Don't mess around, go straight for the Confidor and be sure to follow up spray and drench. If you have quite a few infected plants the 5 pack of powder is good value, otherwise the green spray-bottle will suffice.

Left to themselves they can destroy a cactus collection if the plants are close together. They suck the plants until they rot and die. Even normal mealy bugs can get under a cactus and into the roots unseen and suck a plant to death. I've found if a cactus doesn't seem to be growing as well as it should, mealy bugs are often to blame.

Ants are the culprits for spreading them - they farm them for the excretion the mealy bugs leave behind. If I see ants anywhere near my pots these days, I put ant-powder down straight away. Also watch out for newly purchased plants that may be infected.

Goodluck!