THE ELM APHIS. 279 



Wingless specimen. — Front of the head rather obtusely advanced in the middle^ 

 Honey tubes very short; length less than the diameter; tip of the abdomen extend- 

 ing or drawn out to a point, but no true tail was observed. Along the lateral mar- 

 gins of the abdomen, in front of and behind, the honey tubes are minute tubercles, 

 each giving rise to a hair; these tubercles are quite distinct and about one to each 

 segment. (Thomas.) On the elm in June in Wisconsin. (Bundy). 



55. Schisorteura americana Riley. 



Curling and gnarling the leaves of the White Elm ( Ulvius aviericana), forming 

 thereby a sort of pseudo-gall. The curl made by a single stem-mother in the spring 

 takes the pretty constant form of a rather wrinkled roll of one side of the young 

 leaf; but, according as there is more than one stem- mother, or as several contiguous 

 leaves are affected, the deformation assumes various distorted shapes, sometimes in- 

 volving quite large masses of the leaves. 



Professor Kiley has given the full life history of this species in his 

 Notes on the Aphididge of the United States, published in Bull. U. 

 S. Geol. and Geog. Survey, from which the following is extracted: 



This species is very closely allied to the European S. ulmi (Linn.), and until I was 

 able to compare it with actual specimens, I was in doubt whether to look upon it as a 

 mere variety or a distinct species. Judging from Kessler's figure and description of 

 the European leaf-curl, and by a figure sent me by Mr. Buckton, it differs from ours, 

 Ist, in bending upward, i. e., the stem-mother settles on the upper instead of the 

 under side of the leaf; 2d, in having a number of small, rounded or verrucose swell- 

 ings. These difierences in their dwellings are strongly presumptive of structural 

 differences in the insects themselves ; and the fact that S. americana does not attack 

 the European Elms, either in Shaw's Botanical Gardens at Saint Louis, or in the 

 grounds of the Department of Agriculture, points in the same direction. Differences 

 -are indeed easily enough made out if we take the more or less imperfect descriptions 

 and figures of ulmi,* but are less apparent when the actual specimens are compared. 



The following are the more important differences, least subject to variation, be- 

 tween the winged females of ulmi as compared with those of americana : tilmi is a 

 longer-winged species, averaging 7.3""™ in expanse; the abdomen, wing-veins, and 

 stigma are darker; the terminal distance between 1st and 2d discoidals slightly 

 greater ; the 3d joint of antennte is relatively longer ; the annulations are less deep 

 and more numerous (those on 3d joint averaging 30) ; joints 5 and 6 are smoother, 

 i. e., without annulations, but they are more setous ; joint 5 is shorter than 4 ; the 

 apical, narrowed part of 6th joint is relatively longer and more pointed ; the sub- 

 costal vein of hind wings is less straight ; the cubital vein is often continuous to very 

 near the subcostal, while I have not found any tendency of the kind in americana, 

 the tendency being in the opposite direction, or to become shorter; the 2d discoidal 

 of hind wings shows a tendency to fork ; the booklets on costa of hind wings are 

 3 in number, while in americana there are normally 4 ; * the legs are more setous. 



Among the more prominent of the natural enemies of this species, I have noticed, 

 of Coleoptera, Coecinella 9-noiata, Cocdnella sanguinea (miinda) Say, Hippodamia 

 convergens, and several species of Scymnus. I also found feeding upon them the per- 

 fect beetle of Podabrus modestus, and the Hemipterous Cyllocoris scutellatus, Uhler, 

 and Capsus linearis, Beauv. A Lepidopterous inquiline, namely, the larva of Semasia 

 prunivo7-a, Walsh, is also quite common within the curled leaves, feeding both on the 

 lice and on the substance of the leaf. A large green Syrphus larva and severa^ 

 Chrysopa larvte also prey upon them. 



* Koch's figure (evidently copied by Kessler) is faulty in several respects, and fails 

 to indicate the hook-angle of hind wings, or the corresponding thickening of front 

 wings, a fault that is, however, common to most of Koch's figures. 



