15 



tree; (2) the presence of fungi in the bark and wood. The latter has 

 been investigated by Dr. Herman von Schrenk, for the Division of 

 Vegetable Physiology and Pathology, and his report has appeared in 

 a bulletin of that Division. Therefore, only such reference will be 

 made to these diseased conditions as has a direct or interrelated bear- 

 ing on the insect problem, and methods of preventing losses from 

 their combined attack. 



RELATION OF INSECTS TO THE TROUBLE. 



With very few exceptions r all of the great number of affected trees 

 examined, which were in all stages, from living to old dead ones, 

 throughout the area covered by the trip, showed evidence of depreda- 

 tion by insects; and in nearly every case quite conclusive evidence 

 was found that one species, a bark-mining beetle, had been or was 

 then associated with the primary cause of these unhealthy conditions 

 and death. This evidence consisted in the healed-over burrows in the 

 living bark of healthy, vigorous trees; in broods of this insect which 

 had developed in the bark of living trees during the summer of 1899, 

 the trees yet living in May and June, 1900; in the hundreds of dying 

 and dead trees, with vast numbers of all stages, from young larva3 to 

 adults, of this insect under the bark, where they bred the previous 

 summer and fall; and finally its characteristic galleries in the bark, 

 or on the surface of the wood of old dead trees which had been dead 

 from ten to twenty years, while the logs, stumps, and tops in cuttings 

 showed little evidence of its attacks. 



In addition to this common and primary enemy of the spruce, many 

 other species of bark beetles, flat-headed and round-headed bark and 

 wood borers, occurred in the dying and dead trees, some following 

 closely the first attack by. the primary enemy, others coming later, 

 and still others in succession until the last vestige of the bark and 

 wood is converted back to earth. 



THE SPRUCE-DESTROYING BEETLE. 



The observations of the writer lead him to conclude that of all the 

 insect enemies of the spruce, this beetle must take first place as the 

 most destructive. It is the leader in the attack, while the others, 



1 In all forests, and especially those in undisturbed or natural condition, a cer- 

 tain percentage of trees seem to die naturally. While there is no such thing, per- 

 haps, as a natural deathot' a tree, there are those which, in their struggle for exist- 

 ence with their many younger and more vigorous competitors, become weakened 

 in their vitality and thus are more susceptible to the attack of their numerous 

 enemies among insects and fungi, and also to the injurious effects of unfavorable 

 climatic conditions, which, combined, cause them to die. Trees perishing in this 

 manner, however, occur as isolated individuals, scattered throughout the forest, 

 and seldom, if ever, in clumps. 



