396 NEW YORK STATE MUSEUM 



the life of a colony, and as a rule only two or three generations occur in 

 a large tree trunk, while in smaller ones there may be only one brood. 



A topical life history of these insects is well illustrated by Mr Hubbard's 

 account of Xyleborus pubescens Zimm. A solitary female starts 

 the galleries similar to those illustrated in figure 104. The branches serve 

 as brood galleries and in each, five to six oval, pearly eggs are deposited. 

 The young hatch within a week and begin feeding on the ambrosia at once. 

 The pupae lie free in the galleries, and in somewhat over a month from 

 the eggs perfect beetles appear. The colony, in time, contains beside the 

 mother insect 15 or 20 adult offspring, most of which are females, only one 

 or two males commonly being found. A second brood is started bv this 

 later generation, but the seasoning of the wood and threatening failure of 

 food usually warn the young females to depart and seek fresher trees. 

 This leaves the abandoned males in a sad condition, since they are unable 

 to consume the ripened ambrosia, and they also wander forth, though wing- 

 less and weak, or are suffocated by the superabundant fungus. Sometimes 

 they assemble in certain galleries and form bachelor colonies, where by 

 imited efforts they are able to check the fungus and prolong existence for a 

 time. The watchful care of the mother for the young is well described in 

 the notice of Monarthrum mali Fitch, page 291. 



These little insects are of economic importance, principally on account 

 of their injury to timber. A few species are known to affect living trees, 

 though as a general rule their attacks are confined to dying or dead timber. • 

 The defects in the wood caused by the galleries of these beetles, and the 

 stains left by the fungus, probably entail more loss than the injury caused 

 by attacks on living trees. The presence of their galleries seriously depre- 

 ciates the value of timber used as cask heads, staves, shingles and the like. 

 These defects may be repaired to some extent by plugging, but those made 

 by some species cannot be thus treated. It is possible in some instances to 

 take advantage of the habits' of the insects, and by proper sawing the 

 damage may be reduced to a minimum. The softwood in the Adirondack 

 region is seriously affected by these little borers, and the quality of much 

 of it greatly impaired. 



