INSECT ENEMIES OF WESTERN FORESTS 129 
The hemlock engraver (Scolytus tsugae Sw.) is a small, dark, 
shiny bark beetle about one-eighth inch in length, with the wing 
covers projecting over the concave abdomen. It constructs a short, 
straight ege tunnel across the grain, from one or both sides of a 
small entrance chamber. Both mountain and western hemlocks are 
attacked, and at times, as recently in Crater Lake National Park, 
the species is very destructive. It is distributed from British 
Columbia southward to California. 
The hemlock hylesinus (Pseudohylesinus tsugae Sw.) 1s a stout, 
oval bark beetle about one-eighth inch long, reddish brown and 
sparsely clothed with scales and short stout hairs. It breeds pro- 
lifically in felled and dying western hemlock and also is known to 
attack and kill apparently healthy trees. It is reported from 
British Columbia and Washington, but will probabiy be found 
throughout the range of the host tree. 
BarkK BEETLES AFFECTING LARCH 
Western larch is quite resistant to insect enemies, but it some- 
times is killed by species of bark beetles that work in various other 
coniferous trees. Probably its most serious bark-beetle enemy is the 
Douglas fir beetle (p. 120). Dying and felled trees may be attacked 
by Ips integer or other small engraver beetles. 
The larch engraver (Scolytus laricis Blkm.), which is very similar 
to S. wnispinosus in appearance and habits (p. 122), has recently 
been described by Blackman from specimens found breeding in this 
tree: 
CEDAR BARK BEETLES 
All the closely related trees belonging to the families Taxodiaceae 
and Cupressaceae, such as the various cypresses, incense cedar, Port 
Orford cedar, Alaska cedar, western red cedar, redwood, and the 
various junipers, are attacked by diverse species of one genus of 
bark beetles, Phloeosinus. Not only is this genus practically con- 
fined to this group of trees (one species has been doubtfully re- 
corded from pine), but as these trees have almost no other bark- 
beetle enemies, any species found working in the inner bark of 
cedarlike trees is almost certain to be a species of Phloeosinus. As 
a general rule these small oval beetles are not aggressive in their 
attack and are found working under the bark of trunks, tops, and 
limbs of weakened, dying, or felled trees, or of broken branches. 
Occasionally, however, they become sufficiently numerous and ag- 
gressive to attack and kill apparently healthy trees. Usually the 
ereatest injury by these bark beetles is due to their habit, as newly 
emerged adults, of feeding on the twigs of healthy trees, often caus- 
ing these to break or die. This habit is similar to that of most 
species of Scolytus. In constructing their brood burrows the beetles 
work in pairs, and, while there is some variation in the work pat- 
tern, the typical egg gallery consists of one short, longitudinal gal- 
lery arising from an enlarged entrance chamber, with the eggs very 
uniformly spaced along the sides and the larval mines extending 
laterally in a very regular pattern (fig. 64). Trees are attacked in 
the spring and summer, and there are one or one and one-half gen- 
erations a year. The only method of artificial control is to fell 
136650°—38——9 
