Plagiotrichus frequens
GALL. — Similar to the galls of the other agamic forms of this genus. A stem swelling, up to 25. mm. in diameter and 110. mm. in length, usually smaller; internally rather woody, mostly solid, soft, spongy; the larval cells closely embedded, sometimes somewhat separable. On Quercus Gambelii, its varieties, or closely related oaks.
RANGE. — Colorado, Utah, Arizona, and probably New Mexico. Probably thruout the southern Rocky Mountains and adjacent regions wherever Q. Gambelii varieties occur.
The two known varieties occur in distinct faunal areas of the southern Rocky Mountains of Colorado. Inasmuch as that country involves so many other faunal areas, there are probably many other varieties of the species to be described. I have galls from Q. Gambelii varieties from several localities in Arizona and Utah that probably belong to this species. A, rugulosus Bassett and its varieties produce rather similar galls on evergreen white oaks of parts of the southwest, but those insects are generically distinct from frequens. As far as I know, frequens occurs only on the deciduous white oaks.
The species is most closely related to P. chrysolepidicola of the Pacific Coast, and it is not impossible that we shall consider these one. species after other, intermediate varieties become known. P. elongatus of Texas is the next most closely related species, but frequens does not resemble elongatus nearly as closely as it does some of the varieties of chrysolepidicola.
Gillette described this species as from Q. undulata. I have seen it only from the white oak with large, long, deciduous leaves; this would appear to be Q, Gambelii, or one of its varieties or closely related species, according to the more recent treatments of these difficult oaks.
[Kinsey describes two varieties of this gall; see paper for details]
