12 
BULLETIN 1182, U. S. DEPARTMENT OF AGRICULTURE.- 
For eggs laid about the middle of May (May 9 to 19), from 11 to 14 
days were required for development to the point of hatching, aver- 
aging 12.8 days. For eggs laid in late June, 8 days sufficed for 
development. Fertilized and unfertilized eggs, apparently, did not 
differ in the duration of the incubation period. 
LARVAL DEVELOPMENT. 
The larvae of the imported pine sawfly shed their skins as they 
develop. The periods between moltings of the larva are called in- 
stars. The number of instars, the difference in the number between 
larvae producing female adults and those producing males, and the 
size and appearance of the larvae in each of the various instars have 
been treated under " Larval instars." 
Table 5 shows for a number of larvae the time spent in each instar, 
the average length of the instar, and the total length of the larval or 
feeding period. This table is arranged to show sex and date of 
hatching of each individual or group of individuals, because the sex 
makes a difference in the number of instars, and the rate of develop- 
ment of the larvae appears to be accelerated as the season advances. 
Table 5. — Number and length of larval instar, of Diprion simile, showing individual' s 
date of hatching and sex. 
Sex. 
Length of instar. 
Date egg hatched. 
Instar 
I. 
Instar 
II. 
Instar 
III. 
Instar 
IV. 
Instar 
V. 
Instar 
VI. 
Total. 
May8! 
Male.... 
...do 
Days. 
6 
6 
7 
6 
6 
7 
6 
4 
Days. 
5 
5 
5 
4 
4 
4 
5 
7 
Days. 
3 
4 
4 
4 
4 
4 
5 
7 
Days. 
6 
5 
4 
4 
4 
6 
4 
5 
Days. 
12 
11 
9 
11 
10 
2 
6 
3 
Days. 
Days. 
32 
Do.' 
31 
May 9i 
...do.... 
29 
May 12 1 
...do... 
29 
k D0.1 
...do 
28 
May 222 
...do 
23 
May 25 2 
...do 
26 
Do. 1 
...do.... 
26 
...do. .. 
4 to 7 
6 
4 to 7 
41 
3 to 7 
4f 
4 to 6 
4? 
2 to 12 
8 
23 to 32 
Average early.. 
...do 
...do 
28 
July 1 
4 
5 
2 
3 
2 
16 
...do 
Average mid- 
4 
5 
2 
3 
2 
16 
Female.. 
...do 
...do 
May 9 
9 
6 
6 
4 
4 
4 
5 
4 
4 
3 
2 
2 
6 
5 
4 
•10 
9 
9 
37 
May 12 
Do 
30 
29 
...do 
...do 
Extremes 
Average early.. 
6 to 9 
7 
4 to 4 
4 
4 to 5 
4J 
2 to 3 
4 to 6 
5 
9 to 10 
29 to 37 
32 
1 Isolated for stages. 
J Cage work. 
LARVAL HABITS. 
The larvae from the time of hatching to the latter part of the 
second instar or the beginning of the third feed only on the exterior 
of the needles, expecially from the angles or sides. They then begin 
to consume the entire needle. At about the fourth or fifth instar 
they attack the young shoots, feeding on them basally to an extent 
sufficient frequently to cause the shoots to die and fall. This habit 
of feeding on the shoots is not essential to the development of the 
