78 



THE SCOLYTID BEETLES. 



There. is, therefore, but one generation annually, and it is probable 

 that, like the roundheaded pine beetle, some individuals of the same 

 generation may not complete their development until the second 

 year, and that some adults may live over and deposit eggs the third 

 year. 



HABITS. 



The habits of this species appear to be similar to those of the round- 

 headed pine beetle, with which it is frequently associated in the same 



tree. The character of the primary 

 or egg gallery is distinguished by the 

 larger, coarser appearance and by the 



Fig. 40.— The Colorado pine beetle (Den- 

 droctonus approximatus) : Adult. Greatly 

 enlarged. (Author's illustration. ) 



absence of exposed larval mines on the in- 

 ner surface of the bark. The character of 

 the primary galleries is shown in figures 

 41 and 42. It appears that while some 

 of the larvae may transform to adults' in 

 the inner bark, the majority of them 

 transform in separate cells in the outer 

 bark. The flight and food habits of the 

 adults are evidently similar to those of 

 the other species. 



ECONOMIC FEATURES. 



This species has been found attacking perfectly healthy trees in 

 sufficient numbers to kill them. Therefore, if it should become 

 isolated, and under favorable conditions multiply rapidly, it might 

 easily become very destructive. As a rule, however, it prefers to 



Fig. 41.— The Colorado pine beetle: 

 Single egg gallery. Reduced. 

 (Author's illustration.) 



