Callirhytis quercuscornigera (agamic)

Callirhytis quercuscornigera (sexgen)

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.

Callirhytis quercuscornigera (Osten Sacken)

Diagnosis. Wasps from the tiny, blister-like leaf galls were previously known as the alternate generation (Felt 1940). These galls resemble the leaf galls induced by C. pomiformis (McCracken & Egbert 1922), but leaf galls induced by C. quercuscornigera occur on the midveins, large lateral veins, and infrequently on petioles and tiny lateral veins (Eliason & Potter 2000).

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).

Sexual leaf galls were observed on Q. palustris and Q. phellos.

Biology. The biology of both generations of C. quercuscornigera was recently described in Lexington, Kentucky (Eliason & Potter 2000). 

Asexual females exit ∼33-month-old stem galls and oviposit into swelling buds (Eliason & Potter 2000). Eggs are deposited next to the midvein or large lateral veins, and are slightly embedded into the leaf tissue on the abaxial leaf surface. One larva lives in each leaf gall, but two or more galls may develop next to each other. Maximum leaf gall length (∼2.0 mm) occurs by late May. Larvae completely consume the moist nutritive tissue, leaving only a thin gall layer around the final instar. Pupation occurs in May and adults exit in late May or early June.

DESCRIPTION OF THE SEXUAL GENERATION OF CALLIRHYTIS QUERCUSCORNIGERA AND A NEW INQUILINE (HYMENOPTERA: CYNIPIDAE)