Biting midges(sometimes called "no-see-ums")are a nuisance to people but don't hurt plants. They thrive in wet conditions - is your hibiscus overwatered? Are there wet leaves or bark rotting underneath? The best way to control these flying pests is to clean up any poor drainage or damp rotting matter around your yard. Repellents with DEET that you apply to your skin are listed for biting midges. Most window screens can't keep them out - getting screening that has very small openings can be hot, too. The movement of overhead fans does keep them away.