New insights into Anopheles coluzzii mosquito behaviour can improve methods of malaria control and the development of species-specific traps

High-pitched sound buzzing around your ear unmistakably indicates the presence of a female mosquito, as only females drink blood. And while this sound drives many to try to swat the annoying insect, for the male mosquito, the same sound represents a mating signal. However, new research reveals that this process is not as straightforward as it seems.

A research team led by the University of Washington discovered complex interactions between different sensory systems in mosquitoes. These results could lead to the development of more precise malaria control methods, as well as improvements in the navigation systems of unmanned aerial vehicles. In a study published on August 30, 2024, in the journal *Current Biology*, researchers found that males of the species *Anopheles coluzzii* activate their visual system when they hear the specific sound of female wings buzzing.

As is already known, many mosquito species, including *Anopheles coluzzii*, have relatively poor vision. However, when a male hears the sound produced by female wings, its vision rapidly improves, allowing it to detect and follow a female in the vicinity. This behavior is key to understanding how males manage to locate a mate within chaotic swarms where mating occurs. Despite the dense crowd in swarms, where many mosquitoes fly quickly next to each other, males are able to visually lock onto their target and precisely orient themselves towards it, avoiding collisions with other mosquitoes.

The study also revealed an important link between hearing and vision in mosquitoes, which could open new avenues for controlling the population of these insects. Males react to the sound of female wing buzzing and orient themselves towards the source of that sound, even if it is not a real female but a mosquito trap. This information could be used to develop new generations of traps that are specific to *Anopheles* species, the main malaria carriers.

Interestingly, *Anopheles coluzzii* mosquitoes predominantly form large swarms before sunset, where most of the swarm members are males, with very few females. To the human eye, these swarms may appear chaotic, but mosquitoes use a range of senses to successfully avoid collisions and find rare females. Scientists created a mini-arena for the research that simulates the visual chaos of a mosquito swarm using a curved pixelated screen. This "flight simulation" allowed males, even when tethered, to visually perceive their surroundings and respond to auditory stimuli, mimicking the real conditions within a swarm.

Experiments revealed that males respond differently to objects in their visual field depending on the frequency of the sound they hear. When researchers played a frequency tone of 450 Hz, corresponding to the frequency of female wings, males oriented towards the object. However, they did not show interest in objects when they heard a frequency tone of 700 Hz, characteristic of the wings of other males. Additionally, researchers noted that the perception of the distance to the object plays an important role; if the object was more than three mosquito body lengths away, males did not react, even in the presence of female flight sounds.

This research could open new possibilities for mosquito control by targeting this interaction between auditory and visual signals. The strong and consistent attraction of males to visual signals along with the presence of female sounds could be a weak point that scientists might exploit in designing new generations of traps, especially for *Anopheles* species, which are major malaria pathogen carriers.

Besides this, researchers observed that male mosquitoes also make subtle flight adjustments in relation to other objects in their visual field, even in the absence of auditory signals. For instance, they adjusted the amplitude and frequency of wing flapping in response to nearby objects, suggesting preparatory maneuvers to avoid collisions. Further study of these adjustments could provide new insights into mosquito behavior in swarms and aid in developing innovative methods for controlling mosquito populations in the future.

This research was funded by the Human Frontiers Science Program, the National Institutes of Health, the Office of Scientific Research of the U.S. Air Force, and the French National Research Agency, indicating global interest in finding new ways to combat mosquitoes and, consequently, malaria.

Source: University of Washington