Page:The Gall Wasp Genus Cynips.pdf/68

Author	Species assigned to present genus	Accepted in present revision
Mayr 1870-1905	17	88 per cent
Dalla Torre 1893	42	48 per cent
D. T. and K. 1902	50	46 per cent
D. T. and K. 1910	68	41 per cent
Beutenmüller 1911	43	32.5 per cent
Weld 1922-26	46	37 per cent

Our present delimitation of Cynips is based upon no single character—indeed, we know of no character by which the group may be separated from other groups of oak-inhabiting Cynipidae—but upon a striking, even if not invariable, correlation of insect structures, gall characters, host relationships, life histories, and distributional data that are coordinated for the 93 species which we now bring together.

In nearly every one of the species the agamic form has the thorax hairy, altho there are few hairs on the very small, nearly wingless insects which are the most northern varieties of many of the European and American species in Cynips. In every species without exception the hypopygial spine is broadest posteriorly, and the structure terminates in a well-developed tuft of hairs. A similar spine is found, however, in one or two related genera. In 90 of the species the tarsal claw is rather strongly toothed, but in 3 species of a single stock (Cynips mellea) the claw is so weakly toothed that it is nearly simple. In nearly all of the species the agamic gall is fundamentally spherical and monothalamous, rarely with any remarkable development of the epidermal layer of tissues; but in 8 species of one stock (Cynips pezomachoides) the gall is usually polythalamous. In every one of the 93 species the gall originates from leaf veins, usually on the under surface of the leaf, but in two species (C. multipunctata group) the gall may occur on the leaf petioles and young stems as well as on the leaf. In every one of the 11 species for which the alternating generations are known, the bisexual gall is a thin-walled, seed-like or bladdery, hollow cell located within the newly opened buds of the oaks. All of the 93 species occur on white oaks (Leucobalanus). In nearly every case the agamic generation begins development in early summer, matures by early fall, lies as an adult within the gall for several weeks or months, and finally emerges in the winter. Only the 7 species of the fulvicollis stock modify this procedure by delaying part of the emergence until a second or later winter. Some of the species of the mellea stock also depart from the typical life history by emerging in the early spring instead of the winter season. In distribution the insects show their affinities by occurring in adjacent areas,