Callirhytis quercussuttonii (Bassett)

The cynipid wasp, Callirhytis quercussuttonii (Bassett) produces one of the most conspicuous of the large twig swellings that occur on the black oaks of the Pacific Slope region. Its galls appear as abrupt, woody twig enlargements on the oaks, Quercus agrifolia Nee, Q. wislizenii A. DC, and Q. Kellogii Newb. The galls vary considerably in size and shape, some appearing as stem enlargements, 25-100 mm long, with diameters of 15-40 mm. Others are shorter and more globular attaining diameters of as much as 60 mm (figs. 1 A, B). The gall is polythalamous and its size is determined by the number of tubular, larval cells that extend from the center to the outer bark. Development begins in late summer and continues throughout the fall with the galls growing rapidly until they reach full size during the spring months of the following year. Larval growth is completed in late spring and early summer with pupation occurring in late summer and early fall. Mature adults can be cut out in November and December; however, normal emergence takes place in late January, February and early March of the second year.

The species was originally described by H. F. Bassett (1881:54). Callirhytis polythyra Kieffer is a synonym (Weld, 1951:652). Kinsey (1922:137) described a variety lustrior that occurred on Quercus wislizenii. At the present time, the species is known from descriptions of the agamic or unisexual females only. No males have been described.

The galls of this species are sometimes quite destructive to the host oaks, particularly Quercus agrifolia, when growth is very heavy on single, isolated trees. When species of oaks occur as part of a natural woodland and the individual trees are not widely separated, the gall-producing cynipids usually distribute themselves rather evenly through the area without heavy infestation of the individual trees. When individual trees or small groups of trees become isolated, gall infestation frequently becomes very heavy since the wasps are not as inclined to fly to other trees. For this reason, single ornamental oaks, growing in parks or estates are sometimes damaged by the galls of Callirhytis qucrcussuttonii. The chalcid wasp Eudecatoma isis (Girault) is the most common parasite and is usually reared from mature galls along with the gall maker. Woodpeckers frequently open the galls along with those of other species, in order to reach the developing insects. Chalcids, under natural conditions, seem to be the most important control factor.

Callirhytis suttoni (Ashm.).

Quercus agrifolia
Stem galls, woody stem swellings or cells under bark
Fig 58. Abrupt, large, cells at base of tubes.

Fig 58. Q: agrifolia. The brown bark is thin and cells are in the thickened bast which cuts like cheese in April. The larval cells are at the base of thin-walled tubes. Contained dark pupae and adults on Nov. 27 (Berkeley). The guest fly Euceroptres maritimus Weld emerged May 15 and June 8 - 17.

Callirhytis quercussuttoni

These unisexual-generation monothalamous galls begin their development in summer and continue to grow until the following spring.

Hosts:
Coast live oak (Quercus agrifolia)
Interior live oak (Quercus wislizeni)

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]