GENETIC RELATIONS OF THE WINGED AND 

 WINGLESS FORMS TO EACH OTHER AND 

 TO THE SEXES IN THE APHID MACRO- 

 SIPHITM SOLANIFOLII 



A. FRANKLIN SlIl'LL 

 Michigan, Ann Arbor, ] 



Inteoduction 



Life cycles are known, in many aphid species, from 

 field observations alone. A number of cycles have been 

 determined from breeding experiments upon aphids in 

 confinement. Often, however, these experiments appear 

 not to have used the pedigree method. In the course of 

 some work on the potato aphid, Macrosiphum solam- 

 folii, 1 I observed indications of peculiarities in the ge- 

 netic relations of the various forms to each other, which 

 could be detected only by the pedigree method. Experi- 

 ments designed to demonstrate these relations were in- 

 stituted, with the results described in this paper. 



Macrosiphum solanifolii, as observed in these experi- 

 ments, comprises four kinds of individual: (1) the apter- 

 ous viviparous female, which is green; (2) the alate vivip- 

 arous female, which is also green; (3) the oviparous or 

 sexual female, which is wingless and of a yellowish-green 

 color until late in life, when the abdomen becomes filled 

 with green eggs which impart a green color to the female 

 herself; and (4) the male, which is winged and of a brown 

 or brown and green color. Of these types of individual, 

 the alate female can be recognized when a little more 

 than half grown by her wing pads. The oviparous fe- 

 male has thickened brown hind tibiae covered with sen- 

 soria, which are recognizable with the unaided eye, and 

 which develop a few days before maturity. The male 



