QL 696 UC-NRLF v.l B 3 371 531 MAIN LIBRARY-AGRICULTURE DEPT. - CONTENTS Page. Introductory I Historical .> ( )riginal description of genus 4 Translation 4 Synonymy Revisional notes 1 description of genus 5 Anatomical 5 Nomenclature Illustrations... Q ---------"------....... r7 External characters of the imago 9 The head 11 The thorax 22 Divisions of the thoracic segment 23 Elements of the adult thorax 26 The prothorax 26 The mesothorax 28 Mesotergum 28 Mesoplura fc . . 29 Mesosterna 30 The metathorax 30 Metatergum 30 Metapleura 34 Metasterna 35 The abdomen 35 Abdominal tergites 36 Abdominal pleurites 33 Abdominal sternites 33 Spiracles 39 The legs 39 The wings ^ Mcsothoracic and metathoracic wings 42 Metathoracic or hind wings .j;j Mesothoraric wings or elytra 49 I nt ernal anatomy 5^ 1 i,u r osf ive system 52 Hilary sexual characters - )L > Pu Pa '.^ 53 Larva 5^ External characters 57 Digestive system 6 4 .......'.'..'.'. 64 Shyriological characteristics 554065 IS. X ........ ....THE gCpLSTlD BEETLES. Pago. Specific distinctions 66 Range or limits of specific variation 66 Progressive modifications 67. Distinction of major and minor divisions of the genus 68 Plan of synoptic treatment 69 Synopses of morphological and physiological characters 69 Synopsis of adult characters 69 Synopsis of secondary sexual characters 73 Synopsis of pupal characters Synopsis of larval characters 75 Synopsis of gallery characters 76 Table of distribution 77 Table showing relation of species to host trees Table of host trees 79 Revision and systematic notes, with descriptions of new species ^ 79 Distinctive generic characters 79 Bibliography and synonymy of genus 80 Division 1 81 Subdivision A 81 1. Dendroclonus brevicomis Le Conte . 81 2. Dendroctonus barberi n. sp 85 3. Dendroctonus convexifrons n. sp 87 4. Dendroctonus frontalis Zimmerman 90 5. Dendroctonus arizoni^us n. sp .v 95 6. Dendroctonus mexicanus Hopkins 97 7. Dendroctonus par allelocollis Chapuis 99 8. Dendroctonus approximatus Dietz 101 Subdivision B 105 9. Dendroctonus monticolx Hopkins 105 10. Dendroctonus ponderosas Hopkins 109 11. Dendroctonus jeffreyi n. sp 114 Division II 116 Subdivision C 117 12. Dendroctonus simplex Le Conte 117 13. Dendroctonus pseudotsugse, Hopkins 121 14. Dendroctonus piceapefda Hopkins 126 15. Dendroctonus engelmanni n. sp 130 16. Dendroctonus borealis n. sp 133 17. Dendroctonus obesus (Mannerheim) 135 18. Dendroctonus rufipennis (Kirby) 138 19. Dendroctonus murrayanse n. sp 140 20. Dendroctonus punctatus Le Conte 142 21. Dendroctonus micans (Kugelann) 143 Subdivision D 146 22. Dendroctonus terebrans (Olivier) 147 23. Dendroctonus valens Le Conte 151 24. Dendroctonus adjunctus Blandford 157 Bibliography 159 ILLUSTRATIONS PLATES. Page. PLATE I. Classification of the genus Dendroctonus, showing technical and com- mon names and species numbers 1 II. Map of world, showing geographical distribution of the genus Den- droctonus 80 III. Dendroctonus adults. Fig. 1. D. brevicomis. Fig. 2. D. barberi. Fig. 3. D. convexifrons. Fig. 4. D. frontalis. Fig. 5. D. ari- zonicus. Fig. 6. D. mexicanus. Fig. 7. D. parallelocollis 164 IV. Dendroctonus adults. Fig. 8. D. approximates. Fig. 9. D. monti- colse. Fig. 10. D. ponderosx. Fig. 11. D. je/reyi 164 V. Dendroctonus adults. Fig. 12. D. simplex. Fig. 13. D. pseudo- tsugse. Fig. 14. D. piceaperda. Fig. 16. D. borealis 164 VI. Dendroctonus adults. Fig. 17. D. obesus. Fig. 18. D. rufipennis. Fig. 20. D. punctatus. Fig. 21. D. micans 164 VII. Dendroctonus adults. Fig. 22. D. terebrans. Fig. 23. D. miens 164 VIII. Dendroctonus larvae. Fig. 1. D. brevicomis. Fig. 19. D.murrayanae. Fig. 23. D. valens 164 TEXT FIGURES. FIG. 1. Dendroctonus valens: Adult, dorsal aspect 6 2. Dendroctonus valens: Adult, ventral aspect 8 3. Dendroctonus valens: Adult, lateral aspect 9 4. Dendroctonus valens: Head, dorsal and lateral aspects 12 5. Dendroctonus valens: Head, ventral aspect, and mouthparts 13 6. Dendroctonus valens: Head, oral aspect, epistoma, etc 14 7. Pterostichus californicus: Head, dorsal and ventral aspects 15 8. Pissodes strobi: Head, ventral aspect, and mouthparts 16 9. Pissodes strobi: Head, dorsal aspect, and mandibles 17 10. Dendroctonus: Epistomata 19 11. Dendroctonus: Antennae 20 12. Dendroctonus: Antennae 20 13. Dendroctonus: Antennae 21 14. Dendroctonus valens: Mandible 22 1 ">. Dendroctonus: Eyes 23 16. Dendroctonus valens: Areas of pronotum 23 17. Dendroctonus valens: Areas of prothorax, ventral aspect 24 18. Dendroctonus valens: Mesothorax, ventral aspect 24 19. Dendroctonus valens: Mesotergum and mesopleurum 28 20. Dendroctonus valens: Metatergum and metapleurum 31 21. Dendroctonus valens: Metatergum, inner aspect 33 22. Dendioctonus valens: Abdominal tergites 35 23. Dendioctonus valens: Male, abdominal tergites 7 and 8 36 24. Dendroctonus valens: Female, abdominal tergites 7 and 8 37 XI xii ,* ;:;*: -."ME ^SC^EYTID BEETLES. ,' ,' : ; ; .