29 



it sometimes fails to establish colonies in such trees, through inability 

 to raise its food fungus. 



Xyloterus retusus Lee. — This is the largest of the ambrosia beetles, 

 and resembles very closely X. bivittatus, which has been illustrated in 

 fig. 29. The species has been found only in the broad-toothed aspen 

 (Pojmlus grandidentata)) and occurs in northern regions, following 

 probably the distribution of that tree. Professor Hopkins records it 

 also from West Virginia. 



The galleries of this species are 

 represented in fig. 31. Several 

 pairs of the beetle unite in col- 

 onies having a single entrance, 

 but each family occupies its own 

 quarters, consisting of one or two 

 branch galleries. The galleries 

 do not penetrate deeply into the 

 heartwood. 



Each female attends her own 

 brood, which are raised in cra- 

 dles extending upward and 

 downward at right angles to the 

 main passageway. She feeds the 

 young with a yellowish ambrosia 

 grown in beds in the neighbor- 

 hood of the cradles. The mouth 

 of each cradle is constantly kept 

 filled with a plug of the food 

 fungus. 



The ambrosia, represented in 

 fig. 32, consists of oval cells which 

 form upright sticks resembling 

 some forms of styliform ambrosia, 

 but they do not branch and are 

 capable of being broken up into 

 bead-like masses without losing 

 their vegetative powers. 



Although the color of the fun- 

 dus bed is yellowish, the galler- 

 ies are stained intensely black. 



Xyloterus scabricoUis Lee. — 

 This is a rare species described from the District of Columbia 

 fessor Hopkins records it as infesting pines in West Virginia. 



In Europe a number of species of Trypodendron, the generic name 

 being synonymous with Xyloterus, are known to cause defects in 

 timber of many kinds, including oak and other hard woods. They 

 push their galleries deeply into the heartwood and raise their young 

 in separate cradles in the manner previously described. 



According to Mr. Blandford, the defects caused by one or more species 



Fig. 31.— Gallery of Xyloterus retusus in aspen 

 (original). 



Pro- 



