Interesting NYT piece about the environmental pluses and minuses of eradicating mosquitos.
Another value of mosquitoes, perverse to some, obvious to others, is that they "keep out the riffraff," meaning human beings. Concentrations of pests offer protection to wilderness areas. The tsetse fly, which causes livestock disease as well as human sleeping sickness, has kept humans away from some wildlife refuges and has been called "Africa's best conservationist." Of course, this view has been described by others as ecological imperialism.