INSECT ENEMIES OF WESTERN FORESTS 137 



along the main trunk of a tree from within a few feet of the 

 ground up to the middle branches but may extend from the root 

 collar very nearly to the top and into the larger limbs. During 

 endemic infestations there is a tendency for the beetles to select 

 the weaker, less vigorous trees for attack, but no such selection is 

 apparent during epidemic conditions. Infested trees are recognized 

 first by pitch tubes on their trunk and red boring dust in bark 

 crevices and on the ground at the roots ; later, by discoloration of 

 the foliage, as it changes from normal green to light greenish 

 yellow, and then to red. 



The adults are rather stout, black, cylindrical beetles from % 

 to y 5 inch long. They excavate very long, perpendicular egg gal- 

 leries (figs. 60 and 61) through the inner living bark, engraving 

 both bark and wood. The galleries may be nearly straight or 

 slightly sinuous, and sometimes, particularly in sugar pine, de- 

 cidedly winding, and at the bottom of these galleries there is a 

 short crook, or bend, 1 or 2 inches in length. The perpendicular 

 portion of the gallery ranges in length from 12 to 36 inches and 

 nearly always follows the grain of the wood. 



Eggs are deposited singly in cells or egg niches on alternate 

 sides during the construction of the egg gallery. These hatch in a 

 few days, and the small white larvae excavate short feeding tun- 

 nels at right angles to the egg gallery. These feeding tunnels vary 

 in length and are exposed on the inner bark surface. When full 

 grown, the larvae construct small pupal cells at the ends of the 

 larval mines and in these transform to pupae and then to new 

 adults. These pupal cells are usually exposed when the bark is 

 removed, but in thick-bark trees they may be concealed in the 

 inner bark. The new adults may bore away the intervening bark 

 between pupal cells and congregate beneath the bark, prior to 

 emergence, or individual emergence holes may be constructed di- 

 rectly from the pupal cells. Two or more insects often use the 

 same emergence hole, and the emerging beetles often take advan- 

 tage of cracks in the bark or in holes resulting from woodpecker 

 work. 



The mountain pine beetle passes the winter in all stages of 

 development except the pupa. The overwintering broods emerge 

 in three well-defined 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 cold winter 

 weather again stops development. Normally there is only one gen- 

 eration 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 time during the summer. Late fall, 

 winter, or early spring is therefore the best time to carry on 

 control work. 



A clerid beetle (Enoclerus) , a fly (Medetera), and a parasitic 

 wasp (Coeloides) are the most active insect enemies of this pine 

 beetle. Woodpeckers also prey upon the species, and climatic con- 

 ditions often are important as natural control agencies. 



Direct control methods vary with the region and character of in- 



