SUMMARYDysaphis devectacauses the leaves of its host plant to roll laterally whereasD. plantagineacauses them to roll longitudinally. Both species of aphid are phloem feeders.D. devectaprefers to feed on the smaller veins in the lamina whereasD.plantagineachooses the midrib. However, groups ofD. devectaorD. plantagineaconfined to the stem of an apple seedling induced young leaves several centimetres away to develop leaf rolls characteristic of each species. A single larva ofD. devectaorD. plantagineacan induce a leaf‐roll or a stem‐bend on an apple seedling within 24 h. It is suggested that characteristic abnormalities in leaves attacked byD. devectaandD. plantagineaare caused by specific substances in the saliva of each ap