I have these lovely little so & so's on a Chrysis, check the axis of leaves, roots, medium, and like camille1585 stated "every little nook and cranny". Clean the pots, or replace them, and wipe down the surfaces near the plant, with some luck we might get rid of some potential re infestations by doing this. I've got to admit to not being very aggressive with this one since this orchid is going on yr 8 without any flowers or even a sign of a spike. So it can suffer for a little bit, before I attack again. May be with luck, the pig headed little thing will flower sometime in the near future.
I use several fronts of attack, diazon(sp), neem oil, and endall. First is systemic, neem oil is reproductive inhibitor, and endall is a contact, pyrethorin(sp) based insecticide that kills eggs, juvies, and adult bugs. I start with the endall and neem oil, use this combo for about three weeks, then if they come back, I use the systemic for about a month. If after all this, I still have the little blighters, then I start all over AGAIN.