Beech (Fagus)-Aphid

Several species

See:

For more information

Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 296).

PNW Nursery IPM: Woolly beech aphid (https://agsci.oregonstate.edu/nurspest/aphids/woolly-beech-aphid)