THE OAT APHIS. 3 



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, a, Antenna of same, 

 still more enlarged. (Original.) 



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. Bather 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 



