THE IMPORTED PIXE SAWFLY. 5 
Table. 1. — Average size of larval instars and prepupa of Diprion simile, in millimeters. 
Head. 
Body length. 
Number 
of larvae 
Instar or stage. 
Height. 
Width. 
Young. 
Full 
grown. 
used to 
obtain 
averages. 1 
I . 
Milli- 
meters. 
0.75 
.95 
1.20 
1.60 
2.00 
2.00 
1.95 
2.20 
2.20 
Milli- 
meters. 
0.50 
.75 
1.00 
1.40 
1.80 
1.80 
1.65 
2.00 
2.00 
Milli- 
vieters. 
2.75 
4.00 
7.00 
8.00 
14.00 
2 14.00 
11.00 
15.00 
2 19.00 
Milli- 
meters. 
6.0 
8.0 
12.0 
15.0 
20.0 
3 13.0 
18.0 
25.5 
3 12.0 
Milli- 
meters. 
11 
II 
11 
Ill 
IV 
V (male penultimate ) 
8 
7 
5 
2 
3 
VI (female penultimate) 
3 
2 
1 These larvae were reared in isolation and measurement's were made at frequent intervals. The dimen- 
sions obtained from them are perhaps few in number but accurate and from an instar or stage positively 
known. The averages obtained from these larvae were found to apply to larva* in the general rearing cages. 
2 Largest. Prepupae do not feed and grow. They contract with development and the spinning of the. 
cocoon/ 
s Smallest. 
The different instars of the larvae of Diprion simile are colored as 
follows : 
Instar I. — Before feeding: Head whitish, eye spots blackish. Body dull gray. 
After feeding: Head and legs become blackish. 
Instar II. — Much the same as the first instar. ■ The dorsum darkens somewhat at the 
approach of the time to shed. 
Instar III. — Head black. Body green to bluish gray. The day before molting to the 
fourth instar the larva begins to show dark dorsal, supraalar, and epipleural lines. 
This change previous to shedding is doubtless caused by the darker coloration of 
the approaching instar showing through the skin about to be shed. 
Instar IV. — Head black. Body considerably darkened, greenish black and yellow, 
pattern of mottling similar to that of full-grown larva. The larva pales somewhat 
with age or increased size. 
Instar V. — Head black. Body velvety black and yellow. The black becomes 
greenish with age or increased size. 
Instar VI. — Head black. Body velvety black and yellow. 
Each instar seems to have two poorly marked phases; first, a 
rapid growing period, usually covering the greater part of the instar, 
during which the body increases in length; and, second, a preparatory 
period preceding molting during which there is a retardation in 
growth or even occasionally a contraction. The accompanying dia- 
gram (Fig. 4) shows the records of growth of a male and a female larva 
in body lengths, instars and days, and illustrates this feature. 
PREPUPA. 
The prepupa of the imported pine sawfTy does not feed and its 
development is accompanied by contraction rather than increase 
in size. The cocoon is spun in this stage and, protected within, 
the prepupa changes gradually as it develops into the pupa. 
The following description is from a prepupa preserved in alcohol 
which had not begun the spinning of its cocoon. Prepupre after 
spinning do not differ structurally from those which have not spun 
but are considerably more contracted. A prepupa that is to produce 
a female adult will measure about 19 millimeters in length before 
spinning its cocoon, while, after spinning, it will be about 12 milli- 
meters long. 
