THE GENUS DENDROCTONUS. 



81 



with a few long hairs, the striae narrow, and the spaces between quite 

 broad and roughened with sparsely placed granules. (See &g. 44.) 

 It attacks injured, felled, and healthy silver or western white pine, 

 western yellow pine, and lodgepole pine, in Montana, western Wyo- 

 ming, Idaho, Oregon, and Washington; it also attacks sugar pine, 

 western yellow pine, and lodgepole pine in the mountains of Washing- 

 ton, Oregon, and California. It excavates very long, nearly straight to 

 slightly, and sometimes strongly, winding egg galleries through the 

 inner living bark and grooves the surface of the wood (figs. 45, 46). 

 The eggs are placed in approximate groups at short intervals along the 

 sides, and the short and broad to long 

 and slender larval mines are exposed in 

 the inner bark; the larvae transform to 

 pupae and adults in separate cells, exposed Vi ■■■>--«*■.. 



or concealed in the inner bark. This ^K^^-^Sf^fcvl 



species is sometimes associated with the 

 western pine beetle in the same tree, but 

 usually it works independently and oc- 

 cupies the greater part of the bark on the 

 main trunks. Infested trees are first in- 

 dicated by pitch tubes and later by the 

 fading yellow to reddish foliage. 



SEASONAL HISTORY. 



OVERWINTERING STAGES. 



The winter is passed as larvae, young 

 adults, and parent adults, in the inner 

 bark of trees attacked the preceding sum- 

 mer and fall, the parent adults in the egg 

 galleries or ventilating burrows, and the 

 broods in the larval mines or pupal cells. 



Fig. 44.— The mountain pine beetle 

 (Dendrodonus monticolse): Adult. 

 Greatly enlarged. (Author's illus- 

 tration.) 



ACTIVITY OF OVERWINTERED BROODS. 



As soon as the weather is favorable in April and May the overwin- 

 tered parent adults extend their incompleted egg galleries or excavate 

 new ones in the remaining living bark on the dying trees and deposit 

 eggs. The overwintered broods of young adults begin to emerge in 

 July. The principal period of emergence is in August, but the 

 retarded broods continue to come out until September, or later. 

 The broods of larvae begin to transform to pupae and adults in April 

 and May and continue to do so until September, or later. Some of the 

 larvae evidently pass the second winter as matured larvae and adults. 

 The broods from eggs deposited by the overwintered parent adults 

 evidently develop to adults in July and August. 

 89535— Bull. 83, pt. 1—09 7 



