INSECTS WHICH KILL FOKEST TKEES. 3 



The Douglas fir beetle.— The Douglas fir throughout the region 

 of the Rocky Mountains from southern New Mexico to British Co- 

 lumbia has suflFered severely from the ravages of the Douglas fir 

 beetle, with the result that a large percentage of dead timber is found, 

 much of which will be a total loss. 



Three other species of beetles, having destructive habits similar 

 to those above mentioned, depredate on the pines "of New Mexico and 

 Arizona, and still another has contributed greatly to the destruction 

 of the larch throughout the northeastern United States and south- 

 eastern Canada. 



The hickory harkieetle. — ^Within the past ten years the hickory 

 barkbeetle has caused the destruction of an enormous amount of 

 hickory timber throughout the northern tier of States from Wiscon- 

 sin to Vermont and southward through the eastern Atlantic States 

 and into the Southern States as far as central Georgia. 



The larch worm. — ^There are also many examples of widespread 

 depredations chargeable to insects which defoliate the trees, thus 

 contributing to their death. Notable among these are the depreda- 

 tions by the larch worm, which, during several extensive outbreaks 

 since 1880, has killed from 50 to 100 per cent of the mature larch 

 over vast areas in the northeastern United States and southeastern 

 Canada. It is evident that the amount of merchantable-sized timber 

 that has died as the result of defoliation by this insect will aggregate 

 many billions of feet. 



CONTROL OF BAEKBEETLES WHICH KILL TKEES. 



The barkbeetles which kill trees attack the bark on the trunk and 

 destroy the life of the tree by extending their burrows or galleries in 

 all directions through the inner living bark. The broods of young 

 grubs or larvae develop within the inner bark, on which they feed. 

 Those of some species develop to the adult stage within the inner bark 

 and are exposed when the bark is removed, while those of other 

 species transform to the adults in the outer corky bark and the larvae 

 are not exposed when the bark is removed. Some species have two 

 or more generations in a season or annually, while others have but 

 one, and in a few species it requires two years for a single generation 

 to develop. 



The barkbeetles of the genu's Dendroctonus represent the most 

 destructive enemies of the principal coniferous tree species of Ameri- 

 can forests, and at the same time are among the easiest of control. 

 The general requisites for success are embodied in the following rules : 



(a) Give prompt attention to the first evidence of a destructive 

 outbreak, as indicated by an abnormal percentage of yellow or red 

 topped dying trees, and especially when such trees occur in groups of 

 ten or more or cover large areas ; (b) secure authentic determination 



[Cir. 125] 



