Mosquitoes are very much into the real estate market right now.
Think about it. A lot of houses have pools, and when the bank comes a-knocking, pool maintenance falls to the lowest priority on everyone's list. And as anyone who has ever owned a pool or been involved in maintaining one will testify, those bastards will go rank in a heartbeat if left to their own devices. Even a drained pool can collect stagnant rainwater, after all. And whose job is it to patrol all of these thousands of pools to keep them disinfected?
So, a whole bunch of foreclosed houses end up with musky, slimy cesspits of hell-water in their backyards. If you know anything about swamps, you know that filthy, standing water is the perfect breeding ground for the little blood-sucking bastards.
Still, this is just an increase in annoying bugs we're talking about here. Surely, that's relatively harmless in the grand scheme of things. It's not like they're carrying any potentially lethal viruses or anything.