Mealy plum aphids (Hyalopterus pruni) hatch in spring from eggs that overwinter on plum, gage and damson trees. They form colonies on the undersides of leaves, where they secrete a white, mealy wax with which they cover themselves. Leaves are not usually misshapen, but they do become covered in sticky honeydew, on which grey or black sooty mould tends to grow. Heavy infestations can stunt growth and spoil fruits. However, most of the aphids leave to colonize other plants such as reeds during June and July, only returning in the autumn.