By H. T. FERNALD, Massachusetts Agricultural College.

The insects which attack our ornamental trees and shrubs are of many kinds and work in a variety of ways. Almost every kind of plant has its especial foes, while numerous general feeders may be found on many different plants. Some feed on the roots, others bore in the trunk or branches, many more consume the leaves, and others suck the sap from the branches or leaves.

Such a diversity of methods of attack renders necessary corresponding methods for checking the ravages of these pests, and a knowledge of how the insect causes the injury is in each case necessary before successful treatment can be undertaken. So many different insects are concerned, however, that anything like a careful consideration of them must be left to special works on the subject, and only general considerations and a more complete discussion of a few of the most serious pests can be included here.

In general, insects feed either by biting off and swallowing pieces of the plant, or by sucking its juices. Biting insects are provided with jaws for this purpose, while in sucking insects the mouth-parts are combined to form a sucking tube, together with structures which enable these insects to make holes through the surface of the plant to where the sap is, and then to suck this into their bodies.

With biting insects, a poison spread over the surface, which the insect will swallow as it feeds, will pass to the stomach of the pest and cause it to die, and such poisons are generally called stomach poisons, for that reason. The more usual stomach poisons used are paris green and arsenate of lead. For sucking insects, stomach poisons spread, as they must be, on the surface of the plant are of no value, the sucking tube of the insect being passed through this layer into the hole it makes in the plant, while the plant juices are extracted from beneath the surface. For such insects as these, then, other methods of control must be used, and oils, soaps and similar materials, called contact poisons, are the more usual substances for this purpose. Contact poisons appear to destroy insects by covering them, or at least the openings of their breathing organs, with a film, thus suffocating them, and it is at once evident that unless a sucking insect be actually touched by some of the contact poison, the treatment will fail. With biting insects the poison may be spread over the tree to wait until the insect in its feeding reaches and swallows it; with sucking insects only those touched by the poison at the time it is applied will be destroyed; and if we remember that many of the sucking insects are exceedingly small, the necessity for the most thorough application possible of the poison becomes evident.