Yellow fever mosquitoes (Aedes aegypti)
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Yellow fever mosquitoes Aedes aegypti switched to feeding on human blood due to life in the arid regions of Africa with a high population density. This is the conclusion reached by a team of researchers after studying the food preferences of these insects from 27 populations across the continent. Perhaps mosquitoes originally began to settle next to people in order to have year-round access to water, and their food specialization is a by-product of this process. In an article for the magazine Current Biology authors warn: As African cities expand, more mosquito populations will begin feeding on human blood.
The females of most mosquitoes feed on a variety of animals, but there are also gourmets among them who prefer human blood. One of them is a yellow fever mosquito of the subspecies Aedes aegypti aegypti, a carrier of dengue fever, chikungunya, Zika virus and, of course, yellow fever. The homeland of this insect is Africa, but together with man it spread throughout the tropics and even penetrated into temperate regions.
It is assumed that Ae. ae. aegypti became specialists in human blood nutrition from five to ten thousand years ago, but where and why this happened remains unclear. A team of researchers led by Noah H. Rose from Princeton University decided to sort out this problem. They noticed that another subspecies of the yellow fever mosquito, E. Egypt and fair at least in some parts of its range, it retains wide food preferences and feeds not only on humans.
Scientists have collected eggs of different subspecies Ae. aegypti at 27 locations throughout Sub-Saharan Africa. Collection sites were located both in densely populated areas and where the density of people is low and mosquitoes rarely encounter them. The environmental conditions in different locations varied from tropical rainforests to arid semi-deserts with a pronounced change of seasons.
In the laboratory, adult mosquitoes were removed from the eggs and allowed to breed. The resulting females were used for further experiments. They were placed in a transparent box with two exits, in one of which a human hand was placed, and in the other a guinea pig. When looking for a prey, yellow-fever mosquitoes are guided by smell, so the choice of females would allow them to say who seems more appetizing to them: a man or a rodent.
Most of the individuals flew to the scent of a guinea pig. Only a few West African populations either showed no clear preference or opted for the human smell. The latter included mosquitoes that hatched from eggs collected in Senegal.
The authors hypothesized that a specialization in human feeding developed in populations that live near cities and towns. This idea was confirmed: the number of people living within a radius of 20 kilometers from the point of collection of eggs, positively correlated with the choice of human scent. For example, urban mosquitoes from Burkina Faso, Ghana, and Gabon preferred to feed in public more often than their rural counterparts.
Climatic conditions were found to be another important factor influencing mosquito preferences. Insects from regions where the amount of precipitation varies greatly from month to month, and its minimum falls on the warmest season, more often chose the human smell.
In a hot, dry climate Ae. aegypti often face a lack of water, which they need to lay and develop eggs. Of course, eggs can survive the dry season in a dormant state, however, this reduces their chances of survival. In human settlements, there is always water – for example, in barrels and other vessels. According to the authors, it was the presence of water at any time of the year that initially attracted yellow fever mosquitoes to people. The specialization for feeding on human blood arose later, as a by-product of life next to our species.
The authors suggested that it was the yellow fever mosquitoes from the arid Sahel that became the ancestors of the invasive subspecies E. e. iEijypti, who, together with man, colonized the whole world. This hypothesis found some support in the genetic data, but it turned out to be difficult to obtain strong evidence in its favor due to the complex pattern of dispersal of these insects. The fact is that mosquitoes preferring human blood, populating cities throughout Africa, transmit genes to aboriginal populations that are associated with a narrow food specialization. Among them, for example, genes responsible for the perception of odors.
As African cities grow, more populations of yellow fever mosquitoes find themselves in conditions that favor specialization for human blood. As a result, according to the authors’ calculations, by 2050 the population Ae. aegypti in many parts of the continent will move to feeding in humans. This, in turn, will accelerate the spread of many dangerous infections and endanger the health of millions of people.
Residents of Russia most often encounter another type of mosquito, Culex pipiens… Even one individual that flew into the apartment in the evening can deprive a person of sleep. In the material “Two in a room” we tell in detail what makes representatives of this species attack people and how to protect themselves from them.
Sergey Kolenov
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