Group Aphidina, FajvIily Aphididae 71 



sensilla of the Aphidini. in which tribe the type seems to have arisen. 

 •Sense organs are generally recognized to be of exceptional phylo- 

 genetic values and are much used in taxonomy. To be sure we know 

 next to nothing about their functions, in insects at least. They are 

 very conveniently ignored, but if we persist in ignoring them our ig- 

 norance will only continue as to their functions. If we can do no 

 more than call attention to these structural differences as they can 

 easily be seen, this may be a first step leading to the examination of 

 their histology and later by experimental methods should lead to some 

 clew as to their various functions and phylogenetic values. We do not 

 ask for excuse for bringing in a troublesome question that may lead 

 to re-examination of much of the work of the past. 



The genus was first erected on characters drawn from the frontal 

 tubercles and the first antennal segment. The frontal tubercles have 

 bulges or swellings on the inner side causing them to approach and 

 restrict the concavity between them. The swellings are more notice- 

 able in the larval forms than in the adult and carry the usual number 

 of sensilla. The reticulations on these swellings are very sharp and 

 conspicuous and may be the cause and significant function of these 

 structures. Indications of similar swellings are to be found in both 

 the Aphidini and the Macrosiphini, but never so conspicuous as to 

 draw special attention. Those on the first antennal segment are sim- 

 ilar in structure and are probably but an extension of the first. What 

 the functions of these structures are we do not know, but their con- 

 spicuous presence coupled with Other distinguishing characters en- 

 ables us readily to distinguish the tribe from those closely related. 



The cornicles are usually very long and slender, reticulation broken 

 as in the Aphidini ; often with swellings on apical half, somerimes con- 

 fined to one side. Considerable variation in form of the cornicles is 

 seen, and an extended study may lead to a better understanding of 

 the internal relations of the species and genera than we at present 

 possess. The tribe is a small one in comparison with the preceding and 

 at present no indications of a subdivision have been noticed. 



Tribe MACROSIPHINI (Sanborn) Oestlund, 1919 



Koch. 1855. Die Ptlanzeiil. lilt. ."i. Sub Siphonopliora (geinis) 



Passerlni, 1860. Gli Afidi. Sub Macrosiphum (genus i 



Thomas, 1879. 8th Kept. State Entom. Sub Siphonophoriiii (tribe) 



Sanborn, 1904. Kas. Aphid. Sub Macrosiphini (tribe) 



Wilson, 1910. Ann. Bnt. Soc. Am. Vol. 3. Sub Macrosiphini (tribe) 



Van der Goot, 1913. Tijdschr. Ent, Vol. 56. Sub Siphouophoriiia (tribe) 



Oestlund, 1919. 17th Kept. State Entom. Minn. Sub Macrosiphini (tribe) 



Baker, 1920. Bui. 820, U. S. Dept. Agr. Sub Macrosiphina (subtribe) 



