THE PINE INVESTIGATION. 333 



apparently otherwise vigorous, healthy trees these balls of tur- 

 pentine were so thick on the bark that one could not find a 

 vacant space as much as four to six inches square. Unlike the 

 large infested trees that had previously been studied which 

 bore branches near the top only, these had numerous branches 

 from near the ground to the top. The same characteristic 

 mode of attack was found, however, namely, that the upper or 

 central portion of the main stem or trunk was attacked first 

 the part subsequently infested extending from near the top to 

 within three or four feet of the ground. The bark on the trees 

 recently attacked was full of sap, and would readily separate 

 or peel from the wood. In fact, it would separate as readily 

 and the portion between the galleries made by the insects ap- 

 peared as healthy as that from the most vigorous uninfested 

 trees that could be found. No indication of disease or weaken- 

 ed vitality of the trees and no other species of injurious insects 

 occurred on the foliage or in the wood or bark upon which the 

 destructive bark beetle was just commencing an attack. It was 

 observed, however, in the numerous trees that showed various 

 progressive stages of attack, that soon after the first success- 

 ful attack was made, or as soon as the tree showed the least 

 indications of weakened vitality, that other bark beetles as well 

 as other bark and wood boring insects were attracted to it. 



The second one to appear being the turpentine bark beetle, 

 Dendroctonus terebrans. This species never encroaches upon 

 the portion of the bark chosen by its smaller relative, but, as a 

 rule, enters the bark near the ground and even mines beneath 

 the bark on the roots. Thus it contributes to the death of 

 that portion of the tree which would otherwise remain alive for 

 some time. Numerous other bark beetles then follow, attack- 

 ing all parts of the tree, some boring in the wood, others in- 

 vading the uninfested bark on the trunk, branches and twigs. 

 Remarkable as it may appear, other species of bark beetles 

 appear to respect the rights of the destructive bark beetles, 

 since they seldom infest the bark occupied by it until the latter 

 insect has vacated. Not so, however, with some of the large bark 

 boring larvae which conduct their broad zigzag and winding 



