October, '10] DAviS: Illinois aphidid.e 411 



species excepting Walsh's original observations. First reported by 

 Walsh from Rock Island, 111. 



* P.fraximfolii Riley: Bull. U. S. Geol. Surv., Vol. 5 (1897), p. 17, 

 Very common on green ash throughout the state, and one of the impor- 

 tant pests of that tree. Further than the direct injury, the pseudo- 

 galls (curled leaves) of the insect gives the tree a very unsightly 

 appearance. Specimens of this species were sent to Dr. G. Del Guercio 

 who reported it distinct from the European ash Pemphigus, P. nidi- 

 ficus Low. He has published an account of the differences in the two 

 species in " Rivista di Patologia Vegetale," Anno IV, No. 4. The 

 only additional contribution to the life history that we have to make 

 is that the oviparous females are produced in the fall and are to be 

 found in the crevices of the bark on the ash-tree trunk. These females 

 produce but one egg each as do other Pemphigians. 



P. populicaulis Fitch: Jackson, Columbus Hort. Soc, Vol. 22 

 (1908?), p. 191. This poplar gall-maker is common at Urbana, but 

 I have failed to find it in Northern Illinois. First reported by Walsh. 



* P. populi-transversus Riley: Bull. U. S. Geol. Surv., Vol. 5 (1879), 

 p. 14, 1 fig. Common throughout the state on the cottonwood. 



* P. pseudobyrsa Walsh: Proc. Ent. Soc. Phila., Vol. I (1862), p. 306. 

 This is one of the unknown species. The original collection of the 

 species by Walsh at Rock Island, 111., appears to be the only record of 

 its capture. 



P. rhois Fitch: Jackson, Columbus Hort. Soc, Vol. 22 (1908), 

 p. 202. First reported by Walsh. 



* P. ruhi Thos.: 8th Rept. St. Ent. 111. (1880), p. 147. There is 

 no reference to the collection of this species since the original descrip- 

 tion. First reported by Thomas. 



* P. tessellatus Fitch: Jackson, Columbus Hort. Soc, Vol. 22 

 (1908?), p. 183; Patch, Ent. News, Vol. XIX (1908), p. 484, 1 pi. 

 This species is injuriously abundant on the alders in the Chicago 

 parks. I follow Miss Patch in considering P. acerifolii Riley a syn- 

 onym. It has never been recorded from Illinois, except in Hunter's 

 Catalogue and by Jackson, who seems to have followed Hunter. 



* P. idmi-fusus Walsh and Riley: Amer. Ent. Vol. I (1869), p. 109. 

 A rare species which I have taken on elm at Leroy and Urbana, in the 

 central part of the state. First reported by Walsh and Riley. 



^ Mordwilkoja vagabunda Walsh (oestlundi (Ckll.) : Oestlund, Bull. 

 Geol. and Nat. Hist. Surv. Minn., No. 4 (1887), p. 22. A common 

 poplar gall-maker in Northern Illinois, especially abundant in the vicin- 

 ity of Chicago. Often the street trees are so covered with these galls as 

 to make them quite unsightly in winter. I have never taken this 

 species south of Kankakee, 111. First reported by Walsh. 



