INSECT INJURIES TO FOREST TREES OF INDIANA.

The primary objects of this investigation were (1) to determine the comparative extent of injury to native trees and some of their products and the kinds of insects causing such injury (2) to determine, when possible, some practical method by which to prevent to some degree the annual losses of valuable timber, from this cause.

It is aimed in this report to give a short and concise account of the results of the investigation with recommendations of such methods of prevention or control as seem of a practical nature.

THE CHARACTER OF INSECT INJURIES TO FOREST TREES. The character of insect injury to forest trees may be treated under two distinct heads:

(1) Injuries which cause the death of trees.

(2) Injuries found in the solid wood which do not immediately result in the death of the trees, but cause serious defects in the parts of the tree, which furnish materials for commercial products.

There is also considerable loss experienced from insect injuries to felled trees, saw logs, ties, posts and many other crude products, which will be discussed briefly.

KNOWLEDGE NECESSARY TO PREVENTION OF LOSSES.

In dealing with insects, the methods which always produce the best possible results are those which relate to preventing attacks. Before preventive methods can be applied, however, a complete knowledge of the insects causing the injury, as well as the conditions most attractive to them, is absolutely necessary.

Insects in general have two objects in their attack; one is to obtain food, the other is to prepare for the development of their broods. Different species have special periods during the season of greatest activity when the adults are on the wing searching for suitable places in which to deposit their eggs. Some species fly in April and attack only recently felled pine trees. They are not attracted to any other kind of timber, because they cannot live in the bark or wood of any other tree, and only in such pines as are in the proper condition for hatching their eggs, and favoring the development of their young. There are also forms which attack only oak trees; others infest only hickory, and so on for many classes of trees.

Each of these forms possesses different habits, and has different periods of flight, and requires special conditions of the bark and

wood for its development. Some have but one generation in a year, others have two or more, while some require more than one year for the development of a single generation. Some species deposit their eggs in the bark or wood of trees soon after they are felled; others are attracted only to dead bark or wood of trees which have been felled or deadened for several months. Other variations in season and special conditions are noted, and it is easily seen how important it is to have a knowledge of such of the foregoing facts as is possible in order to meet the requirements necessary for preventing losses.

INJURIES WHICH CAUSE THE DEATH OF THE TREE.

The most important insects which cause the death of forest trees of the broad-leafed type are those which burrow through and beneath the living bark of the tree. There are two distinct classes of these injuries, one caused by the bark-boring beetles, the other by bark-boring larvae or grubs. The adults of this class of insects bore into and beneath the bark for the purpose of excavating galleries in which to deposit their eggs. These galleries are the primary injury which weakens to some extent the vitality of the tree, while the secondary or larval mines (see Fig. 1) complete the

girdling process which completely deadens the tree. The injuries from bark-boring grubs are the work of larvae which hatch from eggs deposited by the adult insect in the outer dead bark, and never in burrows beneath it. Therefore, the burrows made by the young larvae through the living inner bark, in search of food, not only cause the primary injury, but also complete the deadening process.

INJURY TO HICKORY TREES BY BARK-BEETLES.

Considerable attention has been directed to this form within recent years on account of the many dying hickory trees. This has been especially true in the northern and central States. The trouble has been reported and the damage found to be extremely noticeable as far south as central Georgia and westward to Missouri. Thousands of scattered trees have died, and in some sections nearly all of those in forests, parks and farm woodlots have either perished or been seriously injured. This injury is causing a great loss, not only of a valuable timber tree, but of shade trees, and especially is it causing a rapid decrease in the crop of nuts, which latter, in some sections of the country, are of considerable importThis importance extends not only to the commercial product and home consumption, but also influences the natural reproduction of this form and so to a degree determines the future state of our hardwood forests. The dying of the hickory trees has been found in nearly every case investigated and reported upon, to be the direct result of injuries to the buds and twigs and to the bark of the branches and trunks by the bark-beetle (Scolytus 4 spinosus).

ance.

THE HICKORY BARK-BEETLE.

