SOME TREE-DESTROYING INSECTS. 
It is estimated that insects destroy $100,000,000 worth of tim- 
ber in the United States every year. This amount does not include 
the insect injury done to shade trees, the loss in many such cases 
being beyond computation. Trees, at any time in the growing sea- 
son, are subject to insect injury. Some forms attack the leaves, 
others small limbs, and some of the most insidious work, unseen, 
l)eneath the bark in the trunk and in the root. The insects that 
work on the leaves require, usually, only one year for the life cycle. 
Sometimes several generations are produced in a season by a 
single leaf-eating form. Those insects which work beneath the 
bark, however, usually require two or even more years to complete 
their transformations. 
On shade trees, the leaf-eating forms are practically easy to 
destroy, — the ordinary arsenical insecticides being very efficacious. 
Under forest conditions, on the other hand, they are extremely 
difficult to eradicate. A case in point is the larch sawfly. When 
the larva of this insect attacks a tamarack on the lawn, the leaf-eat- 
ers are killed very quickly if we spray the tree with arsenate of lead. 
In the woods, however where trees 
are extremely numerous, it is impos- 
sible to use any spraying compound. 
The only thing to be done in such cases 
is to assist nature as far as possible in 
rearing predaceous and parisitic ene- 
mies. 
The bark borers are hard to eradicate 
under any condition but particularly 
so on shade trees. When they have 
once attacked a shade tree, practically 
nothing can be done to save that partic- 
ular tree. In forests, however, under 
proper management, bark borers may 
be kept in control by a proper utiliza- 
tion of the infected timber. Fig. i. omb and adujt of two- lined 
Among the many leaf-eating forms chestnut borer. Enlarged four times, 
that are plentiful in Minnesota, are: the fall web worm, the fall 
canker worm, tent caterpillars, handmaid moth caterpillars, white- 
