C. q. batatus Fitch.

Quercus alba.

I am satisfied that there are annually two generations of C. q. batatus. The first appears early in May, from galls of the preceding year's growth,--the last late in June, from green galls. I have often found perfect insects in the galls in winter, and have reared flies from them, apparently of the same species reared from the summer galls. Inquilinae in great numbers are produced from the winter galls and few true gall flies, while the reverse is true of the summer form. As many of the summer galls remain green after the flies have left them, and as the tree's annual growth is nearly or quite complete the first of July, it seems probable the June flies oviposit in the galls from which they were produced.

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

Reference: https://www.biodiversitylibrary.org/page/3745772#page/704/mode/1up