BULLETIN 112, U. S. DEPARTMENT OF AGRICULTURE. 
bug.'' although occasionally it may be found in conspicuous and alarm- 
ing numbers, but it is ever present on wheat : and. especially in the fall, 
when it occurs at the base of the plant and on the roots, it is easily 
overlooked by the casual observer. However, there is no doubt that 
these plant-lice, even though they may not be conspicuous and 
apparent, weaken the plants and decrease the yield. This de- 
crease in yield is presumably general, but may not as a rule be 
locally conspicuous as in the case of the " green bug." that is, not 
enough to be recognizable. On the 
whole, however, it can hardly be doubt- 
ed that these little insects are respon- 
sible for the loss in this country of thou- 
sands of bushels of wheat annually. 
DISTRIBUTION. 
The oat aphis is almost cosmopoli- 
tan in its distribution, and in this 
respect rivals such well-known plant- 
lice as Macrosiphum pisi Kalt., M. 
granarium, and Toxoptera graminum. 
It has been found in all parts of 
Europe, as well as in most of the 
States of the United States. Quite 
likely it will also be found to occur 
in Asia, and probably in Africa, 
although we believe it has never 
been reported in literature from 
these countries up to the present 
time. 
The map (fig. 1). compiled from rec- 
ords made by assistants in the Cereal 
and Forage-Crop Insect Investigations and from authentic pub- 
lished records, indicates the present known distribution in the United 
States. It will be observed that the species has not been found in the 
Gulf region. 
DESCRIPTIVE. 
On grain two forms of the oat aphis are found — the winged and 
wingless viviparous females. As will be explained later, it occurs 
on the apple where there are to be found, in addition, the sexual 
forms, namely, the wingless oviparous female, the winged male, and 
eggs. (See fig. 5.) 
The wingless viviparous female (fig. 2) is yellowish green to 
olive green, often somewhat mottled. The stem mothers on apple 
Fig. 2. — The oat aphis {Aphis 
avencE) : Wingless viviparous 
female, much enlarged. a. 
Antenna of same, still more en- 
larsed. (Original.) 
