THE IMPORTED PINE SAWFLY. 
13 
larvae, since caged individuals supplied with needles complete their 
growth successfully and become adults; nor does it, among those 
larvae practicing it, supplant needle eating. 
PREPUPAL AND PUPAL PERIOD. 
When the larvae have finished feeding they evacuate their ali- 
mentary tracts and shed their skins, becoming prepupae. They then 
crawl about until each finds a suitable place and spins its cocoon. 
The length of time spent in the prepupa stage varies considerably. 
When adults emerge the same year this stage may be as brief as 10 
days, when they emerge the following year it may be as long as 341 
days. 
Table 6 records the results of some experiments to determine the 
length of the prepupal period and the time spent within the cocoon. 
The prepupal period as recorded in this table is not separated from 
the pupal period. It is difficult to determine the exact duration of 
the pupal period. It seems to be brief and the pupa is seldom 
obtained by cutting open cocoons, the insects being nearly always 
found in the prepupal or in the unemerged or immature adult stage. 
Table 6. — Dates of becoming prepupa, of cocooning, and of emergence. 
ADULTS EMERGING THE SAME YEAR IN WHICH THEY COCOON. 
Indi- 
^J" Host plant. 
No. 
Date 
individual 
became 
prepupa. 
Date 
cocooned. 
Days 
between 
time 
insect 
became 
a 
prepupa 
and co- 
cooned. 
Date adult 
emerged. 
Days in 
cocoon. 
Days 
between 
time 
insect 
became 
prepupa 
and 
emerged 
as adult. 
1 Pinus cembra. 
2 P. virginiana. 
3 I P. strobus 
4 l P. monticola.. 
5 P. divaricata., 
6 P. sylvestris . . 
7 do 
June 29,1917 
July 2, 1917 
June 29,1917 
June 18,1917 
June 29,1917 
do 
July 
June 22,1917 July 5,1917 
3,1916 , July 7,1916 4 Aug. 1,1916 
7 
8 
10 
9 
10 
10 
13 
25 
29 
Average . 
3.5 
11.7 
19.5 
ADULTS EMERGING THE FOLLOWING YEAR. 
8 
P. flexilis 
P. taeda 
P. monticola 
P. divaricata 
P. virginiana 
P. sylvestris 
'Juiy"ii,'i9i7" 
July 9, 1917 
July 12,1917 
June 29,1917 
do 
. ..do 
l" 
Apr. 15,1918 
May 2, 1918 
Apr. 24,1918 
May 5, 1918 
May 6, 1918 
May 3, 1918 
May 22,1919 
280 !. 
294 
299 
310 . 
311 i. 
315 . 
339 
9 
10 
295 
11 
12 
13 
June 22,19r 
June 17,19x8 
14 
do 
June 15,1918 
2 
341 
Average 
1.5 
306.8 
318 
SUMMARY OF LIFE HISTORY AND SEASONAL HISTORY. 
Variations in the length of the several stages of Diprion simile, due 
to known factors such as season, sex, etc., or to unknown factors 
such as what determines the prepupa to emerge the same or the next 
year, cause variations in the total length of the insect's life cycle. 
Table 7 indicates the various lengths of life and periods to be 
expected. 