*;",' ': i ..: ''.' Page. FIG. 25. Dendroctonus valens: Abdominal sternites, ventral and lateral as- pects 38 26. Dendroctonus nolens: Tibia, tarsus, articulation, etc 40 27. Dendroctonus: Left tibiae, dorsal and ventral aspects 41 28. Dendroctonus: Left tibiae, dorsal and ventral aspects 42 29. Dendroctonus: Left tibiae, dorsal and ventral aspects 43 30. Dendroctonus valens: Diagram of basal area of hind wing 44 31. Dendroctonus valens: Right elytron, ventral aspect 45 32. Dendroctonus valens: Basal process of right elytron 46 33. Dendroctonus valens: Decli vital section of elytra 46 34. Dendroctonus valens: Diagram of elytron, showing striae, interspaces, and tracheae 47 35. Dendroctonus valens: Digestive organs of adult t 52 36. Dendroctonus valens: Fore intestine, showing details 53 37. Dendroctonus valens: Pupa, dorsal, lateral, and ventral aspects 54 38. Dendroctonus valens: Pupa, lateral and anal aspects 55 39. Dendroctonus valens: Larva, dorsal, lateral, and ventral aspects 58 40. Dendroctonus valens: Head of larva 59 41. Dendroctonus valens: Mouthparts of larva 60 42. Dendroctonus valens: Mandibles of larva 63 43. Dendroctonus valens: Digestive organs of larva 65 44. Dendroctonus brevicomis: Egg galleries 82 45. Dendroctonus brevicomis: Bark showing pupal cells, exit burrows, and pitch tubes 83 46. Dendroctonus brevicomis: Distribution map 84 47. Dendroctonus barberi: Egg galleries 86 48. Dendroctonus barberi: Distribution map 87 49. Dendroctonus convexi/rons: Egg galleries and larval mines 89 50. Dendroctonus convexifrons: Distribution map 90" 51. Dendroctonus frontalis: Egg galleries and larval mines 91 52. Dendroctonus frontalis: Termination of egg galleries 92 53. Dendroctonus frontalis: Beginning of egg galleries 92 54. Dendroctonus frontalis: Bark showing pitch tubes, etc 92 55. Dendroctonus frontalis: Old egg galleries in living tree 93 56. Dendroctonus frontalis: Egg gallery in living tree, the resulting wound in process of healing 93 57. Dendroctonus frontalis: Distribution map 94 58. Dendroctonus arizonicus: Distribution map 97 59. Dendroctonus mexicanus: Section of egg galleries 98 60. Dendroctonus mexicanus: Distribution map 99 61. Dendroctonus parallelocollis: Section of egg gallery 100 62. Dendroctonus parallelocollis Distribution map 101 63. Dendroctonus approximatus: Single egg gallery 102 64. Dendroctonus approximatus: Egg galleries 103 65. Dendroctonus approximatus: Distribution map 104 66. Dendroctonus monticolse: Egg galleries and larval mines in bark 107 67. Dendroctonus monticolx: Egg galleries and larval mines grooved in sur- face of wood 108 68. Dendroctonus monticolse: Distribution map. . . .*. 109 69. Dendroctonus ponderosse: Egg galleries and larval mines 112 70. Dendroctonus ponderosx: Tree with bark removed, showing egg gal- leries grooved and marked on surface of wood 113 71. Dendroctonus ponderosx: Distribution map ] 14 ILLUSTRATIONS. XIII Page. FK ; . 72. Dendroctonus jeffreyi: Distribution map 116 73. Dendroctonus simplex: Egg galleries and larval mines 119 74. Dendroctonus simplex: Distribution map 120 75. Dendroctonus pseudotsugse: Egg^galleries and larval mines 122 76. Dendroctonus pseudotsugse: Egg gallery and larval mines 123 77. Dendroctonus pseudotsugse: Section of log with bark removed, showing brood galleries marked and' grooved on surface of wood 124 78. Dendroctonus pseudotsugx: Distribution map 125 79. Dendroctonus piceaperda: Egg gallery and larval mines 128 80. Dendroctonus piceaperda: Distribution map 129 81. Dendroctonus engelmanni: Egg gallery and eggs in living bark 132 82. Dendroctonus engelmanni: Distribution map 133 83. Dendroctonus borealis: Distribution map 134 84. Dendroctonus obesus: Distribution map 137 85. Dendroctonus rufipennis: Distribution map 140 86. Dendroctonus murrayanse: Distribution map 141 87. Dendroctonus punctatus: Distribution map 143 88. Dendroctonus micans: Egg galleries and larval chamber 145 89. Dendroctonus micans: Distribution map 146 90. Dendroctonus terebrans: Distribution map 150 91. Dendroctonus valens: Egg galleries and larval chamber 152 92. Dendroctonus valens: Work in bark at base of stump 153 93. Dendroctonus valens: Basal wound in living tree resulting from primary injury by this species 154 94. Dendroctonus valens: Distribution map 155 95. Dendroctonus adjunctus: Distribution map 158 Tech. Series 17, Part I, Bureau of Entomology, U. S. Dept. of Agriculture. PLATE I. 11 02 H 1. brevicomis Lee. 1. 2. 6ar6m Hopk. 2. 3. convexifrons Hopk. 3. 4. frontalis Zlmm. 4. 5. arizonicus Hopk. 5. 6. mexicanus Hopk. 6. 7. parallelocollis Chap. 7. 8. approximatus Dietz. 8. Western Pine 70,81 Beetle. Southwestern Pine 70, 85 Beetle. Roundheaded Pine 70, 87 Beetle. Southern Pine 70,90 Beetle. Arizona Pine 70,95 Beetle. Smaller Mexican 70, 97 Pine Beetle. Larger Mexican 70,99 Pine Beetle. Colorado Pine 70,101 Beetle. 9. monticolse Hopk. 9. 10. ponderosse Hopk. 10. 11. jeffreyi Hopk. 11. Jeffrey Pine Beetle 71, 114 Mountain Pine 71, 105 Beetle. Black Hills Beetle 71, 109 Position doubtful 12. simplex Lee. 12. Eastern Larch 71, 117 Beetle. 13. pseudotsugte Hopk. 13. Douglas Fir Beetle 71, 121 14. piceaperdct Hopk. 14. Eastern Spruce 71,126 Beetle. 15. engelmanni Hopk. 15. Engelmann Spruce 71, 130 Beetle. 16. ftoreaftsHopk. 16. Alaska Spruce 72,133 Beetle. 17. obesus Mann. 17. Sitka Spruce Beetle 72,135 18. rufipenni* Kirby. 18. Redwinged Pine 72,138 Beetle. 19. murrayante Hopk. 19. Lodgepole Pine 72,140 U Beetle. 20. Allegheny Spruce 72, 142 Beetle. 21. micans Kug. 21. European Spruce 72, 143 Beetle. 22. terebrans Oliv. 22. Black Turpentine 72,147 Beetle. 23. valens Lee. 23. Red Turpentine 72, 151 Beetle. 24. adjunctus Blandf. 