Everyone who has spent an evening or day in the summer attacking mosquitoes or scratching mosquito bites can agree: mosquitoes odor. However, human scents play a significant role in attracting mosquitoes to us. In a scientific report published in May, scientists constructed a testing arena the size of an ice rink and pumped in the aromas of various individuals to identify the specific chemicals in body odor that attract these insects. Mosquitoes are members of the fly family and typically subsist on nectar. However, females preparing to produce eggs require a protein-rich meal: blood.
In the best case scenario, a bite will only result in an irritating, red bruise. However, mosquito wounds frequently prove fatal due to the parasites and viruses the insects transmit. Malaria is one of the most hazardous of these diseases. Malaria is a disease transmitted by blood that is caused by parasites that reside in red blood cells. When a malaria-infected person is bitten by a mosquito, the parasite is sucked up along with the blood. Dr. Conor McMeniman, an assistant professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute in Baltimore, explains that after developing in the mosquito’s stomach, the parasite “migrates to the salivary glands and is then spit out into the skin of another human host when the mosquito blood-feeds again.”
Malaria has been eradicated in the United States over the past century as a result of window screens, air conditioning, and improvements to drainage systems where mosquitoes’ aquatic larvae can develop, but it continues to threaten the majority of the world’s population.
McMeniman, principal author of the study published in the journal Current Biology, stated, “Malaria is still responsible for over 600,000 deaths annually, primarily among children under the age of 5 and pregnant women.”
“It causes a great deal of suffering throughout the world, and part of the motivation for this study was to attempt to comprehend how mosquitoes that transmit malaria are locating humans.”
McMeniman, along with postdoctoral researchers from Bloomberg and the study’s lead authors, Drs. Diego Giraldo and Stephanie Rankin-Turner, concentrated on Anopheles gambiae, a mosquito species native to sub-Saharan Africa. They collaborated with the Macha Research Trust in Zambia, whose scientific director is Dr. Edgar Simulundu.
McMeniman stated, “We were extremely motivated to develop a system that would allow us to study the behavior of the African malaria mosquito in a naturalistic environment that replicated its native habitat in Africa.” In addition, the researchers wanted to compare the mosquitoes’ olfactory preferences between different humans, observe the insects’ ability to follow scents over a distance of 66 feet (20 meters), and investigate them between 10 p.m. and 2 a.m., when they are most active.
Unique Screening Facility Replicates Human Body Odor for Mosquito Study
To meet all of these criteria, the researchers constructed a rink-sized screening facility. Six screened tents were positioned around the perimeter of the facility for study participants to overnight. Air from the participants’ tents, conveying their unique breath and body odor aromas, was pumped through long tunnels to the main facility and deposited onto absorbent pads, which were warmed and baited with carbon dioxide to simulate a sleeping human.
The sleeping subjects’ odors were then fed to hundreds of insects in the primary 20-by-20-meter enclosure. Infrared cameras monitored the insects’ path to the various samples. (The mosquitoes used in the study did not carry malaria, and they were unable to reach the snoozing humans.)
The researchers discovered what many picnic-goers can attest to: Some individuals entice insects more than others. In addition, chemical analyses of tent air disclosed the odor-causing substances responsible for the mosquitoes’ attraction or repulsion.
Mosquitoes were most attracted to ambient carboxylic acids, such as butyric acid, a compound found in “stinky” cheeses like Limburger. Bacteria on human epidermis generate these carboxylic acids, which are typically imperceptible to humans.
While carboxylic acids seemed to attract mosquitoes, eucalyptol, a chemical found in plants, appeared to repel them. The researchers surmised that a sample with a high eucalyptol concentration was linked to the diet of one of the participants.
Finding a correlation between the chemicals present in various individuals’ body odor and the mosquitoes’ attractiveness to those scents, according to Simulundu, was “very interesting and exciting.”
“This finding paves the way for developing lures or repellents that can be used in traps to disrupt the host-seeking behavior of mosquitoes,” said Simulundu, a coauthor of the study.
Dr. Leslie Vosshall, a neurobiologist and vice president and chief scientific officer at the Howard Hughes Medical Institute who was not involved in the study, shared the same enthusiasm. She stated, “I find this study to be very intriguing.” This is the first time an experiment of this type has been conducted at this magnitude outside of a laboratory.
Vosshall conducts research on an additional mosquito species that transmits dengue, Zika, and chikungunya. In a 2022 study published in Cell, she and her colleagues discovered that this mosquito species is also attracted to the fragrance of carboxylic acids produced by microorganisms on human skin. She stated that the fact that these two distinct species respond to similar chemical stimuli is advantageous, as it could make it simpler to develop repellents or traps for mosquitoes across the board.
There may not be immediate implications for averting insect stings at your next barbecue. (According to Vosshall, scouring with unscented detergent does not eliminate the natural odors that attract mosquitoes.) She noted, however, that the new paper “gives us some really good clues as to what mosquitoes are using to hunt us, and it is essential that we understand this in order to determine our next steps.”