LO Rosert MATHESON 
predacious enemies of apple plant lice are deferred until a future time, 
in order to bring together more data and present them in a thoroly digested 
form. : 
Number of generations 
During the season of 1915 there developed in the outdoor breeding 
cages fourteen viviparous generations. The fifteenth generation con- 
sisted of true males and females. This generation reached maturity 
about October 1. Mating began on that date and the first egg deposition 
was observed on October 4. Egg deposition began in the neighboring 
orchards at the same time. . 
Altho in the rearing-cage work the generation maturing on October 1 
proved to consist of true males and females, yet for more than a month 
after that time viviparous females were producing young in the field 
under exactly similar conditions to those in the rearing cages. This 
would indicate that generations starting from young deposited by the 
stem mothers during the early part of June (as shown in the chart) do 
not begin producing the male-and-female generation until later in the 
fall. However, as to the average number of generations in a single season, 
no definite figure can be given without rearing thru a very large series, 
starting with the earliest- and latest-maturing stem mothers. This would 
involve too much detailed labor without adding materially to the 
knowledge of the subject. Judging from rearing work and field observa- 
tions, the writer is led to conclude that in all probability there are ten full 
generations or more in a single season. When one considers the great 
reproductive capacity of each of these generations, it is not to be won- 
dered at that severe infestations may occur at any time provided the 
natural checks are interfered with in any way. 
Reproductive capacity of Aphis poma 
In consulting the reproductive capacity chart, some interesting facts 
may be observed. The maximum productive period (31.6 days) is for the 
stem mothers, and the thirteenth generation follows closely with 30.2 days. 
Unfortunately, no data were obtained on the fourteenth generation, 
owing to the death of the viviparous mothers in the special rearing cages. 
The minimum productive period (13.7 days) occurred only with the 
winged females of the second generation. The productive period varied 
