8 
SOME TREE-DESTROYING INSECTS. 
some species, and during this period, eggs are laid by the mature 
beetle on the bark in crevices or wounds of trees. These eggs hatch 
into little grubs which bore beneath the surface, usually working in 
the growing layer, between the wood and the bark. The burrows 
made by these grubs usually extend across the grain, and hence, 
when in sufficient numbers, the tree is actually girdled. The injury 
can be detected in time for treatment in only one case out of a hun- 
dred. In that case the infected area may be cut out and the wound 
treated with some antiseptic, like pure white lead and linseed oil. 
In the other ninety-nine cases, the trees will die. The next thing 
to do, then, is to cut down these trees and destroy them before the 
borers mature, that is before May. This prevents an .attack from 
the maturing beetles on the healthy trees in the immediate neigh- 
borhood. Treating some of these trees with a spray such as iron 
sulphide will often prevent the beetles laying the eggs where the 
spray has been placed. 
There are some forms of borers, like the coniferous bark beetles 
and the hickory bark-borer, the adults of which bore directly into 
the bark to the wood. Here a burrow is made, usually lengthwise 
of the tree, and along this burrow little excavations are made in 
which eggs are placed. These eggs hatch into grubs which burrow 
out usually at right angles from the main burrow. These secondary 
burrows are made between the wood and the bark. Here again, if 
the insects are in sufficient numbers, the tree is girdled. The most 
of these forms are particularly attracted to the coniferous trees. So 
far as we know, nothing can be done to stop the ravages of such 
pests. Under forest conditions, the proper utilization of the timber 
will control the insect. 
Of the other boring forms of insects, we might mention the oak 
twig-pruner. This form is very abundant in Minnesota. The adult 
insect is a beetle which lays the egg in the twig. The grub hatch- 
ing from the egg burrows in the woody part of the stem. Finally, 
the twig is cut nearly off and the wind blows the twig and its inmate 
to the ground. Here the insect goes through its further transfor- 
mations. The obvious method of combating, therefore, is to pick 
up the fallen pruned twigs and destroy them immediately. 
From these facts it will be seen that insects play a very import- 
ant part in determining whether a tree shall be healthy or not. 
The owner of trees must be continually on the watch to prevent 
the depredations of these pests. The old adage, “An ounce of pre- 
vention is worth a pound of cure,” is well illustrated by the war- 
fare that man must maintain against the* insect enemies that invade 
his forest and shade trees. 
A. G. RUGGLES, 
Head of Section of Spraying and Tree Insects. 
