A SYNOPSIS OF THE APHIDIDAE 



EXTERNAL ANATOMY 



The body 1 consists typically of three divisions, the head, thorax, 

 and abdomen. In the apterous forms the mesothorax and metathorax 

 are closely fused with the abdomen, while the prothorax and head 

 are distinct. In the alate forms the mesothorax and metathorax are 

 fused together and appear as a distinct division, the body appearing 

 to consist of four divisions, viz., the head, the prothorax, the meso- 

 thorax and metathorax, and the abdomen. 



The head bears a pair of compound eyes, usually three ocelli, a 

 pair of three to six jointed antennae, and the beak. Of these, the 

 antennae show the best characters for determinations, not only of 

 species but of higher groups. They are either mounted on distinct 

 tubercles (Macrosiphini, certain Callipterini) or appear to arise from 

 the front of the head. They consist of from three to six segments, 

 the terminal one of which is usually provided with a projection or 

 spur. They are six-segmented in the Aphidinae (except Essigella and 

 Cerosipha), five- or six-segmented in the Pemphiginae (except in the 

 stem mothers of certain genera), and three-segmented in the Phyl- 

 loxerinae (except in Chermisina, in which the alate forms have five- 

 segmented and the sexual forms four-segmented antennae). The 

 spur of the terminal segment may be equal to or longer than the 

 segment (Aphidinae, in the Macrosiphini it attains its greatest length, 

 often being as much as ten times the length of the base) ; it may be 

 merely a short thumblike process (Pemphiginae, Lachnini, and cer- 

 tain Callipterini) ; or it may be apparently lacking (Phylloxerinae). 

 The two basal segments are always short, and quite regular in all 

 species. The remaining segments show the greatest diversity, par- 

 ticularly in number, size, and shape. Sensoria are always present on 

 some of the segments. There is one primary sensorium always present 

 at the distal end of the terminal segment, and when the antennae con- 

 sist of more than three segments, one also at the distal end of the 

 penultimate segment. These sensoria are fairly large and clear (some- 

 times furnished with a hairy fringe) and are more or less circular. 

 The accessory sensoria are a group of small indistinct sensoria, which 

 number from three to six, and which are located in close proximity 



1 For a fuller discussion of the external characters consult the following 

 papers: Vickerey, E. A., A comparative study of the external anatomy of plant 

 lice, 12th Eept. Minnesota State Entomologist 1908 ; Sanborn, C. E., Kansas 

 Aphididae, Kansas Univ. Sci. Bull., vol. 3, 1904; Mordwilko, Alexander, Keys to 

 the groups and genera of the Aphididae, Ann. Mus. Zool. Imp. Acad. Sci. St. 

 Petersburg, vol. 13, pp. 362-364, 1908. 



