Not sure, madhuparc, but I would think the range of frequencies created by the sound of a flyswatter slapping the little bleeders into the afterlife would be somewhat irksome to them.
What a great idea shammydodger! If your researching the development of a mosquito repellant device the recorded screams of a mosquito preparing to meet its maker just must do the trick.
There's some info here on the use of low frequency audio as a repellent. There are high frequency repellers available, but the concensus is that they don't really work.