INSECT LOSSES TO SUSTAINED YIELD 407 



British Columbia. As a basis for future discussion it seems well to 

 give a brief resume of conditions reported throughout the wide range 

 of this species. 



Probably the most comprehensive effort ever made to determine the 

 losses due to insects in the western yellow pine type was the insect 

 survey made by the Forest Service and the Bureau of Entomology 

 during the summer of 1917 in California. It was ascertained from 

 this survey that the average annual loss from insects far exceeded the 

 average annual loss from fire. Men familiar with conditions in Ari- 

 zona, New Mexico, Oregon, Montana, and elsewhere throughout the 

 type in the United States report either evidences of past serious losses 

 represented by large amounts of standing dead timber scattered 

 throughout the stand, or of active infestation taking its toll from these 

 stands year after year. J. M. Swain, of the Canadian Bureau of Ento- 

 mology, in his bulletin, "Canadian Bark Beetles, Part II," comments 

 upon past serious losses and present widespread infestation in the 

 pine stands of southern British Columbia. 



In this State (Colorado) we are faced by widespread infestation 

 throughout the San Juan, Montezuma, and Durango Forests, with 

 reports of other infestations of possibly not so alarming an extent from 

 other Forests on which the species is present. On areas in the Forests 

 above mentioned on which intensive work or examinations have been 

 made we find the annual loss running from 2 to 5 per cent of the 

 stand per annum, and in one or two places on the Durango as much as 

 fiO per cent of the stand by volume killed within the past few years. 

 In this connection it may be well to state that the per cent of the stand 

 killed in any one year in the southern pine belt seems to run consider- 

 ably higher than in the stands in the Pacific Coast belt of western 

 yellow pine. 



From observations made the past summer the problem of the pro- 

 tection of our stands of western yellow pine in the Rocky Mountain 

 region is almost entirely an insect problem after the seedling and sap- 

 ling stage has been passed. In the course of the work on the Dolores 

 Timber Survey project on the Montezuma Forest from May to No- 

 vember, I had the opportunity of examining thousands of dead trees 

 of western yellow pine. Without exception, on all trees which had not 

 been subsequently severely burned, I was able to attribute the death 

 to work of Dendroctonus beetles, through the identification of the char- 

 acteristic pitch stain and surface grooving of the wood. Moreover, 

 where trees were ff)und to be dying in nearlv every case there was un 



