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



nanies are here used: Aphidinae, Eriosomatinae, and Hormaphidinae. 

 Besides these there is the one species, in some ways a relic of the 

 past, forming the Mindarinae. 



As will be seen by the diagram (fig. 1), the Aphidinae is considered 

 the most primitive subfamily of the three main groups. This is 

 substantiated by the habits of the insects, by the structure of the 

 wings, beak, etc., and by the sexual forms. 



Practically all of these insects are foliage or twig feeders. They 

 live, as a rule, in colonies and have not developed any very special 

 methods of life, such as highly complex gall formation. With the 

 exception of the Mindarinae the most primitive wing structure oc- 

 curring in the family is met with here. The media is most commonly 

 twice branched throughout the subfamily and even in the Mindarinae 

 there is more of a reduction than this. The antennae are of six 

 segments, the largest number found in the family, and the sen- 

 soria are simpler in nature than those met with in the other two large 

 subfamilies. The beak in the Lachnini shows also a primitive 

 condition in its segmentation. 



The sexual forms are most primitive in the Aphidinae. Winged 

 sexes often occur, at least the males are very commonly winged. Both 

 sexes still retain their beaks and feed on their hosts in the same 

 way as do the other forms, and the ovaries of the female develop 

 normally, and she produces several eggs. 



When the phylogeny of this subfamily is Studied, there becomes 

 evident the primitive character retained by the Lachnini. In these 

 forms the beak structure and the nature of the antennae and 

 cornicles point to a primitive condition. The sexes, too, indicate 

 this, though not markedly more than in other tribes. But the fact 

 that these forms are mostly conifer feeders should not be overlooked. 

 It is the opinion of the writer that this is a primitive habit. 

 The Lachnus branch, therefore, may be considered the lowest branch 

 of the Aphidinae. If the wings of fossil aphids be examined it 

 will be seen that by far the greater number of them possess a wing 

 structure quite different from that of our living forms. The radial 

 sector arises back of the stigma, which is usually very long and narrow. 

 This character is retained probably only in the Mindarinae. It is 

 evident, then, that during the development of the present Aphidinae 

 this vein migrated toward the tip of the wing until it came to stand 

 either in the middle of the stigma or near its tip. On one line of 

 this migration is the Lachnina wherein the vein has reached nearly 

 to the tip of the wing and become short and straight. The remain- 

 ing characters apart from the wings have in these forms remained 

 quite primitive. The subtribe Eulachnina is evidently a more 

 specialized group on this same line of development, for it possesses 



