males also cannot mature from larvae to adult mosquitoes . “Even if sterile males don’t succeed with females, they continue to transmit the biopesticide,” said Dr. Bouyer. “We have shown that this could increase the impact of control by 10 to 100 times, so we may need to release fewer male mosquitoes.”
To breed enough insects, Dr. Bouyer and his colleagues have developed technologies for authentic mosquito factories at the International Atomic Energy Agency (IAEA) facility in Seibersdorf, Austria, where the larvae are raised in piles of trays submerged in water. each of which supports 18,000 larvae. The larvae are then classified by sex, when they pupate (become pupated) before the young males are sterilized with a finely balanced dose of radiation, enough to achieve almost complete sterility, but leaving them healthy enough to mate when they are released. Sterile males can be shipped in refrigerated boxes.
Drone attack
On Reunion Island, male mosquitoes were previously released in boats placed on the ground. 90% of the insects will not travel more than 100 meters from this place.
In an attempt to improve the distribution of sterile male insects, Dr. Bouyer is also working on a project called MOSQUAREL, which will use drones to release mosquitoes from the air . It has already used a 12kg drone in Brazil to release 50,000 sterile male mosquitoes per flight and hopes to test a lighter 900g drone capable of releasing 30,000 mosquitoes. The advantage of this smaller drone is that it would be allowed to fly over residential areas in Europe.
“To treat a city with sterile insects, you have to drive a vehicle on the road, stop every 100 meters and release a box of mosquitoes,” said Dr. Bouyer. “It takes two hours for two vehicles to treat 30 hectares. A drone launched from the back of a truck could treat the same area in ten minutes, he said, and is faster, cheaper and distributes insects more evenly in an area. .
The new drone will also be tested in Valencia, with the release of sterile tiger mosquitoes in a citrus production area , in collaboration with the Spanish state rural development company Tragsa.
Dr. Bouyer also hopes to use the drone to deliver sterile biopesticide-coated yellow fever mosquitoes on Reunion Island to target three small mosquito populations. But while Reunion has a few isolated pockets of yellow fever mosquitoes that Dr. Bouyer hopes to eliminate, tiger mosquitoes are a bigger problem on the island. Reunion has seen a rise in dengue cases since early 2018 , with a particularly serious outbreak this year producing a series of deaths. Warmer temperatures and humid conditions have allowed tiger mosquitoes to flourish, so Dr. Bouyer plans to attack these insects next. Only the release of sterile males coated with biopesticide will not work.
Both species of Aedes mosquitoes only need miniscule amounts of water for their larvae, which often thrive in garbage items, in discarded plastic, or in old tires . Therefore, reducing this habitat for larvae in urban areas will also be necessary to ensure that drone launches can have a greater impact.
“If we suppress them in one place, then we can prevent dengue there,” Dr. Bouyer said. That is the best success we can hope for, protecting the people.
Artículo original
This article was originally published in Horizon, the EU Research and Innovation Magazine
