Feb. 21, 1916 
Green Apple Aphis 
977 
OCCURRENCE 
Although, as has already been stated, this form is not necessary for 
the successful propagation of the species, it occurs quite commonly 
throughout the greater part of the summer. In the second generation 
the winged form outnumbers the wingless, although the writers were 
unable to determine the exact proportion. Thereafter winged insects are 
always less abundant than wingless. 
This form occurred, in the writers' experiments, in every generation 
from the second to the fifteenth, inclusive. It was of very rare occur¬ 
rence, however, after the thirteenth generation. In the complete life- 
history diagram (fig. 4) it occurred 149 times, each occurrence repre¬ 
senting a different combination of the two factors, form and generation, 
among the ancestors. 
In the field winged forms were apparently present in small numbers 
all summer. Definite observations were made on several days during 
July and August. In all cases migrants were found in every colony of any 
considerable size. 
It is very interesting to note that in only 18 cases were winged forms 
produced by winged mothers, and in only one case did three winged gen¬ 
erations occur in succession. 
The last winged insects were born on September 9; none were found 
after October, either in the experiments or on the trees. 
length of nymphal life 
The immature stages of this form covered a period of two more days 
than did the same stages of the wingless form. This extra time was 
occupied in the pupal instar, the three earlier stages requiring the same 
amount of time as the corresponding stages of the wingless form. 
REPRODUCTION 
Dividing the season into periods similar to those used in the discussion 
of the wingless reproduction, the writers obtain the following figures: 
The average reproduction by 29 winged insects during the first period 
(to July 1) was 50.1 per mother; that of 25 insects in the second period 
(July 1 to September 1), 25.4 per mother. Very few winged insects 
occurred during the third period, and the writers have no complete 
records of progeny from any individuals. During the first period the 
average per insect per day was 2.92. During the second period it was 
2.04. 
The seasonal average production per insect was 39, while the daily 
average was 2.62. The greatest number produced in one day was 6, and 
the maximum number of young produced by one individual was 120 (in 
21 days). The average length of the reproductive period for the entire 
season was 20.75 days. 
