744 Rosert MATHESON 
capacity is greatly lessened. In the case of the summer forms on plantain, 
no attempt was made to determine the daily reproductive capacity, the 
rearing cages being examined only as recorded in the chart. However, 
it will be observed that the daily average, which is very low as compared 
with the forms on apple, is fairly well distributed over a long reproductive 
period. This is not the case with the spring and fall winged migrants. 
On 
Lar GAT? 712 gerreranior7 
| 
St gereranors 
| 
G% VEEL — 
On geele { l0t4 gerreraa, 
20 30 10 20 30 9 19 29 9 19.29 8 18 29 8 18 28 8 18 28 
April May June July August September October 
Fic. 120. GENERATIONS OF APHIS SORBI 
The part of the line between the round dots represents the productive period; the remainder of the 
line represents the period of life after production ceased. The fourth generation all migrated to the 
plantain, and the tenth returned to the apple 
(1) Died November 5; (2) died October 29; (3) ceased reproducing November 5, died November 16; 
(4) died November 4; (5) died October 21; (6) ceased reproducing November 5, died ‘November 16 
In these cases the reproductive period is reduced, whereas a marked 
reproductive activity occurs within the first few days after maturity 
is reached and the new host plant is occupied. The spring migrant gave 
an average daily production of 5.4 for five individuals during the first 
two days, followed by a daily production of only 1.4 during the next 
nine days. The fall migrant gave an average daily production of 3.2 
for five individuals during the first three days, followed by only 0.34 
during the next seven days, when reproductive activity practically ceased. 
