31 



Both egg-cunnels and larval miaes are usually distinctly engraved on the 

 wood surface. They hibernate beneath the bark as young adults, larvae, and 

 parent adults. 



The chief emergence of the over- wintered adults, and attack upon fresh bark, 

 takes place during May, June and early July. Fresh tunnels were started this 

 season until the end of July, and probably later. By the end of July the tunnels 

 which were started earliest contained larvae of various sizes, pupae and young 

 adults. By the end of the season the tunnels which were started in May and 

 early June had the young mostly transformed to adults ; in the tunnels started 

 last many of the young over- wintered as larvae, and will complete their trans- 

 formations in the spring. It is possible that in the southern part of the Interior 

 a moderate number of young adults appear late in the season and start new 

 tunnels, which contain small larvae during winter. There is thus one brood each 

 season, with possibly a partial second brood. 



Fig. 15 The Douglas Fir Bark-beetle. Larval-mines and pupal 

 cells on the inner surface of Douglas fir bark. (Original). 



The abundant reddish boring-dust ejected from the entrance tunnels, and 

 lodged in the bark fissures, distinguishes the infested trunks. During the late 

 fall and spring the foliage of infested trees fades from green to yellow and finally 

 to reddish before summer. W nen on ^y a portion of the tree is attacked during 

 the first summer the remaining portion may be infested the following season. 

 In such cases the foliage may be in part quite red before the broods have 

 emerged; though, as a rule, by the time the foliage becomes red and dry, few 

 living beetles will be left in the bark. 



