Answer: Without seeing the pests I'm only offering an educated guess - I think they are either mealy bugs or cottony scale insects. Scale insects have hard shells; mealybugs are soft and you can squish them. Either pest can be eliminated if you dab them individually with a cotton swab dipped in rubbing alcohol. You can also suffocate them with horticultural oil but the residue will remain on the cactus and change its appearance. I'd vote for dabbing them with Q-Tips dipped in rubbing alcohol. Best wishes with your cacti.
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