In 2020, the World Health Organization estimated that half the world's population was at risk of Malaria, and over 600,000 people died from the disease.
Malaria is one of several mosquito-borne diseases that the WHO recommends for children. Climate change will cause the number of mosquito-related infections to rise.
To reduce the burden of disease from malaria and other mosquito-borne illnesses, we need to continue to develop effective tools to control mosquito populations.
Their mid-air copulation is a prime target. A male mosquito looks for a female by detecting her faint flight tone.
The chase fails if the male can't hear the female. The mosquitoes' sense of hearing is crucial to their reproduction.
We studied the behavior of mosquitoes that cause Malaria to understand how males listen to females to find a mate. The results have been published.
There is a bit of background. The mechanism of hearing in mosquitoes is not well understood.
Both genders' ears are too high to hear each other's flight sounds. They use a trick from physics to hear each other.
When male and female flight tones combine in a mosquito ear, they create lower-frequency "phantom tones", called distortion products.
Distortion products are only found in the mosquito ear and cannot be heard or recorded outside of it.
A male mosquito needs to fly to hear a female mosquito. His own flight tone needs to be within a specific range to generate audible distortion products.
We heard the flight tones.
The flight tones of mosquitoes were recorded in the incubators with the highly sensitive microphones.
Our experiments included looking at 100 males and 100 females in separate incubators, individual mosquitoes, and a mixed incubator, with 50 mosquitoes of each sex.
In the incubators, we wanted to emulate the conditions of their natural environment with lighting and temperature and humidity controls.
We were able to measure the mosquitoes' wing beats at different times of the day.
Male mosquitoes changed their flight tones in a daily pattern, but not females. The males are 1.5 times faster at beating their wings than the females are.
Scientists have proposed and described an acoustic interaction between males and females. We found that the same ratio of wing beats that allow mosquitoes of the opposite sex to hear each other is the same ratio that is used by males and females.
The males beat their wings faster at dusk than at other times of the day. In Anopheles gambiae mosquitoes, males fly around dusk when they form swarms of 1,000 or more mosquitoes.
virgin females occasionally visit these swarms. Finding a partner is not easy.
The distortion products become more audible to the male ear at dusk because of the increase in wing-beat frequencies. By adjusting their wing beat in the swarm, they're able to hear females and increase their chances of finding one to mate with.
The men's flight tone adjustment is influenced by their sleep patterns. Flapping their wings faster is likely to be very energy intensive for the males, so they restrict this behavior to the time of swarming.
It will be important to replicate similar experiments outside the lab, specifically among mosquito swarms in their natural habitat. We've begun working on this.
New avenues for research into the evolutionary ecology of hearing, the unique hearing system in mosquitoes, and mosquito behavior have been opened by these findings.
They could help with mosquito control. Mutant males will be released into the wild to destroy mosquito populations. The offspring of Mutant male mosquitoes are not viable and will die if they mate with a female.
Mating efficiency is dependent on the released males' ability to hear the "resident" females. Our results show that it is important to assess male and female flight tone before releasing the mosquitoes.
This would make any intervention stronger by making sure that the mutants can compete with the male mosquitoes to find and mate with the females.
The Professor of Sensory Biology and Biophysics at the University College London is Joerg T Albert.
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