1907.] Wheeler, Fungus-growing Ants of North America. 787 



graphs I shall confine myself to an account of the investigations of these 

 three authors. 



The ambrosia beetles resemble the ants and termites and differ from 

 other Coleoptera in living in societies and in caring for and feeding their 

 larvse. The arrangement of the galleries, which have walls stained dark 

 by the fungus, differs in different species. Those of Xyleborus celsus Eichh., 

 living in the hickory, are shown in PI. LII, Fig. 64, taken from Hopkins 

 (1904). The galleries ramify into the sap wood from a single entrance 

 gallery that opens on the bark. These perforations do not necessarily kill 

 the tree, but they spoil the wood for many commercial purposes. When 

 made in young growing trees they may be overgrown by succeeding layers 

 of wood. Hopkins (1903) has given an interesting account of this condi- 

 tion in trees infested with the Columbian timber-beetle (Corthijlus colum- 

 bianus Hopkins). This beetle which is responsible for losses to the lumber 

 interests of North America "amounting to millions of dollars, attacks the 

 sap-wood of the young, living, healthy tree, in which the adults excavate 

 their brood galleries and deposit their eggs. These hatch and develop 

 into beetles and emerge within one year. The next year the operation is 

 repeated in another place in the same tree, and so on for hundreds of years, 

 or as long as the tree lives, so that the galleries excavated in different years 

 and periods occupy their respective positions in the heartwood and sapwood 

 of the full-grown and old tree. Nearly all the damage by this insect, as 

 affecting the best part of the trees, Avas done 50, 100, 200 or in some cases, 

 as noted in an old tulip tree, over 400 years ago. The age of each gallery 

 observed in the end of the log is easily determined by counting the number 

 of annual layers of wood between the old healed-over entrance to the galleries 

 and the bark. Within recent years, examples of the species which do this 

 work have been exceedingly scarce; consequently but little evidence of its 

 work can now be found in the sapwood and outer heartwood of living trees. 

 Therefore there is no remedy for the old work and probably no need of 

 trying to combat an insect which is apparently becoming extinct." 



Hubbard's general account (1897a) of the fungus growing habits of the 

 ambrosia beetles is worth quoting in extenso, as it is one of the most impor- 

 tant of recent contributions to the study of insect ethology: "A small frag- 

 ment of ambrosia taken from the gallery of any species of these timber 

 beetles, if placed on a glass slide, with a drop of water or glycerine and 

 examined with an oVjjective of moderate power, is plainly seen to be a fungus. 

 It will be found, however, that the different kinds of ambrosia fungi are con- 

 nected with certain species of the beetles irrespective of the sort of timber 

 in which the galleries are constructed. So far as we yet know the food of 

 each species of ambrosia beetles is limited to a certain kind of ambrosia, 

 and only the most closely related species have the same food fungus. 



