THE OAT APHIS. 6 
in the spring are more often lighter, with a darker green median 
longitudinal area, while those found on wheat in the fall of the 
year are darker, sometimes becoming greenish brown. The bases 
of the cornicles are surrounded, in the spring forms, with areas 
yellowish to orange in color, while these areas are larger and are 
usually orange to dark reddish in the fall and in hibernating indi- 
viduals. The antennae are about one-half the length of the body, 
and the cornicles, or " honey tubes," are slightly vasiform. 
The winged viviparous female (fig. 3) has a black head and 
thorax, the abdomen being olive green, sometimes paler, with a row 
of more or less conspicuous black spots on each side anterior to the 
cornicles, and usually with a rusty or brownish red area about the 
base of each cornicle. The antennae are black and reach a little 
beyond the middle of the body. The cornicles are black and slightly 
Fig. 3. — The oat aphis : Winged viviparous female, greatly enlarged, 
still more enlarged. (Original.) 
Antenna of same, 
vasiform. The last branch of the median vein in the wings branches 
near the apex of the wing. 
The immature aphides are paler green, but almost invariably the 
yellowish to pinkish areas about the bases of the cornicles are quite 
noticeable, although sometimes faint in very young individuals. 
The winged male is similar to the winged viviparous female except 
that it is smaller and has a narrower abdomen, and the color is 
usually more of a dusky green. 
The wingless oviparous female is somewhat like the viviparous 
female, but the abdomen is more tapering toward the tip, and the 
color is pale yellowish green to greenish dusky, or even has an 
orange tint. Rather conspicuous orange or reddish areas are present 
on the abdomen at the bases of the cornicles. 
The eggs (fig. 5, a) are laid in the crevices of the bark or between 
the leaf bud and twig, and when first deposited are pale greenish, but 
