INSECT ENEMIES OF WESTERN FORESTS 123 
The fir engraver (Scolytus ventralis Lec.) is found attacking 
the balsam firs in all the Western States and in British Columbia, 
and at times has been exceedingly destructive to white fir stands in 
California and Oregon. The adult is a short, black bark beetle 
about one-eighth inch in length, without a prominent spine on the 
ventral declivity. The egg galleries are excavated in the inner bark 
and cut transversely across the grain of the wood, which they score 
rather deeply for a 
distance of from 2 
to 6 inches on both 
sides of a central 
entrance chamber. 
Eggs are laid in 
niches along both 
sides of these galler- 
ies and the larvae, 
on hatching, work 
up and down the 
bole (fig. 61), ex- 
tending their indi- 
vidual larval mines 
for a distance of 5 
to 7 inches. A brown 
stain of the cambium 
caused by: a fungus 
is always found in 
the area in which the 
larvae feed. Pupa-. 
tion occurs in the in- 
ner bark at the end 
of the larval mines, 
and the new adults 
bore directly to the 
surface of the bark 
when ready to 
emerge. Frequently 
green trees are at- graver (Scolytus ventralis). 
tacked and new 
broods develop and emerge without destroying enough of the cam- 
bium to cause the death of the tree. The patch of “dead cambium 
heals over and leaves only a brown pitch pocket in the wood to mark 
where the injury occurred. Some wood sections have shown as many 
as seven such attacks during the life of the tree, which indicates that 
a certain amount of activity by this beetle is constantly going on in 
the forest. Trees are attacked during the summer months, and the 
eggs hatch and larvae develop before winter. The winter usually is 
passed in the larval stage, and the new broods emerge the following 
year. There is normally but one generation of these beetles annually. 
Because of the sporadic character of outbreaks and the possible pres- 
ence of healthy broods in living trees no methods of control appear 
practical. 
Other species of Scolytus which may be found in western firs 
include S. subscaber Lec., a large species which makes E-shaped 
Figure 61.—Egg galleries and larval mines of the fir en- 
ae es a eee 2 ee ee le a! SS ee 
