242 



WOOD AND FOREST. 



as they increase in size, extend and enlarge their food burrows in a general 

 transverse but irregular course, away from the mother galleries (see illus- 

 tration). When these young and larval forms are full grown, each exca- 

 vates a cavity or cell at the end of its burrow and next to the outer corky 

 bark. (Hopkins, Agric. Yr. Bk., 1902.) 



Some of the species attack living trees, causing their rapid death, 

 and are among the most destructive enemies of American forests. 



All of the above in- 

 directly affect both the 

 quantity and quality 

 of the wood supply. 

 They can be studied 

 more in detail in the 

 publications of the U.S. 

 Bureau of Entomology. 



Of the insects di- 

 rectly attacking wood, 

 the most important 

 are the ambrosia or 

 timber beetles, the bor- 

 ers, the ants, and the 

 carpenter bees. The 

 most remarkable fea- 

 ture of the beetle is the 

 manner of its boring 

 into the harder parts 

 of the wood. Its jaws 

 are particularly con- 



Fig-. 90. Complete Brood Galleries of the Hickory 



Bark Beetle in Surface of Wood. [Agric. Tear Book, 



1903, Fig. 28, p. 316.] 



structed for this work, 



being heavy and strong. The boring is done something after the man- 

 ner of countersinking, and the jaws are believed to be self -sharpening, 

 by reason of the peculiar right to left and left to right motion. 



Ambrosia or timber beetles, Fig. 92. This class of insects attacks liv- 

 ing, dead, and felled trees, sawlogs, green lumber, and stave-bolts, often 

 causing serious injury and loss from the pin-hole and stained-wood defects 

 caused by their brood galleries. The galleries are excavated by the parent 

 beetles in the sound sap-wood sometimes extending into the heart-wood, and 

 the young stages feed on a fungus growth which grows on the walls of 

 galleries. (Hopkins, Entom. Bulletin No. 48, p. 10.) The growth of this 

 ambrosia-like fungus is induced or controlled by the parent beetles and the 

 your.g are dependent on it for food. (Hopkins, Agric. Yr. Bk., 1904.) 



