The beech blight aphid (Grylloprociphilus imbricator)
The beech blight aphid (Grylloprociphilus imbricator), aka the boogie-woogie aphid.
The white, fuzzy coating on beech blight aphids is a waxy secretion produced by specialized glands on their bodies. It isn't fungus, mold, or cotton. It acts as a form of physical defense from predators by making it harder for predators to reach or grip individual aphids.