Andricus pomiformis
Hosts: Quercus agrifolia, wislizenii
GALL. — Spherical, smooth, compact, in section suggesting an apple with seeds about the core. Polythalamous, often with fifty or more larval cells. More or less perfectly spherical, rarely flattened, or elongate ovate; of all sizes up to 55. mm., averaging nearer 40. mm. in diameter; the surface sometimes entirely smooth, usually finely, irregularly pitted and cracked, sometimes set with low, raised lines or irregular rows of low tubercles radiating more or less from the slightly pointed tip of the gall ; brilliant, rich apple red when fresh, with some apple green and lighter green, becoming bright brownish yellow on aging, weathering darker. Internally like compacted sawdust, crystalline, spongy only in old and weathered specimens; with a hard, woody core originating from the point of attachment, the core flaring and somewhat branching in the center of the gall, with the larval cells arranged radiantly in the extremities of this core, mostly in a single layer centrally of the gall; each cell averaging 2. x 4. mm., with a distinct and easily separable, thin-walled lining. Laterally, less often terminally, attached by a small point, sessile on twigs of Quercus agrifolia and Q. Wislizenii.
RANGE. — California: from the Mexican border to Dunsmuir and Ukiah.
This is one of the most prominent of Californian galls, being surpassed in size and abundance only by Andricus californicus. Both species are known as oakapples. As with californicus, the possibility of more than one variety, each with its own intensely interesting biologic problems, has been heretofore entirely overlooked. The biologist who will learn what these two species should easily disclose in ten years or less work on the held, may contribute as important data as we yet possess on such problems as the nature of alternation of generations, distribution factors, and host effects, for instance.
Adults mature in early spring, earlier at southern localities. The field data indicate that northern varieties (see variety pomiformis) complete the life cycle in a year, with the possibility of an alternation of generations; while southern varieties (see maculipennis) take two years or more to mature, and may not have an alternate generation. This must be considered a suggestion, to be verified only by experimental work. If this is shown to be the true condition, it confirms my previously expressed opinion (1920, Bull. Amer. Mus. Nat. Hist., XLII, p. 372) that alternation of generations is an extreme development of seasonal dimorphism.
If galls are collected too soon before maturity, the larvae will develop into adults altho few insects will emerge. One finds this the case with galls in the laboratory more often than with galls in the open. Under adverse conditions in the field, such as a season of drought, there may be a similar destruction of adults before emergence. An experience with this species in the laboratory alone, in connection with some other similar cases, misled me into an over-statement in a previous paper (1920, Bull. Amer. Mus. Nat. Hist., XLII, p. 383) as to the lack of vitality of Cynipidae in general.
Some of the most illuminating data I yet have on the effectiveness of the host in isolating varieties is that presented under variety distinctus.
Some of the varieties of this species show a median depression of the scutellum much as in the genus Amphiholips. Other varieties do not show this. An evolution of a generic character has occurred within this single species.
Callirhytis rossi Kieffer (1903, Marcellia, II, p. 84, figs. 1, 2) is probably the same as one of the varieties described for this species in this paper. The publication was made without a more definite locality than "California", and with- out a host determination, but with a host description which best fits Quercus chrysolejns. I feel certain there must be a mistake here, just as I do not believe Kieffer's eriophorus came from Wislizenii as published. Until we can see types of rossi it will not be possible to determine the variety it represents. I am inclined to expect to find it a synonym of maculipennis.
[Kinsey goes on to describe several varieties that differ by host, range, and gall morphology; see paper for details]
