[elvia]

I have a mosquito magnet. Probably the type kickaha mentioned. Cost for a 1.25 acre unit costs $1,200.00 It takes 2 weeks to clear out a area. A smaller model (Liberty) costa about $500.00. Mosquitos are territorial.
Another bit of info is that when they head out to feed, they fly against the wind. That way, when they are full they use the wind to help them return to their nesting site. Once you clear out a site, if there is no water or such for them the area will stay clear until a larger than normal wind blows more into your area.