No. 2368. AMERICAN SUBTERRANEAN GALLS ON OAK— WELD. 221 



21. CALLIRHYTIS FUTILIS (Osten Sacken.) 



(Agamic generation=rocfiVw Jlassett=radicicola Dalla Torre.) 

 Plate 33, fig. 21. 



Callirhytis radicis Bassett. Psyche, vol. 5, 1889, p. 237.— Dalla Torre and 

 Kieffer, Wytsman Gen. Ins. Hym. Cynipidae, 1902, p. 66, No. 26.— Das Tier- 

 reich, Lief. 24, 1910, p. 571. — Beutenmueller, in Smith Ins., N. J., 1910, 

 p. 601.— Thompson, Cat. Amer. Ins. Galls, 1915, pp. 5, 30.— Felt, Key to 

 Amer. Ins. Galls, N. Y. St. Mus., Bull. 200, 1918, p. 54. 



Andricus radicicola Dalla Torre, Cat. Hymen., vol. 2, 1893, p. 95. 



Callirhytis radicicola Dalla Torre, Mayr, Verh. Zool-.Bot. Ges. Wien, vol. 52, 

 1902, p. 289. 



Andricus {Callirhytis) radicis Bassett, Yiereck, Hym. of Conn., 1916, p. 426. 



On May 12, 1917, a dozen or more Cynipids of the same species 

 were seen ovipositing in the unopened buds of Quercus alba Linnaeus at 

 Fort Sheridan, Illinois. Investigation showed that there were hun- 

 dreds of cells (radicis form of C.futilis) in the bark of the main roots 

 (Plate 33, fig. 21) at the base of the tree from which these flies were 

 coming and they were seen crawling up the trunk, and from these 

 cells similar flies were cut. On May 6, 1914, at Plummer Island, 

 Maryland, oak-wart galls were seen on the leaves of alba, and a large 

 number of cells were found in the bark of the main roots and from 

 them two living adults were cut. At Starved Rock, near Utica, 

 Illinois, May 31, 1913, the wart galls were very common on one tree of 

 alba, and the old radicis cells in the bark of the root were found, exit 

 holes showing where adults had emerged earlier in spring to produce 

 the current crop of leaf galls. In this thickened bark, however, there 

 were nests of cells with a thick nutritive layer. These were probably 

 formed in the fall of 1912 by flies from the 1912 wart galls and would 

 not give adults until the spring of 1914. Old cells of what is probably 

 this species were observed in the thick bark at the crown of a large 

 tree of Quercus prinus Linnaeus, at East Falls Church, Virginia, on 

 September 1, 1919. 



Measurements of 75 pinned specimens, of which 53 were Bassett 

 "cotypes," gives the range in size as 1.9-3.4 mm. Average, 2.7 mm. 

 Using the width of the head as a base, the length of mesonotum ratio 

 is 1.2; length of antenna, 1.6-1.8; ovipositor, 2.5-2.8; wing, 3.4-3.6. 

 Wing not ciliate on margin. The antennae were described as 

 14-segmentcd. In some of the cotypes they are 13-segmented, the 

 last over twice preceding, but often with a transverse suture, which 

 may completely divide it into two separate segments. 



