Mealybugs mainly attack only plants grown indoors or in the greenhouse. They are particularly troublesome on Cactus plants - Cacti - and also with some of the Orchids. However, they can also be a pest outdoors.
Mealybugs are members of the Aphid family, and as such obtain their food by sucking the sap out of plants.
The actual bug is a pinkish grey/green in colour, but you are more likely to find it by seeing it with its white furry coat on! This coat is made of waxy hairs, and grouped together as they often are, mealy bugs can look like small tufts of cotton wool. The mealy bug is up to 6mm long.
Mainly found on the underside of leaves - but also on top of the leaf - Mealybugs also enjoy the comfort of the snug little corners that they find for themselves in the leaf axils. (The point where the leaf joins the main stem.)
They can be spread from plant to plant by ants! The ants are attracted by the sweet honeydew that the mealybugs excrete. This honeydew also attracts sooty moulds - a fungal disease with a black sooty appearance on the surface of leaves.
Mealybugs are quite difficult to control with chemical sprays - though not impossible - for their waxy coat protects them from the 'contact' effects of many pesticides. The answer is to use a systemic insecticide, that is taken into the plant's sap, which in turn finds its way into the mealybug's digestion system! They can also be controlled by dipping an old toothbrush or similar, into neat insecticide and brushing it on the affected plants. Malathion is one of the best for this job, though be aware that it smells a little (lot) like rotten eggs!
There are also 'Root' mealybugs, which are happy to live down in the soil of your potted plant - happily munching away on the roots of your plant. A good way to sort these out. is by immersing the whole pot into a container of correct strength Malathion insecticide for half hour or so.
Be AWARE, that some plants do not like Malathion - Cucumber family and Fuchsias are amongst them.