Woolly aphids can be a problem if they get into your conservatory, infecting a wide range of plants. Not usually a problem outdoors. Look out for the cotton-wool-like tufts in the angles of stems and leaf-stalks.
Insecticides will help, or there is a biological control, a parasitic wasp which can be released in spring. Remember that you can't use both, as the insecticide kills the wasps as well.