4 THE SCOLYTID BEETLES. 
wick during the past century (Hopkins, 1901a), the widespread 
destruction of pine and spruce by the southern pine beetle (Xo. 4) 
in West Virginia and Virginia in 1891 and 1892 (Hopkins, 1899a), the 
destruction of a large percentage of the timber in an entire Xational 
Forest by the Black Hills beetle (Xo. 10) within the past ten years 
(Hopkins, 19026 and 1905), and the depredations by the western 
pine beetle (Xo. 1) in Idaho, Oregon, and California (Webb, 1906), 
and by the mountain pine beetle (Xo. 9) in Wyoming, Montana, 
Idaho, Oregon, Utah, and California noted in the present paper. 
CHARACTER AXD EXTEXT OF DEPREDATIOXS. 
Living healthy trees are attacked by swarms of the adult beetles^ 
which enter the bark on the mam trunk and excavate their egg 
galleries for a distance of a foot or more through the inner, living 
bark. This weakens the vitality of the tree, and in addition the 
larvae hatching from the eggs mine through and destroy the bark 
intervening between the egg galleries, thus completely girdling the 
trees and causing their death. The amount of timber killed in 
this manner during the past century has been enormous. That 
known to have been killed by these beetles in West Virginia, New 
England, and the Black Hills Xational Forest alone amounts to many 
billions of feet of the best pine and spruce, to say nothing of the 
less conspicuous depredations each year scattered through the 
forested sections of the Rocky Mountain, Cascade, Sierra, and Coast 
regions, and of the Southern States. Very conclusive evidence has 
also been found that some of the great denuded areas in the Rocky 
Mountains region supposed to have been caused by forest fires were 
primarily caused by one or more species of Dendroctonus. From 
our present knowledge of the facts and evidence it is probable 
that if the timber destroyed by these insects in the United States 
during the past fifty years were living to-day its stumpage value 
would be more than $1,000,000,000. 
POSSIBILITIES OF CONTROL. 
The results of our investigations, experiments, and practical 
demonstrations make it clear that wherever private forests or State 
or Xational forests are under organized management for fire pro- 
tection and economic utilization the control of these insects is often 
a less difficult and less expensive problem than that of controlling 
forest fires. In fact, wherever there is a sufficient demand for the 
timber, and where facilities for the utilization of the trunks of the 
infested trees within a specified time exist, the desired control may 
often be brought about and maintained practically without cost 
or even at a profit, especially if the action be taken before the depre- 
dators have spread over extensive areas. 
