Ruptured Twig Gall Wasp

Andricus perdens

Plagiotrichus perdens

Cynipidae

Callirhytis

Quercus agrifolia

California

Quercus kelloggii

Oregon

Quercus parvula (shrevei)

Quercus wislizeni

Cynipid Galls of the Pacific Slope

New Pacific Coast Cynipidae (Hymenoptera)

Callirhytis perdens (agamic)

Andricus perdens, new species

GALLS (P1. XXIV, FFigs. 5-7). Stem swellings, raggedly split open, containing flattened seed-like cells. The swellings are 6.-13. mm. indiameter by1.5-20. cm. long.Within are large cavities, 4 or 5 arranged more or less radially about the axis of the stem, and a great many in series along the stem, each cavity sector shape, extending to the bark, 10. mm. wide or less at the edge. Inserted on the wall of each cavity is a larval cell; each cell is monothalamous, flattened, a somewhat squared oval in outline,4. mm. high by 3. mm. wide, broadest at the top; concave at the base with a projecting tongue by means of which the cell is inserted in the twig; cells smooth, shining,buff-yellowish, finely streaked, more or less, with purplish brown. The cell walls are shell-like, moderately thick, entirely hollow within. At maturity the bark splits raggedly over each cavity, the larval cell drops to the ground, and the affected twigs die. On terminal twigs of Quercus Kelloggii.

RANGE.-Oregon: Ashland and Grants Pass. California: Gilroy (RedwoodSchool), Placerville and Ukiah.

This is a very common cynipid throughout the Pacific Coast region, its presence being made noticeable because the leading shoots and ultimately the whole tree may be killed. I have seen small stands of young black oaks, possibly fifteen years old, almost completely killed out in this way. It has, however, been difficult to obtain the wasp, apparently because the larval cells fall out of the twigs before maturity; possibly the insect completes development and emerges only after it has been on the ground for some time. From galls collected from January through April no adults were obtained, and only two individuals which had failed to quite complete development were cut out of the few larval cells remaining in the twigs. A very similar if not specifically identical gall is found on Quercus Wislizeni.

Plagiotrichus perdens

GALL. — Stem swelling, raggedly split open, containing flattened, seed-like cells. Polythalamous. Up to 13. mm. in diameter by 200. mm. long, averaging somewhat smaller. Within are large cavities, 4 or 5 arranged more or less radially about the axis of the stem, and a great many in series along the stem, each cavity sector shape, extending to the bark, 10. mm. or less in width at edge. Inserted on the wall of each cavity is a larval cell; each cell is monothalamous, flattened, a somewhat squared oval in outline, 4. mm. high by 3. mm. wide, broadest at the top; concave at the base with a projecting tongue by means of which it is inserted into the twig; cells smooth, shining, buff yellowish; finely streaked, more or less, with purplish brown. The cell walls are shell-like, moderately thick, entirely hollow within. At maturity the bark splits raggedly over each cavity, the larval cell drops to the ground, and the affected twigs die. On terminal twigs of Quercus Kelloggii, 

RANGE. — California and Oregon. Probably wherever Quercus Kelloggii and Q. Wislizenii occur. 

This species in several respects represents a considerable specialization for this genus. In no other species, as far as I know the genus, does the larval cell drop out of the gall be- fore the insect emerges. The species is directly related to Plagiotrichus suttonii, which occurs on Pacific Coast black oaks; the galls of the two are distinct. These galls are very common on Querctis Kelloggii and Q. Wislizenii, but I am not certain that they occur on the other black oak of the Pacific Coast, Q. agrifolia. A couple of galls I collected at Descanso, California, on February 23, 1920, are recorded from agrifolia, but I cannot be positive of this determination, especially since the two oaks intergrade regularly in their southern range. 

As I noted before, these galls kill the stems beyond the point of infestation, and thus kill the whole tree. Extensive stands of young black oaks are sometimes badly hurt. 

I do not know when the insect matures ; emergence occurs apparently after the larval cells drop to the ground. I found old galls, with no fresh galls evident, from January in southern California through April in Oregon. 

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

Studies of some new and described Cynipidae (Hymenoptera)

Callirhytis perdens

Quercus agrifolia, kelloggii, wislizeni 
Stem galls, woody stem swellings or cells under bark/cells burst out thru cracks in bark
Fig 66. Spindle-shaped. Polished laterally compressed cells burst out thru cracks in bark and drop in the fall.

Fig. 66. Q. agrifolia. Occurs also on Q. kelloggii and wislizeni. The smooth polished cells burst out thru cracks in the bark and drop in the fall. Cells cut out in the fall of 1949 and kept out-of-doors in a cage all winter gave adults Apr. 15, 1950 and Mar.28 and Apr. 14, 1951.

Calirhytis perdens
(Andricus perdens)

Hosts: Quercus agrifolia, kelloggii, wislizeni

While the gradually tapered galls are bark-colored, the linear black fissures that develop easily distinguish them from other stem galls. 

Plant Galls of the Western United States

Quercus parvula added tentatively as a host based on [this unconfirmed observation](https://www.inaturalist.org/observations/144791104). 