SB 761 HS Copy 1 OF THE PRINCIPAL INSECT ENEMIES OF ' FORESTS IN THE UNITED STATES. A. D. HOPKINS. Ph. P.. In Charge of Forest Insect Investigations, Division of Entomology. [Reprint from Yearbook of Department of Agriculture for 1902.] lliGEOLOGICALSIVEK JUN 16 1904 LIBRARY. <^ Cp \ ^ 9? ^ t. CONTENTS. Page. Introduction 265 The spruce-destroying beetle 266 Description of the various stages of the beetle _ 266 Habits of the adult and larva 267 Methods of preventing losses from future depredations 269 The destructive pine-bark beetle 270 1 description of the various stages of the beetle 270 Habits of the adult and larva 271 Probable beginning of a new invasion in the South 273 Evidence of an old invasion in Texas 273 Methods of preventing destructive invasions 273 Trapping the beetle and its 1 »ro< >ds 275 The pine-destr< rying beetle of the Black Hills 275 Description of the 1 >eetle and its work 275 Characteristic features of the infested ami dead timber. 279 Methods of combating the pest 280 Other destructive species of Dendroctonus 281 Summary 281 General recommendations 282 in ILLUSTRATIONS. PLATES. Page. Plate XXVIII. Work of the spruce-destroying beetle 266 XXIX. Work of the pine-destroying beetle of the Black Hill? 280 TEXT FIGURES. Fig. 23. Spruce-destroying beetle 267 24. Work of the spruce-destroying beetle 268 25. Different methods of girdling trees 269 26. I >estructive pine bark-beetle 270 27. Work of destructive pine-bark beetle 271 28. The pine-destroying beetle of the Black Hills 276 29. Larva of the pine-destroying beetle of the Black Hills 276 30. Pupa of the pine-destroying beetle of the Black Hills 276 31. Work of the pine-destroying lieetle of the Black Hills (chambers) . . . 277 o2. Work of the pine-destroying beetle of the Black Hills (pitch tubes on surface of bark ) 278 v SOME OF THE PRINCIPAL INSECT ENEMIES OF CONIF- EROUS FORESTS IN THE UNITED STATES. By A. I). Hopkins, Ph. D., In Charge of Forest Insert Investigations, Division of Entomology. INTRODUCTION. Within recent years the writer has made a preliminary survey of the principal forest regions of the United States, from southeastern Florida to northwestern Washington, from northern Maine to eastern Texas, and in the middle Appalachian region, the middle Rockies, and the Pacific slope, for the purpose of obtaining information relating- to the principal enemies of the forests, the location and extent of areas of greatest depredation, and the possibilities of preventing losses. It was found that among the many hundreds of insect enemies of forest trees observed and collected there are a few species which are of primary importance in their relation to widespread devastations. Indeed, it would seem that the most important enemies of coniferous forests in this country are restricted to a few species of a single genus of beetles. This genus was described by Erichson, of Berlin, Ger- many, in 1836, under the name Dendroctonus, which means '"killer of trees." It is represented in Europe by only a single species, but in this country some eighteen species have been recognized. With few exceptions, they are all that the generic name implies, and the greater number are even more, for they are real devastators of forests. One of the species of this genus, known as the spruce-destroying beetle, has been, according to published data, a menace to the Northern spruce forests during the past eighty years. Its work has from time to time taken the character of an invasion and destroyed many mil- lions of dollars 1 worth of the best spruce timber in different sections, from New Brunswick to New York. The destructive pine bark-beetle is another species which threatened the entire destruction of the pine and spruce of Virginia and West Virginia between 1890 and 1892, and before its ravages were checked it killed many millions of the best pine and spruce forest and shade trees in the two States. The pine-destroying beetle of the Black Hills has been, within the past six or eight years, devastating the forests of the Black Hills Reserve in South Dakota. It has already killed some 600 million 265 266 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. feet of timber, and is threatening a like fate to the remainder. This involves not only the destruction of the timber, but also that of the great mining and other industries of that region which are dependent on the timber supply. The records and available evidence show that these three species alone have demonstrated their ability, under specially favorable con- ditions, to devastate the pine and spruce forests of the entire country. Therefore they are worthy of general attention and the most detailed investigation. The facts already determined by study of the insects and their work indicate plainly that most of the forests of the country which are avail- able for the application of improved forest methods and systematic working plans can usually be protected from this and like dangerous enemies at a slight cost. The prime requisites for success in combating this class of pests are: First, the prompt recognition of the commencement of a trouble; second, the determination of the insect causing it; and, third, the prompt application of the proper treatment before the depredations have spread like a conflagration. It is the object of this paper to call attention to what are believed to be the worst insect enemies of coniferous forests, also to some of the characters of the insects and their work, by which they may be readily recognized, and to the peculiar methods of control applicable to each. THE SPRUCE-DESTROYING BEETLE (Dendroctonus piceapt rda Hopk. ) This insect was perhaps the first of its class to claim attention in this country, owing to its destructive invasions of the spruce forests of New England and New York from 1818 to 1900, as described by Peck. Hough, Packard, Fisk, and the present writer. DESCRIPTION OF THE VARIOUS STAGES OF THE BEETLE. The adult (tig. 23, , and by the middle of June those that pass the winter in the adult stage emerge and commence to excavate galleries and deposit eggs. The adults, from hibernating. larvae of different stages, develop and con- tinue to emerge from the last of June until the last of August. The eggs deposited by the late-developing beetles produce larva? which do not complete their development until July or August of the next year, and consequently the period from the time the first galleries are exca- vated and eggs deposited until the broods of adults emerge is about Fig. 23.— Spruce-destroying beetle: a, dorsal view of adult beetle; 6, side view of larva; c, dorsal view of pupa — all greatly enlarged; d, natural size of beetle. (Original.) 268 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. one year. Under different conditions of latitude and altitude these (lutes and periods will be different. How the tbees are killed. — The numerous primary or egg gal- leries penetrate the most vital parts of the tree (the cambium), where the principal activity involved in new growth takes place. This causes at once a loss of vitality and a weakened resistance. The exca- Fig. 24. — Work of the spruce-destroying beetle: o, primary gallery; 6, borings packed in side; c, entrance and central burrow through the packed borings;