Well if you want to repell the female mosquitos and you know at which frequency the circuit
should work. Why no prototype with a NE555 and a little piezoelectric buzzer.
With a cheap microphone and your pc, or if you have an oscilloscope, you can set some
frequencies and test them.
Here is a simple circuit but change the values of the resistors and capacitors to fit your
range of frequency.
Here is a online calculator for the 555: http://www.daycounter.com/Calculators/NE555-Calculator.phtml
Well another method i have found on the net is to kill them with a laser.
But it's extremely complicated and you'll need some special programming
experience on image processing and a really fast microcontroller.
It uses some high speed cameras in cooperation with infrared LED's to detect the mosquitos.
Through the shape and size of the detected object, the device can distinguish between mosquitos
and other insect which should'nt be harmed. There is also the possibility to differ between male and
female mosquitos through the frequency of their humming.
If the optical part did detect a proper object and recognizes it as a mosquito it will be shot with a
small high power laser and burned down.
Here are some informations and two videos:
Well I wanted to build a similar system but I can't get any camera parts
and optics which are needed for this.
However. I hope my post helped you a little bit. If still nothing does work,
use some anti--mosquito-spray and have a shower after.
Or I'll send you some of my blood because it seems that mosquitos don't
like it. They never bite me even if I stans in the middle of the pond, surrounded
by billions of them.