Plagiotrichus coxii

GALL. — A globose to elongate, solid twig gall. Polythalamous, averaging twenty or more cells to a gall. Smooth, covered with nearly normal bark, somewhat reddened; up to 20. mm. in diameter and 65. mm. in length. Internally rather solid but not entirely so, the larval cells with a distinct lining-, closely embedded in the less solid part of the tissue. On black oaks.

RANGE, — Arizona. Possibly also in New Mexico, western Texas, and Mexico, wherever Q. Emoryi, Q. hypoleuca, and related oaks occur.

The insect of this species is in several respects, particu- larly the almost naked mesonotum and the 14-segmented, short antennse, extreme for this genus. But species like P. suttonii and P. perdens of California are intermediate between coxii and the white oak species of the genus. This empha- sizes the artificial nature of our sharp generic lines. I doubt whether I should consider the species in this genus except for the additional evidence furnished by the gall. It is typically a Plcigiotrichus gall, related more closely to the other black oak species, as is the insect also, than to any other white oak species.

The insects emerge in midwinter, December and January. The young galls appear immediately, which suggests that they arise from an alternate generation, the whole life cycle taking more than one year.

I have galls from New Mexico which may belong to this species, but rather extensive collecting in both western Texas and New Mexico failed to give me other galls of this species. If the species occurs in those states, it certainly does not there reach the abundance with which it infests the black oaks of southern Arizona.

[Kinsey describes a distinct variety on each of this gall's two hosts; see paper for details]

- Alfred Charles Kinsey: (1922) Studies of some new and described Cynipidae (Hymenoptera)^©

Reference: https://www.biodiversitylibrary.org/page/45387508#page/184/mode/1up