, the cottony maple
scale, the maple phenacoccus on the sugar maples, and the various
aphides on beech, Norway maple, etc.

3. Those that *bore* inside of the wood or inner bark. The principal
members of this class are the leopard moth, the hickory-bark borer, the
sugar-maple borer, the elm borer, and the bronze-birch borer.

The chewing insects are destroyed by spraying the leaves with arsenate
of lead or Paris green. The insects feed upon the poisoned foliage and
thus are themselves poisoned.

The sucking insects are killed by a contact poison: that is, by spraying
or washing the affected parts of the tree with a solution which acts
externally on the bodies of the insects, smothering or stifling them.
The standard solutions for this purpose are kerosene emulsion, soap and
water, tobacco extract, or lime-sulfur wash.

[Illustration: FIG. 97.--A Gas-power Spraying Apparatus.]

The boring insects are eliminated by cutting out the insect with a
knife, by injecting carbon bisulphide into the burrow and clogging the
orifice immediately after injection with putty or soap, or in some cases
where the tree is hopelessly infested, by cutting down and burning the
entire tree.

[Illustration: FIG. 98.--A Barrel Hand-pump Spraying Outfit.]

For information regarding the one of these three classes to which any
particular insect belongs, and for specific instructions on the
application of a remedy, the reader is advised to write to his State
Entomologist or to the U.S. Bureau of Entomology at Washington, D.C. The
letter should state the name of the tree affected, together with the
character of the injury, and should be accompanied by a specimen of the
insect, or by a piece of the affected leaf or bark, preferably by both.
The advice received will be authentic and will be given without charge.

[Illustration: FIG. 99.--Egg-masses of the Tussock Moth.]

When to spray: _In the case of chewing insects_, the latter part of May
is the time to spray. The caterpillars hatch from their eggs, and
the elm leaf beetle leaves its winter quarters at that time. _In the
case of sucking insects_, the instructions will have to be more
specific, depending upon the particular insect in question. Some
sucking insects can best be handled in May or early June when their
young emerge, others can be effectively treated in the fall or
winter when the trees are dormant.

How to spray: Thoroughness is the essential princip