An island tries to evict mosquitoes after a quarter of a century and an uncomfortable coexistence that has been going on since about 2000. “Until then, in Procida, no one has any memory of ankle bites, received during the day”, a typical sign of the tiger mosquito’s mode of action. The landing of the insect on the island “is therefore believed to date back to around that year”. Since then, the alien species Aedes albopictus has prospered, effectively ‘expropriating’ its native colleagues, but today – at least in an initial area of about 20 hectares, in the Chiaiolella area – it is having a difficult life. Thanks to a group of researchers, citizen scientists and the ‘deception’ of sterile males, one of the pearls of the Campania archipelago has been transformed into an open-air laboratory where a ‘green’ control method of the Asian tiger mosquito population is being tested, which would allow insecticides to be relegated to the cellar.
Marco Salvemini, associate professor of genetics at the Department of Biology of the University of Naples Federico II, took stock of the results obtained so far with Adnkronos Salute: “We managed to halve the number of tiger mosquitoes in the area and we are happy because from the interviews with the inhabitants it emerged that this 50% reduction has had a big impact on their quality of life (until a few days ago they had practically no bites, now the density of mosquitoes is increasing again). But we would like it to become more, and we are convinced that if the radius of action were extended to the entire island we could really get close to eradication”. An opportunity to take stock of the project: a meeting underway today and tomorrow in Pavia, which has turned the spotlight on the 2 years of activity of the Mur-Pnrr ‘Inf-Act’ extended partnership on emerging infectious diseases (such as those for which mosquitoes can be vectors).
Salvemini’s group, with the ‘StopTigre’ project, is among those involved in Inf-Act (there are over 700 researchers working on 5 macro-themes of research distributed in 25 institutions and over 40 host partner institutions). The logic of the project is this: male mosquitoes are used, made sterile by isolating them and irradiating them at the pupal stage with X-rays at very low doses. These males are apparently like the others, “they are able to fly, mate, court females, produce sperm. The female mates, but then the eggs she lays do not develop”, explains the expert. The female tiger mosquito can be said to be ‘monogamous’: it mates only once and accumulates spermatozoa that it then uses for multiple fertilization cycles throughout its life. “So once it has mated with a sterile male, it would be out of the game.” The project started in 2016, and from the very beginning it was “participated – explains Salvemini – because without the support of the local community these insect vector control programs are difficult to implement”, given that mosquitoes then settle and proliferate right on their properties, in their gardens and balconies.
Their help was “precious”, both in the initial phase of study and monitoring and in the key phase of control. “The citizens – says Salvemini – participated, they learned to use some of the devices we use, they helped us in producing data and, once the seasonality and peaks of density of the insect on the island were mapped, it was always the citizens who helped us in the release of the sterile insects used to reduce the mosquito population. And it is precisely in this involvement that innovation lies”. The scientists acquired the sterile males in a biofactory in Crevalcore (in the Giorgio Nicoli Agriculture and Environment Centre), a pioneer in the application of this method, an approach that has been experimenting since 2008 after the first Chikungunya epidemic in some areas of Emilia Romagna. For the releases, “we have involved about 300 families from June to today. We gave the containers with the sterile mosquitoes, the citizens returned home, released them in their garden following our instructions and sent us photos and videos of what they had done. Yesterday we had the last of these releases, for a total of 150 thousand sterile males released by the citizens. In parallel, every week since the beginning of May my research team has released 100,000 sterile males into the area, and we are still continuing.”
“We would have liked to get closer to the goal of a 90% reduction in the mosquito population – admits the expert – but we challenged ourselves by choosing not a group of isolated houses, but a more complex area. The impact was significant and people living on the other side of the island even asked us why the intervention was not done there.. We explained that the study is precisely to demonstrate the applicability of the method. But the idea is to do it next year: at least to cover a third of the island, with the maximum ambition of applying the technique to the whole island. Because today the density of mosquitoes is so high that fertile females mate with non-sterile males outside the study area, and return to the study area to lay eggs that can hatch, which affects the final result. We would like to activate mechanisms that could then lead to applying the same technique perhaps also to Capri and then to Ischia, in a condition of increasing complexity”.
The islands are an ideal environment for these studies. As for the economic sustainability of a similar approach, “that’s the goal to aim for,” says Salvemini. As for the study, “the overall resources for this year’s project are around 100,000 euros; to do an experiment on the entire island, we estimate we would need 500,000. However, we believe that in the long term, by overcoming the productive limit of sterile males, this could become a sustainable approach. The aspiration, in the long term, would be to try to structure a productive reality around this idea, also to allow the many young people who have trained with us in recent years to have career opportunities. Maybe starting from a start-up and then arriving at a small company, to treasure this experience. It would be our dream: to be able to not only solve a health problem, but to create lasting opportunities for young people who have done an exceptional job.”
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