28 



distorted, and little pits or pockets are formed on the underside. 

 (See fig. 21, h; fig. 22^) The upper surface of the leaves assumes a 

 more or less reddish color, evident some distance away. When the 

 plants are badly infested these leaves fall and the fruit becomes 

 poor and ripens prematurely. Red currants are most subject to 

 attack, but black currants and gooseberries also are injured. 



The stem-mothers of the species are green, the other wingless forms 

 (fig. 21, a) a yellowish green, while the winged ones have a black 

 head and body and a large black patch on the abdomen. The eggs 

 are polished black. 



SEASONAL HISTORY. 



The stem-mothers hatch from the eggs in the early spring soon 

 after the leaves open. After completing their growth they produce 

 young aphids which infest the lower surface of the leaves. Some of 

 the offspring of the stem-mother are winged and these fly to some 

 unknown host. The wingless ones remain upon the currants and 

 continue reproduction. In each generation some winged forms 

 occur, but wingless individuals are present until late in July upon 

 the currants. In fact, occasional colonies remain throughout the 

 summer. In the fall, during early October, migrants return to the 

 currant bushes and deposit the sexual females. These when mature 

 are fertilized by the winged males and the eggs are laid upon the 

 twigs. 



THE SOW-THISTLE APHIS.^ 



The sow-thistle aphis is at times quite as abundant on currants as 

 is the currant aphis. It is somewhat similar in color but can be 

 distinguished at once from the currant aphis by the swollen honey 

 tubes. (Fig. 21, c.) In the currant aphis these are long and very 

 slender. (Fig. 21, a.) The eggs are polished black. The sow- 

 thistle aphis injures the currant in about the same way as does the 

 currant aphis, though the infested leaves (fig. 21, d) do not take on 

 a reddish coloration. 



SEASONAL HISTORY. 



The seasonal history of this species upon currants is very similar to 

 that of the currant aphis. The winged forms, however, migrate to 

 the sow thistle and upon this they reproduce. After the production 

 of numerous generations here during the summer, fall migrants are 

 developed which return to the currants. Egg-laying females are 

 then produced and these are fertilized by the winged males. The 

 eggs are laid upon the twigs at about the same time as those of the 

 currant aphis. 



^ Rhijpnh/siphinit Uictiicnc (Kalt.). 



