10 BULLETIN 932, U. S. DEPARTMENT OF AGRICULTURE. 



natural or artificial causes, such as death, accidental injury, para- 

 sites, the removal of specimens for other purposes, etc. 



WINTERING LARVJE. 



As previously stated (p. 6), the wintering larvae consist of all of 

 the nontransforming larvae of the first and second broods and all of 

 the larvae of the third brood. (See Plate VI, B.) 



The winter cocoon. — The winter cocoon is a small, well-built struc- 

 ture, having heavy silk walls in which are frequently interwoven 

 small particles of bark. When compared with the more hastily con- 

 structed summer cocoon, it will be noted that the winter cocoon is 

 of heavier construction and thus affords the larva protection against 

 the low temperatures of the winter season. The cocoon is gen- 

 erally more or less oval in form, but varies to conform with the 

 space in which it is built. The winter cocoon is usually found be- 

 neath the bark on the trunk of the tree, well concealed from birds 

 and insect enemies, in the crotches of the larger limbs, or in decayed 

 or partially decayed tree cavities, etc. Not infrequently, in the Grand 

 Valley, a mass of 10 to 20 cocoons, side by side or partially on top of 

 one another, may be found on the tree in places particularly favor- 

 able for hibernation. The cocoons are occasionally to be found 

 around the base of the tree just below the surface soil or within 

 cracks in the soil. Again, a considerable number of winter cocoons 

 are constructed in various cracks and crevices within packing 

 houses and storage cellars where the harvested fruit has been kept. 



Remodeling of the cocoon. — The wintering larva begins activity 

 during the first warm days of spring; it then remodels its cocoon 

 by attaching thereto a slender silken exit tube which provides for 

 the safe issuance of the moth. This tube is usually a fraction of 

 an inch in length, although tubes have been found that were 2 or 

 more inches long, depending upon the location of the cocoon. Upon 

 the completion of the exit tube a lightly constructed silken partition, 

 which serves to separate the tube from the cocoon proper, is frequently 

 built at its base. 



Emergence of the moth. — Shortly before the time the moth emerges, 

 the pupa punctures this silken partition and, by means of its retrose 

 spines, wriggles its way to the end of the exit tube. The moth then 

 ruptures the pupal skin, crawls into clear space, spreads and dries 

 its wings, and in due course of time takes flight. Were it not for the 

 exit tube, many moths would be unable to free themselves from the 

 place in which the larvae have cocooned. 



PUPiE OF THE SPRING BROOD. 



Time of pupation. — Observations of the time of pupation of the 

 wintering larvae were made daily by examination of the larvae within 

 the cocooning racks. The tabulated results showing the time of 



