298 



WEST VIRGINIA EXPERIMENT STATION. 



dying trees on about one hundred to one hundred and fifty thousand acres, 

 as observed during a six days' journey through the forest between the 

 point mentioned, would be about one per cent., possibly not over one-half 

 of one per cent. 



CAUSE OF THE TROUBLE. 



The primary cause of the unhealthy condition of the pine and spruce. 

 I have found to be the result of attacks of a single species of insect known 

 to science as Dendroctonus frontalis, to which we will give the common 

 name of destructive pine bark beetle. Heretofore this species has been a 

 rare insect, and but very little was known of its habits and history. 

 During the two investigations in the region mentioned, I have carefully 

 examined a large number of dead, dying and green trees of all the species 

 of pine and of black spruce. In every case I have found abundant evi- 

 dence that the insect mentioned was the cause of the trouble, the trees 

 having evidently been in a healthy condition at the time they were in- 

 vaded by the beetle. 



The destructive pine bark beetle is a small black, hard-shelled "bug" 

 one-eighth of an inch long. It is found most common in the infested 

 trees under the bark on the main trunks at a point about two-thirds up 

 from their base near the first branches or forks, this being the point where 

 they make their first attack. The beetles evidently attack the tree soon 

 after the sap goes down in August, when they bore through the bark to 

 the outer sapwood, extending their galleries or egg chambers twelve to 

 fourteen inches through the inner portion of the bark and just touching 

 the sapwood. In these galleries, they deposit great numbers of eggs, 

 which soon hatch into minute white grubs which proceed to bore through 

 and feed upon the tender inner bark until they are full grown, (about half as 

 large as rice grains.) They then enter the outer or dry bark where they 

 change to the beetle or perfect form. They probably pass the winter in 

 all stages of growth, from newly hatched to full grown grubs, and in the 

 spring, they change to the beetles and emerge from the bark, leaving it 

 pierced with millions of small round holes. The beetles which emerge in 

 the spring breed in the green portions of the bark on the same trees from 

 which they emerge, and also in trees injured but not killed by the attack 

 of the insect the previous fall. This second brood matures and emerges 

 in time to attack the trees in August and during the fall, as at first. 



Some of the earliest trees attacked may die during the fall and early 

 winter, but by far the larger portion of them die the following spring 

 when, on account of the unhealthy condition brought about as above 

 stated, hundreds of other species of insects are attracted to them and 

 their death is rapidly hastened. 



The yellow, pitch and white pine are rapidly rendered worthless after 

 they commence to die, both from the blue condition, probably caused by 

 the souring of the sap, and by numerous insects boring in the wood; the 

 one which is especially destructive being what is known as the "sawyer." 

 This destructive borer is hatched from eggs deposited in the bark of the 

 affected trees by a large, gray, long-horned beetle. The grubs feed for a 

 time under the bark, and as they attain their growth, they enter the 

 wood, often penetrating the tree to its heart. When they are common in 

 a tree they soon render it worthless for lumber. This large borer also at- 

 tacks the spruce trees and logs, but seldom causes much damage. 



The spruce, on account of its thin sap wood, is not so liable to injury from 

 "bluing" or from wood-boring insects, may remain sound and, all except 

 the sapwood be profitably worked into lumber and pulp for a number of 

 years after they die, varying from three to five or six years. 



