We all know the challenge of navigating a public place full of people while looking for a friend, yet most of us can find a specific person in a crowd without bumping into anyone. Male mosquitos face similar challenges, as they need to identify potential mates while flying in a swarm. They need to dodge other males while being able to identify females. One thing that male mosquitos have going for them is that female mosquitos’ wings produce a lower-pitched sound, helping them to home in on a female in a crowd; hearing was thought to be the key sense used by males in search of a mate. However, Jeffrey Riffell from the University of Washington, USA, and a group of international researchers were curious to figure out how important the insect's other senses are when trying to find a mate in a swarm and how the males manage to avoid collisions while doing so.
To test how mosquitos navigate flying in swarms while looking for their next partner, the team initially analyzed the flight trajectories of individual mosquitos that were tethered to a rod. The researchers then put each mosquito in a circular virtual reality arena, where they were surrounded by LEDs presenting the illusion of fellow mosquitos flying around, with larger, moving spots, produced by multiple LEDs, mimicking mosquitos flying close by. Playing these imitation mosquitoes in combination with male-like or female-like flight sounds, the researchers could examine the flight maneuvers of males in response to females or males flying by. In a second set of experiments, the mosquitos flew freely in all-male swarms and the team tracked 938 individual flight trajectories from which they obtained individual flight paths and flight direction relative to the closest neighbor. To see whether the insect's maneuvers and flight path were influenced by the presence of others, the researchers compared the insect's actual flight paths with the theoretical flight paths that the insect could have taken if no other mosquitos were present.
After the researchers had analyzed the insects’ flights, it was clear that the male mosquitos actively steered towards a light spot mimicking another mosquito when they heard female flight tones. In contrast, when they heard male flight tones, they actively avoided pursing a mosquito-like dot in the virtual reality arena; males do not pursue males when seeking a mate. So, hearing the tones of a female mosquito fine tunes the male's vision to help them home in on a potential mate.
However, the researchers also realized that tethered male mosquitoes changed their wingbeat pattern as an object appeared to approach them, regardless of whether there were any sound effects, adjusting the amount of thrust they produce. In other words, vision alone is sufficient to trigger a change in the insect's flight path to take evasive action. And when the researchers analyzed the trajectories of freely flying males in all-male swarms, it was clear that seeing another close approaching male was sufficient to trigger a mosquito into changing their flight path to avoid a collision.
This study highlights that vision plays a significant role for mosquitoes navigating their way through a swarm; just seeing neighbors close up is sufficient to allow a mosquito to take evasive action, allowing them to dodge other swarm members when searching for a mate. However, hearing is still key when it comes to tracking down a mate, allowing a male to locate a female in the swarm initially by ear, before switching to tracking her by sight during the final approach. Knowing that mosquitos use both their eyes and their ears to maneuver through the swarm while looking for a mate could impact ecological research and public health initiatives regarding control and protection, as mosquitos are still among the most deadly animals on the planet.
