July 8,1918 
Toxoptera graminum in the South 
101 
COMPARATIVE LENGTH OF LIFE OF INDIVIDUALS IN THE DIFFERENT 
SERIES 
The length of life of individuals constitut*ng the generations in the 
different series is clearly represented in figures 4, 5, and 6. In these 
Fig, 5.—Graph showing comparative length of life of the individuals of Toxoptera 
graminum in the B series plotted against the date of birth of the individuals. 
Columbia, S. C., March 23, 1914, to April 26, 1915. Solid lines represent gen¬ 
erations of first-born and broken lines generations of last-bom individuals. 
diagrams the heavy solid lines represent first-born individuals and the 
broken ones last-bom individuals. By referring to figure 4 it will be 
seen that the life of individuals bom during 
the months of May, June, July, and August was 
much shorter than of those born during the fol¬ 
lowing four months; in fact, the individuals bom 
during summer lived only about one-half as long 
as those born during fall. The longest-lived in¬ 
dividual in this series was bom during the latter 
part of October and lived for a period of about 
three months. The individuals bom during 
the summer months of the second year in the A 
series were shorter lived tMn were those bom 
during the same months the preceding year in 
the same series. Similarly the individuals bom 
during the fall and early winter of 1914 were 
also shorter lived than were those bom during 
the same period in the preceding year in this 
series. This fact would seem to indicate that 
the strain became weaker the second year , and 
this presumption is supported further by the 
results obtained from the control experiments 
conducted during the year 1914, known as the B series. By comparing 
the individuals in the A series with those of the B series it will be noted 
APKIU I 
Fig. 6.—Graph showing compara¬ 
tive length of life of individuals 
of Toxoptera graminum in the C 
series plotted against the date of 
birth of the individuals. Colum¬ 
bia, S. C., April 10,1915, to June 
26, 1915. Solid lines represent 
generations of first-born and 
broken lines generations of last- 
bom individuals. 
