Pachypsylla (Blastophysa) celtidis-gemma

This gall is briefly referred to but not named by Osten Sacken (1. c, pp. 422, 423.) It is much smaller than the preceding [Pachypsylla venusta], very variable in size, and of irregular shape, but always bud-like, and looking as if formed by the conglomeration of a number of rounded nodules which are separated from the adjoining ones by shallow furrows. Color varying from light reddish-brown to dark brown or the color of the twig; surface of the young gall usually covered with a dense matting of white woolly hairs, which in the more mature gall are more or less completely lost. As in the preceding species, the gall is hard and woody, but entirely closed. It is usually opaque, rarely a little shining, the surface indistinctly sculptured, but occasionally roughened by adhering particles of the scales of the original bud. It has no inner core, and the cavity is entirely filled with the cells, which vary from one to eight in number. The outer wall is never more than one millimeter thick, often less, while the walls dividing the cells are sometimes very thin and sometimes even thicker than the outer wall. The gall occurs only on one-year-old twigs, and is formed by the young larva? settling on and sinking into such buds as would normally produce a new twig the ensuing year. Each mature pupa saws its way through the wall of the gall in spring and changes to imago immediately after issuing.

- CV Riley: (1890) Insects injurious to the hackberry^©

Reference: https://www.biodiversitylibrary.org/item/42358#page/632/mode/1up