18 



made just before my leaving that region on June 17. It is therefore 

 possible that some individuals pass the dormant period in the outer 

 bark, where they had commenced to excavate entrances in the fall. 



THE SUMMER PERIOD. 



In the course of Mr. Cary's observations in connection with the 

 girdling experiments some important information relating to the life 

 history of this beetle was noted by him. According to his notes the 

 beetles commenced to emerge about the middle of June. Galleries 

 had been excavated in some of the girdled trees and eggs were depos- 

 ited b}^ June 19. The first larvae were noticed on July 28 to 31. Pupa? 

 were common on September 1, with a few recently developed beetles, 

 and on October -1 many of the beetles had f ully matured, but none had 

 emerged. It is therefore probable that the beetles will not emerge 

 and attack other trees before the following summer, although a few 

 early developed beetles may emerge in October and enter the outer 

 bark of living trees. 



Mr. Cary's observations furnish quite conclusive evidence that in 

 northwestern Maine there is but one brood in a season, even from the 

 hibernating adults, and that the period of development from the egg 

 to the adult is about seventy to seventy-five days — from the middle of 

 June to the last of August. 



SUMMARY OF LIFE HISTORY. 



These observations would also indicate that activity ceases in the 

 fall by about the middle of October, when all stages of the insect may 

 occur in the bark of infested trees where they, with the probable 

 exceptions of the eggs and pupa?, remain until the first week in June. 

 Activity then commences, the mature larva? change to pupa?, and bj 7 

 the middle of June those that pass the winter in the adult stage emerge 

 and commence to excavate galleries and deposit eggs. The adults 

 from the hibernating larva? of different stages, develop and continue 

 to emerge possibly until the last of August. Therefore the eggs 

 deposited by the late-developing beetles produce larva? which do no.t 

 complete their development until July or August of the next year. 

 Thus, the period of development may vary from about seventy days 

 to about twelve months, but all broods from eggs to matured and 

 emerging adults remain in the bark about twelve months, of which 

 they are dormant about seven and one-half and active four and one- 

 half. 



The following diagram will indicate the probable normal rate of 

 development from the different hibernating stages: 



