My building in Mumbai sprays a lot of Deltamethryn to get rid of mosquitos. Although in the long run, it isn't safe even for humans, in the near short run it kills all other insects as well, including moths, butterflies, lady bugs, etc, and along with it, prey base for insectivorous birds.

Is anyone aware of an alternate kind of mosquito repellant? I have vaguely read about those based on citronella oil and Neel oil etc, but nothing too concrete?