Aegypti mosquitoes Aedes aegypti switched to the power of human blood by living in the arid regions of Africa with high population densities of people. This is the conclusion reached by the team of researchers, studied the food preferences of these insects from 27 populations across the continent. Perhaps, initially, the mosquitoes began to settle near the people to have year-round access to water, and their food specialization is a byproduct of this process. In an article for the journal Current Biology , the authors warn: as soon as African cities grow, more mosquito populations will switch to feeding on human blood.
Females of most mosquitoes feed on animals, but among them are foodies, preferring human blood. One of them aegypti mosquito subspecies Aedes aegypti aegypti, vector of dengue, chikungunya, zika virus and, of course, yellow fever. The birthplace of this insect in Africa, but with man it spread throughout the tropics and even into temperate regions.
It is assumed that Ae. ae. aegypti have become experts on nutrition in human blood from five thousand to ten thousand years ago, but where and why this happened remains unclear. To sort out this problem was solved by a team of researchers led by rose and Noah (Noah H. Rose) from Princeton University. They noticed that another subspecies aegypti mosquito, Ae. aegypti formosus at least in some parts of the area retains a broad food preference and feeds not only on humans.
The scientists collected eggs from different subspecies of Ae. aegypti in 27 locations throughout Africa South of the Sahara. The collection site was located in a densely populated area, and where density of people is small and mosquitoes rarely encounter them. Environmental conditions in different locations ranged from tropical rainforests to arid semi-desert with a pronounced change of seasons.
In the laboratory from eggs brought adult mosquitoes and allowed them to multiply. The resulting females were used for further experiments. They were placed in a transparent box with two outputs, one of which was placed a human hand, and the other Guinea pig. When searching for the victim aegypti mosquitoes are guided by smell, so the choice of females allowed to say who seems to them more appetizing, man or rodent.
Most individuals flew to the smell of Guinea pigs. Only representatives of several West African populations is either not demonstrated clear preferences or chose the human scent. Belonged to the mosquitoes that hatched from eggs collected in Senegal.
The authors suggested that the specialization to feeding on humans evolved in populations that live near cities and towns. This idea was confirmed: the number of people living in a radius of 20 kilometers from the point of collection of the eggs, were positively correlated with the choice of human odour. For example, urban mosquitoes from Burkina Faso, Ghana and Gabon preferred to feed on humans more often than their rural counterparts.
Another important factor affecting the preference of mosquitoes, turned out to be the climatic conditions. Insects from regions where rainfall is highly variable from month to month, and their minimum falls at the warmest time of the year, most often chose the human scent.
In hot arid climates Ae. aegypti are often faced with a shortage of water necessary for the laying and development of eggs. Of course, eggs can survive the dry season dormant, but it reduces their chances of survival. In human settlements, water is always there — for example, in casks and other vessels. According to the authors, the presence of water at any time of the year initially attracted aegypti mosquitoes to people. Specialization to feeding on human blood came later, as a byproduct of living with our look.
The authors suggested that aegypti mosquitoes from the dry Sahel became the ancestors of the invasive subspecies Ae. ae. aegypti, which together with man colonized the entire world. This hypothesis found some support in the genetic data but to obtain a rigorous proof in its favor was not easy because of the complex pattern of settlement of these insects. The fact that prefer human blood mosquitoes, populating cities across Africa, passed the aboriginal populations of genes that are associated with narrow food specialization. Among them, for example, the genes responsible for the odor perception.
To the extent that, as African cities grow, more and more populations aegypti mosquitoes are in conditions that favor specialization to human blood. As a result, by calculations of authors, by 2050, populations of Ae. aegypti in many parts of the continent will switch to feeding on humans. This, in turn, will increase the speed of spread many dangerous infections and jeopardize the health of millions of people.
The people of often face a different kind of mosquito, Culex pipiens. Even one individual who flew in the evening in the apartment, can deprive a person of sleep. In the material of the “Two in the room” you can find out more that makes the members of this species attack humans and how they protect themselves.