Piant Lick INJuRING FOLIAGE AND FRUIT OF THE APPLE 743 
flower stalks. The young grow very rapidly, and under favorable 
conditions become mature within from ten to fifteen days. Thru- 
out the summer months breeding is continuous and_ generation 
follows generation with considerable rapidity. During the summer of 
1916 at least six generations matured on the plantain. By the first 
week in August of that year the fourth generation was mature and ready 
to produce young. ‘Then there came very dry, hot weather, which con- 
tinued until well into September. During this time the lice were rather 
inactive, failed to grow rapidly, and died off in large numbers. Only on 
the lower leaves and at the base of the flower and leaf stalks did the aphids 
survive, and it was almost impossible to follow closely the number of 
generations. 
During the summer of 1917 a more detailed study was made of the 
reproductive capacity of the summer generations on plantain. Starting 
with the spring migrants from the apple, continuous rearing experiments 
were conducted thruout the season. In 1916 the rearing experiments 
were conducted in large cages, in each of which several narrow-leaved 
plantains were growing under natural conditions (Plate IX). In this way 
enormous numbers of the young were obtained, considerable crowding 
occurred, and, as later noted, winged forms appeared in several generations. 
In 1917 the rearing work was all done on young narrow- and broad-leaved 
plantains growing in small pots in an outdoor insectary. By this method 
close observation could be made on the individual reproductive capacity, 
and, tho many hundreds of individuals were reared, only one winged form 
appeared on the plantain. This occurred. in the third generation on 
plantain, counting the winged as the first. 
In Reproduction Chart II and figure 120 is presented a rather interesting 
study of longevity and reproductive capacity of the spring and fall 
migrants, as well as the true summer forms, on their preferred host plant 
(Plantago lanceolata). . It will be noted at once that the spring migrant 
shows a shorter longevity and a remarkable reduction in reproductive 
capacity as compared with the spring forms on the apple. The succeeding 
wingless generations are more productive than the winged migrants, the 
productive period is much longer, and the longevity is greatly increased; 
as compared with the forms on the apple, the longevity on the average 
is greater and the productive period is longer, whereas the reproductive 
