Is this scale?

[quiltergal]

As long as it's the one formulated for roses it won't hurt orchids. Obviously you will not want to spray the flowers. Several people here use it. It's active ingredient is imaclopitrid. I think bugs develop resistance to any insecticide. That's why it's important to use different ones.

I have also ordered some Sucrashield from Ray. We'll see how that works.