348 

 A CECIDOMYIID THAT LIVES ON POISON OAK. 



I'.V D. W. COQUILI.ETT. 



Up to the present time no case has been recorded in this country of 

 any species of Cecidoniyiid;e living on plants beionging to the genus 

 Ehus, which contains our various kinds of sumacs. The rearing during 

 the past summer of a species of Cecidouiyia from galls on the roots of 

 the common poison oak or poison ivy {Rhus to.vieodeudron) \\iU theve- 

 fore not to be without interest. 



Ou the 20th of March, 181>4, Mr. W. 11. Harrison, of Lebanon Springs, 

 N. 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 larvae 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: 



Cecidoniyia rhois n. sp. 



Brownish-black, the hypopygiuiu of the male and the abdomen of the female 

 yellow. Thorax tinged with red, considerably produced anteriorly, its front end at 

 the attachment of the head being nearly horizontal to the i)laue of the body. Anten- 

 na- of male nearly as long as the body, 15-jointed, the joints pedunculated, the 

 jieduncles being one-half as long as the thickened part of the joints; the latter 

 are furnished with numerous rather long, yellowish hair.s. Antennip 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 in 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 tothe wiug-margin, while the upper one continues 

 in the same course as the praifurca, 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 l.o to 2""". Three males and one female. 



Gall. — Pale 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""". Occurs singly on 

 the small, fibrous roots of Blms ioxicodeiidroii, at a point where the root forks. 



