BARK-BEETLES; ENGRAVER-BEETLES. 



227 



.are not confined wholly to the pear, but the same insect occurs also 

 on the apple, the plum, and the apricot. 



According to Hubbard the members of this genus of beetles 

 also exist upon ambrosia, which is grown by the females for the 

 purpose of feeding the young, as has already been described. 



Each species of beetle grows its own kind of ambrosia, and 

 the galleries made are of a different character, as may be seen in 

 the case of X. xylographus Say, illustrated in Fig. 240, where 

 the young are assembled in a large brood chamber, constructed 

 at the end of a gallery which penetrates deeply into the heart of 

 the tree, or remains in the sap-wood, according to the amount of 

 moisture in the trunk. The chamber is somewhat leaf-shaped, 

 and stands vertically on edge, parallel with the grains of the wood. 



Fig. 241. — Ambrosia of Xyleborus xylographvs, Say. 

 tnology, U. S. Department of Agriculture. 



After Division of Bnto- 



The space between the walls is not much greater than the thick- 

 ness of the bodies of the adult beetles. The larvae of all ages are 

 able to cling to the vertical walls, and to progress over them by 

 an adaptation of the end of the body, which aids them in advanc- 

 ing. The entire surface of the walls in the brood chamber is 

 plastered over with ambrosia fungus, a representation of which is 

 given in Fig. 241. It consists of short, erect stems, terminating 



