INSECT ENEMIES OF WESTERN FORESTS 127 



insect enemy of this tree. It will also attack other species of spruce 

 AAdthin its range, which covers Oregon, Washington, Idaho, Montana, 

 Wyoming, the Black Hills of South Dakota, Utah, Colorado, Ari- 

 zona, and new Mexico. Large, overmature trees are preferred 

 for attack, as are also trees w^eakened by mechanical injuries, logs, 

 and windfalls. With large standing trees the base is seldom at- 

 tacked, and examinations must be made at a height of 6 feet or 

 more from the gTound if the insects responsible for the injury are 

 to be found. 



The adult beetles are about one-fourth inch in length, reddish 

 brown, with the body sparsely clothed with long hairs. They exca- 

 vate a short, nearly straight, longitudinal egg gallery in the inner 

 bark, slightly scoring the sapwood. The gallery is much wider 

 than the beetles and is packed with boring dust, through which the 

 adults keep a passageway open. Eggs are laid side by side in elon- 

 gate cavities alternating from side to side of the egg gallery. The 

 larvae at first bore out en masse, transversely from the egg gallery, 

 but later make separate mines. The pupal cells are usually con- 

 structed in the inner bark, being exposed when the bark is removed, 

 but are sometimes deeper in the bark, and quite concealed in thick- 

 bark trees. 



There is only one complete generation annually, but it shows con- 

 siderable overlapping of broods. The winter is passed in all stages 

 of development, except the pupal stage, with new adults predomi- 

 nating, in trees attacked the preceding summer. The overwintering 

 adults emerge rather early in the season, but the emergence from the 

 overwintering larvae is spread over a rather long period, owing to 

 variations in individual development. The time of emergence and 

 attack will vary materially, according to differences in elevation 

 and exposure, but the period of heaviest attack is in June and July. 



Since the developing larvae and pupae of this species are exposed 

 when the infested bark is removed, such removal through peeling of 

 infested trees will result in their destruction if the broods are in the 

 larval or early pupal stage. The burning or severe scorching of 

 infested logs is also an effective method of destroying the broods, 

 especially when the beetles are in the adult stage. Owing to dense 

 forest cover in most forests of Engelmann spruce the use of fire in 

 beetle control will often be impractical because of the danger 

 involved. As with the Douglas fir beetle, fall control is to be pre- 

 ferred to spring control. 



The Alaska spruce beetle {D endroctonus horealis Hopk.) attacks 

 white and Engelmann spruce in Alaska and northwestern Canada. 

 In appearance and habits it is very similar to the Engelmann spruce 

 beetle, to which it is closely related. 



The Sitka spruce beetle {Dendroctonus ohesus Mann.) is usually 

 considered as a secondary enemy of the Sitka spruce, but it has the 

 potentiality of becoming destructive. At times it has killed a con- 

 siderable volume of Sitka spruce along the coast of Oregon, Wash- 

 ington, and British Columbia. 



Many species of small engraver beetles which breed in the dying 

 bark of felled or weakened trees sometimes become so plentiful as 

 to become dangerous to small spruce trees and the tops of older 



