Mosquito Music

Chris - Now you work on mosquitoes and you published a paper the other day that everyone was buzzing about, you might say, about how they tell males from females. I'd never really considered before that that might be a problem.

Gay - It's not so far off the topic that the other people have been talking about because when mosquitoes get together, they usually do so in a crowd of males. They all gather in the same place at the same time.

Kat - A bit like a mosquito night club.

Gay - That's right.

Chris - But why do they do that? Why do all the males get together?

Gay - Well the males really have nothing else to do in life except hang about and mate. It's the females that go about biting people and drinking blood but the males really don't have anything much else to do.

Chris - The males just drink sugary solution don't they?

Gay - Yes that's right.

Chris - The reason females drink the blood is because it's rich in protein.

Gay - Yes and they need that protein to help make the next generation.

Chris - So you've got a big flock of males hanging about. How does an interaction between a male and female mosquito happen then?

Gay - Well the first problem is that all these males are swirling around each other and they've got to not waste too much time chasing each other because that would lead to nothing. And that's really where the problem started for me. I wondered about how they save their energy for actually chasing the right female when she comes along. It's taken a long and hard think about things. Mosquitoes have very specialised antennae and males have very elaborate ones. We already know something about this, and when you hum at a group of males, they will come right into your face. So don't sing because they'll go right into your mouth if you do that! Those males are coming at your face because they think you might be a female.

Chris - How are they sensing that?

Gay - It's the vibration of the wing beats of an actual female or the vibration of your hum. It stimulates their antennae and that signal goes to the mosquito's brain and it transforms that into a change in its wing beats moving towards the sound it heard.

Chris - So could you use that as a way of baiting a trap for mosquitoes then? Could you have something that releases a rather aggravating sound that then sucks all the males in, leaving nothing to mate with the females and the population would plummet?

Gay - Yes this is exactly the idea that had come to several scientists a few decades ago and you can build huge loudspeakers and you can pull in millions of males that way. The problem is that it doesn't take many males to be left behind to do the job for the rest of the females.

Chris - But what about the females? Do they not respond in the same way?

Gay - No-one really knew what behaviour there was with females because if you play a sound to them, they don't really change the way that they fly. But it bothered me because we hadn't investigated females very deeply. So I went to see a colleague of mine at the University of Sussex and said 'hey you know about sound, and do you think that it's possible that these two might be able to hear each other?' We did a series of experiments to try and investigate what kind of behaviour the females might have. And indeed we uncovered a lovely duet.

Chris - So you've given me the sound samples. Anyone who is mosquito-phobic or who doesn't like the sound of things that resemble dental drills, you might want to cover your ears. Gay, talk us through this and tell us what they are.

Gay - The first thing to do is to see what two males sound like. So you've got this cloud of swarming males and two males close to each other. That's what we did in our experiment: we tethered two mosquitoes close to each other and we let them listen to each other and recorded what the effect was. So this is what it sounded like when you put two males together.

Chris - So first you hear the first one and then you hear the other one coming in subsequently. Ok here we go.

Gay - That's the first one coming in... and the second one. Now if that doesn't grate upon your ears, nothing will!

Chris - So basically there's just two pairs of wings flapping away there.

Gay - That's right and it's a really discordant sound and it doesn't have anything attractive about it. Now let's do something else this time. Let's start off with the male and then a female comes along. Let's see what that sounds like. Here's the male... and then here's the female.

Chris - So actually they synchronise their wing beats.

Gay - They do. They move towards each other. It's a little hard unless we listen to it again more carefully, but they both move a little bit towards each other and they overshoot and it's a little bit all over the place, but if you give them enough time they get right into the same register.

Chris - So by synchronising their wing beats, one is telling the other that I'm male, and the other is saying that they're female, and they both know that they should pair off. So does then vision take over? Do they get close enough so they can then see each other and then they know who they're dealing with?

Gay - Their vision is not good enough for that. They've got very poor resolution in terms of vision. What I mentioned earlier is that males move towards that source of sound and when their wing beats are flapping at around the same speed, they get in gear and the male catches up and grabs the female. Once this has happened, contact senses take over.

Chris - People probably don't realise quite how hard it is to do and record two individual mosquitoes in an apparatus. How did you do that?

Gay - Well we needed lots of the fine engineering from the University of Sussex Neurobiology department. They have the kind of recording equipment and tiny little microphones that just pick up the sound near where the wing beats are. Then you put a little drop of beeswax on the back of each mosquito.

Chris - It sounds easy but how big is that?

Kat - You're lassoing mosquitoes!

Gay - Yes indeed.

Chris - So the obvious spin off of this as we've already explored, is that it's possible to lure mosquitoes into traps and things. But does this add any additional details that we might be able to exploit in control of diseases like malaria and things like that?

Gay - There's a misconception that you can affect female behaviour with a sound. There are these repellent buzzers that are meant to repel female mosquitoes. We've tested them scientifically and there really isn't much evidence that these work. It's really the upside down version of the story. Males are attracted to females; females aren't really repelled or move about. So this is one kind of product that is slightly misguided in its premise. But the more important thing I was trying to understand is why these mosquitoes can establish themselves in an environment where there are only a few of them left, such as at the end of the season. I wouldn't day there was a good practical outcome to come out of this immediately from sound and mating behaviour, but of course that's only one part into my research into mosquito behaviour, and those are far more applied.