Callirhytis quercussuttoni (sexgen)

Callirhytis quercussuttoni (agamic)

Callirhytis quercussuttoni (Bassett)

Description of the Gall (figs. 1C, D, E, F). The adults of the bisexual generation develop in small, monothalamous, blisters that appear mostly on the leaves or leaf petioles. They are 3-4 mm in length and the young galls are the same color as the leaves; thus in the early stages of development they are very difficult to detect. At maturity they are larger and easier to locate since the thickened cell can be contrasted with the thin leaf blade. Exit is made either through the upper or lower surface of the leaf. A few galls develop in the stems or buds of the staminate flowers. This leaf blister had been known to others although its maker had never been reared. Photographs of it appear in Weld's "Cynipid Galls of the Pacific Slope," figures 125 and 129. It is quite similar to the gall produced by the bisexual generation of Callirhytis quercusagrifoliae (Bassett) however, the latter develop earlier in the year, are reddish-green during development and tan at maturity. 

Host: Quercus agrifolia Nee. 

Habitat: The types were reared from galls produced on oaks in containers at La Canada, California. Additional specimens were reared from galls collected on the native oaks in the Los Angeles area. 

In February and March of the past two years, mature, agamic females emerged from rearing cages and were placed on young Quercus agrifolia growing in large containers. The insects were allowed to move freely on the trees and were not confined to the cloth bags that have frequently been used in this work. Some of the insects flew off the plants but a number immediately began to oviposit in the tightly packed, unopened leaf buds. Most females remained on the buds for periods of 20-25 minutes, moving from bud to bud and remaining on the tree for most of the day. All sites of oviposition were carefully marked. 

When the new leaves opened in early March, there were no signs of gall growth and another month passed before it became evident that tiny, green blister galls were developing in the leaf veins and on the leaf petioles. On the mature oaks in the field, these blister galls could also be located on the stems of the staminate flowers. The galls were completely mature in May and the males and females of the bisexual generation emerged from May 7 to May 26. Mating took place immediately and the females began to explore the trees in search of appropriate twigs for oviposition. They invariably selected small twigs, 3-5 mm in diameter, preferably green twigs of the previous year's growth; however, some females laid their eggs in the older growth. The ovipositing females remained all day in one location, moving spirally around the twig as they deposited their eggs. 

Nearly all twigs, both new and older ones, subsequently developed galls. Shortly after the bisexual generation has oviposited into the twigs, the inquiline Euceroptres maritimus Weld emerges from the old twig galls and places its eggs in the stems at the same places. This inquiline develops in the gall along with the gall maker and may be a predator feeding on its host, rather than a "guest." When the new galls appear in the fall, they are parasitized by the chalcid Eudecatoma isis, and the adults of this parasite can often be observed as they deposit their eggs in the thickened tissue of the developing galls.

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. 

ALTERNATE GENERATION OF CALLIRHYTIS QUERCUSSUTTONII (BASSETT)-(HYMENOPTERA-CYNIPOIDEA)