67 



Table XXII. — Rate of growtJi of larvx at different temperatures. 



Location. 



Average 

 tempera- 

 ture. 



Larval 

 stage. 



Sums of ef- 

 fective tem- 

 peratures. 



Incubator . 

 Laboratory 

 Ice box 



o p^ 

 85.4 

 71 

 57 



Days. 



14 



2. 



"41 



° F. 



425 



077 



'( 51() 



« Three molts. 



The effect of severe cold on larv^ was also tried in a number of 

 cases. All subjected to temperatures somewhat below freezing were 

 killed outright by an exposure of from twenty-four to forty-eight 

 hours, but of those kept at 34° F. for forty-eight hours a small per- 

 centage survived and matured successfully. 



The a])ilit3^ to live for any length of time without food is not very 

 great. Newl}^ hatched larva3 live about twenty-four hours in the 

 hiboratory, i)ut it is probable that in nature the drying effect of the 

 sun and other untoward conditions would shorten this period consid- 

 erably. Larger larvie usually live several da3^s, and occasionally 

 three-fourths or nearly grown ones will pupate successf ulh^ if deprived 

 of food. 



NUMBER OF MOLTS. 



The number of molts has already been stated. Of 100 larvj^e reared 

 in the laboratory at Paris, Tex., in 1904, 90 per cent molted 5 times, 

 8 per cent 4 times, and 2 per cent 6 and 7 times, respectivel}. 



The cause of this variation in the number of molts in regard to the 

 10 per cent thus varj'ing could always be traced to abnormal condi- 

 tions. Highly nutritious food and excessive care in breeding appar- 

 ently caused less than the normal number of molts. Seven out of 

 eight larvae reared on cowpeas molted thus. Molts in excess of the 

 normal were caused b}^ neglect and insufficient or disagreeable food. 



PROCESS OF MOLTING. 



The process of molting is normal. A fews hours after ecdysis the 

 larva stops feeding and remains in an extended, slightl}^ arched posi- 

 tion. In this condition it is very helpless, especiall}^ when nearly full 

 grown. At the time of molting the body contracts spasmodicall}^, the 

 skin splits back of the head, and the head is thrust out. Three or four 

 minutes more pass before the larva has shed the skin entirely, and 

 after three or four hours feeding begins again. 



In midsummer the stages preparator}^ to molting are very short (15 

 to IS hours), and in the fall longer (8 to 4 days). After the earlier 

 molts the larvte sometimes devour their own shed skins, as do also the 

 older ones, but more rarely. 



