SEASONAL HISTORY. 



PUPAL CELLS. 



67 



As the larva becomes larger it gradually forms about itself a 

 hardened black cell, composed of its cast skins and excrement. This 

 cell is of a very tough leathery nature and seems to hold its moisture 

 for a considerable period. In bolls the cell is even harder, as it 

 becomes more or less mixed with lint and attains a considerable 

 firmness, which often gives the cell the hardness and appearance of 

 a seed. These pupal cells frequently include a portion of the hull 

 of a seed, and it has also been found that the larva sometimes forms 

 its cell within a single cotton seed. In these cells the larva trans- 

 forms to the pupal stage. (See PL IX.) 



PUPATION. 



The formation of the adult appendages has progressed considerably 

 before the last larval skin is cast. The wing pads appear to be nearly 

 one-half their ultimate size. The formation of the legs is also dis- 

 tinctly marked, and the old head shield ap- 

 pears to be pushed down upon the ventral 

 side of the thorax by the gradual elongation 

 of the developing proboscis. Finally, the 

 tension becomes so great that the tightly 

 stretched skin is ruptured over the vertex 

 of the head, and it is then gradually cast 

 off, revealing the delicate white pupa. The 

 cast skin frequently remains for some time 

 attached to the tip of the abdomen. The 

 actual period of ecdysis is about 45 minutes. 



THE PUPA. 



ACTIVITY. 



Fig. 10. — Diagram illustrating rela- 

 tionship between temperature and 

 the pupal period of the boll weevil 

 and showing variations due to 

 humidity. (Original.) 



The pupal stage of the boll weevil is more 

 or less an active stage. The pupa is so con- 

 structed, with a forked prong at the posterior 

 tip and with two strong tubercles on the thorax, as to have an axis 

 upon which it can revolve without injuring its more delicate append- 

 ages. As the cell is almost round, this movement of the pupa is more 

 or less free in all directions and tends to make the cell harder and 

 more durable. A person with acute hearing can detect the presence 

 of a pupa by holding a square close to the ear. (See PL VI, c, d.) 



DURATION OF THE PUPAL STAGE. 



In general, it may be said that the length of the pupal stage is 

 about equal to that of the larval stage minus the length of the egg 

 stage. This stage varies considerably, as do the two previous stages, 

 the range being from 2 days at high temperature to 14 or more 

 days at low temperature. During the winter it may be as long as 

 several months. Table XXV and figure 10 are presented to illustrate 

 the variations in the pupal period in their relationship to mean tem- 

 perature. It may be stated briefly that the length of the pupal 

 stage increases as the temperature decreases, and that the average 

 humidity also influences the stage in the same manner. 



