1907.] Wheeler, Fungus-growing Ants of North America. 789 



"The ambrosia does not make its appearance by accitlent or at random 

 in the galleries of the beetles. Its origin is entirely under the control of the 

 insect. It is started by the mother beetle upon a carefully packed bed or 

 layer of chips, sometimes near the entrance, in the bark, but generally at the 

 end of a branch gallery in the wood. In some species the ambrosia is grown 

 only in certain brood chambers of peculiar construction. In others it is 

 propagated in beds, near the cradles of the larvae. The excrement of the 

 larvae is used in some and probably in all species to form new beds or layers 

 for the propagation of the fungus. 



"It is not alone, however, the excreta of the living beetles or their young 

 that is required for the development of ambrosia; there must be present a 

 certain amount of moisture or sap, and the sap in most species must be in a 

 condition of fermentation. Certain ambrosia beetles, as for example the 

 species of Corthylus, seem not to need fermentation in the propagation of 

 their fungus; their galleries are constructed in the sap-wood of vigorous 

 plants. The great majority of the species, however, attack the wood of such 

 trees only as are moribund; in which the natviral circulation of the sap has 

 ceased, and fermentation has begun. Some of the number are also able 

 to produce their food fungus in wood which is saturated with a vinous or 

 alcoholic ferment, and they attack wine and ale casks, perforating the 

 staves with their galleries and causing serious loss by leakage. 



"The precarious conditions under which their food is produced limit 

 the life of a colony of ambrosia eaters in most cases to a single generation. 



"Under favorable conditions, and in large tree trunks, colonies may 

 continue their excavations during two or three generations before the failure 

 of the sap or change in its condition puts an end to their existence and 

 forces the adult beetles to seek new quarters. 



"When iheir galleries are disturbed and opened to daylight, the adult 

 beetles generally fall to eating their ambrosia as rapidly as possible. Like 

 other social insects they show their concern at the threatened loss of their 

 most precious possession and try to save it, just as bees, when alarmed, fill 

 themselves with honey. 



"As iis honey is to the bee, so to the ambrosia-feeding beetle its food 

 fungus is the material the propagation and preservation of which is the 

 chief concern of its life. Its solicitude concerning it is not surprising m hen 

 one considers the herculean labors which it undergoes in the effort to pro- 

 duce it, the frequent failures, and the difficulties and uncertainties that at all 

 times attend its preservation in the vegetative form, in which alone it can 

 .serve the insect as food." 



The life-histories of the ambrosia beetles described and copiously illus- 

 trated by Hubbard suggest a wide range of habits within the group. The 



