In the last issue of mosquito science, we mentioned a new type of mosquito control method - using music to make mosquitoes lose their appetite.
According to the research of scientists, after playing the platinum gold song "Horror Monsters and Beautiful Elves" from the famous American electronic musician Skrillex, the female mosquitoes take an average of 3 minutes to bite successfully, not only that, after playing the music, the number of female mosquito bites will also drop significantly.
However, the impact of this music on mosquitoes is not limited to appetite, and under its "harassment", the number of matings between female mosquitoes and males in the box has also decreased.
Please listen to the mosquito "cut off the children and grandchildren" song ↓↓↓
Why?
Where are the "ears" of mosquitoes?
Apparently, the mosquito's response to the song suggests that they can also hear sounds. However, the "ears" of mosquitoes are not the same as those of us humans, the hearing organs of mosquitoes are the two long flagella on their heads, and careful observation will also find that there are many fine villi on these two flagella, which increase the surface area of the flagella and improve the efficiency of mosquitoes collecting sound waves.
Flagella of mosquitoes Image source: blogs.biomedcentral.com
The role of flagellar can not only be to receive sound waves, specifically, the flagellar of mosquitoes is divided into three sections: whip, stem and stalk. The whip is the furry part that everyone can see most intuitively, which is used to feel the vibration of the air; The stem node is the middle spherical segment, also called Johnston's Organ, which converts vibrations into electrical signals; The stalk joints the flagella and the mosquito's torso.
When the whipl feels the vibration, its root will conduct the vibration to the base disc in the Jiang's apparatus connected to it, and there are a large number of sensory tubes around the basal disc, and the tactile receptors of the nerve cells in the sensor tube will emit nerve pulses after receiving the vibration, so that the mosquitoes can "hear" the sound.
Structure of mosquito flagella Image source: Reference 2
It should be noted that the flagellar of mosquitoes actually feels the displacement of air molecules, that is, the flow of air near the sound source, but the net displacement of this air molecule decays quickly with the distance, so mosquitoes can only "hear" sounds that are very close to themselves. Because of this, the flagellar of mosquitoes can also feel the wind, and when we slap past, the mosquitoes that feel the palm wind have sensed the danger and "buzzed" away.
You say, this cunning mosquito, is not angry!
"Listen" to the melody of love
The hearing of mosquitoes helps them perceive their environment and avoid danger, but the role of hearing can not be limited to this. In 2009, a study published in the journal Science showed that sound signals play an important role in the mating process of mosquitoes.
Scientists have found that when Aedes aegypti mosquitoes mate, there is a phenomenon of "harmonic convergence": the hum of female mosquitoes when flying as a mating signal will attract the surrounding males, but the male mosquitoes do not passively feel this signal, but will adjust the frequency of their wings to match the frequency of female mosquitoes.
Harmonic convergence during mating in Aedes aegypti Image source: Reference 3
However, for male mosquitoes, it is not easy to find a mating partner, and the success rate of finding a mating partner and successfully mating is even lower than that of sympathy. In Aedes aegypti, mating between male and female mosquitoes can be roughly divided into 6 steps. First of all, after the male mosquito and the female mosquito meet, the male mosquito will try to contact the female mosquito and chase in the air, the male mosquito will try to catch the female mosquito for mating, then the female mosquito will make her own "Foshan shadowless foot" kick away the male mosquito. If the female mosquito no longer expels the male mosquito, the male mosquito will immediately crawl in front of the female mosquito and grab the female mosquito for mating.
According to the scientists' estimates, only 14.5% of the male mosquitoes that can successfully advance to "Bao Dad" after the above 6 steps are really the "Black Mosquito Prince" in ten.
Behavioral steps of Aedes aegypti mating and the probability of failure of each step Image source: Reference 4
Although the role of sound signals in the mating process of mosquitoes is not fully understood, scientists speculate that female mosquitoes, when choosing a mate, will judge whether males are suitable for them based on whether the frequency at which males flap their wings matches themselves. Interestingly, once mated, female mosquitoes respond much less to the frequency with which males flap their wings and are less likely to match the males' frequencies, meaning that initial mating reduces the likelihood of subsequent mating.
As for why there is a phenomenon of "harmonic convergence", some studies believe that mosquitoes are actually deaf to high-frequency vibrations, and only when the frequency of male and female mosquitoes flapping their wings matches, a low-frequency sound that can be "heard" will be produced.
Studies have shown that male mosquitoes want to match with female mosquitoes, hear signals of love from each other, need to make a lot of effort, female mosquitoes every time they flap their wings, male mosquitoes need to flap 1.5 times to match, in order to reach harmonic convergence.
