INSECT ENEMIES OF WESTERN FORESTS 167 



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. 155). Dying and felled trees 

 may be attacked by Ips integer or other small engraver beetles. 



The larch engraver (Scohjtus laricis Blkm.), which is very simi- 

 lar to S. unispinosus in appearance and habits (p. 158), has 

 recently been described by Blackman (14) from specimens found 

 breeding in this tree. 



CEDAR BARK BEETLES 



All the closely related trees belonging to the families Taxo- 

 diaceae and Cupressaceae, such as the various cypresses, California 

 incense cedar, Port Orford cedar, Alaska yellow cedar, western 

 redcedar, redwood, and the various junipers, are attacked by 

 diverse species of one genus of bark beetles, Phloeosinus. Not only 

 is this genus practically confined to this group of trees (one spe- 

 cies has been doubtfully recorded from pine), but as these trees 

 have almost no other bark-beetle enemies, any species found work- 

 ing 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 aggressive 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, causing them 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 pattern, the typical egg gallery con- 

 sists of one short, longitudinal gallery 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. 77) . Trees are attacked in the spring and summer, 

 and there may be one or one and one-half generations a year. The 

 only method of artificial control is to fell and burn the infested 

 trees or severely scorch the bark. No control work has been at- 

 tempted in the West, except in California for the control of a 

 species affecting ornamental Monterey cypress. Approximately 20 

 species have been described from western cedars and related trees. 

 Many of these are rare and of little economic importance. 



The western cedar bark beetle (Phloeosinus punctatus Lee.) at- 

 tacks the trunk and larger limbs of western red cedar, California 

 incense cedar, and Sierra juniper in the mountains of the Pacific 

 Coast States and eastward through the range of western red 

 cedar. It is a common species and at times injurious to living trees. 

 The galleries consist of either one short tunnel, not over 1 inch 

 long, or two short tunnels in the form of a V. The beetles are dark 

 red to black and about % inch long. 



The juniper bark beetle (Phloeosinus juniperi Sw.) is black 



