Psocidae nymph, possibly T. majus
Tiny nymph of a Barklouse (Psocoptera) in the family Psocidae. The nymphs of some species secrete a "glue" that makes all sorts of particles of algae and dirt stick to their body for camouflage. One such species would be Trichadenotecnum majus that I found on the same tree (the only adult Psocidae on the tree and I searched the whole stem thoroughly). So chances are pretty good that the nymph belongs to this species :o)
Trichadenotecnum majus is a species of Barklouse in the family Psocidae. It is widespread but not recorded very often.