I expect they are actually Scale Insect but in their breeding state, when
it
can look like woolly aphids although you can still see the old large
female
scale on top of the woolly stuff.

I've not found much that will treat Scale effectively so I treat mine by
using a hand sprayer full of water with a drip of washing up liquid in it,
and constantly keep it up to maximum pressure. I then go around the plant
slowly from the top to the bottom, around every leaf and stem, in effect
pressure washing off all scale. With a bad infection you may have to do it
again after a couple of weeks, and you will get wet doing it and it does
take time but it works (and no chemicals).

--
Regards
Bob

I have this problem on my citrus that is encouraged by ants - I periodically
do just what you have suggested but it comes back within 6 months or so.
Plants are much better when I move them outside for the summer.

Ann