Page:Life histories of American Cynipidæ.pdf/17

 [Redescribed from New England specimens compared with Bassett's morphotypes.]

.—Moderate-sized swellings (Figs. 8 and 9) of young stems and petioles, essentially the same as the galls of the agamic generation (q. v.), but differing in being often much smaller, often having tufts of short, woolly pubescence. On stems, petioles, or midveins of Quercus alba.

—Bassett's morphotype females, males, and galls in the collections of The American Museum of Natural History, of the Academy of Natural Sciences of Philadelphia, and of the Museum of Comparative Zoology.

In 1864 Bassett reported that he had observed for a number of years the alternation of two crops of galls on a small tree near his house. The abundance of each crop in turn suggested the relationships of the two. Moreover, the insects proved indistinguishable except through a slight difference in size and in the then unexpected condition of having only females in the winter galls, with both males and females in about equal numbers from the spring galls. Neither Bassett nor later workers have actually seen the oviposition of the species, nor obtained under controlled conditions the gall of one generation from an egg deposited by a female of the previous generation, but Bassett's field experience is regularly confirmed by later collectors of gall-wasps. I have examined material from the Bassett collection which shows this, also photographs of material collected by Miss Cora Clarke, and a quantity of material collected and bred by Millett T. Thompson. This latter material shows the two generations often close together on successive parts of the same branch. The descriptions here given are made from a study of many specimens which I have compared with the Bassett types. No previous separation has been made of descriptions of the two forms of adults, and the gall of the bisexual generation has never been described in detail, nor have Latin names been applied to distinguish the forms.

The galls of the bisexual generations appear about the middle of May and the adults emerge, in about equal numbers of the sexes, by the middle of June. These oviposit in the new wood of the stem on which the better-known gall of the agamic generation develops.

Neuroterus batatus form batatus (Fitch) Plate XXIX, Figures 10 to 13

—Almost identical with the female of the bisexual generation, but with the thorax usually less wrinkled and, in consequence, the anterior parallel lines more evident. The insect averages slightly larger than the female of the other generation, the abdomen being somewhat less angulate in outline. 1.7-2.2 mm.

Large, woody, stem swellings (Figs. 10 to 12). Polythalamous. Averaging 40×10 mm., often larger; tuber-like, irregular, but usually roughly cylindrical, elongate, involving stems and bases of petioles on terminal twigs; inseparable