24. Guatemala Beetle 157 Classification of the Genus Dendroctonus, Showing* Technical and Common Names and Species Numbers. This diagram will enable the reader to refer at once to the technical and common names of any species number mentioned in the text, an d will show at a glance the position and relations of the divisions, subdivisions, sections, subsections, series, and species into which the genus is divided. T. S. D. A.. B. K. Tech. Scr. 17. I't. I. F. I. I., June 30,1909. CONTRIBUTIONS TOWARD A MONOGRAPH OF THE SCOLYTID BEETLES. I. THE GENUS DENDROCTONUS. By A. D. HOPKINS. In Charge of Forest Insect Investigations. INTRODUCTORY. The active work on forestfinsects conducted by the West Virginia Agricultural Experiment Station in 1890- 9 i, and by the Division and Bureau of Entomology of the U. S. Department of Agriculture since 1899, has resulted in the accumulation of a mass of systematic and biological data on the principal described and undescribed insect ene- mies of forest trees and forest products of the United States. When- ever an attempt has been made, however, to work up the material relating to a given species, or group of species, it has been apparent that the publication of anything without first describing the new species and revising the data in both the systematic and economic literature would contribute to confusion rather than to advancement. Indeed, it becomes more and more evident that in order to give reliable information on applied entomology we must have at our command the knowledge gained by careful technical, or systematic, studies of the insects with which we have to deal. Therefore, when we find, as we do in many cases, that the published results of systematic work on a given genus or species are meager or otherwise unsatisfactory, it becomes necessary to revise and verify the descriptions and biological records, and to adjust the classification to meet the requirements of the newly dis- covered facts relating to the described and undescribed species. The genus Dendroctonus presents a striking example of the need of systematic study as a basis for economic investigation. It is both the most important group of insect enemies of the coniferous forest trees of North America and one of the most difficult for systematic study. Le Conte (1876) expressed the difficulty met with in a study of the species when he said in his later revision : If I have failed to indicate more strongly the differences between these species, it is because they are not distinguishable by any prominent or definite characters; and the student who may have difficulty in identifying the species as here defined would have almost equal difficulty if the specimens in my collection were before him. 1 THE SCOLYTID BEETLES. within' recent years little progress had been made toward the *aKd : .cl^ definition of the specific and sexual characters. In* consequence the identification of the species was both difficult and uncertain and has led to much confusion in both systematic and eco- nomic literature. With our prasent knowledge of the genus, based on an exhaustive study of the systematic and biologic details, most, if not all, of the difficulties have been removed, so that the identifi- cation of the species is comparatively easy. It is the purpose of this paper to revise and bring up to date the available information on the described species, to describe those that appear to be new to science, and to record the results of original inves- tigations relating to the more technical details that can not well be included in the paper which is to follow as a part of a bulletin in the regular series and which will give full information on the bionomic features. The material which has served as a basis for the study of this genus consists mainly of the notes and specimens taken by the writer in the field during his connection with the West Virginia Agricultural Experiment Station, between 1890 and July, 1902, including special investigations for the Division of Entomology, U. S. Department of Agriculture, in 1899, 1900, and 1901, and those taken during the investigations by this Bureau between July, 1902, and July, 1908. In addition to the large amount of material thus accumulated the writer has studied the type and other specimens in the larger collec- tions of this country. The writer desires to acknowledge, in this connection, the assist- ance rendered by the following gentlemen in providing facilities for the study of specimens in the collections of which they have charge : Mr. Samuel Henshaw, in charge of the Le Conte collection in the Museum of Comparative Zoology, Cambridge, Mass., and of the Harris collection, Boston Society of Natural History; Dr. Henry Skinner, in charge of the Horn collection of the American Entomological Society and the general collection of the American Entomological Society, Philadelphia, Pa.; Mr. E. A. Schwarz, honorary custodian of Coleoptera in the Division of Insects, U. S. National Museum; Dr. W. G. Dietz, who loaned type and other specimens from his collec- tion, and Mr. C. O. Waterhouse, of the British Museum, who com- pared specimens with the type of Dendroctonus rufipennis Kirby. It also gives the writer pleasure to acknowledge the efficient assist- ance of Messrs. J. L. Webb, II. E. Burke, and W. F. Fiske in the field and office work, of Mr. E. J. Kraus in the more recent office work, and of Messrs. J. F. Strauss and R. E. Snodgrass in the preparation of the illustrations for this part of the bulletin. THE GENUS DENDBOCTONUS. 