I find that Orthene (acephate) and Merit (imidicloprid) are quite effective.
I discovered some recently on some cymbidiums that were "hidden" amongst others in the greenhouse, and decided to "get serious", so used a combo of the two plus Enstar II (kinoprene-s), an insect growth regulator.
Ray are you using the Merit systemic granules or the liquid? I just found mealies on one of my Catts, and my Aer. I wiped with alcohol, and am treating with Bonide systemic granules, which I believe has the same active ingredient as Merit. The problem with the granules is they wash through the pot very quickly.