UBRARY 
 STATE PLANT BOARD 
 
 Issued November 25, 1910. 
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ENTOMOLOGY— CIRCULAR No. 125. 
 
 L. O. HOWARD. Entomologist and Chief of Bureau. 
 
 INSECTS WHICH KILL FOREST TREES: 
 
 CHARACTER AND EXTENT OF THEIR DEPREDATIONS 
 AND METHODS OF CONTROL. 
 
 A. D. HOPKINS, 
 
 In Charge of Forest Insect Investigations. 
 
 G4136°— Cir. 125—10 
 
 WASHINGTON : GOVERNMENT PRINTING OFFICE : 1910 
 
 
BUREAU OF ENTOMOLOGY. 
 
 L. O. Howard, Entomologist and (Jh'wf of Bureau. 
 
 C. L. Marlatt, Afisistant Entomologist and Acting Chief in Ahsnicc of Chief. 
 
 R. S. Clifton, Executive Assistant. 
 W. F. Tastet, Chief Clerk. 
 
 F. H. Chittenden, in charge of truck crop and stored product insect investigations, 
 
 A. D. Hopkins, in charge of forest insect investigations. 
 
 W. D. Hunter, in charge of southern field crop insect investigations. 
 
 F. M. Webster, m charge of cereal and forage insect investigations. 
 
 A. L. QuAiNTANCE, in charge of deciduous fruit insect investigations. 
 
 E. F. Phillips, in charge of bee culture. 
 
 D. M. Rogers, in charge of preventing spread of moths, field work. 
 RoLLA P. Currie, in charge of editorial icork. 
 
 Mabel Colcord, librarian. 
 
 Forest Insect Investigations. 
 
 A. D. Hopkins, in charge. 
 
 H. E. Burke, J. L. Webb, Jose*^ Brunner, S. A. Rouwer, T. K. Snvdkr, W. D. 
 
 Edmonston, agents and experts. 
 Mary E. Faunce, preparator. 
 
 William Middleton, Mary C. Johnson, student assistants. 
 [Cir. 125] 
 n 
 
Circular No. 125. Issued November 25, 1910. 
 
 United States Department of Agriculture, 
 
 BUREAU OF ENTOMOLOGY. 
 L. O. HOWARD, Entomologist and Chief of Bureau. 
 
 INSECTS WHICH KILL FOREST TREES: CHARACTER 
 AND EXTENT OF THEIR DEPREDATIONS AND METH- 
 ODS OF CONTROL." 
 
 By A, D. Hopkins, 
 In Charge of Forest Insect Investigations. 
 
 It has been conclusively demonstrated that certain species of insects 
 are the direct or primar}^ cause of the death of forest trees of all 
 ages, and that from time to time they multiply to such an alarming 
 extent that their depredations assume the character of a destructive 
 invasion, which results in the death of a large percentage of the best 
 timber over thousands of square miles. 
 
 There are many species of barkbeetles which prefer to attack 
 matured and healthy trees, and there are many examples of whole 
 forests of century-old trees that have perished from the girdling effect 
 of the mines of the beetles, which are extended in all directions 
 through the inner living bark on the main trunks of the trees. 
 Indeed, we find among these bark-boring beetles the most destructive 
 insect enemies of North American forests. Some notable examples 
 of the depredations of these barkbeetles are given below. 
 
 The southern pine beetle. — In 1890-1892 a destructive invasion of 
 the southern pine beetle extended from the western border of AYest 
 Virginia through Maryland and Virginia into the District of Colum- 
 bia, northward into southern Pennsjdvania, and southward into North 
 Carolina. In this area, aggregating over 75,000 square miles, a very 
 large percentage of the mature and small trees of the various species 
 of pine and spruce was killed by this beetle. In many places in West 
 Virginia and Virginia nearly all the pine trees of all sizes on thou- 
 sands of acres were killed, while shade and ornamental trees within 
 the same area suffered the same as those in the forest. Since 1902 
 
 « Revised extracts from Bulletin No. 58, Part V, Bureau of Entomology, U. S. 
 Department of Agriculture, 1909. 
 
