Soil mealies are little white bugs that crawl around in the soil, attach themselves to roots and suck plant sap. They excrete a sweet substance that ants feed on. Therefore ants will protect them, cultivate them. Ants will also move soil mealies from one pot to another in order to open up new mealybug pasture land, and create more food for themselves. Soil mealies are extraordinarily tenacious pests. They are covered with a protective woolly layer that makes them completely impermeable to pesticides. You think you've got rid of them, but sooner or later, if you aren't vigilant, the re-colonise your garden.
If the plant is easily propagated, I throw plant and soil all away and start anew.
If the plant is not so easily propagated, here is what I do. I mix up 15 litres of water with 40ml of rotenone concentrate and 40ml of dishwash. I make sure the mixture is 40 deg Celsius i.e., the temperature of a nice hot bath. I then immerse the whole pot of soil into the hot water solution for 15 minutes. The dishwash dissolves the protective covering on the mealybugs' bodies, and allows the rotenone to penetrate and kill the insect. The hot water makes them squirm about and this movement damages even more of the protective layer.
The results were good. No more live mealybugs in my pots. More spectacular were the ants' reactions. As the water seeped into the soil from the holes at the bottom of the pot, the ants milled out of the soil depths and ran around the surface of the soil. As the hot water solution caught up with them, they all perished.
I now feel very satisfied. I shall have to repeat this 4 days later to catch the newly hatched eggs.