The Breaking Science team met two researchers who've been following the hum of insect wings
Chris Smith: In some countries it's traditional to woo or serenade a woman by singing beneath her balcony. Well now it turns out that things aren't so different in the insect world. Here’s Lauren Cator.
Lauren Cator: I'm interested in how mosquitoes choose their mate, and my hypothesis is that they may use flight tone as a way to get information about the quality of potential mates.
Chris Smith: So in other words how fast the wings are flapping?
Lauren Cator: It's not a direct relationship but that sound that’s created by the wings flapping, yes.
Chris Smith: So what was the big unknown then that you were trying to investigate here?
Lauren Cator: There was a paper published in 2006 by Gibson and Russell, and they found that in Toxorhynchites, a large non-blood feeding mosquitoes, that a similar behaviour was occurring, and, as a medical entomologist, I was interested in seeing if medically important mosquitoes, mosquitoes that feed on human blood and transmit pathogens that infect people, were doing similar things.
Chris Smith: Well this seems like a very good time to bring in Ben Arthur who’s another researcher on this paper. Ben, how did you actually investigate what was going on with these mosquitoes to see how they were tuning into each other’s wing beat frequencies?
Ben Arthur: Well it was a two-part study. We had behavioural methods and some physiological data as well. In the behavioural data, what we did was we tethered individual mosquitoes to a fine insect pin with some glue and positioned them next to a special microphone which could sense the wing flight tone very finely and just listened to what they were doing.
[Sound of mosquito]
So what you’re listening to right now is a male mosquito singing along at around 600Hz, and he’s next to a microphone. And we’re going to bring in a female here.
[Sound of mosquito]
And she’s singing at 400Hz. And the higher harmonics at 1200Hz, the shared harmonic, if you listen real close, you can hear the beats produced because those two frequencies are so close together. And that’s what’s happening when they’re courting.
Chris Smith: So which sex is changing its wing beats in response to the other?
Ben Arthur: They both do. So if the male’s relatively stationary and the female comes in she’ll modulate her tone up or down to match his, or if the female is stationary and then the male can move his and they’ll just synchronise to actively both match each other.
Chris Smith: You’re saying it's not actually the frequency the wings are beating at, but the harmonics, the multiples of the frequency the wings are beating at, which seems to be important?
Ben Arthur: That’s right. So the natural occurring frequency of the female wing beat is at 400Hz and that of the male’s at 600 and those are different enough that they don’t try to match the fundamental but rather the shared harmonics are the integer multiple at 1200Hz.
Chris Smith: How does the mosquito that’s the recipient of these frequencies, how does it actually detect them, and how do you know that it's actually responding to the frequencies, and then how does it then know, right now I need to mate?
Ben Arthur: Right, well it has these very plumose antennae, and these antennae sense the movements of the particles in the air, and there’s a sensory organ at the base of the antennae called the Johnston’s organ which transduces that movement of the antennae into an electrical voltage that the nervous system can then use to detect where the sound is, and what it is and whether it's a mate or not.
And the second part of our study then recorded from the Johnston’s organ and saw these electrical voltages and we found that we could measure electrical voltages all the way up to 2kHz which includes that shared harmonic at 1200Hz.
Chris Smith: Wasn’t there some claim previously by other people though that mosquitoes a) were deaf anyway and b) that they couldn’t hear sounds that high in frequency, so you’ve really scuppered both those myths haven't you?
Ben Arthur: That’s right, exactly, and we've shown it with both behavioural data and physiological data in the same paper.
Chris Smith: Lauren, what do you think that the major impacts - apart from obviously this being academically very interesting - what do you think the main other impacts are from a medical point of view?
Easy to repel - but how would you attract a mosquito?
Lauren Cator: Well just generally we know very little about mosquito mating behaviour, and we have no idea who’s choosing who or how they’re choosing them, and one of the control strategies that’s been proposed is to create transgenic mosquitoes - so mosquitoes that through genetic manipulation are either unable to transmit pathogens or are sterilised. The idea would be that if you release these into the wild that males carrying your desired genotype would be able to compete with wild males for female mates, and drive the genotype through the population. Unfortunately we have no idea what constitutes a sexy male mosquito.
Chris Smith: Hopefully they’ll find out soon. That was Lauren Cator and before her Ben Arthur. They’re both based at Cornell University, and they’ve published that work in this week’s edition of the journal Science. And if you’d like to read a bit more about how animals use sounds to track down a mate or find their way around there are links to a number of articles about those subjects on the Breaking Science website.
You can hear the mosquitos - and the whole programme - on the Breaking Science website. This interview was originally broadcast in January 2009 on BBC Radio Five Live
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