Pests and diseases - Mealy Bugs

Signs - small fluffy white lumps about 5mm (1/4") appear on plants, often in the axil - where the leaf meets the stem. Leaves turn yellow and may wilt and die.  There are a large number of different types which are frequently specific to the host. Usually affect house and greenhouse plants, but also Pyracantha and fruit trees. Stick honeydew and black sooty moulds may accompany. Despite being insects, they don't look like insects, just a shapeless piece of cotton wool.

Damage - plants are rarely killed unless very heavily infested over a long period. Commonly weakened, a heavy infestation is very unsightly from the pests themselves and from the sticky honeydew that they secrete and possibly even black moulds that grow on the sticky honeydew. Root mealy bugs damage the roots.

Treatment - difficult to attack from the outside, any of those organic soapy sprays just fall off from the hydrophobic (water repellant) hairs that cover the insects. Powder form insecticides sit on the hairs and again don't get the insect inside. In small numbers they can be picked off manually before they build up a larger population, otherwise it's biological control (the predators are hungry critters so you need a heavy infestation) or a systemic insecticide that is taken up by the plant and passed along in the sap right to the mealy bug.