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. 



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 of 

 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 



° F. 

 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 



