DESCRIPTION OF SUMMER FOEMS. 



59 



Fig. 12. — The spring grain-aphis: 

 Young, first instar. Enlarged; 

 actual size, 0.75 mm. (Original.) 



Measurements of antennal joints (average from 16 specimens): I, 0.066 mm.; II, 

 0.049 mm.; Ill, 0.226 mm.; IV, 0.140 mm.; V, 0.152 mm.; VI, base, 0.091 mm.; VI, 

 filament, 0.225 mm. ; total length, 0.951 mm. They are slightly pruinose in each stage. 



The material from which these data were taken is mounted on slides and is in the 

 collections of the Bureau of Entomology, bearing Webster number 5151. 



The first generation, or stem mothers, is always wingless. All of the following gener- 

 ations differ in color, more especially in the first and second instars. The adult stem 

 mothers, so far as we have been able to learn, never 

 have the darker green dorsal stripe. The antennae 

 are shorter throughout the different instars, and in 

 the adult also, than in the summer forms. 



DESCRIPTION OF THE SUMMER FORMS. 



First instar (fig. 12). — Before first molt: General 

 color very pale green, the thorax probably the palest; 

 head pale green with a dusky tinge; eyes brownish 

 black; tip of cornicles black, bases dusky; articula- 

 tion of femora and tibiae and distal portion of tibiae 

 dusky; tarsi black; two apical segments of antennae 

 black, remaining segments concolorous with head. 

 Antennae 4-segmented. 



Measurements of antennal joints (average from 3 specimens): I, 0.032 mm.; II, 

 0.033 mm.; Ill, 0.118 mm.; IV, base, 0.049 mm.; IV, filament, 0.154 mm.; total length, 

 0.386 mm. 



Second instar (fig. 13). — Before second molt: General color slightly paler now; head 

 not dusky; eyes same as in preceding stage; legs with a more greenish tinge now, other- 

 wise same as in previous stage; the two basal joints and the proximal portion of the 

 third joint of antennae concolorous with head, other portion black. Antennae 5-jointed. 



Measurements of antennal joints (average from 2 

 specimens): I, 0.041 mm.; II, 0.035 mm.; Ill, 0.106 

 mm.; IV, 0.075 mm.; V, base, 0.062 mm.; V, fila- 

 ment, 0.204 mm.; total length, 0.523 mm. 



Third instar. — Before third molt: Coloration prac- 

 tically same as in second instar; eyes almost black; 

 bases of cornicles paler than abdomen. Antennae 

 5-jointed. 



Measurements of antennal joints (average from 2 

 specimens): I, 0.056 mm.; II, 0.045 mm.; Ill, 0.172 

 mm.; IV, 0.099 mm.; V, base, 0.076 mm.; V, fila- 

 ment, 0.259 mm.; total length, 0.707 mm. 



Fourth instar. — Before fourth molt: General color 

 deeper green now, very close to apple green; dorsal 

 stripe apparent in this stage at times, eyes of young 

 showing through body wall at this time, head a shade 

 lighter than body and sometimes seeming to be tinged 

 with yellow; eyes brownish black; beak black at tip; legs more of a yellowish green 

 now, the articulation of femora and tibiae and the distal portion of the tibiae dusky; 

 tarsi black; the two apical segments of antennae black, next much fighter, third 

 slightly dusky, and the two basal segments concolorous with head. Antennae 5-seg- 

 mented, although sometimes they appear to have 6 segments. 



Measurements of antennal joints (average from 2 specimens): I, 0.060 mm.; II, 

 0.045 mm. ; III, 0.272 mm. IV, 0.120 mm. ; V, base, 0.086 mm. ; V, filament, 0.282 mm. ; 

 total length, 0.865 mm. 

 All of the above stages slightly pruinose. 



Fig. 13. — The spring grain-aphis: 

 Young, second instar. Enlarged; 

 actual size, 0.922 mm. (Original.) 



