I agree Meyermike. No matter how well you care for your plants, infestations will occur. They may be more likely on sick plants but healthy ones also get hit. The same species seem to attract them in my collection eg Ferocactus robustus, Sulcorebutia arenacea, Astrophytum myriostigma to name a few.
I use a systemic insecticide called Suscon G which are granules mixed in with my potting mixture when repotting. I have not had a case of root mealies for over 10 years, even when the plant has not been repotted for many years. Mealies on the plant body are another matter and are dealt with as needed with a contact insecticide. With a large collection, it is impractical to seek them out and manually deal to them eg by squashing them or paint brush dipped in alcohol.
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Suscon G
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