Persistent Mealybug Problem

[Taceas]

I bought some orchids from an Indiana grower a couple of years ago, and thoroughly inspected each and every plant for problems. Upon getting home and getting them set up they thrived, for a few months anyway.

Then I noticed white cottony mealybugs on one orchid, a Sedirea japonica, and then on others as I looked around and in all the nooks and crannies. The Sedirea eventually succumbed to either the bugs or the various treatments I tried.

I've tried Safer's soap, I've tried the recipe with rubbing alcohol, dishsoap, and water, I've tried the systemic insecticide from Bayer...with no real success. Each time it knocks them back a little, but they always come back in a few weeks.

Right now they're mainly on one particular Phalaenopsis, down in the leaf folds near the center of the plant...and a few here and there on others. Lately I've been washing them off with a higher pressure stream of water, which does remove them and their sugary residue, but still nothing seems to kill them completely.

Is there a regimen that works? How often do you recommend treating a plant?