Adult fungus gnats do not really cause much direct damage to plants, though they can be a nuisance to you as they fly about. The larva, however, can cause a great deal of damage to seedlings and other young plants because they feed on their tender roots. Although it is not yet know for certain, most experts also believe they feed on the developing callus of plant cuttings. This results in a delay in new root development.The overall stress fungus gnats...