3 HISTORICAL. The genus Dendroctonus was described by Dr. W. F. Erichson (1836) > include (Bostrichus] micans^ Kug., (Scolytus} terebrans Oliv., (Dcnnestes) piniperda L., (Hylesinus) minor Hartig, and (Hylesinus} minimus Fab. " Eichhoff (1864) revised the genus and referred D. piniperda (L.) and D. minor (Hartig) to Blastophagus Eichh. and later (1879) to MyelopJii- lus Eichh., and D. minimus (Fab.) to Carphoborus Eichh., leaving D. in leans (Kug.) as the type. Lacordaire (1868) referred to the synonymy and revised the descrip- tion, including Dendroctonus junipiri Doeb. [ = PJilwosinus junipfri &> (Doeb.)], D. valens Lee., and D. similis Lee. / Zimmerman (1868) divided the genus into three groups, placing D. bifurcus (= Carphoborus bifurcus Eichh.) in the first, none in the second, and D. terebrans (Oliv.) and D. frontalis Zimm. in the third group. Le Conte (1868) revised the classification for the North American species to include D. terebrans (Oliv.), Hylurgus obesus Mann., Hylurgus rujiprnnis Kirby, D. frontalis Zimm., and two new species, D. punctatus Lee., and D. simplex Lee. He here referred D. valens Lee. to D. tere- brans (Oliv.), and D. similis Lee. to D. obesus (Mann.) . He recognized t wo divisions, Division B represented by D. frontalis, and Division A by the other five species. Chapuis (1869) included D. micans (Kug.), D. valens Lee., D. tere- brans (Oliv.), D. obesus (Mann.), and added one new species, D. paral- lelocollis Chap., but did not recognize D. frontalis Zimm. Le Conte (1876) included D. terebrans Lac. ( = Oliv.), D. similis Lee., D. rujipennis (Kirby), D. punctatus Lee., D. simplex Lee., D. fron- talis Zimm., and one new species, D. brevicomis Lee. He here restored D. similis and omitted D. obesus. Dietz (1890) in his " Notes on the Species of Dendroctonus of Boreal America," revised the classification, principally on the char- acter of the epistoma, which he considered of primary importance in separating the species. He included D. terebrans, with varieties a, 6, c-j d, D. rufipennis, D. similis Lee., D. simplex Lee., D. frontalis, added one new species, D. approximatus Dietz, and referred D. puncti- collis Lee. to D. rufipennis (Kirby) and D. brevicomis Lee. to D. frontalis Zimm. Blandford (1897) mentioned D. terebrans (Oliv.), D. parallelocollis Chap., and an undescribed species from Texas probably D. terebrans (Oliv.) and added one new species, D. adjunctus Blandf. The writer (Hopkins, 1899a) referred to D. terebrans, D. rufipennis (Kirby), D. simplex Lee., and D. frontalis Zimm., with descriptions of 7998009 2 4 THE SCOLYTID BEETLES. different stages, habits, etc., of D. frontalis, and larvae and habits of D. terebrans ( = D. valens). In 1901 he described D. piceaperda in all stages in connection with an account of habits, seasonal history, etc., and referred to the type of D. rufipennis (Kirby). In 1902 he described D. ponderosse in all stages, in connection with an account of habits, seasonal history, etc. In 1 902, under " Some Notes on the Genus Dendroctonus," he referred to a statistical method of determining natural positions of the species, and gave a list of described species and manuscript names of undescribed species, as follows: D. pinicida MSS., D. arizonicus MSS., D. monticola MSS., D. ponder osse Hopk. MSS., D. Jceeni MSS., D.fletcheri MSS., D. piceaperda Hopk., D. dietzi MSS., D. californicus MSS., D. shoshone MSS., D. wickJiami MSS., and D. borealis MSS. He restored D. brevicomis Lee. and D. punctatus Lee. from Dietz's synonymy, and recognized D. obesus (Mann). In 1905 he described D. pseudotsugse and D. monticola in connection with accounts of habits, seasonal history, etc. ORIGINAL DESCRIPTION OF GENUS. Dr. W. F. Erichson (1836) described the genus Dendroctonus as follows : DENDROCTONUS. [p. 52] Antennae funiculo 5-articulato, capitulo 4-annulato, suborbiculari, com- presso. Tibiae extus denticulatae. Palpi maxillares articulo primo brevissimo, secundo maximo, sequentibus duobus sensim minoribus. Labium fortiter compressum. Palpi labiales articulo primo longiore, subclavato, secundo tenuiore, cylindrico, minuto, tertio obtuse subulate. Antennae breves, scapo clavato, funiculi articulo primo breviter clavato, secundo obconico, reliquis brevibus transversis; capituli segmentum primum reliquis con- junctis aequale, politum. [p. 53] Corpus oblongum, cylindricum. Rostrum brevis- simum. Prosternum antice obsolete impressum. Coxae anticae approximatae. Tibiae compressae, extus denticulatae. Tarsi articulo tertio dilato, bilobo. Elytra margine antico elevato. [Translation.] Antennae with 5-jointed funicle; the club suborbiculate, com- pressed, with four segments (annulae). Tibiae externally denticulate. Maxillary palpi with the first joint very short, the second the longest, the two following gradually smaller. Labium strongly com- pressed. The labial palpi with the first joint rather long, subclavate, the second joint more slender, cylindrical, small, the third obtusely subulate. Antennas short, scape clavate, first joint of funicle shortly clavate, second joint obconical, the remaining joints short, trans-' verse; first segment of club equal to the others conjointly, polished. Body oblong, cylindrical. Beak very short. Prosternum ante- riorly obsoletely impressed. Anterior coxae approximate. Tibiae compressed, externally denticulate. Tarsi with the third joint dilated and bilobed. Elytra with the anterior margin elevated. THE GENUS DENDROCTONUS. 