44 
THE SCOLYTID BEETLES. 
pupa? about the middle of August, and continue transforming until 
cold weather, the principal period of transformation being from the 
middle to the last of August. The pupa? begin to transform to adults 
after the middle of August, and continue transforming until cold 
weather, but the principal period of transformation is between the 
middle of August and the middle of September. 
The adults begin to emerge from the trees toward the last of 
August, and continue to come out until in October, or later, but the 
principal period of flight appears to be from the last of August to the 
middle "of September. YVhile the majority of the broods of this 
generation emerge before cold weather, it is evident that some of 
them overwinter in all stages from larvae to young and parent adults. 
/lierfiarrA- 
Fig. 8. — The western pine beetle: Bark showing, a, a. pupal 
cells: b, exit burrows; c, pitch tubes. Reduced. < From 
Webb.) 
larvae, together with some of the parent 
complete generation annually and a parti 
SECOXD GEXERATIOX. 
The records of observa- 
tions indicate that the ear- 
lier emerging adults of the 
first seasonal generation 
begin to deposit eggs about 
the last of August, and 
that the principal period 
of attack is from the last 
of August to the middle of 
September. The larva? be- 
gin to appear about the 
first of September, and 
continue to hatch until in 
October, or later. Xo evi- 
dence has been found that 
the larva 3 of this genera- 
tion transform to pupa 3 
before winter, but it ap- 
pears that the broods pass 
the winter in all stages of 
adults. Thus, there is one 
al second one. 
HABITS. 
The adults attack the living bark on healthy, felled, and weakened 
standing western yellow pine and sugar pine. They excavate long, 
winding galleries (fig. 7) through the inner layers of bark, along the 
sides of which single eggs are deposited at intervals of one-half inch 
or more. The larva 1 normally do nut exeavate their mines through 
the inner layers of bark, but through the middle or outer portion of 
the inner bark. When the larvse have fully developed, they bore 
