50 MASS. EXPERIMENT STATION BULLETIN 189. 



Changes undergone by the Labva previous to Pupation. 



In the semi-quiescent state the larva is very sluggish, but is still capable 

 of locomotion. Soon after entering this stage the head starts to bend 

 downward, and the mouth parts become ventral instead of anterior. The 

 second thoracic segment becomes swollen, and the third thoracic and first 

 abdominal segments become compressed as a result of pressure exerted 

 at the anterior and posterior ends of the larva. The second and third 

 abdominal segments remain about normal, while the fourth to seventh 

 become enlarged and swollen, and show distinctly the outlines of the pupal 

 abdomen. At the termination of the semi-quiescent stage, which lasts 

 for about twenty-four hom-s, the larval head is fully inflexed and the use 

 of both thoracic and abdominal legs is lost. The larva then enters the 

 true quiescent state. 



In this stage the larva is not capable of locomotion, but has the char- 

 acteristic movements of a pupa. Soon after entering this stage the con- 

 tents of the terminal segments of the larva shrink away from the larval 

 body wall to form the terminal segments of the pupa. At this time the 

 anal legs consist of only the external chitinous covering, with their crotch- 

 ets firmly attached to the bottom silken partition. When disturbed the 

 larva twitches and turns with a movement resembUng that of the pupa, 

 while the empty anal legs remain attached to the silk and are often twisted 

 around each other during the twisting movements of the larva. At this 

 time the abdominal legs are flush with the venter, and the thoracic legs 

 are folded close to the bod}^ The quiescent stage requires from twelve 

 to twenty-four hours for its completion, and then the larva begins the 

 process of pupation. 



Process of Pupation. 



After a few straining movements forward, and as a result of pressure 

 exerted from within, the larval skin suddenly spHts along the dorsal line 

 of the head and thoracic segments, and also down each side of the frontal 

 head plate. After a few wriggling movements the larval skin slips down 

 to the terminal segment, which then is liberated. As soon as it is freed 

 from the larval skin the newly formed pupa turns around two or three 

 times, thus firmly attaching its cremaster to the angle of the lower silken 

 partition in the pupal chamber, at the point formerly occupied by the 

 anal feet of the larva. A timed individual required two and one-half 

 minutes to shed its larval skin, except the terminal segment, and the 

 total time required to completely shed this skin and attach the 

 cremaster was eight minutes. 



Changes undergone by the Pupa. 



The newly formed pupa is white in color, with a longitudinal pink line 

 down the dorsum. Transverse pink lines extend across the center of the 

 dorsum of each abdominal segment, but fade away laterally. The wing 

 pads are yellow with a tinge of pink. The venter of the abdomen is 



