Plagiotrichus suttonii

GALL. — Rather large, solid stem swelling. Polythalamous, with a great many cells. The swelling elongate or globose to massive, distinct but only moderately abrupt, solid, covered with normal bark, a some- what distinct, smoother ring about the exit hole; internally very solid, entirely woody, the larval cell distinctly lined but closely embedded. On stems of all of the Pacific Coast black oaks.

RANGE. — California, Oregon. Probably also Washington and British Columbia, wherever black oaks occur.

The insects of this species emerge early in the spring, in February and March, earlier further south. The galls are hard and solid, and I have not found them eaten into by birds and mice as are the white oak species of Plagiotrichus.

The three varieties described here are confined to black oaks, each to a single species, all of the Pacific Coast black oaks being affected. Probably several varieties occur on each oak as it occurs in different faunal areas, but this has been proved only for the agrifolia varieties. This species is not so radically different from Plagiotrichus chrysolepidicola, but shows characters typical of the other black oak species of the genus. Its intermediate nature may be due to the close relations, probably dating from more remote geologic ages, of the black live oaks and the white live oaks of the Pacific Coast. I have included coxii and asymmetricus in this genus, even tho they are not closely related to some other species, mainly because suttonii nicely connects these more extreme species. The species is very closely related to Plagiotrichus perdens which occurs on two of the same oaks over much the same territory.

[Kinsey describes three varieties of this gall; see paper for details]

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

Reference: https://www.biodiversitylibrary.org/page/45387508#page/196/mode/1up