54 BULLETIN" 351, U. S. DEPARTMENT OF AGRICULTURE. 



westward slope and is located at an altitude of 1,100 feet, with a 

 mountain crest extending 1,000 feet above it. There is consequently 

 a good air drainage and a partial exclusion of the sun's rays during 

 the forenoon. The Newcomer orchard, upon the other hand, is 

 located upon a slight knoll, with relatively level surroundings. Its 

 altitude is less than 900 feet. Consequently the air drainage is not 

 good and the sun's rays are unobstructed. 



Four prepupse were measured in 1912, with the following results: 

 Length, maximum 1.29 mm., minimum 1.08 mm., average, 1.208 mm.; 

 width, maximum, 0. 618 mm., minimum, 0. 562 mm., average, 0.587 

 mm. On April 28, 1913, 8 specimens gave the following measure- 

 ments: Length, maximum 1.420 mm., minimum 1.25 mm., average 

 1.33 mm; width, maximum 0. 6 mm., minimum 0. 525 mm., average 

 0.559 mm. 



Third Molt. 



The prepupa starts the third molt by a series of convulsive move- 

 ments which cause the dorsal skin to split over the thoracic region. 

 The skin is loosened and removed almost entirely by extending and 

 contracting the abdomen. The extension thrusts cause a tension 

 upon the ventral part of the molt skin which draws the head down- 

 ward and under. This causes the dorsal thorax to protrude through 

 the split in the molt skin. This tension increases with each thrust 

 of the abdomen, so that the head is drawn farther and farther down- 

 ward and backward until it finally slips free from the skin. The 

 larva then assumes its regular position. In stripping the molt skin 

 from the legs and antennae the thrusting movements of the abdomen 

 are aided by the puparium, which, owing to its attachment with 

 elastic bands, yields to the molting movements and serves as a 

 clamp to hold the skin in place while the abdomen contracts for the 

 next thrust. The thrusting movements of the abdomen usually 

 cease before the skin is completely expelled from under the puparium. 

 Because of this the cast skins are mostly found clamped under the 

 posterior end of the puparium. 



The duration of this molt varies with the temperature at the time 

 of molting and also with the vigor of the specimen. The molt 

 usually starts in the forenoon with the resumption of the daily 

 activity. The average time for this molt is less than an hour. Upon 

 days when the temperature reaches 70° F. before 9 a. m., practically 

 all the molts for the day will be completed by 10 a. m. At low 

 temperatures many specimens die without completing it. Some 

 specimens kept in the laboratory where the temperature did not rise 

 above 70° F. required 18 hours for this molt. They started molting 

 about 4 p. m. and became dormant before completing it. These 

 molts were completed the following day. 