5 SYNONYMY. The following species were included, all but two of which were subsequently referred by Eichhoff (1864) to other genera: Bostrichus micans Kugelann = Dendroctonus micans (Kugelann) . (Type -of genus.) Scolytus terebrans Olivier = Dendroctonus terebrans (Olivier). Dermestes piniperda Linnaeus = Myelophilus piniperda (Lin- naeus). II)/lurgus minor Hartig = Myelophilus minor (Hartig). Ilylesinus minimus Fabricius = Carphoborus minimus (Fabri- cius.) BE VISIONAL NOTES. The generic characters mentioned by Erichson in the original description are recognized in the type and other species except that the maxillary palpi are not 4-jointed. The first or basal joint has a basal ring or outward curved basal margin for the attachment of the membrane connecting the joint with the palpiger. This might have been mistaken for the "very short first joint" referred to, but it is evident that this or any other structure does not represent such a basal joint. In the type species the first joint of the club is equal to the others, but ranges from shorter to longer in the other species. Le Conte's added characters in his revision of 1868 and 1876 are generally correct, except that the antennal club is not always concave on one (external) side or anterior face, the sutures are more often curved than straight, and in some species only two sutures are visible on one side of the club. The prosternum is sometimes flat, the fifth joint of the tarsus is never longer than the others united, and the ventral segments are only approximately equal in length, the last one being usually as long as the two preceding combined. Dietz (1890) called attention to the unreliability of the sutures and joints of the antennal club in dried specimens, and laid special stress on the value of the epistoma in distinguishing the species. It appears, however, that while the form of the epistoma is a good generic and Bubdivisional character, it is of little or no value in distinguishing the species. The additional generic characters recognized by the writer will be found described under external and internal anatomy, and the char- acters distinguishing the major and minor divisions will be found in the synoptic tables. REVISED DESCRIPTION OF GENUS. ANATOMICAL. The following discussion of anatomical details includes the imago, larva, and pupa, and is based primarily on the results of original dissections and anatomical investigations by the author during the 6 THE SCOLYTID BEETLES. past eighteen years, and of those conducted by assistants under his immediate supervision during the past three years. OOOOOO 6^0 oooV 00000000009-6 Dendroctonus valens Lee. has served as the principal subject for dissection, comparison, and illustration, both on account of the THK GENUS DENDHOCTONU8. 7 abundance of material at hand and because of the comparatively large si/e of the individuals of this species. Sufficient comparative studios have been made, howeve^, of the other species of the genus and of representatives of other genera of the family and suborders to form a reliable -basis for the interpretations and conclusions relating to the more important taxonomic characters and the significance of their modifications in the distinction of species, genera, etc. Through the assistance of Mr. R. E. Snodgrass an extensive investi- gation has also been made of the thoracic segments of representa- tives of all of the principal orders of insects. The results have served as additional data and evidence on which to base conclusions in this paper, and will be utilized by Mr. Snodgrass as a basis for a more detailed discussion in a paper entitled "The Thorax of Insects and the Articulations of the Wings/' to be published later. This will include a quite complete bibliography and references to the principal systems of nomenclature proposed or adopted by the lead- ing authors, thus rendering it unnecessary to include extensive bibliographic references in the present paper. In all of this anatomical work the object of the author has been to acquire direct information on the facts as they exist in the subjects ex- amined ; such information to furnish a basis for the determination, naming, description, and illustration of the anatomical elements as represented in the scolytid beetles, and at the same time to serve as a guide to the determination of further facts relating to insect anatomy in general. The literature on insect anatomy has been utilized as a guide in securing additional information on the facts and principles involved, and with the idea of adopting such interpretations and nomen- clature as appeared to conform more nearly to the facts and con- tribute to uniformity. No attempt is made to discuss the merits of opposing opinions or theories, or to prove or disprove them. In this presentation of the results of independent investigation and discussion of the facts as interpreted by the author, it is hoped that something has been accomplished toward the advancement of information on the general subject of insect anatomy, and that its special reference to the anatomy of the scolytid beetles will make tlu' future systematic study of this troublesome group less difficult and more accurate, and thus lead to the determination of bionomic and economic data of immediate practical importance. NOMENCLATURE. There is yet much confusion in the literature and considerable difference of opinion among the best authorities in regard to ana- tomical nomenclature as applied to the structure of insects in gen- eral and especially to representatives of different orders. There is THE SCOLYTID BEETLES. ~^__ Epistemw _ Exocoxal piece Epimerum Stcrndlar area ~ 'Coxa Sternum Episternum Median line Sternellar piece 2. Dendroctonus valens: Adult, ventral aspect. , Sternellar area. (Original.) \ S THE GENUS DENDROCTONUS. 