A new study, which has not yet been peer-reviewed and will be published in an academic journal, finds that some mosquito species have a clear preference for men, while others rely more on specific odors emitted by human skin to choose who to bite. However, some media biology experts have reservations about the significance of the results.
Mosquitoes are one of the most important "natural enemies" of humans. They have been biting humans and other primates for at least millions of years, and in the process they are highly effective in transmitting serious diseases such as dengue fever, Zika, yellow fever and malaria. The scientific community has long known that mosquitoes use a combination of carbon dioxide, body temperature and odor signals to find their hosts. But human odor is extremely complex, consisting of more than a thousand volatile organic compounds and skin microbiota, making it difficult to pinpoint exactly which odor components attract mosquitoes.
Previous research has demonstrated differences in people's attraction to blood-sucking insects, but no study has conducted a systematic cross-comparison of preferences for different mosquito species among the same subjects. To this end, Matthew DeGennaro's team at Florida International University in the United States selected three species of mosquitoes—Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus—to test their responses to the odors of 119 human subjects. The first two are the main vectors of dengue, Zika and chikungunya, while the third is an important vector of West Nile virus.
The research team used a device called a Uniport olfactometer to quantitatively assess how many mosquitoes flew toward a specific odor source. The subjects put their arms into the device, allowing the mosquitoes to touch and "smell" their body odors, thereby counting the preference of different mosquito species for each individual.
Experiments have shown that of the three mosquito species, Aedes aegypti is the most "specific" to humans, with an average of 89% of released individuals attracted to human odor. At the same time, it is also the only mosquito species that has shown a significant preference for men and a higher willingness to bite than women in experiments.
Further chemical analysis showed that different mosquito species prefer different "human odor profiles". For example, the presence of certain ketone compounds in skin odor was associated with greater attraction to Aedes albopictus, whereas the absence of these compounds was associated with greater attraction to Aedes aegypti and Culex quinquefasciatus. "Each mosquito species responds differently to different individuals, highlighting that they both rely on unique cues and share some target cues when identifying their hosts," the team wrote in their paper.
It is worth noting that different mosquito species often do not "fancy" the same people at the same time. Those "human magnets" that were highly attractive to Culex quinquefasciatus tended to have little overlap with the subjects most "favored" by the two Aedes species.
Experts outside the study also conducted preliminary assessments of the work. Jeronimo Alencar, a mosquito scientist who specializes in diptera (public health researcher at the Osvaldo Cruz Foundation in Brazil and head of the Diptera Laboratory at the Osvaldo Cruz Institute in Brazil) believes that this study "reveals that different mosquito species preferentially select bite targets based on the unique chemical characteristics of humans, which is an important advance in the field of vector biology." He pointed out that Aedes aegypti is highly adapted to urban environments, while Aedes albopictus originates from forest edges, which may explain why the two closely related mosquitoes rely on different cues to find their hosts. "If a certain lineage starts to exploit different subsets of the population, or prefer different times of activity, the two could coexist without being mutually exclusive," he added. In his view, this means that the research perspective is shifting from "what smells attract mosquitoes" to "who attracts which mosquitoes."
However, many other vector biology researchers are more cautious. They pointed out that effects such as Aedes aegypti's preference for males appear to be relatively limited in the data and may not be easily reflected once placed in a real-world scenario disturbed by environmental noise. It has also been emphasized that there are obvious regional differences in mosquito preferences, and the genetic background of local mosquito populations and genetic differences in local human populations may significantly affect the results.
In addition, the research team also reminded that there are essential differences between laboratory conditions and the natural environment. Devices such as olfactometers are often designed to ignore visual cues such as carbon dioxide, temperature, humidity and color. These limitations do not negate the phenomena observed in the current experiments, but methodological and conceptual constraints must be fully considered when extrapolating the results to broader contexts.
Professor Richard Wall of the University of Bristol in the UK pointed out that differences between individuals in the propensity to be bitten have long been well documented and are mainly driven by differences in body temperature and odor, so "it is expected that blood-sucking insects show different responses." He also reminded that this was a correlational study rather than a strict cause-and-effect experiment.
The relevant paper has been published on the preprint platform BioRxiv, and will need to undergo peer review to test the applicability of its conclusions in different environments and populations.