The ones that I have came to me resistant and it has been a lovely time ever since. They really go for my banana, citrus, figs and coffee trees...and the two Phals. I never saw these until I began to collect orchids.
I began using the immersion technique on cacti bought in California. Mealies are famous for living on the roots of cacti, crawling above to lay eggs in cases on spines. I suspect there are no effective insecticides used in nurseries in California, and almost every cactus or succulent I buy there arrives with mealy bugs.
I treat all of those newly arrived cacti with a dunk as soon as weather permits. It really does kill all the bugs and all the eggs.
I don't see scale nor mealy bugs on many orchids. When I do I dunk the plant. I have rarely had to dunk a second time. Most of the time the first dunk takes care of the problem.
__________________ May the bridges I've burned light my way.