Dryocosmus favus Beutenmuller

This species was originally described from Louisiana and Pennsylvania from galls on Quercus rubra Linnaeus and Q. coccinea Muenchhausen. The writer has collected galls on Q. rubra in Illinois at River Grove, Willow Springs, Evanston, Winnetka, Ravinia, and Fort Sheridan; and at Ironton, Missouri; Hot Springs, Arkansas; and Plummer Island, Maryland. He has also taken the galls on six other host oaks not previously recorded, as follows:

Q. catesbaei Muenchhausen at Jacksonville, Palatka, Madison, Marianna, Ocala, Clearwater, Florida, and Troy, Alabama.

Q. marilandica Muenchhausen at Marianna, Florida.

Q. nigra Linnaeus at Gainesville, Florida.

Q. brevifolia Sargent at Marianna and St. Petersburg, Florida.

Q. myrtifolia Willdenow at Daytona, Florida.

Q. texana Buckley at Boerne and Kerrville, Texas.

The appearance of the fresh galls has never been described. As many as 400 often occur in a cluster, which may measure 6 cm. in diameter (fig. 6) and is found just at or below the surface of the ground and is usually hidden by debris. The cluster sometimes entirely surrounds the host stem when the latter is not more then 1 cm. in diameter. In the fall about one-half of the clusters found are galls that are just starting in early October or nearly full-grown later in the month and containing larvae and they still contain them as late as November 14 and through the winter. These fresh galls are white and fleshy, smooth on the surface, blunt-pointed at the tip (fig. 5). The other half are white and juicy or just beginning to turn brown. These contain adults as early as September 15 about Chicago, and they were still inside the galls on November 14. These galls were put out of doors in breeding cage and three flies issued by December 1, and on December 28 twenty-seven were found, the thermometer having registered — 14° F. in the interval. On the 19th of the next February over 200 were found alive in the cage, which had been buried up in the snow for six weeks without a thaw. On March 12 there were two more out. In Florida pupae were found in galls on October 11, 21, 23, and November 3, and the earliest record of finding adults in the galls was November 20 and the earliest emergence December 1.

The life history suggested from the above data is that the galls start in the autumn and get their full size quickly the first season and that the larvae do not transform until the next autumn when the galls are over a year old. After the larvae transform, the galls soon turn brown, the proximal part about the larval cell becomes hard and brittle, and during the winter the distal fleshy half of the gall becomes converted into soft spongy granular tissue through which the adults can easily chew their way (fig. 7) and it finally decays away entirety leaving the hard wedge-shaped bases containing the cells to persist for years. The adults either emerge in very late autumn or very early spring, and are wonderfully resistant to cold. But if there is an alternating generation it is unknown.

Dryocosmus favus

Quercus catesbaei [laevis], cinerea [incana], laurifolia, marilandica, myrtifolia, nigra, palustris, rubra, texana [buckleyi],
"Root" galls
Dense clusters at or below surface, up to 60 mm in dia, consisting of up to 250 individual cells, 11 mm.

[Photo caption]
On Q rubra. Also on Q marilandica, nigra, catesbaei [laevis], laurifolia, myrtifolia, texana [buckleyi]. Galls become full-grown in the late fall, larvae transform the next autumn and galls turn brown; during the winter the fleshy distal half becomes converted to spongy tissue as in Fig 47 and finally decays leaving the wedge shaped bases to persist for years. Adults, all females, emerge in late Autumn (Dec 3-Feb 27 (FL); Dec 28 (after -14 F), Feb 19 (after six weeks without a thaw) and Mar 2 (IL) from galls collected in MO in Oct.

Dryocosmus favus sp. nov.

Gall. — In clusters from about fifty to one hundred on the trunks of young red and scarlet oaks (Quercus rubra and coccinea), immediately above the ground, in autumn. Hard and woody (when dry) probably soft when fresh, monothalamous. Oblong, narrower at base than at apex, which is flat. In form they are somewhat like square tubes or five or six-cornered tubes, giving them the appearance of cells of a honeycomb. Hollow inside and rather thin-walled. The fly emerges from the apex of the gall. Length, 5 mm. ; width of apex, 3 mm. ; diameter of cluster, 28 mm.

Habitat: Phillips Bluff, La.; Fleetwood, Pa.

The fly was described from many specimens loaned to me by Prof. A. D. Hopkins. The species belongs to the European genus Dryocosmus Giraud not heretofore recorded from North America. The fly emerges very early in spring and the gall reaches maturity late in fall.

Dryocosmus favus (Beutenmueller 1911)

Hosts: Quercus laevis, myrtifolia

[Asexual generation root galls found in Florida in the fall.]