20 



to develop until toward the last of September, but they remain in 

 the bark until activity ceases. The hibernating, unmatured, and very 

 young adults appear ten to twenty days later than the fully matured 

 ones; they continue to emerge and deposit eggs until about the last 

 of July. 



The few pupa3 present when activity ceases evidently perish by the 

 last of January, as do also the eggs. 



The three stages of hibernating larva? develop to adults after 

 activity commences in the same ratio as the hibernating adults, but 

 owing to retarded development some of them probably do not attain 

 the adult stage until late in September. Thus adults would be com- 

 ing out during the entire period of activity, which accounts for the 

 existence of all stages when activity ceases in the fall. 



SPECIAL FEATURES OF THE BEETLE'S WORK. 

 KINDS OF TREES ATTACKED. 



So far as known this beetle attacks only the spruce, and the most 

 striking and important feature is its habit of attacking only the 

 larger trees. It is rarely found in trees below 10 inches in diameter 

 breast-high, but in all infested areas is exceedingly common in those 

 over 18 inches at the same height. It also appears to have a decided 

 preference for standing trees, although some evidence was found that 

 it will breed in wind-felled trees and rarely in stumps and logs in 

 cuttings. 



HOW AND WHEN THE ATTACK IS MADE. 



A study of the living trees which had recovered from a slight attack, 

 as well as those that were infested by different stages of the insect, 

 indicated quite clearly that the first entrances are made in the bark 

 of the healthy tree at a point from 6 to 10 feet from the base, and that 

 trees which are weakened in vitality from disease or other causes ma}' 

 be attacked from near the base to near the first large branches. 



The fact that as a rule the infested trees are found in clumps or 

 confined to definite areas of greater or less extent would indicate a 

 social habit, and that the individuals may migrate in swarms from an 

 old to a new locality and settle without any special choice except as 

 to size or number of trees. Thus they invade the trees on all sides, 

 and usually in such numbers as to prevent recovery from the first 

 attack. As soon as the trees commence to decline they are invaded 

 by other bark-mining beetles and grubs, which aid in their final death 

 and decay. 



ITS AVORK IX AND BENEATH THE BARK. 



The entrance and the primary gallery. — This is started, probably 

 by the male, hidden in a crevice or beneatli a flake of bark, and, if in 

 a living tree, is gradually and obliquely extended upward or to one 

 side through the inner bark. The male is then joined by a female, 



