I finally decided that my bug problems were bad enough that I needed to take some stronger steps. The bug problem started with my Dendrobium Victoria-Reginae, and has spread around the orchid room from the east-facing lower shelf to the west-facing lower shelf. Most of the Dendrobiums have had the infestation, and some of the Oncidiums. I have used insecticidal soap up to today, which seemed to kill the bugs, but not stop the spread.
[My Dendrobium Victoria-Reginae is in the master-bath shower, and still has significant bug problems, even with repeated sprayings. The feathered covering on the canes hides the bugs, and the spray cannot contact them.]
On the recommendation of a friend, I decided to use Merit, which is an insecticide that is applied as a drench, and the plants take through the roots, producing an environment that is not conducive to insects. Merit contains the systemic insecticide Imidacloprid (75%), which is known to work well for mealybugs and scale. One uses a very small amount per application, and it should be applied only every six months or so.
It also fit my environment, where I could mix the 1/2-tsp-per-five-gallons-of-water solution in my mixing tank (mixed with 1 tsp of MSU fertilizer to help the uptake of the solution into the plant), and apply in my usual Monday watering. Even the orchids on a winter’s rest received this solution. I will water again on Thursday with clean water, and then continue my winter schedule of watering (Monday, Friday, Wednesday, Monday…)