 [Cir. 125] 1 
 
2 INSECTS WHICH KILL FOEEST TREES. 
 
 this barkbeetle has been more or less active in the Southern States 
 from Virginia to Texas, and in some localities and during certain 
 years it has killed a large amount of timber. Records of extensive 
 destruction of timber in the Southern States are found dating back 
 to the early part of the nineteenth centuiy. This species may be 
 considered one of the most dangerous insect enemies of southeastern 
 conifers and, therefore, a constant menace to the pine forests of the 
 Southern States. 
 
 The eastern spruce heetle. — During the period between 1818. and 
 1900 there were several outbreaks of the eastern spruce beetle in the 
 spruce forests of New York, New England, and southeastern Canada. 
 This species caused the death of a very large percentage of the ma- 
 ture spruce over an area of thousands of square miles. In the aggre- 
 gate many billions of feet of the best timber were destroyed. The 
 larger areas of this dead timber furnished fuel for devastating for- 
 est fires, with the result that in most cases there was a total loss. 
 
 The Engelmann spruce heetle. — The Engelmann spruce beetle, 
 with habits similar to the eastern spruce beetle, has from time to time 
 during the past fifty years caused widespread devastations in the 
 Rocky Mountain region to forests of Engelmann spruce, in some sec- 
 tions killing from 75 to 90 per cent of the timber of merchantable size. 
 
 The Black Hills heetle. — One of the most striking examples of the 
 destructive powers of an insect enemy of forest trees is found in the 
 Black Hills National Forest of South Dakota, where during the past 
 ten years a large percentage of the merchantable timber of the entire 
 forest has been killed by the Black Hills beetle. It is estimated that 
 more than a billion feet of timber have been destroyed in this forest 
 as the direct result of the work of this beetle. This destructive 
 enemy of the western pine is distributed throughout the forests of 
 the middle and southern Rocky Mountains region, where, within 
 recent years, it has been found that in areas of greater or less extent 
 from 10 to 80 per cent of the trees have been killed by it. 
 
 The mountain pine heetle and the western pine hectic. — The sugar 
 pine, silver pine, western yellow pine, and lodgepole pine of the 
 region north of Colorado and Utah, westward to the Cascades, and 
 southward through the Sierra Nevadas are attacked by the mountain 
 pine beetle and the western pine beetle, and, as a direct consequence, 
 billions of feet of the timber have died. In one locality in northeast- 
 ern Oregon it is estimated that 90 to 95 per cent of the timber in a 
 dense stand of lodgepole pine covering an area of 100,000 acres has 
 been killed within the past three years by the mountain pine beetle. 
 Through many sections of the sugar-j)ine districts of Oregon and 
 California, as the result of attacks by this same destructive barkbeetle 
 a considerable percentage of the largest and best trees is dead. 
 
 IClr. ILT.I 
 
INSECTS WHICH KILL FOREST TREES. 3 
 
 The Douglas fr beetle. — The Douglas fir throughout the region 
 of the Rocky Mountains from southern New Mexico to British Co- 
 lumbia has suffered severely from the ravages of the Douglas fir 
 beetle, with the result that a large percentage of dead timber is found, 
 much of which will be a total loss. 
 
 Three other species of beetles, having destructive habits similar 
 to those above mentioned, depredate on the pines of Xew ^lexico and 
 Arizona, and still another has contributed greatly to the destruction 
 of the larch throughout the northeastern United States and south- 
 eastern Canada. 
 
 The hickory harhheetle. — Within the past ten years the hickory 
 barkbeetle has caused the destruction of an enormous amount of 
 hickory timber throughout the northern tier of States from Wiscon- 
 sin to Vermont and southward through the eastern Atlantic States 
 and into the Southern States as far as central Georgia. 
 
 2' he larch icorm. — There are also many examples of Avidespread 
 depredations chargeable to insects which defoliate the trees, thus 
 contributing to their death. Notable among these are the depreda- 
 tions by the larch worm, which, during several extensive outbreaks 
 since 1880, has killed from 50 to 100 per cent of the mature larch 
 over vast areas in the northeastern United States and southeastern 
 Canada. It is evident that the amount of merchantable-sized timber 
 that has died as the result of defoliation by this insect will aggregate 
 many billions of feet. 
 
