Cynips quercus cornigera n. sp. (as yet unknown) [ie gall named without an adult wasp specimen]

Quercus palustris Pin oak.

Woody knots on the limbs, emitting pale yellow, conical, brittle projections.

Of all excrescences on oaks in general, the present one, wherever it occurs, is perhaps the most conspicuous, as by its abundance it deforms the tree and seems to cause considerable injury. It consists of woody knots on the limbs, looking usually as if many of them were closely packed together and thus forming an oblong, woody irregular mass, sometimes two inches or more long. Its most striking character are its slightly curved conical projections, hollow on the inside, which bud forth from all sides of the gall. On dry, dead galls, these horn shaped projections are for the most part broken off, so that their bases alone are visible, projecting like short tubes from the cracks of the woody tubercle.

After having very frequently observed dead galls of this kind, I finally succeeded on the 13th of May, 1862, to find some young and growing ones. They were of moderate size; their back was greenish and their wood soft and succulent. The conical projections were just beginning to bud forth; when laid bare, by removing with a knife the wood around them, they appeared to extend deep inside of the gall, almost down to the twig. Their color was whitish, their consistency soft, apparently fibrous, and not woody. At that time, they were not hollow yet, and I could not find any larvae in them. When I visited the same spot during the latter part of June, I found some of the horn-shaped bodies already projecting about one-tenth of an inch; their substance had become harder and more woody; their inner end had become club-shaped, distinctly isolated from the surrounding wood, so that the whole of these bodies could be easily removed by cutting away the wood around them. On the inside, the inner end was hollow and contained a small larva.

[Eliason and Potter provide a thorough description of the phenology, morphology, and parasitoid and inquiline communities of both the agamic generation, forming large horned stem galls, and the sexual generation, forming inconspicuous galls on leaf veins. Pictures are included of both galls.]

Callirhytis cornigera (O.S.)

Quercus catesbaei [laevis], falcata, ilicifolia, imbricaria, palustris, rubra, texana [buckleyi]
Stem galls, woody stem swellings
Horned Knot Gall. Abrupt, cuts like cheese when growing in May-June, becoming woody, the horns finally protruding and even dropping out.

Quercus myrtifolia
Stem galls, woody stem swellings
Callirhytis cornigera or Callirhytis clavigera. A horned knot gall.

[Photo caption]
Horns picked up on ground under Q rubra July 15, 1917 (IL). Horned Knot Gall. Similar to [C q clavigera]. Adults were cut out Nov. 26 and some emerged May 12, 1918. Occurs also on Q. palustris, imbricaria, ilicifolia, cinerea [incana], catesbaei [laevis], texana [buckleyi].

Callirhytis quercuscornigera (Osten Sacken)

Diagnosis. The galls of the asexual generation of Callirhytis quercuscornigera (Osten Sacken) are similar to those of C. pomiformis (Bassett), C. punctata (Osten Sacken), C. quercusclavigera (Ashmead), C. quercuspunctata (Bassett), C. quercussuttonii (Bassett), and C. seminosa (Bassett) (McCracken & Egbert 1922, Weld 1959, Lyon 1969b). However, the only other gall in which the larval chambers protrude externally is induced by C. pomiformis (McCracken & Egbert 1922).

Taxonomic comments. Osten Sacken (1862) first described the gall-maker, based on stem gall characteristics, as Cynips quercus cornigera. He later reared two specimens, a female and possibly a male, from the same gall and named the wasp Cynips cornigera based on the female (Osten Sacken 1865). Because species names based on gall descriptions before 1930 are valid, the appropriate name for this species is Callirhytis quercuscornigera (Osten Sacken 1862), comb. rev.

Distribution. Canada: Ontario; USA: New York, Massachusetts, Connecticut, District of Columbia, Maryland, west to Illinois, Indiana, Montana, Iowa, Arkansas, Tennessee, Colorado, Texas, south to Virginia, North Carolina (Q. hemisphaerica and Q. falcata), Alabama, Georgia. New for Florida (Q. hemisphaerica. Trees in May 1995 were heavily infested; entire branches were killed by the galls and inducers).

The asexual generation develops on Q. incana Bartr., Q. imbricaria Michaux, Q. ilicifolia Wangenh., Q. laevis Walt., Q. nigra L., Q. palustris Muenchhausen, Q. rubra L., and Q. velutina Lamarck (Weld 1959). This species was very common on Q. hemisphaerica, Q. laurifolia Michaux, Q. phellos L., and Q. myrtifolia Willd. in Florida, and on Q. falcata in North Carolina.

Biology. The biology of both generations of C. quercuscornigera was recently described in Lexington, Kentucky (Eliason & Potter 2000). Sexual females lay eggs into young shoots, and the subsequent stem galls, in which the asexual generation develops, begin visibly growing the following spring. Twelve-month-old galls appear as slight swellings on small diameter branches. Twenty-two month old stem galls are smooth in texture, green-colored externally, and the internal gall tissue is pale yellow. The larval chambers, or horns, begin to push through the thin gall epidermis when galls are ∼24 months old. Horns project up to 6 mm from the rounded, succulent stem galls, and harden after about a month. One asexual C. quercuscornigera larva develops at the base of the larval chamber. Horns break off several months after adults chew a circular exit hole and leave the galls at bud burst in the spring.

Plagiotrochus cornigerus O. S.
Agamic form, cornigerus O. S.

Irregular, ovoid, horned woody twig and branch galls, dia. 1-3 cm.

Adults in April.

On Q. rubra, Q. palustris, Q. imbricaria, Q. ilicifolia.

Callirhytis cornigera (Osten Sacken 1862)

Hosts: Quercus laevis, myrtifolia

[Asexual generation stem swelling galls found in Florida in the fall.]