THE SUGAR-CANE MOTH BORER. 
25 
period the larvse attain a length of from 6 to 9 mm. The third 
instar is somewhat longer and requires from 6 to 9 days, the larvse 
reaching 10 to 15 mm. in length, while the fourth instar lasts from 
4 to 6 days, at the end of which the larvse are 15 to 20 mm. long. 
From 3 to 6 days are spent in the fifth instar, and the larvse attain a 
length of from 20 to 30 mm. 
The usual time required for the larva stage under favorable con- 
ditions is from 25 to 30 days in summer and from 30 to 35 days in 
the cooler weather, but it may be much longer. Larvse from the same 
mass of eggs and reared under exactly the same conditions vary a 
great deal, and some of them require two or three times as long as 
others to pupate. Under the most favorable conditions the larval 
period has been as short as 18 days, and has varied from this to 276 
days for hibernating larvse. The larvse are very adaptable in this 
9o 
X 
/O 30 SO 70 SO //O /30 /SO /TO A. 
?0 2>, 
'O &. 
bo a. 
<so s. 
*0 23 
••»« 
In'"* 
sv.-: 
P 
*•*. 
. 
'. 
y 
.> 
.55 
Fig. 8. — Diagram showing relationship of mean temperature to length of larval period 
of the sugar-cane moth borer. The dots represent period means of individuals. 
way and can pass over periods of cold or food shortage without 
serious inconvenience. Typical life histories at different seasons of 
the year are shown in Table V and figure 8. 
Table V. — Relationship of mean temperature to developmental period in larva 
stage of the sugar-cane moth l>orer. 
Mean tem- 
Average 
Number 
Mean tem- 
Average 
Number 
perature. 
period. 
of records. 
perature. 
period. 
of records. 
°F. 
Days. 
°F. 
Days. 
59.4 
246.5 
2 
78.7 
25 
1 
59.6 
216 
2 
79.1 
42 
4 
59.8 
232.5 
5 
79.5 
24 
60 
221 
79.6 
29 
60.3 
225 
79.7 
26 
60.4 
224 
79.8 
23.5 
60.5 
233 
79.9 
23 
60.7 
2*8 
80 
28 
60.9 
262 
80.1 
33 
61.4 
242 
80.3 
48.5 
65.3 
63 
80.4 
31 
65.6 
76 
80.5 
57 
65.7 
74 
80.6 
38 
67.6 
65 
80.7 
49 
68.7 
56 
80.8 
42 
68.8 
52 
80.9 
46 
