THE PEA APHIS WITH RELATION TO FORAGE CROPS. 49 
An average of all experiments for the two years, carried through 
out of doors and apparently under normal natural conditions, was 
12.1 + days. As would be anticipated, and as is sho^\^l in Tables IV 
and V, the age at which females began reproducmg was shortest 
durmg the warmer parts of the year and longest durmg the early 
spring and late fall months. In the case where immaturity lasted 56 
days the aphis would doubtless have remained immature for a much 
longer time, possibly all winter, had it been left out of doors under 
natural conditions. (See footnote 1, Table VI.) From 16 individual 
experiments, between March 23 and September 21, Mr. R. L. Webster 
(Folsom, 1909) found that a female begins to reproduce 11 days after 
birth, on an average. 
REPRODUCTIVE PERIOD. 
The reproductive period — that is, the time or period during which 
the insect gave birth to young — varied from 2 to 68 days in 1912 and 
from 2 to 61 days m 1913, or an average for the two years (53 exam- 
ples) of 22 days. In computmg these averages some records, where 
the apliis was known to have died from other than natural causes, 
were not considered. Except m cases where death was due to other 
than natural causes, the female almost invariably lived several days 
after the birth of its last young, the length of time varying from 2 
or 3 to 28 days. 
LONGEVITY. 
As is the rule ^vith all of the Aphidid?e, the pea aphis lives for a 
much longer time in the sprmg and fall, especially in the fall, than in 
the suromer. In our records the total length of life — that is, from 
date of birth to date of death — of individuals varied from 10 to 85 
days in 1912 and from 10 to 78 days in 1913, or an average of 39.1 + 
days from 51 records made during the two years. Tables IV and V 
may be referred to for the variation in lengths of life at the different 
times of the year. In Mr. Webster's experiments reported by Dr. 
Folsom (1909) the length of life of 16 individuals from as many con- 
secutive generations varied from 13 to 50 days, "svith an average of 
25.4 days. 
FECUNDITY OF VIVIPAROUS FEMALES. 
The aphis under discussion is one of the most prolific of all plant- 
lice. We find that a female may give birth to as many as 14 young 
in a period of 24 consecutive hours. The average number of young per 
female for all individuals where records were kept in 1912 and 1913 
(59 examples) was 3.7+ per day, but this is the average for the 
entire reproductive period of each female, and as we learned, tho 
birth rate greatly diminishes toward the latter days of its life, often 
not averagmg one young a day. Takmg this mto consideration 
we find the average birth rate during the active life of the mother 
