THE GENUS DENDROCTONUS. 55 



and adults before cold weather, but evidently no adults emerge before 

 winter. 



It is very evident that there is only one partial generation annually, 

 and that some individuals may not complete their development 

 until the second year. It is evident, also, that the most retarded 

 adults of the first generation may live over and deposit eggs the 

 third year. 



HABITS. 



So far as known, this species confines its attacks to the western 

 yellow pine, but it is probable that it will attack other species of 

 pine growing within its range. It is nearly always associated with 

 the other species of Dendroctonus and other barkbeetles in injured, 

 dying, and felled trees. The adults enter the living to dying bark 

 on the main trunk of the trees and excavate long, slightly winding, 

 longitudinal, oblique, or nearly transverse and sometimes branched 

 galleries through the inner bark, and often groove the outer layer 

 of wood. In contrast with other species of Dendroctonus which 

 are usually associated with it, except the Black Hills beetle, the larval 

 mines are usually, but not always, exposed in the inner bark, and 

 often mark the surface of the wood. Some of the larvse may trans- 

 form to adults in the inner bark, but as a rule they enter the outer 

 corky bark for this purpose. The young adults remain there until 

 time for them to emerge and fly. Nothing is known of the food 

 and flight habits, and many other facts are obscure, owing to the 

 confusion of this with other species before it was recognized as 

 distinct. 



ECONOMIC FEATURES. 



The fact that this species is usually associated with one or more 

 of species 2, 3, 5, 8, and 10 renders its specific relation to the death of 

 trees doubtful. It is evident, however, that if it should become iso- 

 lated from the other species and occur in large numbers, it would be 

 fully capable of killing trees on its own account. During the past year 

 it was found associated with the Black Hills beetle in the destruc- 

 tion of a large amount of timber, with evidence that some of the 

 trees were killed by it alone. 



METHODS OF CONTROL. 



Whenever it is found that this species is causing the death of 

 timber or is associated with other species in doing so, the bark should 

 be removed from the main trunk of the infested trees and burned. 

 The work should be done between the first of October and the middle 

 of the following June. (See also " General methods of control/' pp. 

 29-35.) 



