348 
A CECIDOMYIID THAT LIVES ON POISON OAK. 
By D. W. COQUILLETT. 
Up to the present time no case has been recorded in this country of 
any species of Cecidomyiida? living on plants belonging to the genus 
Bhus, which contains our various kinds of sumacs. The rearing during 
the past summer of a species of Cecidomyia from galls on the roots of 
the common poison oak or poison ivy (Rhus toxicodendron) will there- 
fore not to be without interest. 
On the 29th of March, 1894, Mr. W. H. Harrison, of Lebanon Springs, 
Y., sent to the Division of Entomology roots of the poison oak upon 
which were numerous Cecidomyiid galls which at that date contained 
only the reddish larva?. The perfect flies began to issue May 3, and 
continued issuing up to the 18th of the same month. The species is 
evidently new to science, and may be characterized as follows: 
Cecidomyia rhois n. sp. 
Brownish-black, the hypopygium of the male and the abdomen of tbe female 
yellow. Thorax tinged with red, considerably produced anteriorly, its front end at 
the attachment of tbe head being nearly horizontal to the plane of the body. Anten- 
na? of male nearly as long as the body, 15-jointed, the joints pedunculated, the 
peduncles being one-half as long as the thickened part of ihe joints; the latter 
are furnished with numerous rather long, yellowish hairs. An tenure of female less 
than one-third as long as the body, rather long pilose, 13-jointed, the joints sessile. 
Pile of thorax short, dark brown, disposed iu four longitudinal rows, that of the 
abdomen rather long, pale yellow. Wings grayish, the pubescence and fringe of long 
hairs on its posterior margin dark brown ; veins brown, the small cross vein and 
forks of the last vein almost colorless; the first vein lies close to the costa, and the 
second issues from it slightly before its middle, is nearly straight, and terminates at 
the last fourth of the distance between the tip of the first vein and the extreme 
apex of the wing; the third vein forks slightly beyond its middle, the lower fork 
extending in an oblique direction to the wing-margin, while the upper one continues 
in the same course as the prsefurca, but curves slightly upward throughout its entire 
course; it is twice as long as the lower fork, and terminates twice as far from the 
extreme tip of the wing as the second vein does; small cross vein very oblique^ 
slightly shorter than the lower fork of the third vein, joining the second vein near 
the base of the latter. Legs covered with a sericeous, somewhat yellowish pubes- 
cence. Length 1.5 to 2 mm . Three males and one female. 
Gall. — Palo brown, elongate-oval, but somewhat irregular in outline, from once 
and a half to twice as long as broad ; naked, sparsely covered with small raised spots 
of various shapes and sizes. Length of the largest specimen, 5 mm . Occurs singly on 
the small, fibrous roots of Rhus toxicodendron, at a point where the root forks. 
