Callirhytis glandulus (agamic)

Cynips Gall Quercus-glandulus

The new gall is more or less completely imbedded in the cup, and, on account of its resemblance to a diminutive acorn, I name it glandulus. 

I have seen it on Q. prinoides and Q. bicolor.* The parent Cynips lays the egg very early in summer, as the gall is often formed on the aborted or blighted acorns, in which case, however, it seldom attains perfection. The ripe and well developed gall falls out of its cavity on to the ground, where the larva remains within it till the following spring. Those galls which remain within the cavity are generally imperfect. The fly producing this gall has not yet been reared nr described.

Cynips Gall Quercus-glandulus: — An elongate, pip-like body, averaging, when well developed, 5 mm. long, and not quite half as wide; sides sometimes parallel, but more often slightly bulging, more or less deeply corrugate longitudinally, and whitish-green; base truncate and covered with whitish down ; crown flattened or slightly concave, with a central, conical nipple; color yellowish, often with a roseate tint. Larva lying in a cell near the crown. Formed in a cavity, and causing more or less bulging and swelling of the cupule. The mouth of the cavity either strongly fimbriated, or simple, according to the nature of the cup scales, and thus either hiding the gall or exposing a large part of it. This gall is allied in structure to that described by Mr. Bassett as Quercus frondosa, which is a deformation of an oak bud. The axillary bud is made by the sting of the Cynips to prematurely develop a number of lanceolate or ovate leaves which surround one or more cells, which loosen from their leafy matrix when ripe and drop to the ground. An analogous deformation of an oak bud, caused by Cynips fecundatrix Hartig, is very common in Europe, and is known in England as the Artichoke-gall. The cell of this gall has been described as an aborted acorn by Mr. Albert Muller,f who has made a special study of galls. It is not surprising, therefore, that our glandulus gall should very generally be looked upon as a diminutive or secondary acorn. Yet such views are quite erroneus. The cells of very many other Cynipidous galls resemble acorns in form, and the resemblances to different fruits among these singular plant- and-insect productions is often so striking as to easily mislead. 

* Dr. Engelmann has noticed it on Q Prinus [montana], Q. michauxii, and Q. muhlenbergii. It thus occurs on every form of the Prinus Group, to which it is apparently confined. 

A new oak-gall on acorn cups