The problem, then, is that the male mosquitoes always move at such high speeds, and the body must not be able to eat, so the male mosquitoes form a biological rhythm: at dusk than at other times of the day, they flap their wings faster than at other times of the day. In natural circumstances, the period before and after sunset is a good time for mosquitoes to "talk about love", and it is not difficult to understand that male mosquitoes try to express themselves at this time.
At dusk, mosquito swarms flock to it, it is the season of mating~ Image source: theconversation.com
A "out-of-tune" courtship song
When they understood the important role of sound signals in the mating process of mosquitoes, scientists found that Grammy quds can affect the number of mating times of mosquitoes, and there is a reasonable explanation.
This increasing frequency and intensification of the song obviously affects the communication between female and male mosquitoes, when both sides turn a deaf ear to each other, even if they fly in front of each other, they cannot rub the spark of love. It's like a lover is whispering in your ear, pouring out feelings, and the Divine Comedy coming downstairs destroys all the atmosphere...
But for mosquitoes, the most terrible thing is not a brainwashing divine comedy noise disturbance mosquitoes, but the love party sings "out of tune", how the two sides can not "harmonic convergence", and finally can only fall a "chicken and duck talk".
In order to fight mosquitoes, people have come up with a variety of methods, such as mosquito nets, screens, insecticides, mosquito repellent water, and scientists have even used genetic engineering to make mosquitoes infertile, when they destroy the sex differentiation gene dsxF in The Gambian Anopheles mosquitoes, female Anopheles gambian (dsxF -/-) will have a bisexual phenotype and be infertile.
Anopheles gambian anopheles that has undergone gene editing Image source: Reference 5
In addition to infertility, these female mosquitoes also have the organs of male mosquitoes, and they cannot even produce normal courtship melodies, losing their attraction to normal male mosquitoes. The researchers recorded the vibration frequency of different genotypes of female mosquitoes as they flew, and found that the normal female mosquito was 389 Hz, the hybrid female mosquito was 432 Hz, and the homozygous, completely destroyed female mosquito was 497 Hz.
After the dsxF gene is completely destroyed, the high-frequency sounds made by female mosquitoes lose their appeal to male mosquitoes Image source: Reference 6
You can convert according to the ratio of 1:1.5 above, when mating, the vibration frequency of the wings of male mosquitoes when flying is about 1.5 times that of normal female mosquitoes, at such a frequency, male mosquitoes and female mosquitoes can be qinser and chirp. Those homozygous female mosquitoes with hermaphroditic characteristics flapp their wings at a frequency close to 500 Hz! In the eyes of male mosquitoes, it is estimated that which companion also came to court, right? Of course, there is no attraction for both sexes.
But who would have thought that the buzz that disgusts us is so important to mosquitoes?
Bibliography:
[1] Avitabile, D., Homer, M., Champneys, A. R., Jackson, J. C., & Robert, D. (2010). Mathematical modelling of the active hearing process in mosquitoes. Journal of the Royal Society Interface, 7(42), 105-122.
[2] Dieng, H., The, C. C., Satho, T., Miake, F., Wydiamala, E., Kassim, N. F. A., ... & Morales, N. P. (2019). The electronic song “Scary Monsters and Nice Sprites” reduces host attack and mating success in the dengue vector Aedes aegypti. Acta tropica, 194, 93-99.
[3] Cator, L. J., Arthur, B. J., Harrington, L. C., & Hoy, R. R. (2009). Harmonic convergence in the love songs of the dengue vector mosquito. Science, 323(5917), 1077-1079.
[4] Aldersley, A., & Cator, L. J. (2019). Female resistance and harmonic convergence influence male mating success in Aedes aegypti. Scientific reports, 9(1), 1-12.
[5] Kyrou, K., Hammond, A. M., Galizi, R., Kranjc, N., Burt, A., Beaghton, A. K., ... & Crisanti, A. (2018). A CRISPR–Cas9 gene drive targeting doublesex causes complete population suppression in caged Anopheles gambiae mosquitoes. Nature biotechnology, 36(11), 1062-1066.
[6] Su, M. P., Georgiades, M., Bagi, J., Kyrou, K., Crisanti, A., & Albert, J. T. (2020). Assessing the acoustic behaviour of Anopheles gambiae (sl) dsxF mutants: implications for vector control. Parasites & vectors, 13(1), 1-9.
Author: EVEE (Peking University School of Life Sciences)
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