THE WESTERN PINE-DESTROYING BABKBEETLE. 



25 



It is probable that at higher elevations and farther north the 

 majority of the broods would not develop in much less than a year's 

 time and that at more south- 

 ern and warmer localities in the 

 Pacific Coast region there would 

 be two complete generations 

 and possibly a partial third. 



When first transformed, in 

 May and June, the young bee- 

 tles have very soft, delicate tis- 

 sues. They therefore remain 

 in their pupa cases until their 

 bodies are fully hardened or 

 chitinized . When ne ar ly re ady 

 to emerge, the adults bore their 

 way almost to the surface of 

 the bark (fig. 12, a), but pause 

 before epierging, appearing to 

 rest in the burrows they have 

 just made. They do not, how- 

 ever, hollow out the space im- 

 mediately adjoining the pupa 

 case, as is the habit of another 

 species of this genus. When 

 quite ready to emerge, the bee- 

 tles continue their burrows out 

 through the remaining portion 

 of the bark. The individuals 

 of a brood do not appear to 

 emerge simultaneously, but 

 they come forth at irregular in- 

 tervals until all are out, leaving 

 the bark thi ckly punctured with 

 small, round, clean-cut holes, 

 as shown in figure 12. 



After leaving the tree or trees 

 in which they went thi-ough 

 their transformations the bee- 

 tles fly away to find trees in 

 which to deposit eggs. They 

 may select trees close at hand 

 or may fly quite a long distance before making a selection. They will 

 also enter the living bark of recently felled trees. Large numbers of 



F.G. 11. — The western pine-destroying barkbeetle 

 {Dendroctonus brevicomis): Pitch tubes on barJc of 

 tree. (Original.) 



