In just a few years, the tiger mosquito has become one of the most annoying and potentially dangerous pests in many areas of our country. In addition to the pain caused by the bite of the females of these diptera, experts warn that this invasive species, with the scientific name Aedes albopictus, It is a vector (potentially transmitting agent) of various viral diseases, such as dengue or yellow fever.
Trying to control the populations of these insects, easily identifiable by the white stripes on their bodies, has become one of the priority objectives of pest and public health experts.
The traditional method of fumigation with insecticides has relatively effective local effects, but in addition to not being a lasting solution, it entails environmental and health risks. In some especially affected countries, methods such as mass production and release into the environment of males sterilized by irradiation or genetic manipulation are being tested, with the aim of reducing the reproductive success of the species.
Innovative alternative
One of the most innovative alternatives for controlling mosquitoes such as Aedes albopictus is based on treatment with bacteria of the genus Wolbachia. These parasitic microbes, of which there are numerous species, are naturally present in the cells of many arthropods and are harmless to humans.
“Various studies have shown that if male tiger mosquitoes are infected with bacteria, specifically, of the species Wolbachia pipientis and these are crossed with wild females, the reproductive system is altered due to cytoplasmic incompatibility and the eggs do not prosper,” he explains to The Vanguard Roger Eritja, doctor in entomology, researcher at CEAB (CSIC) and head of entomology and data validation for the Mosquito Alert project. This reproductive problem can remain, through the mother, for several generations of mosquitoes.
“This suppression strategy is difficult to put into practice, but it can be temporarily effective locally, for example in countries like ours where the risk of dengue outbreak is increasing,” says Eritja.
The first test of this technique in the European Union has been carried out by experts from the Italian National Agency for Biotechnology, Energy and Sustainable Economic Development, University of Valencia, La Fe Health Research Institute, Lokimika laboratories and Rentokil Initial. The trial was carried out in Italy and some of the mosquitoes used came from the Valencian Community and Catalonia.
The results of this study, published last March in the journal Insects, show that 99.9% of the eggs produced by crossing infected males and wild females were sterile.
First trial in Spain
Researchers from the University of Valencia and technicians from the specialized company Rentokil Initial are now working on the first pilot test in Spain with this tiger mosquito population suppression strategy. “We are in the last phases in the laboratory, with the cleaning of mosquitoes, to check that they do not have species different from the one Wolbachia pipientis and we hope that at the end of this summer or spring of 2025 we will be able to carry out the first field trials in Spain with already established strains of mosquitoes”, he advances. The Vanguard Rubén Bueno, technical director of Rentokil Initial, associate professor at the University of Valencia and co-author of the study published in the journal Insects mentioned above.
For this trial, in addition to the technical preparations, authorizations from the Ministry of Health and the Valencian Community are being processed. “With the serial release of male tiger mosquitoes with W.pipientis We hope to demonstrate that it is possible to reduce the population of these insects that can transmit dengue,” says Rubén Bueno.
The test can be carried out with eggs or with male tiger mosquitoes infected with this bacteria, a “complex but not impossible” task. “Once the initial population is generated, its effect can be maintained and thus reduce the number of these mosquitoes, as a complementary tool in integrated control and in a way that reduces dependence on chemical insecticidal treatments,” explains Rubén Bueno.
Global fight against dengue
Actions to control mosquitoes such as Aedes albopictus are part of the international fight against serious diseases such as dengue. Rubén Bueno and Roger Eritja explain that in areas like South America, where dengue is endemic, a different strategy has been chosen. Instead of seeking to suppress mosquito populations – in some cases totally impossible – attempts are made to replace current populations (with a high capacity for transmitting the virus) with less infectious ones. This replacement strategy is carried out by releasing large numbers of male and female mosquitoes infected with the bacteria. Wolbachia.
The most important global initiative in this field is led by the World Mosquito Program, a non-profit entity. In countries like Honduras, and in collaboration with Doctors Without Borders, the project has released large numbers of mosquitoes Aedes aegypti bacteria carriers Wolbachiawhich has managed to reduce the ability of these insects to transmit viruses such as those that cause dengue. The procedure in this case consists of extracting the Wolbachia from fruit flies (naturally present) and inject it into eggs of Aedes aegypti. The mosquitoes that are born after hatching will carry this parasite, so they may have dengue, but not transmit it, or at least their contagion capacity will be considerably reduced.
World Mosquito Program calculates that the method Wolbachia It has already helped protect some 11 million people in the 14 countries in the world in which it has been applied. “We estimate that we have prevented nearly 600,000 cases of dengue in the countries where we operate and more than 40,000 hospitalizations as a result of complications from these viruses,” they say from this non-profit entity. A study carried out in Yogyakarta (Indonesia) revealed that, after releasing mosquitoes carrying Wolbachiatransmission for mild cases was reduced by 77%, while severe cases decreased by 86%.
Saving an endangered bird
The method Wolbachia Not only can it help avoid diseases in humans. The most recent test with this application of the bacteria in mosquitoes has the specific objective of reducing avian malaria that affects the populations of a small bird endemic to Hawaii known as ‘i’wi (scientific name Drepanis coccinea). In the last two months, some 10 million male mosquitoes infected with the virus have been released on these islands with the help of helicopters. Wolbachia. Avian malaria is one of the causes of the extinction of several species of honey climbing birds similar to the ‘i’wi that have been recorded in Hawaii in recent years. In the case of Drepanis coccineait is estimated that about 350,000 specimens survive, but the downward trend is constant and avian malaria infections are increasing at a worrying rate.
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