9 evidently much room for improvement in the line of uniformity in names and interpretations. In the present paper the writer has endeavored to adhere to the more generally accepted names proposed HEAD Afesosternum '.pisi E.Tocoxal area Epnncrinn - - - Metaslernum '-.Pri-scutal lobe - - : /-^- - - Clavicle process *-- --^ I ^"""Coracoid process Trochanter --/- Hind leg FIG. Z.Dendroctonus valens: Adult, lateral aspect, a, Pleural clavicula; 6, pregena. (Original.) by Audouin and other writers for the principal parts, and to suggest only such revisions and new names as the immediate requirements of clear definition in comparative anatomy and taxonomy appear to demand. 10 THE SCOLYTID BEETLES. ILLUSTRATIONS . The figures are intended to be sufficiently complete to leave little to be added in the way of description, except to emphasize and elucidate some of the more important features, or to call attention to the variation within the genus or species. EXTERNAL CHARACTERS OF THE IMAGO. The structural details and general external anatomy and sculpture are shown in figures 1, 2, and 3. The principal characters peculiar to the genus. are found in the large, prominent head, the epistomal process (figs. 2, 3, 4, 6, 10) (referred to by Dietz as the median seg- ment of the epistoma), the form of the antenna (figs. 11, 12, 13), the approximate or subcontiguous anterior coxse (fig. 2), and the strongly recurved hypopleural sutures 4, 5, and 6 of the abdominal sternites (fig. 25). Length and relative proportions. The length of the imago ranges from 2.5 mm. in D. frontalis to 9 mm. in D. valens. There is con- siderable range in length within the limits of some of the species, while in others the length is more constant. The relative propor- tions of the width of the head, width and length of the prothorax, width and length of the elytra, or a composite of the ratios, serve as a taxonomic index for the classification of the species, and, together with other characters, serve to distinguish the major and minor divisions and, to a certain extent, the species. The progressive modification appears to be from a head nearly as broad as the pro- notum and the latter as broad as the elytra, with the sides nearly parallel, to a head much narrower than the pronotum, the latter slightly narrower than the elytra, with the sides narrowed and con- stricted toward the head; also, from a slender, subelongate, to a stout body. Color. The color ranges from pale yellowish-red to brown and deep black, but is fairly constant in the matured individuals of a species. The immature individuals are always lighter, and some of those of the black species are reddish. In some species the head, prothorax, and ventral surface of the body are darker than the elytra, while in others little or no difference is noticeable. Vestiture. The body is more or less clothed with short to long hairs, the presence or absence of which on different areas is of far more taxonomic significance than was at first recognized. Except in old rubbed specimens, the vestiture serves as one of the important characters distinguishing the major, as well as some of the minor, divis- ions. See synopsis, Divisions I and II, sections al and a2 (PL I) . Sculpture. Within the genus and also within each species there is considerable variation in the sculpture of the front, pronotum, and elytra. Nevertheless, such characters as the presence or absence TIIK (IKNTS. DKNDKOrTONUS. 11 of frontal grooves and tubercles serve to distinguish some of the minor divisions of the genus, while the presence or absence of a posterior median impression in those species without a frontal groove is of considerable importance in "distinguishing some of the minor divisions. The relative size, density, and arrangement of the punc- tures of the pronotum, while variable within the species, is of con- siderable taxonomic value. The character of the rugosities of the interspaces and the punctures of the striae are also variable within the species and are of secondary value in distinguishing minor divi- sions. The sculpture of the elytra! declivity is of special specific and sexual importance, and in some cases the characters are of value in distinguishing minor divisions. THE HEAD. The general characters and details of the external skeleton and appendages of the head are shown in figures 4, 5, and 6. It will be noted that the elements which in some other Coleoptera and other insects are more or less clearly defined are quite completely fused and obscured in this genus as in other rhynchophorous beetles. The labrum and clypeus are obsolete. The epistoma, or "post-clypeus," or "pre-front," as recognized by different authors, is not separated from the front by a line or suture, but is quite clearly defined, and the epistomal process is far more prominent than in other allied genera. The front is completely fused with the epicranium, which in turn is fused with the gense, the latter joined beneath with a single gular suture. Anterior to the gular suture there are three quite clearly defined sclerites, which may be designated as pregula, pregena, and hypos toma (fig. 5, E). By comparing the head of Dendroctonus with that of a carabid beetle, Pterostichus (fig. 7), and a typical curcu- lionid beetle, Pissodes strobi (figs. 8, 9), the striking difference in struc- ture and relative position of the corresponding elements and their extreme modification are at once apparent. Labrum. The labrum is not present as a distinct element, but may be represented by a part of the anterior margin of the epipharynx beneath the anterior median section of the epistoma (fig. 6, A). Clypeus. The clypeus is not represented unless it is by the pro- duced anterior margin of the epistoma, and by the long epistomal bristles. Kpistoma (figs. 2, 3, 4, 5, 6, 7, 10, 40, B, D, E.) The epistoma is apparently represented in both the larvae and adults of all true man- dibulate insects, but is more distinctly defined in some than in others. In some insects it is separated from the clypeus by a suture, line, or articulating membrane, while in others there is no evidence of sepa- ration or the clypeus is not represented. Its separation from the front is often defined by a line, impression, elevation, or otherwise, although sometimes it is so completely fused that the line of junction 12 THE SCOLYTID BEETLES. is entirely obscured, as in Pterostictius. It serves the important function of a rigid bridge over the oral foramen and support for the clypeus, labrum, and epipharynx, and at its lateral angles provides the necessary rigid support for the dorsal articulation of the man- Mandiblt eral impression il axillary palpus--^, ^ \ ,, .Labial palpu*/ Antennal scrobe FIG. 4.Dendroctonus valens: Head, dorsal and lateral aspects. A , Dorsal aspect of head; B, lateral aspect of head; C, dorsal aspect of right mandible; D, ventral aspect of right mandible; c, dorsal area; b, dorsal impression; c, anterior condyle; d, median fossa; e, median condyle;/, posterior fossa; g, basal ridge; ft, apical tooth; i, acute margin;,/, subapical tooth; fc, median tooth; I, molar; m, anterior condyle; n, me- dian fossa; o, posterior condyle; p, lateral area; r, dorsal bristles of mandible; s, lateral bristles of man- dible; t, epistomal bristles; u, lateral angle of epistoma. (Original.) dibles. In fact the latter function serves to distinguish it from other parts. The median area is variously and sometimes greatly modified in insects of the same order or family, and it appears that in Coleop- tera generally this element is of much greater taxonomic value than has been usually recognized heretofore. THE GENUS DENDROCTONUS. 13 Epistomal process. In Dendroctonus the epistomal process serves to clearly distinguish the genus from other genera of the suborder to which it belongs. This process is usually composed of a median and FIG. 5. Dendroctonus valens: Head, ventral aspect, and mouthparts. A, Labimn; B, maxilla, interno- lateral aspect; C, same, externo-lateral aspect; D, hypostomal region, dorsal aspect; E, head, ventral aspect; a, basal fossa of mentum; 6, joints; c, basal membrane; d, palpiferal area; e.stipal area;/,sub- galeal area; g, fossa; h, muscle processes; k, median condyle; I, lateral fossa; TO, anterior condyle; n, median fossa; o, posterior condyle; p, hypopharyngeal bracon; q, submental process; r, maxillary con- dyle; s, gular apodeme; u, oral foramen; v. occipital apodeme; w, postgular piece. (Original.) two lateral sections and is fringed anteriorly with thickly set, long bristles which completely cover the anterior median epistomal area. Hypostoma (fig. 5). This, as here interpreted, is a ventral piece or area which corresponds in general function to the epistoma in forming a rigid ventral rim of the oral foramen for the support of the 14 THE SCOLYTID BEETLES. articulatory accessories of the labium and maxillae, and at the lateral angles supports the ventral articulations for the mandibles. It seems to the writer that this part or area, whenever sufficiently dis- tinct to be recognized, should be designated as the hypostoma, not Gular suture* FIG. ft.Dendroctonus valens: Head, oral aspect, epistoma, etc. A, Ventral aspect of epistomal rogion; B, dorsal aspect of epistomal region; C, oral aspect of head; c, median impression and longitudinal ele- vations; 6, median condyle; c, lateral fossa; d, posterior fossa; dd, projection over median condyle; e, base of epistomal bristles; /, median section of epistomal process; ff, lateral angles of epistoma; g, ante- rior fossa; h, anterior condyle of ventral articulation; i, posterior condyle of ventral articulation ;j, median fossa of ventral articulation; fc, hypopharyngeal bracon; I, maxillary condyle; TO, submental processes; n, ventral view of hypopharynx; o, oral foramen; p, dorsal articulation of mandible; q, ventral articu- lation of mandible; r, apex of hypopharynx. (Original.) on account of any theory of origin from a primitive segment, but because its location and function are similar to those of the epistoma. Front (figs. 3, 4). The front is not defined by sutures or lines, but is fused anteriorly with the epistoma and laterally and posteriorly with THE (iKM'S DENDROCTONUS. 