62 
THE SPRING GRAIX-APHIS OR 
During the summer of 1907, at Richmond. Inch, careful observa- 
tions were made on 7 individuals of the summer forms, and in the fall 
Mr. R. A. Yickery. of this bureau, made observations on 6 indi- 
viduals. 3 of which proved to be males and 3 oviparous females. 
In each case there vrere 4 molts. In the spring of 1908, 4 stem moth- 
ers were found to molt 4 times only. In the spring of 1909 at Lafay- 
ette, Ind.. 1 stem mother was found to molt 4 times. Later on in the 
summer. Mr. T. H. Parks, of this bureau, ran a series of experiments 
with the summer forms and, of the 30 individuals under observation, 
some of which were winged, he found that all without exception 
molted 4 times. In the faU of 1910 several additional oviparous 
females were found to molt 4 times only. This makes a total of over 
50 specimens that came under our observation, under conditions that 
would absolutely preclude error, and there was not a single excep- 
tion — aU molting 4 times. 
As it was found that the period between molts varied, experiments 
were begim in the summer of 1907 at Richmond, Ind., in order to 
learn how great the variation was when each individual was subjected 
to the same conditions. 1 This experiment was carried on indoors 
and all individuals were subjected to the same conditions. Table II 
will show the variations. 
Table II. — Variation in the duration of the different instars in Toxoptera graminum. 
From time 
Individual. of birth to 
first molt. 
From first 
molt to sec- 
From sec- 
ond molt to 
third molt. 
From third 
molt to 
fourth molt. 
V 
H. m. 
38 35 
H. 771. 
28 29 
29 15 
26 40 
54 
H. m. 
31 37 
34 36 
35 4S 
40 
36 50 
H. m. 
39 40 
B 
40 15 
34 37 
c 
50 20 
40 22 
D 
45 
64 
E 
44 30 
32 35 
39 37 
There is also considerable variation in the time from birth of 
individuals to the fourth molt and the appearance of the first yoimg, 
as will be seen from Table III. Individuals in Table III are the 
same as in Table II, with the addition of "F" and "1& 3 ." 
Table III. — Variation in the time from birth of individuals to fourth molt and appearance 
of first young in Toxoptera graminum. 
Individual. 
From time of birth to 
fourth molt. 
From time of birth until 
first young appear. 
A 
Hours. Dags. 
143-144 5. 9 
143 5.9 
153 6. 3 
153 6.3 
204 S.5 
195 S. 1 
170-175 7. 1 
H. 
144 
14S 
164 
165 
246 
205 
M75 
771. 
35 
Day*. 
6.02 
B 
6.1 
C 
6.8 
D 
6.8 
E 
10.02 
F 
S.5 
lb 3 
7 9 
1 Proc. Em. Soc. Wash. 
vol. 10, Xos. 1-2, pp. 
11-13, 1908. » I 
approximate. 
