Oct. is, 1917 
Life History of Macrosiphum Illinoisensis 
89 
mm. Cornicles cylindrical, often slightly tapering toward the tip. Byes black. 
Length from vertex to tip of cauda, 0.64 mm. 
Third instar. —General color deep reddish brown with black eyes; antennae 
dusky toward the tip and composed of five segments. Segment III, 0.112 mm.; 
IV, 0.064 mm.; V, 0.048 plus 0.192 mm. Cornicles 0.064 mm., somewhat tapering. 
Length from vertex to tip of cauda, 0.8 mm. 
Fourth instar. —Color characters similar to those of the third instar, but some¬ 
what lighter in general color. Antennae of five segments. Segment III, 0.192 mm.; 
IV, 0.112 mm.; V, 0.08 plus 0.208 mm. Cornicles 0.96 mm., tapering, and rather 
broad. Hind tibia somewhat swollen. Length from vertex to tip of cauda, 0.96 mm. 
Fifth instar (adult). —General color yellowish to reddish brown, eyes black; 
cauda and anal plate dusky; antennae with the basal two segments and with the 
distal segment dusky; legs dusky, sometimes lighter on the median area of the tibiae. 
Antennae of six segments; segment III, 0.16 mm.; IV, 0.128 mm.; V, 0.128 mm.; 
VI, 0.08 plus 0.224 mm. All segments except the first two distinctly imbricated, 
no sensoria except the usual ones present. Cornicles distinctly tapering and imbri¬ 
cated, 0.096 mm. long, dusky in color; hind tibia somewhat swollen, 1.36 mm. long 
and armed with about 50 small, irregularly placed, circular sensoria. Length from 
vertex to tip of ovipositor, 1.44 mm. 
