INSECT ENEMIES OF WESTERN FORESTS 147 



Species of Trypodendron Hosts and distribution 



T. dorealis Sw Eiigclmanu spruce and white-bark pine. 



Idaho and Montana. 

 T. ponderosae Sw Ponderosa pine, Engelmann spruce, Douglas 



fir, and mountain hemlock, British Colum 



bia and south to Oregon, 

 T. retnsns Lee Poplar and aspen. Western States and 



Canada. 



The oak timber beetles of the genus Pterocyclon {Monarthrum) 

 are small, elongate, cylindrical, da^k-b^o^Yn ambrosia beetles which 

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

 trees. After the beetles have entered into the wood they excavate 

 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 

 Avood. Pterocyclon scutellare Lee. (fig. 72), about one-eighth inch 

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

 California. P. dentiger Lee. is a smaller species, about one-sixteenth 

 inch in length, which works in the same 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- 

 lorum Hopk. works in the dead wood of ponderosa pine and Coulter 

 pine in California, Oregon, and South Dakota. X. arhuti Hopk. 

 works in madroiia in California. X. xylograiilius Say is the very 

 common eastern species which attacks a large variety of hardwoods. 

 Similar species in the Western States have been referred to this spe- 

 cies. The galleries consist of simple branching tunnels in which the 

 larvae live and feed upon ambrosial fungus without constructing an 

 enlarged cavity or larval cradle. 



THE FLATHEADED WOOD BORERS 



(Buprestidae) 



The flatheaded borers have been previously discussed under the 

 section on cambium or inner-bark miners (p. 132). By far the larger 

 number of species, however, are of more economic importance as 

 wood borers than as killers of living trees. Many species work first 

 in the inner bark of dying trees, then extend their tunnels into the 

 sapwood and even into the heartwood. The flattened oval wormholes 

 that are made by the horseshoe-nail-shaped grubs are usually tightly 

 packed with boring dust and may wind in a tortuous fashion back 

 and forth through the wood so as to riddle it completely. Even a 

 few such wormholes greatly lower the quality of the lumber, and a 

 large number make it unfit for any but the roughest use. Some of 

 these wood borers attack the pitchy fire scars on living trees and 

 gradually extend their mines into the sounder portions. Many others 

 attack trees that have been killed or felled and do most of their 

 dama^-e while the wood is still unseasoned. Others will attack wood 

 after it has been run through the mill and is placed in storage, or 

 even after it has been put into use. 



The prevention of fire scars and other injuries to standing trees 

 and the prompt utilization of dead or felled trees will reduce this 