 CONTROL OF BARKBEETLES WHICH KILL TREES. 
 
 The barkbeetles which kill trees attack the bark on the trunk and 
 destroy the life of the tree by extending their burrows or galleries in 
 all directions through the inner living bark. The broods of young 
 grubs or larvae develop within the inner bark, on which they feed. 
 Those of some species develop to the adult stage within the inner bark 
 and are exposed when the bark is removed, while those of other 
 species transform to the adults in the outer corky bark and the larva? 
 are not exposed when the bark is removed. Some species have two 
 or more generations in a season or annually, while others have but 
 one, and in a few species it requires two years for a single generation 
 to develop. 
 
 The barkbeetles of the genus Dendroctonus represent the most 
 destructive enemies of the principal coniferous tree species of Ameri- 
 can forests, and at the same time are among the easiest of control. 
 The general requisites for success are embodied in the following rules : 
 
 {a) Give prompt attention to the first evidence of a destructive 
 outbreak, as indicated by an abnormal percentage of yellow or red 
 topped dying trees, and especially when such trees occur in groups of 
 ten or more or cover large areas; (6) secure authentic determination 
 
 [Cir. 125] 
 
4 INSECTS WHICH KILL FOREST TREES. 
 
 of the particular species of insect responsible for the trouble; and 
 (c) take prompt action toward its control according to specific expert 
 advice, published or otherwise, on the best method for the destruction 
 of the necessary 75 percent or more of the insects in the infested trees. 
 Some of the methods to be adopted to meet the requirements of 
 various local conditions are as follows: 
 
 (1) Utilize the infested timber and burn the slabs during the 
 period in which the broods of the destructive beetles are in the imma- 
 ture stages or before the developed broods emerge from the bark ; or 
 
 (2) Fell the infested trees and remove the bark from the main 
 trunk and burn the bark if necessary ; " or 
 
 (3) Remove the infested bark from the standing timber and burn 
 the bark when necessary ; « or 
 
 (4) Immerse the unbarked logs in ponds, lakes, or streams, where 
 the bark will remain soaked long enough to kill the insects; or 
 
 (5) Remove the unbarked logs or products to a localit}^ Avhere 
 there are no trees liable to attack within a radius of 20 miles or more. 
 
 Maintaining Control of Barkheetles. 
 
 Future trouble of a serious nature from barkheetles which kill 
 trees can be prevented within a given forest or area of greater or less 
 extent if an insect-control policy is adopted in connection with, or 
 independent of, a fire-control policy b}^ which groups of dying trees 
 will receive similar prompt attention as that required for the pre- 
 vention or control of forest fires. 
 
 In state and national forests. — In all forest reserves in which there 
 is an organized force of rangers and fire wardens or patrols each 
 officer should be furnished with instructions for the location of 
 beetle-infested trees, and with equipment and directions for taking 
 the necessar}^ action whenever the conditions demand or warrant it. 
 
 In private forests. — Private forests should receive the same atten- 
 tion as public forests, but this is often far more difficult on account 
 of intervening forests where the owners either can not or will not 
 give the matter the required attention. AVhile it may be advisable 
 to have some laws to govern the treatment of timber infested with a 
 dangerous pest when the owner refuses to take any action, such a 
 law should apply only to the more extreme cases or as a last resort 
 on authoritative advice. It is probable that in most cases legislation 
 will not be necessary, and more ultimate good will result without 
 than with strict laws, especially when it can be made clear to the 
 
 ° If the broods develop to adults in the outer l)ark, it must he burned ; if they 
 develop in the inner barl< and are expos(Ml when the bark is removed, burning 
 is not necesstiry. As a rule the burning of the tops to destroy the insects is 
 not necessary. 
 H'lr. 125] 
 
INSECTS WHICH KILL FOREST TREES. 5 
 
 owner that his personal interests demand that he take the proper 
 action and that, when necessary, his neighbors will render assistance, 
 as is done in the case of a forest fire. 
 
