104 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
groups, (1) in June, (2) late in July and early in August, and (3) 
in September. New attacks are made immediately after emergence, 
and the resultant broods develop to new adults, mature larvae, or 
small larvae before the cold winter weather again stops develop- 
FIGURE 51.—Stages and typical work of the mountain pine beetle (Dendroctionus monti- 
colae). Adults, larvae, and pupae, at lower right. Natural size. 
ment. Normally there is only one generation a year, but owing to 
the uneven development there is considerable overlapping of the 
various broods, so insects in all stages may be found at any one time 
during the summer. Late fall, winter, or early spring is therefore 
the best time to carry on control work. 
