66 



THE MEXICAN COTTON-BOLL WEEVIL. 



MOLTS. 



/S 2Q 



To accommodate the rapid growth of the larvae two or three molts 

 occur. The first occurs at about the second day, and the second at 

 about the fourth day. Whether a third molt occurs before pupation 

 can not be positively stated, but having occasionally found larva? which 

 had certainly just molted, but which were not larger than the usual 

 size of the second molt, we are led to suspect that three larval molts 

 may sometimes occur, though possibly not always. In bolls where 



the length of the larval stage is 

 often three or four times as great as 

 that usually passed in squares, it 

 seems almost certain that more than 

 two larval molts occur regularly. 

 According to Dr. Hinds's obser- 

 vations the skin splits along the 

 back, starting at the neck, and is 

 then pushed downward and back- 

 ward along the venter of the larva. 

 The cast head shield remains at- 

 tached to the rest of the skin. 



DURATION OF LARVAL STAGE. 



The length of the larval stage, as 

 a rule, is about equal to the sum 

 of that of the egg and pupal stages. 

 It lengthens as the temperature 

 falls and also as the amount of mois- 

 ture decreases. It is also probably 

 influenced by the nature and con- 

 dition of the food supply. These influences will be discussed more 

 fully under the subject of developmental period, as more data are 

 available for the entire period than for any of the stages in this period. 

 The observations which have been made upon the duration of the 

 larval stage are tabulated and charted below (Table XXIV and fig. 9). 



Table XXIV. — Duration of the larval stage of the boll weevil. 



Fig. 9. — Diagram illustrating relationship of tem- 

 perature to larval period of the boll weevil and 

 showing range due to humidity. (Original.) 



1 The extremes were 5.2 and 7.3 days. 



