20 N. H. AGRI. EXPERIMENT STATION [Bulletin 247 



maturing Ian 33. Consequently, shallow pupal cells are constructed in 

 the outer wo id parenchyma next to the dead bark. In such a case the 

 outer surface . of the larva is covered over with an arched mass of chips 

 removed in making the pupal cell. These peripheral pupal cells cause a 

 bulging of the bark and can be readily detected without its removal. 



In New I Hampshire larvse are first found about the last ten days of 

 May. Som ; are present, though in greatly diminished numbers, the mid- 

 dle of Sep^ _;mber. (Chart I). There is a marked tendency for the larval 

 stage to b considerably longer in the spring and early summer. This 

 is followed by a period in mid-summer when optimum development takes 

 place. This in turn gives way to another period of lower mean tem- 

 peratures during which larvae that failed to complete development dur- 

 ing the previous period maj' linger for several weeks as larvse or pre- 

 pupse before transforming to pupse. In that part of the larval stage 

 known as the prepupal period, varying from one to three weeks in length, 

 the larva remains in a sluggish condition within the newly constructed 

 pupal cell before transfgrming to a pupa. 



Table III, including studies in the summer of 1928, shows the maximum 

 length of the larA-al stage for one individual hatching in the cage June 28, 

 to be 42 days; in the greenhouse the maximum was 41 daj's for two lar- 

 vae hatching July 16. A minimum length of 26 days was recorded for 

 four larvse hatching July 7 in the cage. The same minimum was found 

 in the greenhouse. The average length of the larval stage was 36.1 days 

 in the cage and 33.4 days in the greenhouse. 



PUPAL STAGE 



The pupal stage is passed in the pupal cells previously described. In 

 1928 the first pupa was found in field material July 13. Six more were 

 taken from leaders examined July IS. Puijce were present m infested 

 leaders until September 26. The greatest number were found between 

 August 10 and September 10, before and after which dates comparatively 

 few were in this stage of development. Twenty days, the maximum pu- 

 pal length in the cage (Table IV), were required for two larvae pupating 

 August 9; in the greenhouse 19 days were required for one larva pupating 

 August 7. In the cage the minimum was 10 days, observed in the case 

 of several larvae pupating between August 6 and 9. A nine-day mini- 

 mum was required in the greenliouse for larvse pupating July 30 and 

 August 26. The average length was 13.9 days in the cage and 12.2 da5's 

 in the greenhouse. 



PERIOD FROM EGG TO ADULT 



Table V shows the wide range of time that was necessary for develop- 

 ment from egg to adult, in 1928, under cage and greenhouse conditions. 

 The maximum total of 69 days in the cage is shown for an egg laid June 

 14; in the greenhouse 61 days for an egg laid June 26. The minimum in 

 the cage was 44 days for an egg laid July 2; in the greenhouse, 46 da3's 



