786 Bulletin American Museum of Natural History. [Vol. XXIIl 



2. TJie Ambrosia Beetles. 



The beetles of the family Scolytidje may be divided into two groups 

 exhibiting very different ethological peculiarities: the bark-borers, which 

 excavate and inhabit tubular galleries between the bark and the splint and 

 eat the substance of the tree, and the wood-borers, or ambrosia beetles, 

 which extend their galleries into the wood and subsist on delicate fungi 

 growing on their walls. All Scol}1:ida^ are of small size and dark color, 

 with cylindrical bodies and short legs adapted to the shape and size of their 

 galleries (PI. Llli Figs. 62 and 63), but the mouth-parts differ in the two 

 groups; the bark-beetles having strong maxillae armed with 12-20 spine- 

 like teeth in adaptation to their hard food, whereas the fungus-eating wood- 

 borers have weak maxillfe with 30-40 flexuous bristles. Unlike the Attii 

 and fungus-growing termites, the wood-borers are not confined to the tropics 

 or to a single hemisphere, but are cosmopolitan in their distribution and 

 well represented even in the noith temperate zone. The species have been 

 assigned to a number of genera (Plati/pus, Gnathotrichus, Trypodetidron, 

 Xylehorus, Xyloterus, Corthylus and Pterocyclon [Monarthrum]). As these 

 insects are very destructive to wood, they are well known to economic ento- 

 mologists, who have described their habits in journals or text -books devoted 

 to forestry. The remarkable habits have therefore been little noticed by 

 entomologists interested in general biological questions. 



There has been considerable difference of opinion in regard to the feed- 

 ing habits of the ambrosia beetles since the time of Schmidberger (1836) 

 who believed that Xylehorus dispar Fabr. fed on the sap exuding into its 

 burrows from the surrounding wood. The mother beetle was supposed 

 to mould this sap into a coagulated, albuminoid mass and to feed it to her 

 young. This substance Schmidberger called "ambrosia." Various con- 

 jectures concerning its nature were expressed by Ratzeburg (1839-1844), 

 Altum (1872-1875), and Eichhoff (1881). In 1844 Hartig discovered a 

 fungus in the galleries of Xylehorus dispar and described it as Monilia Candida. 

 Several years later (1872a, 1872t) he described similar conditions in Xylo- 

 terus lineatus Oliv., which lives only in conifers, and X. domesticus L., 

 which is confined to deciduous trees. In 1895 Goethe published a good 

 description and figure of the fungus of A", dispar. At about this time 

 Hubbard took up the study of the North American ambrosia beetles and 

 published most interesting accounts of their habits (1897a, 18976). Hop- 

 kins, too, who has given special attention to our Scolytidae, has published a 

 number of valuable observations (1898-19046), and Hedgcock (1906) has 

 made some important observations on the fungi. In the following para- 



