Several years ago it was an accepted practice for control districts to spray as a routine, meaning the trucks would be in a certain area on a given day on a weekly basis. Spraying in the evening and early morning hours, the most effective time for most species, is normally done on an as-needed basis - when surveillance data indicates that the mosquito populations are great enough to warrant the spraying to lessen the risk of disease and reduce the annoyance factor for outside activities.
With the extensive research and development of safer, more environmentally sensitive and more selective larvicides, the need for "fogging" or Adulticiding has decreased and control efforts have focused more on controlling mosquitoes before they become adults and begin biting. However, in an area like Chesapeake, our proximity to saltwater marshes and swamps such as the Great Dismal Swamp significantly reduces the effectiveness of Larviciding against some species.
The homeowner can play a very important role in reducing some of our most problematic species, which breed in artificial containers and tend to stay near humans. Our control efforts, though an important part of, are limited in controlling these species. Especially the "tiger" mosquito!