When we first moved here in 1993, we didn't have many mosquitoes. Our house is on a gentle hill, and there's not any standing water nearby, so our native mosquitoes weren't a problem.
The advent of Asian tiger mosquitoes, however, as a problem throughout the Southeast has changed that. These mosquitoes are day-fliers, unlike our native mosquitoes, and can breed in damp soil, moistened by relatively small amounts of rain (think damp mulch) or in plant saucers, pot edges, etc. and love to hang around vegetation. Their bite stings quite a bit initially, but doesn't (yet) produce the itchy welts that native mosquitoes do.
Deet-based repellents are effective, but it's so unpleasant to spray just for a brief garden check, I find it hard to do that, unless I'll be out there for awhile.
This photo (from an excellent article about mosquitoes in National Geographic) shows the distinctive markings of the Tiger mosquito.
I'm thinking I need to get rid of ALL the empty pots, broken dishes, etc. that are behind the potting bench; they don't harbor standing water, but certainly could have a few tablespoons of moisture available on a saucer edge. Even the rimmed edges of traditional hanging baskets are probably enough to support their reproduction.
An article in NC Wildlife magazine first alerted me to their advance, as we wondered why we had started being bothered by mosquitoes.