Synergus lignicola (Osten Sacken, 1862)

Nomenclature:
Cynips (Synerges [sic]) lignicola Osten Sacken, 1862
Synergus davisi (Beutenmüller,1907)
Andricus davisi Beutenmüller, 1907
Synerges [sic] rhoditiformis Walsh, 1864

Feeds on: Inquiline of: galls of Andricus quercuslaurinus Melika & Pujade-Villar, 2009; galls of Callirhytis cornigera (Osten-Sacken, 1865); galls of Callirhytis quercusgemmaria (Ashmead, 1885); galls of Callirhytis quercuspunctata (Bassett,1863); undetermined galls on Quercus incana and other Quercus sect. Lobatae spp.

Distribution: United States: District of Columbia, Indiana, Michigan, Missouri, NewJersey, New York, Virginia

[Synergus sp. parasitoid(s)]

Quercus catesbaei [laevis], cinerea [incana], falcata, ilicifolia, imbricaria, laurifolia, myrtifolia, nigra, rubra, texana [buckleyi]
Stem galls, detachable
Fig 155. Small ribbed galls in early spring, secreting honeydew when young, dropping when mature in fall. When parasitized they do not drop but enlarge, become woody and persist over winter.

[Photo caption]
On Q rubra. When attacked by guests the galls do not drop, enlarge, become woody and remain on tree over the winter. These were once described as an Andricus but the types were all Synergus. These woody galls often bear traces of the truncate and ribbed surface of the original gall.

Synergus davisi (Beutenmuller)

Andricus davisi Beutenmuller

NJ. Guest in gall of Callirhytis gemmaria (Ashmead).

Synergus lignicola [Kinsey, apparently mistakenly, states that these galls are induced by Andricus punctatus and modified by Synergus lignicola as inquilines]

Hosts: Quercus ilicifolia, rubra, velutina, coccinea

The galls from which these [Synergus lignicola adult males and females] were bred appear to be deformed specimens of Andricus punctatus.

The parasitized or inquiline-inhabited galls are quite different from normal galls of the species. Infested galls are usually more or less globular, in groups, but not so completely fused into a single mass as normally. Internally these galls are only loosely woody, with several small larval chambers (without a distinct larval cell-wall) arranged somewhat radially and near the bark. Each portion of the fused mass of the normal gall is woody and will contain toward the center one to three good-sized larval cells with a distinct cell-wall. This is a typical instance of the change effected in the structure of a gall when it becomes inhabited by inquilines.

Andricus davisi sp. nov. [Beutenmuller's wasp was later recognized as an inquiline of Callirhytis quercusgemmaria.]

Gall: Polythalamous. Brown, sometimes speckled with pale brown. Smooth or somewhat roughened. Globular, irregularly rounded or somewhat elongate. They are single or in clusters, or a number of them coalesce forming a large knot-like mass. They are very hard, solid and woody, and contain many larval cells. The individual gall measures from 4 to 15 mm. in diameter, and the knot-like mass measures about 40 mm. in width.

The gall occurs singly or in clusters of from two to about twenty individuals around the twigs and branches of scrub oak (Quercus nana [ilicifolia]). They sometimes coalesce and form a large knot-like mass, not unlike Andricus cornigerus, but without the horn-like projections which characterize the latter. The galls reach maturity late in September and the flies emerge the following spring. The flies are very distinct and may be known by the very rough, transversely rugose thorax and the absence of the median groove at the scutellum.

Habitat.- Lakehurst, New Jersey. September.

Callirhytis gemmaria

The young galls may be found forming from late May to early June, secreting honeydew from a gland at apex and at this stage containing a thick translucent nutritive layer inside, with a scarcely discernable larval cavity in center. On June 16, 1917, a cluster of developing galls was found at Fort Sheridan on rubra and watched at intervals during the summer. "When visited a month later many of the galls were found to be plump and green, with a nipple at apex and many cells inside and they continued to enlarge and finally become woody and covered on outside with normal brown bark and remained on the tree all winter. They became the characteristic galls known in literature as Andricus davisi Beutenmueller, and from them only guest flies are reared. The types of davisi seen by the writer in six different collections are all guest flies of the genus Synergus. When attached by inquillines the galls, instead of dropping to the ground, keep on growing and remain on tree.

In the Bulletin of the American Museum of Natural History (vol. 42, 1920, p. 295), Doctor Kinsey, working with museum specimens only without field observations on the growing galls, recognizes that the characteristic galls of davisi yield only a Synergus, but he is in error in thinking that they are derived from Callirhytis punctata (Bassett). In favorable specimens one can often find on the summit of the davisi galls a trace of the nipple and ribbed surface of the normal gemmaria gall. In a footnote he admits the possibility of his error, but does not say from what they are derived.

True parasites by killing the maker may stunt the growth of a gall and cause a characteristic appearance, and guest flies may also modify it. Cecidologists when describing galls should be sure they are describing a normal structure, and one can not always be sure of this from single specimens. They may be sure it is normal if they rear the maker, or, failing in this, find the gall in numbers and especially season after season.