| Are they actually pests?
Insects tend to get a very bad press and we are too keen to reach for the chemicals whenever we see them. Only a small proportion of the million or more species harm man, plants, or animals. A great number assist in the breakdown of dead material and help to recycle nutriments. Thus, the gnats could well be emerging from larvae that have been feeding on (and breaking down ) the compost in the pots; they are just doing what they have been doing for the past 200 million years - long before we began to love orchids!
Unless they are seen to be causing harm, it is better not to try to eradicate them. As 'duhhdog' says, find out what they are first. Having said that, the identification of insects is not the easiest task to undertake.
Les |