INSECT INJURIES TO FOREST PRODUCTS. 383 



responsible for it is seldom seen, or it is so difficult to determine by 

 the general observer, from descriptions or illustrations, that the 

 species is rarely recognized. Fortunately, the character of the work 

 is often sufficient in itself to identify the cause and suggest a remedy, 

 and, in this paper, primary consideration is given to this phase of the 

 subject. 



AMHKOSIA OK TIMHKK BEETLES. 



The characteristic work of this class of wood-boring beetles is shown 

 in figures -H, 4-t, and 45. The injury consists of pinhole and stained- 

 wood defects in the sapwood and heartwood of recentl} 7 felled or gir- 

 dled trees, sawlogs, pulp wood, stave and shingle bolts, green or 



, 



b. 



a. 



a 



FIG. 43. Work of ambrosia beetles in tulip or yellow poplar wood: a, work of Xyleborus- affinis and 

 Xyleborus inermi*; f b, Xyleborus obcsits and work: c, bark: d, sapwood; c, heartwood. (Original.) 



unseasoned lumber, and staves and heads of barrels contain ing alcoholic 

 liquids. The holes and galleries are made by the adult parent beetles 

 to serve as entrances and temporal' v homes or nurseries for the devel- 

 opment of their broods of yoUng, which feed on a kind of fungus 

 growing on the walls of the galleries. The growth of this ambrosia- 

 like fungus is induced and controlled by the parent beetles, and the 

 young are dependent upon it for food. The wood must be in exactly 

 the proper condition for the growth of the fungus in order to attract 

 the beefles and induce them to excavate their galleries; it must have 

 a certain degree of moisture and other favorable qualities which usually 

 prevail during the period involved in the change from living, or 

 normal, to dead or dry wood; such a condition is found in recently 

 felled trees, sawlogs, or like crude products. 

 There are two general types or classes of these galleries one in 





