124 THE CULTIVATED EVERGREENS 



INSECTS OF CONIFEROUS EVERGREENS.— Crosby and Palmer 



The number of insects doing serious damage to conifers 

 under conditions of cultivation is relatively few, and the 

 discussion of the depredations need not be extensive. This 

 account begins with insects more or less common to all conifers 

 — the borers and bark-beetles, the bag-worm, and the gipsy 

 moth. Then follow the insects preying specially on pines, 

 spruces, and larches. 



Borers and bark-beetles. 



Conifers that are in a weakened or unhealthy condition 

 from insect depredations or other causes are subject to attack 

 by a host of borers and bark-beetles of many kinds. The borers 

 may burrow just under the bark or in the solid wood, often 

 causing decay to ensue. Bark-beetles bore through the bark 

 and construct brood chambers between the bark and the 

 wood in which they deposit their eggs. The larvae or grubs 

 form burrows which gradually increase in size as they become 

 larger. These burrows are half in the wood and half in the 

 inner bark. When abundant they girdle the tree or branch, 

 causing its death. When the bark is removed, their burrows 

 are evident in impressed grooves in the surface of the sap wood. 

 These engraved patterns are characteristic of the species and 

 have given the insects the popular name of "engraver beetles." 



The depredations of borer and bark-beetles can only be 

 prevented by keeping the trees in a healthy and vigorous 

 condition, since most of these pests are unable to gain entrance 

 or breed in thrifty trees. After the tree has been weakened so 

 that the infestation has begun, there is little that can be done 

 to prevent its death. 



The bag-worm {Thyridopteryx ephemeraeformis, Ha worth). 

 Arbor- vitae and cedar in southeastern NeW York, central 



