Cynips dimorphus, sp. nov.

Gall.— In masses on the basal part of the midrib or petiole on the underside of leaves of burr oak (Quercus macrocarpa), dwarf chestnut oak (Q . prinoides), white oak (Q. alba) and other trees belonging to the white oak group. They occur in rounded masses from a few to about thirty in each cluster. They are closely packed together, but each gall is separate and easily detachable. They are fastened to the leaf by a point, rounded on top and but slightly pressed out of shape, except basally. Monothalamous, almost globular, pointed basally, with the surface roughened, greenish, and more or less tinged with pink when fresh. Grayish when old and very hard. Hollow inside with a single round larval chamber. The individual gall measures from 2.50-3 mm. in diameter. The masses are from 6-15 mm. long and almost as wide.

Habitat. — Evanston, Illinois, collected by Lewis H. Weld. The galls occur from the latter part of August until late in October, or into November, when they become mature and detached from the leaf. The flies emerge during the spring the following year. I have found the galls of this species on Quercus alba and Q. prinoides on Long Island, New York, and in New Jersey, but never succeeded in obtaining the flies. The four females described above were cut from galls by Mr. Lewis H. Weld, May 11, 1911. Mr. Weld's galls were taken on Quercus macrocarpa late in August the preceding year. The name for this species was proposed by the late Dr. W. H. Ashmead for specimens in his collection, but which he never described. Prof. C. P. Gillette recorded C. dimorphus from Michigan taken on the leaves of Quercus prinus, Q. macrocarpa and O. bicolor (Rep. Mich. Bd. Agricul., 1888, p. 469). Ashmead's specimens were collected in Florida.

- William Beutenmuller: (1913) Descriptions of New Cynipidae (1913)^©

Reference: https://www.biodiversitylibrary.org/item/27823#page/321/mode/1up