24 



GROWTH. 



It is impossible to follow the growth of an individual larva with- 

 out interfering so greatly with its normal conditions of life as to 

 make the observations unreliable. It seemed more accurate to meas- 

 ure larvae of approximately known ages. In these measurements the 

 natural curve of the body was not interfered with, but the measure- 

 ment taken across the tips of the body. In this way it was found 

 that in squares during the hot Aveather the length of the body 

 increases quite regularly by about 1 mm. a day. As it becomes 

 cooler the daily growth is less. In bolls which grow to maturity the 

 rate of growth is less and the length of the growing period is much 

 greater. Full-grown larvae vary in length from 5 to 10 mm. across 

 the tips of the curve. Larvae of normal size in squares average from 

 6 to 7 mm. The largest larvae are developed in bolls which grow to 

 maturity (PI. Ill, fig. 19). 



MOLTS. 



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

 occur. The period of change from one instar or stage to the next is 

 so short that the chances of opening a square at just the right time 

 to observe the process are very small indeed. However, it has been 

 ascertained bej^ond question that two molts occur before the larva 

 reaches half its growth. 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 occa- 

 sionally found larvae which had certainly just molted, but which were 

 much larger than the usual size at the second molt, the writer is led 

 to suspect that three larval molts may sometimes, though possibly 

 they do not always, occur. 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. Counting only the first two molts which have been often 

 found, a third occurs at the time the larva pupates. 



PROCESS OF MOLTING. 



So little is known in regard to the molting of Curculionidae that the 

 process as observed is here recorded. In the cases observed, starting 

 at the neck, the skin split along the back, and was then pushed down- 

 ward and backward along the venter of the larva. The cast head 

 shield remained attached to the rest of the skin. 



Immediately after casting the skin the head, as well as the rest of 

 the body of the larva, was of a pearly-white color. The tips of the 

 mandibles first became brown, and within a short time a yellowish- 

 brown color marked the entire integument of the head. 



