THE GENUS DENDROCTONUS. 



135 



healthy trees when there are plenty of felled and injured ones for it 

 to infest. So far as observed it attacks only the Sitka spruce, but 

 it is probable that it will be found in the Engelmann and white 

 spruces, if they grow in the vicinity of the Sitka spruce. 



The gallery is very much the same as those of the eastern spruce 

 beetle and the Engelmann spruce beetle, except that the larval mines 

 appear to be even more generally connected toward the egg gallery. 

 The larvae and pupae are either exposed or hidden in the inner bark, 

 and the pupal cells are sometimes grooved in the surface of the wood. 

 Sufficient observations have been made on the flight of this species 

 to indicate that it flies during the day, and even in bright sunshine. 



Fig. 86.— The Sitka spruce beetle: Distribution map. (Author's illustration.) 

 ECONOMIC FEATURES. 



So far as observed, this species has not been found attacking 

 healthy trees in sufficient numbers to cause their death, but it is not 

 improbable that under specially favorable conditions for the increase 

 of its broods the older living timber might be attacked and killed as 

 it is by the eastern spruce beetle. If so, the evidence of attack would 

 be similar to that described under Nos. 14 and 15. 



METHODS OF CONTROL. 



If this barkbeetle should be found killing trees, the method of con- 

 trol would be similar to that recommended under the eastern spruce 

 beetle, except that summer operations of barking or utilizing the 



