Odontocynips nebulosa Kieffer

This new genus and species was described in 1910 from flies only, captured in Georgia by King and in Texas by Boll. The types are in the Museum of Zoology, Berlin.

The writer recognized the genus in March, 1917, in specimens from Woodstock, Georgia, bred from a root gall on oak received by Doctor Felt and submitted to William Beutenmueller for examination. The flies agree fairly well with the published description of nebulosa Kieffer. As the only description of the gall is the brief characterization by Doctor Felt in 1918 in his Key to American Insect Galls (p. 54) as "Irregular, polythalamous root gall, diameter 3.5 cm. on Q. minor," a more extended description may be given here.

Host. — Quercus stellata Wangenheim.

Gall. — On the roots of young shoots that come up under larger trees. These shoots are only 30-90 cm. high and often occur in large numbers so that their tangled roots form a mat, and it is on these horizontal roots where the thicket is dense enough to accumulate humus that the galls are found. They occur on roots 5-15 mm. in diameter and are sometimes 5-10 cm. underground. Single galls are globular, 10-13 mm. in diameter, but they are usually aggregated into irregular lobed polythalamous masses as large as a man's fist or 8 cm. in diameter. They are covered with smooth bark, light colored like the normal bark of roots, but brown when dry. They are easily cut when fresh, but very hard and woody when dry. The larval cavities are about 6-8 mm. in diameter and the walls about 2 mm. thick. Exit holes 3 mm. in diameter. They are often attacked by whitish wingless plant lice attended by a pale yellowish ant.

Habitat. — The writer first collected the galls on September 9, 1915, at Webster Groves, Missouri, on Quercus stellata. They contained pupae on October 3, and adults October 26, but a few had a thick nutritive layer instead. The galls were buried in soil in greenhouse to determine date of emergence and still contained living flies January 17, 1916, but by March 20 all were gone. On October 4, 1917, the same locality was again visited and only one gall found where they had been very abundant two years before. Collected galls at Hoxie, Arkansas, October 10, 1917, and cut out living flies November 16. At Hot Springs, Arkansas, galls contained pupae on October 12. From others collected at Palestine, Texas, October 16, flies emerged indoors the next spring from February 20 to March 8. Old galls were seen at Marianna, Florida, October 11, 1919.

Note. — Found a similar old gall on Quercus lyrata Walter and from it cut out a moldy fly belonging to the genus Odontocynips; and it is probably the same species, as these two oaks have many galls in common, but until reared it is better not to publish lyrata as a host of nebulosa.

At Cuero, Texas, October 23, and Austin, Texas, October 30, similar galls were found on roots of Quercus virginiana Miller, and a fragment of an adult in an old gall showed it to be due to an Odontocynips. Three stages of the galls were observed: 1, old galls with numerous exit holes where flies had emerged the previous spring; 2, fresh galls containing pupae; 3, fresh galls not distinguishable from the above but containing a thick transparent mass of nutrient material with a barely visible larval cavity. This suggests that the galls take two years to develop. Similar empty galls were seen at Kerrville, Texas, July 21, 1918. Until adults can be reared it is better not to publish virginiana as a host of nebulosa, however.

- LH Weld: (1921) American gallflies of the family Cynipidae producing subterranean galls on oak^©

Reference: https://www.biodiversitylibrary.org/page/7562993#page/264/mode/1up