 Inaccessible areas. — There are yet large inaccessible areas in the 
 East and West where it is not practicable or possible at present to 
 control the depredations by these beetles and which must therefore 
 be left to the same natural adjustment that has been going on in 
 all forests from their beginning. While under such natural control 
 much of the older matured timber will be lost it will usually be re- 
 placed by young growth, either of the same species of trees or of a 
 different species, so that under normal conditions the forest will be 
 perpetuated ; but under exceptional conditions and combinations of 
 detrimental influences, such as secondary insect enemies, fire, and 
 drought, extensive areas may be completely denuded, never to be 
 reforested under natural conditions. Therefore it will evidently not 
 be very long before it will pay to adopt insect-control policies even in 
 the areas that are inaccessible for profitable lumbering. 
 
 Examples of Successful Control of Barkbeetles. 
 
 The practicability of the advice based on the results of recent ento- 
 mological investigations is demonstrated by a number of examples of 
 successful control of depredations by destructive barkbeetles. 
 
 CONTROL OF THE EASTERN SPRUCE BEETLE. 
 
 The control of an alarming outbreak of the eastern spruce beetle 
 in northeastern Maine in 1900 and 1901 was effected by the concentra- 
 tion of regular logging operations into the areas of infested timber 
 and placing the logs in lakes and streams and driving them to the 
 mills on the Androscoggin River. Thus, with little or no additional 
 expense, there was a saving to one firm, according to its estimates, 
 of more than $100,000. 
 
 CONTKOI. OF THE HICKORY BARKBEETLE. 
 
 The complete control of the hickory barkbeetle, which threatened 
 the total destruction of the hickory trees on Belle Isle Park, at Detroit, 
 Mich., in 190fi, was effected by felling and removing the infested trees 
 and converting them into merchantable products, all without cost to 
 the park conmiission. 
 
 CONTKOI. OF THE HIJACK HILLS BEETLE. 
 
 An extensive outbreak of the Black Hills beetle in the vicinity of 
 Colorado Springs, Colo., in 1905-G, which was threatening the living 
 pine timber of the entire section, was brought under control through 
 the efforts of the private owners of forests and those of forest offi- 
 cials in the adjoining National Forests. It was accomplished by 
 
 [Cir. 12.-1 
 
6 INSECTS WHICH KILL FOEEST TREES. 
 
 cutting aild barking about 1.000 beetle-infested and beetle-killed pine 
 trees. The cost of the operations was largely, if not entirely, coy- 
 ered by the utilized felled timber, although there was considerable 
 unnecessary expense inyohed through the felling and barking of 
 trees from which the beetles had emerged and from the unnecessary 
 burning of the bark and tops. 
 
 The successful control of another serious outbreak of this beetle, in 
 1906. on an extensive private estate in southern Colorado, was effected 
 through the efforts of the owners, who had some 500 infested trees 
 felled and barked within the necessary period to destroy the broods. 
 A large percentage, but not all. of the infested timber was thus 
 treated. These operations were so successful that not a single in- 
 fested and dying tree could be found when the area was inspected in 
 1908. In this, as in the other case, considerable unnecessary expense 
 was involved in the burning of the bark and tops, but the value of 
 utilizable timber was probably more than enough to pay all expenses. 
 It is evident that in this case a destructive invasion was prevented. 
 