The hickory bark-beetle, or engraver beetle, is a short, shining black or reddish brown beetle, averaging about .14 of an inch in length. The wing covers are short and project over the abdomen, which in the male is excavated beneath and armed with four somewhat prominent spines, which suggest its technical name. It flies about from May to August and generally begins its attacks on the living trees at the base of the buds and leaves. Injuries of this nature were noted in two localities in northern Indiana during the latter part of July. Many twigs had been injured just back of the terminal bud, and as a consequence many of these buds were dead. Also many twigs and even small branches were showing the effect of this early attack. In another instance a small grove of secondgrowth hickory was examined where this same injury was interfer

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ing seriously with the development of the young trees. The injuries in both of the above-named cases were confined to the young and more tender parts of the trees, and at this early stage of the season were apparently a result of the insects' efforts to obtain food. Later they enter the bark of the larger branches and top of the trunks and begin excavating short longitudinal burrows (Fig. 1, F) in the inner bark and surface of the wood. The eggs, which are placed along the sides of these primary galleries, hatch into small white grubs or larvae, which burrow at right angles through the inner bark and groove the surface (Fig. 1, H) of the wood to some extent. The broods of larvae pass the winter in these brood galleries, and transform to the adults in the spring, in the outer portion of the inner bark. These adults emerge through holes bored through the outer bark (Fig. 1, G) to continue their work on the buds, branches and remainder of the trunks that were not killed by the first attack. In this locality they begin to emerge about the first of June and many individuals of the brood continue to emerge until late August. They may be found depositing eggs as late as September and are thus found attacking trees all through the summer.

The first evidence of an attack is generally shown by the leaves, some of which die and remain on the twigs, while others fall early. Late in July and especially in August, the large branches in the top of the tree begin to die and in some cases the entire tree is killed the first season. More often, however, the lower portion of the large tree does not die until subsequent attacks are made upon it. Upon removing the bark from some of these injured parts the characteristic brood galleries will be found in the inner bark and to some extent on the surface of the wood (Figs. 1 and 3). If the tree is infected, the parent beetle will be found in the primary longitudinal gallery, and many of the small, white grubs in the larval burrows in the bark. If the broods have emerged, the outer dead bark will be found perforated with numerous small round holes, as indicated in Fig. 1, G.

Damage from this destructive form was found to be most extensive in the central portion of the State. In Howard County, examples were found where trees ranging from 10 to 18 inches in diameter were in various stages of destruction from attacks by this form. The trunk of a dead but apparently sound tree was closely examined. The numerous exit holes of emerging broods aroused suspicion, and upon removing portions of the bark the cause of the tree's death was unmistakable. The inner bark was

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reduced to a powdered condition by the brood galleries and extensive larval mines which extended entirely around the tree and as high up on the trunk as a man could reach.

The extent of the loss from this insect, in central and northern Indiana, is limited to a large degree by the scarcity of hickory. Should the form spread to southern counties, however, the loss would be considerable. Consequently, all possible means should be taken to confine the injury to the smallest possible territory and to keep it from entering the larger stands of hickory.

METHOD OF CONTROL.-A peculiarity in the life history of this form makes it a comparatively easy pest with which to deal. In this locality there is but a single generation annually, and the immature stage of the generation passes the winter in the bark of the infested trees. These are two facts which assure its easy destruction, since it is only necessary to determine the trees which are actually infested, at the beginning of winter and to be sure that these are all cut and the bark burned before the first of the following May. June was stated as the time when the brood emerges in this State, but this date varies considerably, according to conditions, and it would not be considered a safe plan to delay such treatment longer than the first of May. If the greater number of infested trees over a considerable area are thus treated, the number of insects will be so reduced that they cannot continue their destructive work on living trees. It must be remembered that nothing is to be gained by cutting and burning the dead trees after the broods have emerged, but that the greatest importance lies in locating all trees which have died within a year from May or June and are infested, and that these be cut and the insects destroyed before the following spring. In many cases it would be advisable, where only the top or side branches are attacked, and the remainder of the tree living, to cut out and destroy this part and thus save the more valuable portion of the tree. The broods can be destroyed without loss of the entire tree by utilizing suitable parts for fuel or other purposes, if consumed within the specified time. When the logs are still valuable, the bark can be removed and burned or the logs placed in water until the insects are dead.

The practical application of this method of cutting and burning the infested trees was made by the commissioner of parks of Detroit, Mich., in Belle Isle Park, May, 1903. Many hickory trees were infested, and indeed all were threatened with destruction by this insect. Upon request of the commissioner, investigations were made by A. D. Hopkins of the United States Department of Agri