124 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
galleries in the limbs of balsam firs: S. praeceps Lec., a small species 
about one-eighth inch in jength, which attacks the limbs and small 
tops of white fir and other firs in the Western States; and S. mon#i- 
colae Sw., about one-eighth inch in length, which is recorded by 
Swaine as attacking western white pine and Douglas fir in British 
Columbia. rs 
Some of the species of the genus Pseudohylesinus are also quite 
frequently found in various firs. They usually are secondary in 
habit but at times 
some species are de- 
structive. Their work 
is very similar to that - 
of Scolytus in that the 
typical egg gallery 
consists of two short, 
straight branches from 
a central entrance tun- 
nel. The work usu- 
ally can be distin- 
guished from Scolytus 
in that no enlarged 
nuptial chamber, scor- 
ing the sapwood or 
visible on the inner 
surface of the bark, is 
constructed, as is the 
case with Scolytus. 
Another distinguish- 
ing feature between 
these two genera is 
that the wing covers 
of Pseudohylesinus are 
densely covered with 
scales, and therefore 
are dull in appearance 
instead of shiny. 
Moreover, the beetles 
are nearly oval in out- 
line and do not have 
the concavity at the rear of the abdomen which is such a distinctive 
feature of Scolytus. 
The Douglas fir hylesinus (Pseudohylesinus nebulosus Lec.) is fre- 
quently found attacking recently felled or injured small Douglas 
firs through the range of this tree from British Columbia to central 
California. It seems to prefer the thin bark of saplings, or poles, 
or limbs of larger trees, and frequently kills trees of small diameter. 
The adults are small, grayish to yellowish-brown, variegated bark 
beetles about one-eighth inch in length. Usually a short longi- 
tudinal egg gallery is constructed in the cambium layer, often with 
two branches, originating from a central entrance tunnel, one up 
and one down the trunk, parallel with the grain of the wood (fig. 
62). Their work is very similar to and easily confused with that 
of Scolytus unispinosus, but is distinctive in that no well-defined 
FIGURE 62.—Adults and galleries of the Douglas fir hylesi- 
nus (Pseudohylesinus nebulosus), natural size. 