 The practicability of controlling this most destructive enemy of the 
 pine timber of the central Rocky Mountain region, not only without 
 ultimate cost but at a profit on the oi)erations. was demonstrated on 
 a large private estate and the adjoining Pike National Forest in 
 north-central Colorado. An examination of the timber on this estate 
 in the spring of 1907. by a ranger detailed from the Forest Service to 
 work under instructions from the Bureau of Entomology, showed 
 that the depredations by the beetle had been going on for the past ten 
 years or more and had resulted in the death of the choicest timber to 
 the extent of more than 800.000 board feet. About 65,000 board feet 
 of timber was found to be infested by the beetle at the time of the ex- 
 amination. The owner was notified by the Bureau of Entomology 
 of the dangerous character of the infestation and the required action 
 for its control was recommended, but no action was taken. Another 
 examination of the property was made in the fall of 1907, when it 
 was found that the new infestation resulting from swarms of beetles 
 that had been allowed to emerge from the old infested trees involved 
 nearly four times as much timber, or i^-tO.OOO board feet. This alarm- 
 ing increase led to the prompt adoption of the recommendations 
 by the owner and the Forest Service, and by ^lay of the following 
 spring (1908) the small number of trees on the National Forest was 
 cut and barked, to kill the insects in the inner bark, and the 1,000 
 trees on the private estate were felled, the logs converted into lumber, 
 and the slabs burned, which accomplished the desired purpose of de- 
 stroying the broods of the beetle. The owner realized a sufficient 
 revenue from the timber thus involved to cover all expenses and leave 
 a net profit of over $1,200. Examination of the area in the fall of 
 1908 showed that this prompt and properly conducted effort to con- 
 [rir. lunj 
 
INSECTS WHICH KILL FOREST TREES. 7 
 
 trol the beetle was a complete success. Thus the average death rate 
 of some 100,000 feet of timber annually during the past ten or more 
 years was reduced to a minimum, at a net profit on the cost of doing it. 
 
 In addition to infested trees disposed of by the Forest Service in 
 timber sales, 165 infested trees in one section of the Las Animas 
 National Forest were cut and barked in May and June, 1908, at a 
 direct cost of $177.50. and at the same time a considerable amount of 
 infested timber was disposed of by sale in the Wet Mountains section 
 of the San Isabel National Forest. This had a decided effect in 
 checking the ravages of the beetle in both of these forests and it was 
 followed up in the latter forest the next spring (1909) by the proper 
 disposal of over 1,000 infested trees by free use, ranger labor, and 
 direct expenditure of funds appropriated by the Forest Service. 
 According to the forest supervisor's report, 80.7 per cent of the 
 infested trees were treated, ranging from 70 per cent to 92.5 per cent 
 on the five units of infestation: 795 trees were treated (535 barked, 
 and 2G0 felled and bark scorched) at the expense of the Forest Serv- 
 ice, including salary and expenses of rangers. The cost per tree was 
 about 60 cents for felling and barking, and ranged from 52 to 78 
 cents for felling and scorching the bark on the infested trunks. The 
 average cost per tree was 68.2 cents. Six hundred and twenty-six 
 trees were treated by temporary labor, at an average cost of 61 cents 
 per tree under contract at $1.50 to $2 per hundred feet in length of 
 trunk peeled. The same rate was allowed for scorching the infested 
 bark instead of removing it. Two hundred and seventy-five trees 
 were treated under administrative use without cost to the Forest 
 Service. 
 
 In September, 1909, a very thorough examination was made of 
 the timber in and adjacent to the areas involved in the control opera- 
 tions, and it was found that the thorough, prompt, and proper manner 
 in which the instructions of the Bureau of Entomology were carried 
 out in this case resulted in bringing the beetle under complete control. 
 Only 7 trees had been successfully attacked by the beetles which had 
 emerged from some 400 infested trees which were not cut during the 
 previous control operations. Over 100 trees were found that had 
 been attacked by the beetles, but, owing to the limited number of 
 the latter, the trees were able to resist them and recover. 
 
 It is now evident that the control operations carried on in southern 
 Colorado during the past three years, on the Trinchera estate near 
 Fort Garland in 1906, in the Las Animas National Forest and Wet 
 Mountains section of the San Isabel National Forest in 1908, and 
 the more extensive work in the latter area in 1909, had a far-reaching 
 effect in bringing the Black Hills beetle under control within the 
 forested areas of southern Colorado, and that the loss of timber 
 
 [Cir. 125] 
 
8 INSECTS WHICH KILL FOREST TREES, 
 
 from this source, amounting to an average of bome 300,000 board feet 
 annually, has been reduced to a minimum. 
 
