[LUM#11] Sterile mosquitoes for a peaceful island
"Fighting evil with males." This is the strategy chosen by researchers at the Mivegec laboratory to reduce the risk of epidemics of mosquito-borne diseases on Reunion Island. Their method: the sterile insect technique, which involves mass breeding of male tiger mosquitoes, sterilizing them, and then releasing them into the wild.
266,000. That is the number of inhabitants of Réunion affected by the chikungunya epidemic that struck the island in 2005-2006. How did the virus responsible for this disease manage to infect 30% of Réunion's population? "Chikungunya is transmitted by the tiger mosquito, Aedes albopictus, which also carries the dengue virus, which has affected more than 50,000 people on the island since the beginning of last year," explains Frédéric Simard of the Infectious Diseases and Vectors: Ecology, Genetics, Evolution, and Control laboratory.
In the absence of a vaccine, the only way to limit the transmission of these diseases is to reduce contact with mosquito vectors. While mosquito control has long taken the form of massive insecticide spraying, this practice is now reaching its limits: not only do the products used have an impact on the environment and on populations, who now view them with suspicion, but "mosquitoes are becoming resistant to insecticides, which considerably reduces their effectiveness, " explains Frédéric Simard.
Insecticide resistance
How can we curb the proliferation of Aedes albopictus while limiting the use of insecticides? Researchers at the Mivegec laboratory are banking on a promising strategy: the sterile insect technique. This involves sterilizing male mosquitoes raised in the laboratory using X-rays and then releasing them en masse into the wild. "The females that are fertilized by these males will lay eggs that will never hatch, " explains researcher
This method is particularly effective because female mosquitoes mate only once in their lifetime and then store the sperm in their spermatheca to fertilize their eggs. "If a female mates with a sterile male, she fills her spermatheca with non-functional sperm and will never have offspring." Given that a single female can lay more than 1,000 eggs in her lifetime, this means that fewer mosquitoes will be born.
The sterile insect technique has already proven its worth, particularly in agriculture, where it has been used for around 50 years to combat certain insect pests. But in order to apply it to the tiger mosquito, researchers had to overcome specific challenges.
Mass breeding
First step: mastering the techniques for mass breeding of Aedes albopictus in the laboratory, then sexing the individuals, i.e., separating the males from the females. "This is a crucial step because only the males will be released into the wild, " explains Frédéric Simard. To sort the males from the females, the researchers pass the mosquito nymphs through a sieve, which eliminates the females, whose nymphs are larger.
The second decisive step is to sterilize the male nymphs using X-rays. "At the end of this stage, we had to check that the irradiation did not affect the males' health or their ability to mate," explains the researcher.
Generate buy-in
Last step: testing the method in the field! "In June 2019, we released 3,000 sterile males for the first time," explains Frédéric Simard, who points out that these releases do not cause any nuisance to residents, since only females bite in order to collect blood to feed their eggs. "We have also done a lot of educational and awareness-raising work with the local population and institutions, whose involvement is absolutely necessary in the development of this ecological technique for controlling the tiger mosquito. To make it sustainable, it must not only be effective and clean, but also socially acceptable, economically viable, and implemented within a legal framework. This is a huge undertaking for truly transdisciplinary research," says Frédéric Simard .
This dialogue is taking place in a favorable context, as more than two out of three Réunion residents spontaneously express support for the initiative. Given the success of these initial phases, researchers carried out a second release in September 2019 and are planning more extensive releases in 2020. "Ongoing field studies will enable us to determine where, when, and how often to release the mosquitoes to ensure maximum impact on the Aedes albopictus population. This will significantly reduce the risk of new chikungunya or dengue epidemics. We are going to fight the disease... with the male."
Find UM podcasts now available on your favorite platform (Spotify, Deezer, Apple Podcasts, Amazon Music, etc.).