86 INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



THE OAT APHIS 56 



Aphis avence Fabricius" 



(Siphocoryne avence Fabricius) 



(Aphis annw CEstlund) 



(Aphis fitchii Sanderson) 



(Fig. 69) 



Description. — The wingless, viviparous females, which are common 

 during the spring and summer, are yellowish or dark olive-green, 

 often with a mottled effect on the dorsum and with orange-colored 

 areas around the hases of the cornicles. The latter markings are 

 usually present only in the spring forms. The winged viviparous 

 females or migrants are olive-green with black head, thorax, antennae 

 and honey tubes, black spots on the sides of the abdomen in front 

 of the honey tubes, and the characteristic orange spots at the bases 

 of the latter. The young of the wingless and winged forms are light 

 green with the orange-colored areas at bases of cornicles very dis- 

 tinct. The egg-laying females, occurring upon the trees in the fall, 

 are pale yellowish-green or orange-colored with conspicuous orange 

 or pinkish spots at base of cornicles. The males occurring with the 

 egg-laying females are of the same color, smaller and have wings. 

 The eggs are first light green, but soon become shining black. 



Fig. 69. — The oat aphis, Aphis avenw Fab. Greatly enlarged. (Author's 

 illustration, P. C. Jr. Ent.) 



Life History.— The winter is spent either in the egg stage, around 

 the buds and upon the smaller twigs of trees, or as often the case 

 in California as viviparous females on the roots or stems of grasses. 

 Those hibernating on the grasses are the viviparous females which 

 give rise to the generations of viviparous wingless females and winged 

 migrants so common throughout the late spring and entire summer. 

 The eggs hatch into stem-mothers in the spring and these give birth 

 to viviparous females which also produce the common summer forms. 

 In the fall the migrants or winged viviparous females leave the 

 grasses, weeds, etc.. and seek fruit or other trees where they give 

 birth to the true sexual males and females which mate, and the lat- 



TMs species has also been known as "The European Grain Louse." 

 "Much of the information contained in this description is derived from Bui. 

 NQ. 112, U. S. Dept. Agiic, Aug. 1914, by Mr. John J. Davis, 



