While dull colors can sway humans in search of a mate, they also appear to be important to male mosquitoes: researchers have found that the insects only chase others when they hear the hum of a female.
Male mosquitoes form swarms involving thousands of individuals to attract potential mates, but must avoid bumping into each other as they pursue the arriving females.
Dr Saumya Gupta of the University of Washington, Seattle, said it was previously thought that mosquitoes had such poor eyesight that they could not see each other. What’s more, male mosquitoes are known to tune out the sound of other males – meaning they couldn’t rely on their acute hearing to avoid collisions.
Now Gupta and colleagues have shed fresh light on how the insects manage the feat.
“Not only [have] we found [mosquitoes] can see visual cues from other individuals flying around,” Gupta said, “but we found that males can actually integrate acoustic cues with visual cues [to find a female]”.
Writing in the journal Current Biology, Gupta and colleagues report how they fixed anopheles mosquitoes inside an arena whose walls were covered with an LED panel displaying a static pattern of bright pixels. This, they say, mimics aspects of what a mosquito would see in a swarm.
The team then placed a large moving blob of light on the LED screen to represent another mosquito very close.
The researchers found that the tethered mosquitoes showed no tendency to steer toward or away from the large blob, although they did change the frequency and amplitude of their wingbeats.
However, when the high-pitched whine of a female was played, males steered strongly in the direction of the blob’s movement.
“As soon as they hear female noises, they try to intercept the object,” said Gupta. In other words, the sound of a female mosquito appears to cause a shift in the visual processing of males.
The team also looked at free-flying mosquitoes and found that they did try to avoid collisions when they were close together in a swarm.
However, rather than steering away to avoid collisions, the insects made other changes in their acceleration – consistent with the results of the earlier experiments.
While malaria is spread by female mosquitoes – as males do not bite – Gupta suggested that the study could be used to improve male traps to help control the spread of the disease.
“Mostly females bite and transmit [malaria] after mating,” Gupta said, noting that by trapping males, these processes can be disrupted.
Dr Francesco Baldini from the University of Glasgow, who was not involved in the work, said the results were exciting. “They reveal that mosquitoes respond to visual cues based not only on what they see, but also on what they hear,” he said.
Baldini added that the work could help improve the effectiveness of mosquito traps, not only for monitoring specific mosquito species, but also, if highly effective, for population control.
“Additionally, with increasing interest in targeting male mosquitoes, traps designed to attract the non-biting sex can help reduce reproductive rates and ultimately reduce the overall mosquito population,” he said.
However, Dr Lauren Cator of Imperial College London said the most important implication of the study was that it improved our understanding of how mosquitoes use their senses when trying to mate.
“This behavior is important for the design of control tools such as those that rely on the release of sterile males,” she said.
