Cynips quercus tuber [contains the first description of the anatomy of the true inducer]

Nine specimens.

I have a single male gall fly reared from the same galls, but it differs so much from the female that I am inclined to think it belongs to a different species.

Though the galls are very much alike, the venation of the wings, the pleurae, and several other points of difference mark it as a distinct species from C q. similis. Dr. Fitch has figured the gall of his C. q. tuber which he found "quite common particularly upon the soft and tender limbs of young (white oak) trees" (N. Y. Rep., Vol. 2d, No. 309). He describes (1. c. No. 310) the galls of C. q. arbos as "swellings similar to that above described, growing on the tips of the limbs of aged and large white oak trees."

My galls, which are probably identical with his C. q. tuber, were gathered from low, shrubby white oak bushes, though I have often Been precisely similar ones on large trees. Dr. Fitch's descriptions of the flies from C. q. tuber or C. q. arbos will apply, so far as they go, to either the gall flies, or to the guest flies as the inquilinae are termed by Mr. Walsh. For the reasons that follow, I am led to think that the species he described under the above names are both inquilinious species.

1st. My galls were gathered about the 20th of June, and were then green and soft like the wood of the young shoots on which they grew. The insects were then in the pupa state, and the imago came out early in July. The gall from which Dr. Fitch's C. q. arbos was reared was found in March, and were of the preceding year's growth, as were also those of C. q. tuber, if we may judge from his description of the color of the gall, which will only apply to the galls long after the true gall- flies have left them.

2nd. My galls gathered from young white oaks, and which answer perfectly to his figure and description of C. q. tuber, produced females with 13-jointed antenna?, while his have but 12 antennal joints.

3rd. I have gathered several hundreds of these galls in the autumn, winter and early spring within the last two or three years, but have never reared from them one true gall-fly, though they have produced large numbers of male and female guest-flies — the male answering perfectly to Dr. Fitch's description of C. q. arbos. The female he had not seen.

4th. The galls I collected in June have not yet produced any guest- flies, but cutting open several to-day I found in one a large living larva — the others were empty or contained dead gall-flies that had not been able to eat their way out of the dried gall. From the above facts I am forced to believe that the galls C. q. tuber and arbos Fitch are both produced by the same fly, and that it is the same species that I have described above and for which I retain Dr. Fitch's name, C. q. tuber. Dr. Fitch has, no doubt, described two distinct flies, for Mr. Walsh, who has devoted much attention to the guest-flies of the oak galls, finds that not only do some species live in several different species of galls, but that the same kind of gall may produce more than one species of guest-fly. (Proc. Ent. Soc. Philad. Vol. 2d, p. 465.)

Mr. Walsh, in the article referred to, mentions other of Dr. Fitch's , species which he is satisfied are inquilinae, and not the producers of the galls from which they were reared. (See pp. 464-5, 484 and 494.) His remark that "C. q. tuber Fitch is in all probability a guest-fly," escaped my notice till this moment.

- HF Bassett: (1864) Descriptions of several new species of Cynips and a new species of Diastrophus^©

Reference: https://www.biodiversitylibrary.org/item/23810#page/705/mode/1up