How mosquitoes choose who to bite

Mosquitoes seem to be attracted to some people more than others. But on the basis of what factors do they choose who to sting? And how do they find us over long distances? A new study provides a really insightful explanation of how these insects are able to locate and choose their human blood meal even a hundred meters awayproviding new foundations for the development of control interventions malaria, among the most dangerous infectious diseases transmitted by mosquitoes, mainly spread in tropical countries. The objective of the scholars was in fact to identify the olfactory preferences of Anopheles gambiae, the African malaria mosquito that likes to hunt at night, when humans are asleep. And evaluate how specific components of human body odor modulate their behavior under natural conditions.

The scholarly tests, detailed in a study just published at Current Biologywere in fact held in an open-air flight cage with a volume of about 1,000 cubic meters set up in a forested savannah area in Macha, Zambia, thus simulating the experience of mosquitoes in nature. “In the laboratory, most studies aimed at testing the olfactory preferences of mosquitoes are performed on very small scales, using small boxes with volumes of about 0.5 cubic meters or less – explained the corresponding author of the study, Dr. Conor McMeniman of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland – . For the study in Zambia, we used a structure called a semi-field flight cage, a shielded structure that has a volume that is about 2,000 times that used for normal laboratory tests”.

Mosquitoes choose who to bite based on body odor

In this flight cage, the scholars were able to channel the body odors of humans who slept in nearby tents, performing an analysis of mosquito landing behavior on several targets heated to human skin temperature, each of which carried a different body odor. These experiments, conducted by releasing 200 hungry mosquitoes into the flight cage, made it possible to evaluate the importance of temperature in attracting mosquitoes (a factor which, by itself, without even carbon dioxide emitted with the breath, did not attract them) and to compare up to six human odors at a timerevealing that insects, night after night, always chose the same smell, preferring it to that of other humans.

In addition to recording the mosquitoes’ preferences, the researchers collected samples of these odors directly from the air in the tents to characterize and compare the chemical components present. “These mosquitoes typically prey on humans in the hours before and after midnight McMeniman added. They follow scent trails and convective currents given off by humans, and typically enter homes and sting between about 10pm and 2am. We wanted to evaluate the olfactory preferences of mosquitoes during their peak activity period, when they are around and active, and also evaluate the smell of sleeping humans during that same time window”.

Overall, the team identified 40 different chemicals emitted by all humans, albeit at different rates. “Mosquitoes probably follow a specific mixsaid Stephanie Rankin-Turner, a postdoctoral fellow at the Johns Hopkins Bloomberg School of Public Health and co-lead author of the study who, together with colleagues, identified some of the most frequent blends.

In particular, people who were most attractive to mosquitoes constantly emitted more carboxylic acids, including butyric acid, which are probably produced by skin microbes. In contrast, the person least attractive to mosquitoes emitted fewer carboxylic acids but approx triple the amount of eucalyptola compound found in many plants.

Researchers hypothesize that high levels of eucalyptol may be related to the person’s diet, although more research is needed to understand exactly which components of body odor, microbial metabolites and breath emissions are really responsible for this behavior. However, what the results suggest is that high levels of eucalyptol in the body can be a great deterrent for mosquito bites. “It is likely that this person ate foods high in this chemical, which is commonly found in herbs and spices – say the authors – . But it’s also possible that he used products that contain it, such as toothpaste and mouthwash”.

“Understand what chemicals in human perfume they drive the differential attraction to certain human beings it’s important, because if we can identify these chemicals, we can predict each person’s risk of mosquito bites McMeniman concluded. This research could also help develop better baits or traps”.a