186 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



The species most frequently encountered in the Western States 

 are as follows : 



Species of Trypodendron Hosts and distribution 



bivittatum (Kirby) Pines, spruce, hemlock, Douglas-fir, and other 



conifers. Pacific coast and Rocky Mountain 

 regions. 



borealis Sw White spruce, Engelmann spruce, western 



white pine, and white-bark pine. Northern 

 Rocky Mountains. 



cavifrons (Mann.) Douglas-fir, fir, spruce, hemlock, western red 



cedar, alder, and poplar. Pacific Northwest. 



ponder osae Sw Ponderosa pine, Engelmann spruce, Douglas- 

 fir, alpine fir, Pacific white fir, and mountain 

 hemlock. British Columbia and south into 

 Oregon. 



retusum (Lee.) Poplar and aspen. Canada and Northwestern 



States, and east to West Virginia. 



rufitarsis (Kirby) Lodgepole pine. Idaho, Montana, Oregon, and 



Washington. 



The oak timber beetles, of the genus Monarthriim (Pterocyclon) , 

 are small, elongate, cylindrical, dark-brown ambrosia beetles, 

 which work in the wood of oak and various other hardwoods and 

 deciduous trees. After the beetles have entered the wood, they ex- 

 cavate a central nuptial chamber from which secondary tunnels 

 branch in three or four directions. From the secondary branches 

 the larval cradles are excavated at right angles and parallel to 

 the grain of the wood. M. scutellare (Lee.) (fig. 85), about *£ inch 



Figure 85. — The oak timber beetle Monarthriim scutellare: A, Tunnels; 

 B, adults, male above, female below, X 8. 



long, works in various species of oak from Oregon to southern 

 California. M. dentiger (Lee.) is a smaller species, about 1 16 inch 

 long, which works in oak trees in California. 



Species of Xyleborus make very small pinholes in the dying or 

 dead wood of a wide assortment of fruit, shade, and forest trees. 

 Larval cradles are not formed, and the tunnels are either plain or 

 enlarged into cavities where the larvae feed. Most frequently their 

 work is found in dying or recently dead wood. Xyleborus scopu- 



