68 BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE. 



Genus TETRANEURA Hartig. 



Hate X, H-M. 

 1841. Tclraneura Hartig, Germar's Zeitschrift fur die Entomologie, v. 3, p. 366. 



In 1841 Hartig erected the genus Tetraneura under which he gave 

 Tetraneura ulmi Lin. ? questioned thus and described. He also 

 listed T. rugicornis Hartig. One of these species was questioned 

 and the other merely listed. Ulmi L., however, was questioned only 

 in the sense of the determination, and a good description was given 

 so that it is known what insect Hartig had. 



In 1843 Kaltenbach gave a description of the genus Tetraneura 

 crediting it to Hartig and described thereunder one species, Aphis ulmi 

 De Geer. Apliis ulmi De Geer (1773) is the same species as Aphis 

 ulmi Geoffroy (1764) but this name can not be used, since Linnaeus 

 used Aphis ulmi for a different insect. This is the same insect de- 

 scribed by Hartig as T. ulmi L. ? and it is evident that it requires a 

 new name, to which ulmifoliae is given. 



Characters. — Cornicles very slightly elevated rings, not at all prominent. Stem 

 mother with, four-segmented antennae; apterous form with five-segmented antennae. 

 Wax glands present. Alate form with six-segmented antennae which are armed with 

 narrow annular sensoria almost completely encircling the segment. Fore wings with 

 the media simple; hind wings with only the media present. 



Forms living in galls and migrating in spring to otherplante. Sexes small, apterous 

 and beakless. Oviparous female developing only one egg. 



Type, Tetraneura ulmifoliae Baker (Aphis ulmi L. of Hartig). 



Tribe PEMPHIGINI. 



The tribe Pemphigini is composed of forms which are highly spe- 

 cialized and most of which have developed the habit of true gall 

 formation. The secretion of wax also occurs but wax secreting plates 

 are not developed to the extent met with in some of the other tribes 

 of the subfamily. Alternation of hosts is found to occur, migrants 

 leaving the galls in early spring or summer and returning in autumn. 

 In some species, however, the insects do not leave the galls until the 

 mothers of the sexual forms are produced. Distinct cornicles are 

 present and by this character forms in some of the other tribes which 

 are suggestive of the Pemphigini may be distinguished. The typical 

 host group is Populus and the galls are normally spring galls. 



Characters .—Forms usually inhabiting true galls and often migrating to other plants 

 during the summer. Antennae of six segments in the alate form and in nearly all 

 genera armed with linear, oval, or somewhat irregularly shaped sensoria. Small wax- 

 secreting areas present. Sexual forms small, apterous, and beakless, the oviparous 

 female developing only one egg. 



Six genera may be included in the tribe and these genera may be 

 separated by the following key : 



