FOREST INSECTS 81 



must assume the place of the leader, and when it does, the 

 axis of the tree is displaced to one side. Commonly the same 

 tree may be attacked several times in succession, and its 

 value to the lumberman greatly lessened. 



At the present time in New England much attention is 

 being given to the propagation of white pine, owing to the 

 lessened supply of this valuable wood, and to the fact that it 

 appears to be the species most suitable to replace much of the 

 hardwood timber that is being decimated by the gipsy moth 

 and other insects. 



The white pine, both as seedlings in natural reproduction, 

 and in areas where small nursery-grown trees have been set 

 out for reforestation, is often severely injured and extensively 

 killed by a small beetle, Hylobius pales, the adults of which 

 eat the succulent bark from the tiny trees. The preparatory 

 stages of the Hylobius are passed in the stumps of the cut- 

 over areas, where their feeding causes no harm, but the vo- 

 racious adults kill a large proportion of the seedling trees in 

 the vicinity of their breeding places, and are thus a very im- 

 portant factor affecting the growth of the incipient white pine 

 forest. 



The saplings of certain deciduous trees also have insect 

 pests which select them in preference to their older compan- 

 ions in the forests. The aspen and other poplars are fre- 

 quently killed in considerable numbers by a wood-boring 

 beetle of the genus Saperda. A single Saperda larva develops 

 within the stem of small poplars, producing a gall-like swell- 

 ing which usually spells death for the young tree. 



Thus far we have considered the forest, or the individual 

 trees, as living plants whose successful growth, or even life, 

 may be endangered by the presence of destructive insects. 

 From a purely economic standpoint, however, the value of a 

 forest is measured by the quantity and quality of timber 

 which it produces, and it is perfectly true that the lumber in 

 mature trees killed by caterpillars or bark-beetles, is not ap- 

 preciably decreased in commercial value. From an esthetic 

 standpoint there is a vast difference between a growing or a 



