Adult and nymphs
Andrea Battisti, Universita di Padova,

One of the great things about beech, Fagus spp., is that the tree is less susceptible to insect and mite pests than many other specimen trees. However, there is one insect, the woolly beech aphid, Phyllaphis fagi, that may be a problem when populations are excessive. This aphid has only a single host: beech.

Growers report seeing them on several cultivated varieties including Fagus sylvatica ‘Asplenifolia,’ ‘Fastigiata,’ ‘Roseo-Marginata’ and ‘Purpurea Pendula.’ The sap-sucking insects coat the upper leaf surface with honeydew, making the foliage sticky and opening the door for black, sooty mold to develop.