40 BULLETIN 826, IT. S. DEPARTMENT OF AGRICULTURE. 



mediates between apterous and alate viviparous forms are of quite 

 common occurrence and indicate possible origin of the apterous 

 forms. It is no doubt true, boy/ever, that in members of this tribe 

 the equilibrium is disturbed more easily than in some of the others, 

 and that external influences have a more sudden and noticeable 

 effect. 



yVe have divided the tribe into four subtribes which may be 

 separated as follows: 



Key to the Subtribes oe the Aphidini. 



1. Body covered with long projections Cervaphidina. 



Body naked with the exception of a few hairs 2. 



2. Head without prominent antennal tubercles Apbidina. 



Head with prominent antennal tubercles 3. 



3. Y/ings with the radial sector normal Macrosipeina. 



Wings with the radial sector more or less united with the upper branch of 



the media or hind wings reduced Pentalonina. 



Subtribe APHIDINA. 



The insects in the Aphidina show a great variation in regard to 

 the cornicles and cauda. Some have very markedly developed 

 cornicles, others have extremely small ones, while one genus lacks 

 them altogether. The cauda varies from very large in genera like 

 Hyalopterus to scarcely any visible cauda in some of the other 

 genera. Certain of the genera appear more similar than others, for 

 example, Hyalopterus, Pergandeidia, and Brachycolus all have small 

 cornicles and somewhat large cauda?. Certain other genera, while 

 appearing quite different in some ways, are evidently related. 

 Cavariella, Hyadaphis, Aspidaphis, and Vesiculaphis all have char- 

 acters which are very suggestive, although there are differences 

 between thsm. So also there is a group suggesting Aphis. The 

 various genera may be separated as follows: 



Key to the Genera of the Aphidina. 



1. Cornicles absent. Asiphonaphis. 



Cornicles present. 2. 



2. Cornicles swollen, not subcylindrical or tapering 3. 



Cornicles eubcylindrical or tapering but sometimes extremely short and 



ringlike 12. 



3. Fore wings with the media once branched; apterous form with very much 



swollen cornicles Vesiculaphis. 



Fore wings with the media twice branched 4. 



4. Hind wings with the cubitus lacking Carolinaia. 



Hind wings with both media and cubitus present 5. 



5. Abdomen with a dorsal projection or tubercle above cauda 6. 



Abdomen without this structure 7. 



