Cynips (Atrusca) centricola
agamic forms
GALL. — A large, spherical, spotted or unspotted, thin-shelled leaf gall with rather sparse, radiating fibers. Monothalamous. Strictly spherical except where flattened a bit at the point of attachment; ivory to apricot or more pinkish in color, some galls well covered with purplish spots; smooth and often shining, only very microscopically roughened, young galls with a microscopic, stellate pubescence; up to 26.0 mm., averaging under 20.0 mm. in diameter. Internally hollow except for the thick-walled larval cell which is up to 4.0 mm. in length, for the relatively few, silky, radiating, branched fibers that hold the larval cell in position, and for a few shorter, incomplete, branched fibers also located on the inner wall and on the larval cell. Attached by a minute point to a vein; usually on the under surface of a leaf, on Quercus stellata. Figure 197.
RANGE. — Known from New York to Florida, Missouri, and Texas; probably not extending much further than this. Figures 47, 48.
This is the oldest and most commonly known American species of Cynips, but it is poorly represented in most collections. None of the published data, nor most of the collections I have made would indicate that it is ever abundant in any part of its range, but 1 have on several occasions found individual trees bearing more than fifty galls each. These galls are confined to the post oak, Quercus stellata, on the leaves of which they are strikingly beautiful objects. There are four known varieties, centricola from the Coastal Plain and its inland extensions, clivorum from the Southern Appalachians, strians from the Ozark area, and Karsch’s rubrae from Texas. The varieties are separable on only a few insect characters, and on the presence or absence of spots on the galls, and altho typical material from the center of each range is definitely determinable, hybrid material from areas between two of these ranges is not easily analyzed. The slow evolution in this species is in contrast to the more rapid evolution of such a species as Cynips mellea in the same range.
The presence or absence of spots on the galls of this species was taken by Osten Sacken, in the original description of the typical variety, to vary with the age of the gall. It is possible that the amount of weathering has something to do with this, but I have unspotted galls of the normally unspotted variety clivorum collected on various date from October 24 to November 16, and spotted galls of the normally spotted varieties rubrae and strians from September 9 to January 21. Only with variety centricola do we regularly find galls of both types, and the data do not seem to show whether hereditary or environmental factors are concerned in this instance.
The galls of centricola superficially resemble those of Amphibolips inanis, a black-oak species of the eastern United States; but inanis galls are distinguishable by their host and by their fewer, coarser fibers, and by numerous other points. The galls of centricola even more closely resemble those of the Pacific Coast species, Cynips mirabilis, but the galls of mirabilis have denser fibers inside. Mirabilis and centricola belong to distinct subgenera. Some of the unspotted galls of Cynips centricola clivorum also approach near identity with the galls of Cynips bella and Cynips dugesi.
Centricola is in several respects distinct from the other species of the subgenus Atrusca, but these differences are not fundamental enough to warrant the establishment of another subgenus for one species.
[Kinsey goes on to describe four varieties; see paper for details]
