4 MISCELLANEOUS STUDIES 



by the author in so far as it was possible to obtain specimens. Inci- 

 dentally it may be stated that the author has personally collected by 

 far the larger number of the species recorded in this paper. In other 

 cases the fact is noted. A host plant index (appendix 2) is also 

 included. 



The system of classification followed is the one most generally 

 accepted by American aphidologists at the present time. The keys 

 to the species have been formulated by the author, those to the genera 

 and higher groups have to a large extent been adapted from other 

 workers, particularly Wilson and Essig (Aphidinae), Borner (Phyl- 

 loxerinae), and Tullgren (Pemphiginae). The papers of Baker, 

 Clarke, Davidson, Davis, Essig, Gillette, Oestlund, Patch, Pergande, 

 Williams, Wilson, and other American aphidologists have been found 

 invaluable. Of the works of the European aphidologists, those of 

 Borner, Buckton, Del Guercio, Koch, Mordwilko, Tullgren, and Van 

 der Goot have been in constant use. The classification suggested by 

 Van der Goot ("Zur Systematik der Aphiden, " in Tijdschrift voor 

 Entomologie, vol. 56, p. 1913) has proved interesting, and although 

 the author has not felt at liberty to accept it in full, a translation of 

 his keys to the groups and genera has been included herewith (appen- 

 dix 1), which, it is hoped, will be of assistance in the making of 

 determinations. 



CLASSIFICATION 



The Aphididae belong to the order Homoptera, being closely 

 related to the Psyllidae, or jumping plant lice, the Aleyrodidae, or 

 white flies, and the Coccidae, or scale insects. The Aphididae, or 

 plant lice, are small, soft-bodied insects, ranging from less than one 

 to five or six millimeters in length. Typically there are four forms : 

 the apterous and the alate viviparous females, and the sexual forms, 

 the oviparous females and the males. There is considerable variation 

 from the above in different groups and species, as will be pointed 

 out under the discussions of the various species. The alate viviparous 

 females are the individuals most commonly taken by the collector and 

 the ones that usually show the best characters for determinations. 

 In the keys in this paper all characters refer to the alate viviparous 

 females (the alates) unless otherwise mentioned. 



