THE GENUS DENDROCTONUS. 
107 
mines extend at right angles from the main galleries and are exposed 
in the inner bark, often marking the surface of the wood (figs. 66, 67, 
68). The stout, whitish, grublike larvae transform to pupa3 and adults 
in cells, either exposed or not, in the inner bark. The broods usually 
work independently of the other species, and often occupy and 
separate the bark on the lower to middle trunks of standing and 
felled trees. The fresh attack on living or freshly felled trees is 
indicated by red borings at the entrance to the galleries and lodged 
in the loose bark on the trunk or around the base; the leaves of the 
dying trees fade, turn pink- 
ish yellow, or remain green in 
the fall succeeding spring and 
summer attack, but turn 
brown during the winter and 
spring. 
SEASONAL HISTORY. 
OVERWINTERING STAGES. 
The winter is passed in the 
inner bark of trees, logs, etc., 
attacked the preceding spring 
and summer, principally as 
developed broods of adults, 
but also as young to matured 
larvae and probably parent 
adults. 
ACTIVITY OF OVERWINTERED 
BROODS. 
Activity begins during the 
first warm weather in April, 
when the parent adults ex- 
tend their galleries and de- 
posit eggs. The young adults 
of the developed broods be- 
gin to emerge by the middle of 
April, and continue to come out during June or July or later. The 
overwintered, large larvae evidently complete their development and 
emerge by the first of August, while the broods of young larvae of 
the possible second generation from eggs deposited in the fall evidently 
complete their development and begin to emerge in August, and 
continue to do so until cold weather, when some will begin their 
second hibernation as fully developed broods of adults. 
Fig. 65. — The Douglas fir beetle (Dendroctonus pseudo- 
tsugse): Adult. Greatly enlarged. (Author's illustra- 
tion.) 
