Life History.

The life history of this species of aphis, like that of many other species of aphis, is not yet completely clear. It has not yet been accurately ascertained as to whether the continuity of existence is maintained by eggs laid up during the winter, or by hibernating larvæ. It is believed that it is carried on by larvae, because larvae have been seen very early in the spring on the stems of the wheat plants, and upon the stems and blades of couch grass, close to the ground. Drs. C. Thomas and Asa Fitch and other American entomologists have also seen the larvae of this aphis at the roots of wheat plants during the winter, together with the females producing them.

The winged female insect is light brown in colour, with the abdomen green, with legs of a dark yellow hue with black knees and feet. The eyes are red and the cornicles black.

In colour the larvæ or lice—wingless females bringing forth successive generations of live larvae (Fig. I. 3, 4)—differ from the perfect insects, being green or dark green with brown antenne, having, however, legs of the same shade of yellow and black. Their beaks or rostra are short, as in the case of the perfect insects.

The winged, egg-laying female (Nos. 1, 2) is not developed until late in the season, but winged females bringing forth live larvæ are generated at various times and intervals, as in the case of the hop aphis, Aphis humuli, when, as is commonly supposed, the food supply fails and the insects become too thick to thrive.