for signs of tree infection. Whenever they notice red-brown
masses of pitch and sawdust on the bark of the trees, they know
that insects are busy there. Where the needles of a pine or
spruce turn yellow or red, the presence of bark beetles is shown.
Signs of pitch on the bark of coniferous trees are the first
symptoms of infection. These beetles bore through the bark and
into the wood. There they lay eggs. The parent beetles soon die
but their children continue the work of burrowing in the wood.
Finally, they kill the tree by making a complete cut around the
trunk through the layers of wood that act as waiters to carry the
food from the roots to the trunk, branches and leaves. The next
spring these young develop into full-grown beetles, and come out
from the diseased tree. They then attack new trees.

When the forest rangers find evidences of serious infection, they
cut down the diseased trees. They strip the bark from the trunk
and branches and burn it in the fall or winter when the beetles
are working in the bark and can be destroyed most easily. If the
infection of trees extends over a large tract, and there is a
nearby market for the lumber the timber is sold as soon as
possible. Trap trees are also used in controlling certain species
of injurious forest insects. Certain trees are girdled with an ax
so that they will become weakened or die, and thus provide easy
means of entrance for the insects. The beetles swarm to such
trees in great numbers. When the tree is full of insects, it is
cut down and burned. In this way, infections which are not too
severe can often be remedied.

The bark-boring beetles are the most destructive insects that
attack our forests. They have wasted enormous tracts of pine