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How male mosquitoes target females—and avoid traps

Even in the chaotic swarms where they reproduce, male mosquitoes possess a remarkable ability to pick up on the faint sound of a potential mate.

A new study from Nagoya University in Japan suggests that males do this by being tuned into a broader range of sounds than females. The findings of this study offer fresh insight into the complex mating behavior of mosquitoes and why catching them in traps in the wild remains such a challenge.

Sound-based traps that mimic the wingbeat of female mosquitoes have long been used in population control to capture males and sterilize them. However, the real-world performance of these devices has often been disappointing, typically catching just a handful of insects each day.

An intriguing possibility suggested by the study is that this underperformance stems from males responding to complex acoustic cues, which current traps fail to fully engage.

The findings, in Science Advances, highlight the sophisticated information-processing mechanisms in male brains that enable them to locate the source of faint female sounds in noisy environments.

The group used a technique known as calcium imaging to visualize neuronal activity in the brains of male and female mosquitoes during exposure to different frequencies of sound.

"We found that male brains showed responses not only to the same frequencies of sound as female brains, but also to much higher frequencies," Designated Assistant Professor Matthew Su from the Graduate School of Science said.

"Male brains therefore show responses to a highly diverse range of sounds, including not only the sounds of female wingbeats, but also 'distortion products', which are the sounds made by mixing male and female wingbeats. This finding shows the complex information processing required for males to identify the location of females."

To investigate the molecular mechanisms that lie behind these sex differences in brain sound reception, the research group used "transcriptome analysis" and "proteome analysis" to comprehensively compare the genes expressed at the base of the antennae in males and females.

It was found that molecules related to cilia—the small, hair-like structures that mosquitoes use to detect vibrations—were significantly more expressed in males than in females. This included a specific group of genes known as dyneins, which are more expressed in males and have previously been linked to hearing function in various species of insects.

"Cilia are thought to function to increase receptive sensitivity to certain sounds. This indicates that the type and amount of cilia-related genes expressed in the mosquito 'ear' may result in sex differences in auditory function," Professor Azusa Kamikouchi at the Graduate School of Science/Institute of Transformative Bio-Molecules said.

"This sound processing mechanism may be a specialized and sophisticated mechanism that is not found in other insects."

"Male mosquitoes rely on the sound of female wings to find mates. Therefore, mosquito hearing is a promising target for preventing the reproduction of mosquitoes," she continued.

"By uncovering how male mosquitoes process sound at the neural level, we hope to pave the way for more effective mosquito control tools that disrupt breeding behavior at its source."