For no-see-ums I've found that Pyrethrins work the best. While at the Everglades my younger son was getting absolutely eaten alive by the bastiges that were small enough to fit through the mesh in the top of the tent, at the advice of the rangers we bought some coils that contained Pyretherins and once we lit them in our tent you could literally see a light rain of dying no-see-ums falling out of the air as the smoke reached them. They say not to use them in the tent, but when your kid looks like he has chicken pox because he's been bit so many times the minor health effects of breathing in the smoke seem pretty trivial.
