INSECT ENEMIES OF WESTERN FORESTS 



161 



Some of the species of the genus Pseudohylesinus are also fre- 

 quently found in various firs. They usually are secondary in habit 

 but at times some species are destructive. Their work is very simi- 

 lar to that of Scolytus in that the typical egg- gallery consists of 

 two short, straight branches from a central entrance tunnel. The 

 work usually can be distinguished from Scolytus in that no en- 

 larged nuptial chamber, scoring the sapwood or visible on the 

 inner surface of the bark, is constructed, as is the case, with 

 Scolytus. Another distinguishing 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 outline and do not have 

 the concavity at the rear of the abdomen which is such a distinc- 

 tive feature of Scolytus. 



The Douglas-fir hylesinus (Pseudohylesinus nebulosus Lee.) is 

 frequently found attacking recently felled or injured small Doug- 

 las-firs through the range of this tree in the West. 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 y 8 inch 

 long. Usually a short longitudinal 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. 75). Their work is very similar 

 to and easily confused with that of Scolytus unispinosus, but is 





A \Ytl 



J M, 



Sill 



/ 



ill ' 



Figure 75. — Adults and galleries of the Douglas-fir hylesinus 

 (Pseudohylesinus nebulosus) . 



