The mosquitos have already started "blooming" and will last though July - when it's hot and dry and there are no puddles left anywhere. Of course, there's a great cross-over between the mosquito and fly population - the flies bloom a little later than the mosquitos - maybe in May but they stick around through Thanksgiving.
If you've got a fish pond, bird bath or water troughs for outside animals - the mosquito fish are free through the Mosquito Abatement program in Solano County. Napa County has something similar.
Aah, free fish. That's what it's all about. (at least for mosquito abatement!)