16 THE SPRING GRAIN-APHIS OR " GREEN BUG. 
JJ 
an average of 34.25 young to each individual. While too small a 
number of individuals was taken to make the result conclusive, it 
plainly indicates that fecundity is greatest among the "wingless 
individuals. 
AVERAGE NUMBER OF YOUNG PRODUCED DAILY. 
By "the average daily number of young produced" is meant the 
daily average for the reproductive period only of each individual. 
At Kichmond and La Fayette, Ind., the average number of young 
produced daily for those born from March to the middle of June is 
1.9; the daily average for those born from the middle of June to the 
middle of August is 1.7; the daily average for those born after the 
middle of August is 1.2. These figures, of course, include only those 
individuals in the generation experiments. The average number of 
young produced daily for the entire year is 1.6. The final average 
remains the same when all individuals are considered, irrespective 
of generation experiments. 
From the above it will be seen that the daily average is greatest 
in the spring, the summer coming next, and the fall last. This 
corresponds also to the average total number of young for each indi- 
vidual for these periods. 
Mr. Urbahns found that the average number of young produced 
daily at Dallas, Tex., for those individuals that began reproducing 
during December and January was 1.5; the daily average for those 
that began reproducing during April and May was 3.4; the average 
for those that began reproducing during June, July, and August was 
2.1 ; the average for those born after August was 2.5. These averages 
will be seen to agree proportionately with the average number of 
young produced by a single individual during these periods, with the 
exception of the daily average for December and January, which is 
considerably lower. The average daily number of young for the 
entire breeding season for which Mr. Urbahns has any data is 2. 
From the above data it will be seen that the average daily number 
of young for Texas is far above the average for Indiana. Tins can 
probably be accounted for from the fact that the reproductive 
period is much longer in the North and the young are distributed 
over a longer period. Also the average number of young for each 
individual is greater in the South. 
SEXUAL FORMS. 
The first young of the sexes in Indiana are apparently born the 
last week in September, the first adults oftentimes appearing as early 
as the first week of October. The adults can be found from this time 
on until December, or until they are killed off by extreme cold. 
The males can easily be distinguished by their small size. The 
oviparous females (iig. 9) can be readily distinguished without a hand 
