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



Tribe LACHNINI. 



The tribe Lachnini is the most primitive of all living aphids, with 

 the exception of the Mindarinae. The genus Mindarus shows in its 

 wing structure characters more primitive than any of the Lachnini, 

 but in other characters such as those of the beak, cornicles, cauda, 

 sensory structures, etc., the Lachnini are very primitive insects. In 

 examining the fossil wings it is to be noted that the radial sector is 

 situated back of the stigma. In practically all living aphids, with the 

 exception of Mindarus, this vein has migrated toward the tip of the 

 wing. In primitive forms the stigma is long and narrow, whereas in 

 most living forms it has become more or less compact. In the subtribe 

 Lachnina the radial sector has become a very short, straight vein almost 

 at the tip of the wing. This shows that the Lachnina are evidently 

 more advanced than the Pterochlorina in which the radial sector is 

 somewhat curved and situated near the middle of the stigma. The 

 subtribe Eulachnina is considerably specialized, as indicated by the 

 eves, the shape of the body, and the cornicles. It is, however, as 

 closely related to the Lachnina as are any of the other tribes, as will 

 be seen from the formation of the whig. The Anoecina in the typical 

 genus shows a wing with a short blocky stigma, a condition quite 

 different from that seen in the Lachnina, and the radial sector is here 

 curved. (In Nippolachnus, however, the stigma is still long and 

 straight.) Moreover, the sexual forms are more specialized, being 

 apterous in both cases. Anoecia, therefore, is somewhat removed 

 from Lachnus. The genus Trama is considerably specialized, in 

 that it lacks cornicles in the apterous form. It is, however, related 

 to Lachnus through Neotrama with small cornicles, and Protrama 

 with large hairy cornicles. 



The rostrum in the Lachnini is in many species five-segmented, a 

 primitive character most marked in this group. The freshly emerged 

 wing of a lachnicl shows that M 15 M 2 , and M 3+4 are the veins repre- 

 sented when the media is twice branched, and that in some species no 

 vein is formed about M 2 . The cubitus and first and second anal 

 are present in the forewing. As in other Aphididae, however, no 

 vein forms about the second anal. The radial sector is in Lachnus 

 a short, straight trachea and a prominent vein forms about it. The 

 stigma, as in all members of the family, is formed by radius a . In the 

 hindwing both media and cubitus are present and form distinct 

 veins. 



The antenna? of the Lachnini are six-segmented with a short 

 unguis. They are usually armed with oval or subcircular sensoria 

 and prominent hairs. In fact, the entire body of the insect is hairy. 



The cornicles are characteristic. They are situated on distinct 

 cones which are constricted before the somewhat flanged opening 

 which is not situated over the center of the cone. The cones are arm- 



