Mosquitoes: 5 'stinging' curiosities

With the arrival of summer, the days get longer and the evenings warmer, leading us to spend more time outdoors between dinners under the stars and moments of relaxation. However, just as we soak up the summer atmosphere, they enter the scene: the mosquitoes, unwelcome protagonists of the hot season. These diptera of the Culicidae family number some 3500 species distributed worldwide, with a greater concentration in tropical areas. Just over 60 species are present in Italy, including the common mosquito (Culex pipiens), which is indigenous, and the tiger mosquito (Aedes albopictus), an invasive species. During their short lifespan, which can vary greatly but usually lasts about a month, mosquitoes feed mainly on plant sugars: while males feed exclusively on these substances, females - who need more energy and protein to reproduce - add the blood of other animals, including humans, to their diet.

But how do mosquitoes choose their victims? These insects, incredibly, have developed a sophisticated detection system to locate their victims. First of all, they are sensitive even at long distances to carbon dioxide, which humans and animals emit through breathing. Furthermore, they are able to detect body heat through thermal receptors, which help them to identify areas with higher temperatures and thus belonging to a living being. They have highly specialised olfactory receptors to pick up the smell of the skin and are also able to distinguish, through sight, different lights, contrasts and movements. These sensors, combined in a highly integrated system, make mosquitoes extremely adept at locating and stinging humans.

According to statistical studies conducted by CNET and by Business Insider, mosquitoes are the world's deadliest creatures to humans, with between 750,000 and one million deaths annually. This impressive figure is due to their ability to transmit serious diseases through contact with the blood of their victims, spreading dangerous pathogens. Mosquitoes are in fact the main vectors of infectious diseases such as malaria, dengue, Zika virus, yellow fever and West Nile virus. Malaria, for example, is responsible for more than 600,000 deaths annually, mainly in sub-Saharan Africa. By taking infected blood from one victim and transmitting it to others, female mosquitoes are the main means of transmission of this disease.

The dangerousness and adaptability of mosquitoes have prompted scientists to explore genetic engineering strategies to reduce their populations. One example is the pilot study led by Dr Crisanti of the University of Padua, which investigated the use of gene editing to influence mosquito fertility. His group, by editing a gene called 'doublesex' and which represents a kind of genetic switch for determining the sex of insects, was able to give birth to sterile female mosquitoes (or not to give birth at all). Even if the males remain fertile after this procedure, they still carry the modified sterility gene and by breeding with the few remaining fertile females, they transfer the mutation, leading in the long term to mass sterilisation and the collapse of a mosquito population.

The possibility of the extinction of populations of these insects - albeit local - poses several bioethical problems, particularly when we consider the impact that some unforeseen genetic mutations could have on large mosquito populations and by consequence on the environment. Contrary to what everyone thinks, in fact, mosquitoes are not 'useless animals' and play a very important ecological role in maintaining life on Earth. For instance, their larvae, living in aquatic environments, filter small organic particles in their early life stages, feeding on valuable nutrients that will later be assimilated by other animals. In fact, larvae - occupying a fundamental level of the food pyramid - are an essential food source for fish, amphibians and other aquatic animals. Not only that, mosquito adults, in turn, are the main food for bats, birds and other predators, whose survival depends on the presence of these insects.

The ecological significance of mosquitoes does not stop at feeding other species. When mosquitoes feed on plant sugary substances such as nectar, and settle on plants and flowers, they contribute - like many other insects - to the transfer of pollen from one plant to another, a process that is essential for the reproduction of many plant species. Although mosquitoes are not pollinators as primary as bees and butterflies, they can still influence flower fertilisation and the life cycle of plants. Their presence helps maintain ecological balance, and a reduction or extinction of these species could have negative impacts on ecosystems, affecting plant biodiversity and the habitats that depend on it.

The final curiosity about mosquitoes concerns their evolutionary history. Mosquitoes are among the oldest insects, and their haematophagous behaviour has very remote origins. In fact, a study published in Proceedings of the National Academy of Sciences confirmed that the blood-sucking habit of female mosquitoes dates back at least 46 million years, during the middle Eocene. This conclusion was made possible through the analysis of a well-preserved mosquito fossil found in a marly formation in Montana. The scientists used mass spectrometry to detect the presence of porphyrins, essential components of haemoglobin, in the insect's stomach contents. The exceptional preservation of the fossil, which probably occurred immediately after the blood meal, made it possible to study this parasitic behaviour. In short, mosquitoes have been pestering other species with their bites for millions of years!.

If you want to find out more about the world of mosquitoes and their relationship with biodiversity, now is the time to listen to the sixth episode of the "Biodiverse Podcast", entitled "Biodiversity that stings. Mosquitoes: small insects, big problems", with host Maurizio Casiraghi, Professor of zoology and evolution at the University of Milan-Bicocca. "Podcast Biodiverso" is the first podcast show by naturetech 3Bee, which stands out in the panorama of climate podcasts for its ability to weave irony, lightness and information into a unique format that is accessible to all. The first season is composed of 6 episodes, available on Spotify and YouTube, and tackles key current issues, such as the climate crisis and biodiversity, in a sparkling and original way.