THE PEA APHIS WITH RELATION TO FORAGE CROPS. 
43 
Figure 1 1 shows grapliically the hues of generations carried through 
in 1912 and the different individual experiments in each generation, 
including the cage number and dates of birth above the line and the 
date of death or termination of the experiment below the hne^ for each 
cage record. Figure 12 shows the length of each generation of the 
same series (1912). 
Thus it will be noticed tliat the first generation in the series (prob- 
ably the second generation from the egg) was the shortest, while the 
ninth generation was the longest, extending over a period of 156 days. 
Likewise it will be seen that on June 1 two generations coexisted; 
on July 1, four generations, from the second to the third; on August 1, 
seven generations, from the third to the ninth, inclusive, and on Sep- 
tember 1, eight generations, from the fifth to the twelfth. 
1 
OCT 
17SC. 
/* 
/S • 
/■^ 
30£>. 
2 
3 
70- 
4 
68- 
S 
63- 
6 
/8 
7S- 
7 
30 
79- 
3 
/43' 
9 
/ 
/S6" 
/O 
/4S- 
/2 
// 
/S 
/a 
27- 
/3 
/4 
/s 
/<5 
38 ■■ 
/r 
3a. 
^7' . 
Fig. 12.— reriods and succession of generations in Macrosiphum pisi, Ld Fayet' e, Ind., 1012. 
* This is the first generation found in the fiald and is jirobably about the third from the egg. 
HATCfflNG OF THE EGG. 
At La Fayette, Ind., the eggs of M. pisi hatch the latter part of 
March; in the cases recorded in 1913 they hatched March 31. Folsom 
(1909) records the hatching of eggs at Urbana, 111., March 23, in 1905. 
MOLTING. 
According to our experiments this plant louse, like others of this 
family of insects, has five ins tars and never molts more than four 
times. In 1905 ^Ir. R. L. Webster, then an assistant of Dr. S. A. 
Forbes, State entomologist of Illinois, observed 10 individuals, all of 
which molted four times, although Mr. J. P. Gilbert, at the same 
laboratory, claims to have observed an individual molt five times 
(Folsom, 1909). Table IV gives our detailed records. 
