INSECT ENEMIES OF WESTERN FORESTS 129 



The hemlock engraver {Scolytus Uugae 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 ^g^ tunnel across the grain, from one or both sides of a 

 small entrance chamber. Both mountain and Avestern 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. 



Tlie hemlock hylesinus {Pseudohylesinus tsugae Sw.) is a stout, 

 oval bark beetle about one-eighth inch long, reddish brown and 

 sparsely clothed wdth scales and short stout hairs. It breeds pro- 

 lifically in felled and dying w^estern hemlock and also is known to 

 attack and kill apparently healthy trees. It is reported from 

 British Columbia and Washington, but will probably be found 

 throughout the range of the host tree. 



Bark 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. tmispinosus in appearance and habits (p. 122), has recently 

 been described by Blackman from specimens found breeding in this 

 tree. 



Cedar Baek 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 

 greatest 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 o^gg 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 



130643°— 39 9 



