24 
BULLETIN 746, U. S. DEPARTMENT OF AGRICULTURE. 
just back of the head, and by a series of contractions and contortions 
it is worked back over the body. Sometimes the head capsule is cast 
before the skin and at other times not until afterwards, but usually 
it is cast during the process of molting. The capsule is worked loose 
by the movements of the body and is deposited at one side. 
The freshly molted larvae are white and almost colorless, or show 
faintly purplish markings running the length of the body. The head 
is white and soft when first molted, but it turns mahogany brown 
in a few hours and the markings deepen. Eosenfeld and Barber 
(137) say that the color of the protective fluid secreted by the larvae 
is determined by the color of the head and that the fluid is white in 
freshly molted larvae. 
The whole process of ecdysis requires about 15 minutes. The larvae 
then turn, eat the discarded skin, and recommence feeding on the 
cane. 
Ordinarily there are 5 molts, but sometimes there are only 4 in 
rapidly-developing larvae. More than 5 are fairly common, as many 
as 14 having been observed in hibernating larvae. When the larval 
period is prolonged by low temperature or other conditions, the larvae 
continue molting, with little or no increase, or even a decrease, in size. 
IN STARS. 
The period from hatching until the first molt is called the first 
instar. Between the first and second molts the period is known as 
the second instar, and so on until the larva reaches the pupa stage. 
The last instar is the period between the last larval molt and the 
beginning of the pupal period. The number of instars has been 
found to be from 3 to 10, with 5 as the most common number. The 
number in relation to mean temperature is shown in Table IV. 
Table IV. — Relationship of mean temperature to the number of instars of the 
larva of the sugar-cane moth borer. 
Number pf 
instars. 
Average 
mean tem- 
perature. 
Number of 
records. 
Number of 
instars. 
Average 
mean tem- 
perature. 
Number of 
records. 
3 
4 
5 
6 
F. 
74.8 
80.3 
81.1 
82.2 
14 
65 
102 
50 
7 
8 
9 
10 
o Fm 
78.9 
69.8 
68.8 
65.5 
18 
11 
8 
4 
DURATION OF LARVAL PERIOD. 
The larval period is the most variable of all the stages in the life 
history of this insect, as it is this stage which is prolonged by 
hibernation or adverse conditions. The first molt takes place from 
3 to 6 days after hatching, when the larvae are from 2 to 4 mm. long. 
From 4 to 8 days are spent in the second instar, and during this 
