Andricus rhizoxenus (Ashmead)

Callirhytis rhizoxenus
Callirhytis rhizoxena

This species was described as Callirhytis rhizoxenus from a gall "on the roots of a live oak at Fort Grant, Arizona." The type gall in the United States National Museum is ellipsoidal, 36 by 22 by 25 mm., smooth on outside, very dark brown, hard and granular inside instead of woody but contains no normal cells or exit holes. The type flies have the tarsal claws with a tooth and run to Andricus. They agree with adults the writer has reared from a rougher brownish (not carbonaceous black) gall terminal on twigs of Quercus oblongifolia Torrey at Patagonia, Arizona. They were collected July 6, 1918, and contained pupae, the flics issuing by July 19. The types agree also with flies from a similar gall on Quercus toumeyi Sargent collected at same time and place and from which living adults were cut out August 21. Similar galls occur also on Quercus arizonica Sargent in this region, but no adults were reared. A smoother gall quite similar to the type of rhizoxenus in shape and size and color occurs on Quercus reticulata Humboldt, Bonpland, and Kunth (Plate 32, fig. 14) (seen in the Santa Catalina and Huachuca Mountains) but no adults were reared. As these always occur in the lower part of the clump of bushes, within 1 or 2 feet of the ground, terminal on the oak runner sprouts characteristic of this oak, it may well be that it was galls from this oak, occurring under debris perhaps, that were originally collected and described as root galls. The species should be considered as producing a stem gall, not an underground gall, and is treated in this paper merely to clear up the error in the literature.

Andricus rhizoxenus

Quercus reticulata [rugosa]
Stem galls
Stem swellings
Hard and granular inside. Fig 38.

Callirhytis rhizoxenus, new species.

A large, irregular, more or less globular, fleshy swelling, occurring on the roots of an oak in Arizona, and containing numerous larval cells; some galls measure about 4 cm. in length; others are much smaller.

Specimens reared June 24 and 28 and July 6, 1882, from galls received from Mr. H.K. Morrison, collected on roots of a live oak at Fort Grant, Arizona.

[Russo states that "given the repeated finding of this gall on Emory Oak in the Santa Catalina mountains on separate trips, I believe the netleaf host was misidentified or this is a new species." Since we have seen several galls matching Weld's description of A rhizoxenus on Q rugosa, we tentatively assume that Russo's gall is a new species pending further research]