Weldia washingtonensis, new combination
Cynips washingtonensis
Disholcaspis washingtonensis
Gall: Monothalamous stem galls occurring singly on young stems; some mature galls spherical others oblate; surface of mature galls smooth, pebbled or somewhat wrinkled due to shrivelling; growing galls green or reddish with a long whitish pile which weathers away at maturity, mature galls medium brown, turning black with age; epidermis thin, brittle; parenchyma light brown, with large, parallel, columnar cells radiating away from larval capsule; larval capsule positioned in center of gall, oval, large, thick-walled, nutritive and protective layers usually distinct; weakly attached to stem by a small, circular projection allowing some galls to drop to the ground in severe weather. Horizontal diameter of 50 mature galls, 9.7 mm.
Galls of W washingtonensis, in their various forms, are occasionally difficult to separate from those of W californica and W plumbella (when the apical projection is absent) in outward appearance. However, in galls of W washingtonensis, the larval capsule is, without exception, centrally located (subcentral in W californica), large relative to gall size and oval (smaller and spherical in W plumbella). Growing and newly mature galls are covered with a long, whitish pile which turns rust-colored with age, a characteristic unique in the genus Weldia.
Galls are highly variable in size, shape, and epidermal sculpture which appears, at least in part, to be host related. For example, galls growing on Q garryana, near the summit of Liebre Mountain in northern Los Angeles Co., are small (5-8 mm in diameter), spherical and studded over the surface with numerous, blunt-tipped projections. At the same location, only 20-30 geet away, galls on Q dumosa are subspherical with an entirely smooth surface and average 3 mm larger in horizontal diameter. Adults from galls on the different hosts are not separable. If two species are represented by the different gall forms, I am unable to distinguish them using established taxonomic characters based on the few specimens at hand. All gall forms of W washingtonensis are similar internally and during the growing stage.
Hosts: Quercus douglasii, dumosa, durata, garryana, and lobata. Quercus lobata records are questionable. I have not found galls of W washingtonensis to occur on any of the hundreds of "valley oak" inspected over the years since I first became interested in cynipid galls. But, on several occasions I have observed these galls on Q lobata X douglasii, many trees of which could easily have been casually taken for Q lobata.
Range: Weldia washingtonensis is the most widely distributed species in the genus. Known to occur from southern San Diego Co CA, more or less continuously, to Benton Co in northern WA, west of the Sierra Nevada and Cascade Mountains of the Pacific Slope.
[From key to galls, page 176 of the pdf]
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Subglobular stem and leaf petiole galls without apical projection or strong surface tubercles; surface may be smooth or bumpy
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Stem galls on white oaks of the Pacific Slope from northern Baja California to points north; larval capsule spherical or oval, positioned centrally or basally in parenchymal tissue; under 14 mm in diameter.
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Compressed oval in outline; larval capsule large relative to gall size, oval, centrally positioned in parenchymal tissue; surface smooth (wrinkled or pebbled on Q garryana), with long whitish pile while growing; common on most white oaks from Baja California to Canada
