Where do mosquitoes go during the dry season? – 03/29/2023 – Fundamental Science

In Africa, the rainy season is always a time of great anticipation and celebration: after months of heat and drought, they bring enormous relief and renew the environment. However, not everything is shade and fresh water, as they are also responsible for new cases of malaria, as conditions become ideal for the proliferation of anopheles, the mosquitoes that transmit the disease. When the rains begin, these insects find pools of still, clear water, where they lay eggs and propagate. And the scientific community is grappling with a question: if they appear in the rainy season, where were they during the dry season? Where are they from? In regions of sub-Saharan Africa, the dry season can last from three to eight months, that is, it can extend longer than the average lifespan of mosquitoes. With no water to lay the eggs in, you’d expect them to die before reproducing, right? So what happens?

A potential alternative would be for them to move to warmer places, like migratory birds, but it must be taken into account that the flight range of these beings is limited. A study by scientist Tovi Lehmann, from the National Institutes of Health (NIH), suggests another reality. By tagging a population of anopheles coluzzii in villages in Mali, West Africa, researchers observed that some mosquitoes were still alive up to seven months after tagging. If this is true, at least this species of mosquito might be able to survive typical dry seasons, and it is extraordinary to think that some ancient mosquitoes manage to stay alive for so long in the environment.

But if, on the one hand, these patterns do not seem to apply to all anopheles species, on the other hand, dry seasons can extend beyond these periods, a pattern that is becoming more and more frequent given the effects of climate change. In another set of investigations, this research group perhaps achieved more impressive results.

Relying on meteorological data, climate models and high-altitude insect collections, Lehman’s team suggests that mosquitoes from the Sahel — a semi-arid region that runs across the African continent from Mauritania to Sudan — are capable of migrating long distances: some could travel more than 300 kilometers, hitchhiking on air currents. Recent studies suggested that these migratory movements do not significantly affect the feeding and reproductive capacity of these animals. In other words, no jet lag for them. If the scientific community confirms these data, it means that some mosquitoes are capable of crossing enormous distances in a true migratory movement that makes it possible to transmit malaria to the regions where they go. And they could come back from these places when the weather becomes milder.

In addition to these natural migration movements, mosquitoes can hitch a ride on human activity, and thus are able to spread further, as is the case with the mosquito. Aedes aegypti and the Aedes albopictus, main vectors of viruses such as zika and dengue. Contrary to what it may seem, given its vast presence in our country, the Aedes he is not native to Brazil or other parts of America: it seems that he landed among us at the beginning of the 20th century, by sea.

Some theories suggest that they were transported in the water used to cool the holds of ships, while others say that they arrived in the region through the importation of used tires, which can retain water and serve as breeding grounds. In case of Aedes, this process was facilitated by their eggs being resistant to desiccation. Rapid population growth and accelerated urbanization in the period, as well as the lack of vector control measures, facilitated the entry of these insects into our country, which adapted extremely well to climatic conditions and urban infrastructure. This optimal adaptation explains why it is so difficult to control the transmission of diseases caused by them.

And this is the opposite case of most anopheline mosquito species in Africa, which are averse to urban conditions, a limitation that conveniently keeps malaria away from large African urban centers. Unfortunately, migration associated with urban transport also seems to change these scenarios. That’s because the mosquito Anopheles stephensi, native to Asia, it has been found in several countries in Africa over the decade. And it is not only very efficient in transmitting the disease, but it also spreads happily in cities. In other words: the presence of this mosquito in Africa can cause a significant increase in the spread of malaria, even in urban areas that were relatively free of the disease before.

The circulation of the disease in large urban centers in Africa could have devastating consequences and jeopardize the enormous progress made in reducing the incidence of this disease made over the 21st century. WHO recognized the danger and launched an initiative to stop the spread of this mosquito in Africa. Surveillance and entomological control, essential to interrupt the transmission of the anopheles gambiae in Brazil in the last century, will be crucial.

No continent is immune to invasions like this: you have to be prepared and attentive to face any challenges that may arise.

*

Fabio Gomes is a professor at the Carlos Chagas Filho Institute of Biophysics at UFRJ and a member of the Hertha Meyer Cellular Ultrastructure Laboratory. Twitter: @plasmovet

Subscribe to the Serrapilheira Institute newsletter to follow more news from the institute and the Fundamental Science blog.

PRESENT LINK: Did you like this text? Subscriber can release five free hits of any link per day. Just click the blue F below.