I wouldn't worry about these guys too much, for in all my years dealing with plants I have yet to see damage caused by fungus gnat maggots. Mealy bugs are tiny, white insects that look like tufts of lint. They are another of the sap suckers' and bad infestations will cause stunted growth and eventually kill the plant. You will find them on the underside of leaves and where the leaves branch off from the main stem of the plant. Use the same controls as for aphids.
Mites are generally too small to be seen without a magnifying glass.
They are brownish in colour and look like dust. Mites suck plant juices and leave foliage speckled and yellow. If not controlled the leaves will turn brown and fall off, and new growth will be stunted with deformed buds. Spider mites produce webs on the leaves to hide and feed under. Plants growing in hot, dry locations are most susceptible to mite attack.