134 
THE SCOLYTID BEETLES. 
GENERATION. 
The adults begin to attack the trees, excavate galleries, and 
deposit eggs early in May, and continue to do so through June, 
probably until August, though the principal period is in May and 
June. Fresh attacks and eggs are also found in September, either 
by adults of overwintered broods or those developed from eggs 
deposited early in the spring. The larva? begin to hatch in May, 
and probably continue hatching until in August, but the principal 
period is in June and July. The principal period of larval develop- 
ment is during June, July, aud August. The larva 3 begin trans- 
forming to pupae toward the last of July, and continue transforming 
probably imtil winter, but the princi- 
pal period is in August and September. 
The pupae begin to transform to adults 
probably during the second week in 
August, and continue transforming un- 
til winter. The principal period of 
transformation to adults is during the 
month of September. The period re- 
quired for the development from eggs 
to adults is about three months. 
The more advanced broods of the 
generation complete their development 
by the last part of August and first 
part of September, while the later ones 
evidently pass the winter as mature 
larvae and immature adults, to com- 
plete their development the following 
spring. There is, therefore, one com- 
plete generation during the year. 
The fact that eggs and young larva? 
are common in September indicates 
that some of the broods of the first 
generation may emerge in the fall and deposit eggs from which there 
is a partial second generation, but it is not improbable that some of 
the parent beetles of the overwintered broods may leave the trees 
after they have completed the first set of galleries, and excavate 
galleries in the same or other trees. If there is a partial second 
generation the brood passes the winter in the larval stage, possibly 
together with the parent beetles. 
HABITS. 
This species appears to prefer to attack the living bark on the 
trunks and stumps of felled trees and on the trunks of those still 
standing but weakened and injured. Apparently it will not attack 
Fig. S5.— The Sitka spruce beetle (Den- 
droctonus obesus): Adult. Greatly en- 
larged. ( Author's illustration.) 
