12 



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 iu 

 the propagation of their fungus ; their galleries are constructed in the 

 sap wood of vigorous plants. The great majority of the species, how- 

 ever, attack the wood of such trees only as are moribund; in which the 

 natural 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 gener- 

 ation. 



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 exist- 

 ence and forces the adult beetles to seek new quarters. 



When their 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 its 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 

 when one considers the herculean labors which it undergoes in the 

 effort to produce it, the frequent failures, and the difficulties and uncer- 

 tainties that at all times attend its preservation in the vegetative form, 

 in which alone it can serve the insect as food. 



INJURIES CAUSED BY AMBROSIA BEETLES. 



To living plants. — As a rule, populous colonies of these beetles and 

 galleries so numerous and extensive as to be capable of doing serious 

 harm are found only in trees, which before the attack began were sick 

 unto death with maladies for which the timber beetles are in nowise 

 responsible. The few species which enter the sapwood of vigorous 

 trees do not form large colonies, and the effect upon the health of the 

 tree is not appreciable. One or two species, it is true, have the habit 

 of sapping the life of twigs or small branches with an encircling burrow, 

 and a species of Corthylus does considerable injury in this way to 

 young trees and to shrubbery in the forest. 



Injuries to timber, — The defects in wood caused by the galleries and 



