47 



appear, to carry away much of the source of infection. The bunchy way in 

 which the dead timber stands is also in our favor. Evidently the normal flight 

 of the beetle is short, for the dead trees, as a rule, stand in groups; those killed 

 one, two, or three years ago. together with the insect colony working perhaps in 

 green timber close beside them. This trouble, indeed, may also be regarded, in 

 one way, as a benefit to our forests. So far as it may determine a policy of thin- 

 ning rather than stripping the land, it will exert a favorable action which will 

 never be entirely lost on the reproduction of spruce. 



SUMMARY. 



The results of the investigation and review of literature relating to 

 the unhealthy condition of the spruce in the Northeast may be sum- 

 marized as follows: 



Extensive dying of spruce from New York to New Brunswick has 

 occurred at various times and periods from about 1818 to 1900. 



Within this period spruce to the amount of many billions of feet 

 has died, and much of it has been a total loss. 



The cause of the death of a greater part of this spruce has been 

 the depredations of insects. 



The primary depredator in the forests investigated is a bark-mining 

 beetle, the spruce-destroying beetle, Dendroctonus piceaperda, n. sp. 



Vigorous trees, to all appearances in perfect health, are attacked 

 and killed by this beetle. 



The largest trees and best stands of timber suffer most from its 

 ravages. 



It passes the fall, Avinter, and spring in all stages from young to 

 matured larvae, and immature to matured and old adults, in the bark 

 of trees attacked by it in the summer. 



Activity commences early in June; the beetles commence to emerge 

 from their winter quarters about the middle of June, and continue 

 to come out probably until about the 1st of September. 



In the latitude and altitude of northwestern Maine there is but 

 one brood of the insect each year from the first parent beetles that 

 emerge in June, while those that emerge later in the summer do not 

 develop broods of adults until the next summer. 



The broods of the beetle do not remain in a djang or dead tree 

 more than one year after it commences to die. The estimated num- 

 ber of adults which, under favorable conditions, may emerge from 

 an average-sized tree is from five to seven thousand. 



It is estimated that an average of three pairs of beetles to the 

 square foot of bark on 10 to 15 feet of the trunk of an average-sized 

 tree are sufficient to kill it, and that 6,000 beetles breeding in one 

 tree may be sufficient to kill from 20 to 25 more trees. 



The principal insects that aid the primary enemy in killing the 

 trees after the first attack has been made are (1) a smaller bark 

 beetle (Polygraphias rufipennis) and (2) a round-headed bark and 

 wood miner (Tetropium cinnamopterum). 



