SOME MISCELLANEOUS RESULTS OF THE WORK OF THE 

 DIVISION OF ENTOMOLOGY. 



THE AMBROSIA BEETLES OF THE UNITED STATES. 

 By H. G. Hubbard. 



The term ambrosia beetles is here used as a convenient one to distin- 

 guish from the true bark-borers and. bark-eaters the timber-boring 

 Scolytidae, which push their galleries deeply into the wood, and which 

 feed upon a substance called "ambrosia." 



Superficially the resemblance between the two groups is very close. 

 They are small elongate beetles, with compact cylindrical bodies, short 

 legs, and dull coloration of varying shades of brown. Although differ- 

 ences in structure exist, these have not hitherto been considered of 

 sufficient importance to warrant their separation into different families. 



Although in external form the bark-boring and timber-boring Scoly- 

 tids resemble each other, in their habits and mode of life they have 

 little in common. The entrances to their galleries in the outer rind of 

 trees are precisely similar, and the designation "shot holes" would be 

 equally descriptive of either group. The variations in diameter are 

 very well covered by the different sizes of small shot. An examination 

 of the galleries into which these openings lead reveals at once the 

 widely different character of the two groups. 



The galleries of the bark-borers are superficial and lie within or just 

 under the bark. The galleries of the ambrosia-eating beetles penetrate 

 into the wood, and in all their ramifications are of uniform size and tree 

 from wood dust or other refuse. 



Their food consists not of wood, but of certain minute and juicy 

 fungi propagated on the walls of their galleries. The action of the 

 fungus produces a stain in the wood, giving to the galleries the appear- 

 ance of having been bored with a red hot wire. These characteristic 

 "black holes" serve to distinguish their work from that of all other 

 deep-boring timber beetles. 



The ambrosia beetles, in the care which they give their young, exhibit 

 characteristics utterly foreign to most Coleoptera, and such as are 

 usually attributed only to the social Ilymenoptera and Neuroptera. 



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