 These results mark the most important events in the control of 
 forest insects in this country- and serve as striking demonstrations of 
 what can be accomplished when cooperative efforts are directed along 
 the proper lines and based on the results of scientific investigation. 
 The attainment of these results was due to three important factors: 
 First, a knowledge of the insects on which the recommendations by 
 the Bureau of Entomology were based : second, a knowledge of local 
 conditions and requirements and of the habits of the insects in rela- 
 tion to newly infested trees, which enabled a forest ranger to locate 
 the infested trees and give instructions to the forest officials in regard 
 to such locations and the essential details in the recommendations; 
 third, a prompt and proper practical application by the Forest Serv- 
 ice of the recommendations according to improved forestry methods 
 to meet the requirements of a forestry problem. 
 
 Ten years ago it would have been absolutely impossible to have 
 accomplished this result, owing to the utter lack of knowledge of the 
 first two of these features, and at the present time it would have 
 been impossible without the assistance of the Forest Service. 
 
 CONTROL OF THE MOUNTAIN PINK BEETLE. 
 
 A very threatening outbreak of the mountain pine beetle was lo- 
 cated, in 1909. in the Snowy Mountains section of Montana, adjacent 
 to and within the Jefferson National Forest, involving, at the time, 
 more than 1.500 infested and dying trees. The infestation included 
 timber on the National Forest, public domain, state lands, and private 
 lands, thus involving a complication of federal, state, and private 
 interests with which to deal in securing the required action. The 
 case was so successfully managed that an agent of the Bureau. Mr. 
 Josef Brunner. was placed in complete charge to carry out the recom- 
 mendations and instructions of this Bureau, and. through the aid of 
 the Forest Service, state officials, and private owners, 1.3r).5 infested 
 trees were cut and barked to kill the broods of beetles. The cutting 
 was started about June 15, 1909. and was completed about July 24 
 of the same year. Four hundred and twenty-two trees were cut at 
 private expense, 783 at the expense of the Forest Service, and the re- 
 mainder by local owners. Tlie average cost for felling and removing 
 the bark from the infested portion of the trunk was 30 cents per tree. 
 
 Early in December, 1909, a careful examination was made of the 
 area for evidence of new infestation. It was found that, while some 
 5G trees had bei'n attacked by the mountain pine beetle, the broods 
 were being destroyed by woodpeckers and other natural enemies, and 
 that, therefore, the efforts to control the beetle depreilations were a 
 complete success. 
 
INSECTS WHICH KILL FOREST TREES. 9 
 
 The examples of practical control given above have demonstrated at 
 least two important facts : One, that extensive outbreaks by two of the 
 most destructive bark-beetle enemies of the pine timber of the Rocky 
 Mountain forests can be controlled at moderate expense when the tim- 
 ber is not accessible for utilization, or at a profit whenever the condi- 
 tions are favorable for the utilization of the infested timber ; the other, 
 that the essential details of the recommendations and expert advice, 
 based on the results of scientific research, can be successfully applied by 
 a manager of a private forest or by the rangers of national and state 
 forests. Furthermore, these results indicate quite conclusively that 
 the widespread depredations in the Black Hills Xational Forest could 
 have been prevented with very little expense to the Government if the 
 matter had received prompt attention in 1901, when the first investi- 
 gations were made and essentially the same recommendations sub- 
 mitted as in the cases mentioned. Failure to do so was through the 
 lack of public appreciation of the importance of the problem at the 
 time and the lack of sufficient authority and funds later. Therefore 
 the outbreak was allowed to extend beyond practical control, and in 
 consequence a large percentage of the timber of the entire Xational 
 Forest has been killed. There were then no forcible examples of the 
 practical value of recommendations based on scientific research, and 
 no other argument was effective in arousing public interest in the 
 threatening character of the outbreak or confidence in the advice and 
 methods of control. Now that the practicability of controlling the 
 most destructive insect enemies of North American forests has been 
 demonstrated, this should lead to a more general interest in the subject 
 and confidence in the results of scientific research as a basis for success 
 in practical application. 
 
 Approved : 
 
 James Wilson, 
 
 Secretary of Agmculture. 
 Washington. D. C, October 7, 1910. 
 
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