Well, I've now found mealies on some of my plants... annoyingly, I've even found some evidence of mealy infestation on some plants that I bought yesterday from a certain well-known specialty nursery out Keysborough way.

Oh well, out comes the Rogor I guess.

Try to alternate between the systemic chemicals (eg. Confidor and Rogor) to avoid resistance build-up to one or the other in the mealies.

Wettasoil is great stuff. I used it with excellent results for root mealy recently. two advantages are; it is non-toxic and it kills on contact (or rather destroys the mealies white waxy coating) so they cannot gain resistance to it like an insecticide.

an easy non toxic weapon a is spirit-soap solutiond it works pretty well I have used it for root mealy too, not sure if it's very good for root infestations. Spirit destroys the coating you mention as well. Which is great, because you can to do it at any time, easier, no washing hands and toxicity worries no need to do it manually [except from big infestation in a small spot, then you remove with the hand of course] killing one by one, as we all do from time to time

IME, spraying chemicals for mites [we had a bad year] might be very the only way to go, but not so with mealies, but I am only 2,5 years in cacti, so what do I know?

I actually have found mealy it's pup-inducing qualities very interesting especially, say, for my penis plant. I actually left in on for a while, while the penis plant pupped irregularly...

I have been trialing dipping pots infected with root mealy's into tobacco tea with a little wetting agent for good measure. 100 g to 5L with a capfull of wetting agent. so far its working really well, the big test will be my 250L tubs with my columnar's, i can feel my back aching at the thought of it.

Nicotiana rustica is the ultimate tobacco to use for pest control. Very potent in nicotine.

my experience has been with this plant, and it even works for mites IME