15 the epicranium. It is represented by a frontal area, however, which not only in this genus but in other scolytids presents characters of special value in distinguishing major and minor divisions, species, sexes, etc. The significance of frontal characters in this genus is defined in the synopses of adult and secondary sexual characters and shown in trie figures. AnttnnsR (figs. 1-6, 11-13). The characters of the antennae are clearly shown in the figures. The scape, funiculus, and club are ?. Pterostichus californicus: Head, dorsal and ventral aspects, and maxillae. A, Ventral aspect; B, dorsal aspect; C, dorsal aspect of left maxilla; D, lateral aspect of left maxilla; E, ventral aspect of left maxilla; a, stipal foramen; b, muscle processes; c, lacinial digitus; d, cardo fossa; e, basal membrane; /, palpiferal bristle; g, stipal bristle; h, median fossa of ventral articulation of mandible; i, labral bristles; j, clypeal bristles. (Original.) nearly equal in length. The scape toward the apex is clavate cy- lindrical to angular. The funiculus is 5-jointed and always slightly longer than the club. The first joint (or pedicel of some authors) is of the usual form and as long or longer, rarely shorter, than the second. The second joint is as long as the third, fourth, and fifth together, or slightly shorter in some species, and the second to fifth increase in width toward the club, which is broad, thickened toward the base and compressed toward the apex, and has three or four distinct segments, with two or three slightly to strongly curved 16 THE SCOLYTID BEETLES. sutures. The relative concavity or convexity of the anterior face, as well as the relative lengths of the segments on the opposite faces, Palpi Palpifer.., Mentum Occipital FIG. S.Pissodesstrobi: Head, vent nil aspect, and mouthparts. A, Ventral aspect of apical region of beak; B, ventral aspect of head; r, iult rno-latcral aspect of maxilla; Z>, externo-lateral asp* ct of maxilla; a, apical tooth; 6, subapical tooth; c, lateral arm of hypostoma; d, pleurostoma; e, mandibular scrobe;/, hypostomal area; g, lacinial bristles; h, antennal groove; i, joints; j, cardo fossa; k, hypostomal puncture. (Original.) contour of the suture, etc., are shown in figures 11 to 13, but often appear different in dried specimens. The articulatory attachment THE GENUS DENDROCTONUS. 17 of the scape is in a rather deep scrobe (figs. 4, 5), situated in front of the eye near the base of the mandible and lateral angle of the epistoma. Fi< ;. '.). -Pissodes strobi: Head, dorsal aspect, and mandibles. A , Dorsal aspect of left mandible; B, ventral aspect of left mandible; C, dorsal aspect of head; a, apical tooth; b, subapical tooth; c, median tooth; d, molar; e, median condyle;/, lateral muscle process; g, lateral condyle; h, lateral fossa; i, extensor tendon; j, pharyngeal bracon; k, retractor tendon; I, ventral area; m, dorsal area; n, median condyle; o, anterior fossa; p, anterior section of beak; q, posterior section of beak; s, dorsal area; t , anterior condyle; u, lateral fossa. (Original.) Epicranium. The epicranium is not defined from the front or gena by sutures or lines, but the area is quite clearly indicated by the 18 THE SCOLYTID BEETLES. smoother surface and by the presence of the compound eye, which is situated on the side of the head near the base of the antennse. The anterior end of the epicranial suture defines the anterior dorsal limit of the epicranium, designated as the vertex, while the gena is repre- sented by the ventral area between the eyes and the gular suture. The epicranial suture is more distinct in some species than in others. Eyes. The eyes vary from slightly oblong oval to oblong ovate and are obliquely placed in the anterior angle of the epicranial area, just posterior to the base of the antennae. The variation in form within tlie genus and within the same species is shown in figures 1 to 6 and 15. There are about four hundred facets, which are small and densely placed. Occiput (figs. 4, 5). The occiput is not clearly defined, as it is in Pterostichus , but the posterior area of the cranium to the occipital foramen may be designated as the occipital region or area. Occipital foramen (fig. 5). The posterior opening in the head, or occipital foramen, is small as compared with the oral foramen. The invaginated wall forms a part and posterior support to the tentorium, and the dorsal apodeme is continuous with the epicranial suture. Gula. The gula is not represented by a space defined by two longitudinal sutures, as in most Coleoptera other than the Rhyn- chophora. The gular apodemes are present (fig. 5, D), but the gular space is invaginated, so that there is but a single gular suture. Pregula. In Dendroctonus there is a small sclerite immediately anterior to the gular suture (figs. 5, 6) which is distinctly separated from the gula and gense by an invaginated apodeme, laterally from the pregena by an evident exterr^al line, and anteriorly from the hypostoma by a ridge which defines the anterior margin. In the rostrate beetles this is extended with the pregena and forms a more or less distinct gular space of the rostrum to a similar anterior space which supports the so-called gular peduncle, or submentum. There- fore it appears that the term pregula should serve to distinguish this important element, which is also more or less distinctly represented in Coleoptera other than the Rhynchophora. (Compare figs. 6, 7, 8.) Gena. The gena is not defined by lines, but it is represented by the ventral area between the gular suture and the epicranial area, as described under epicranium and gular suture. Pregena (figs. 5, 6). The pregena is a distinct pleural area situ- ated between the base of the antennse and the pregula, bounded posteriorly by the genal area and anterior angle of the epicranium, and anteriorly by the hypostoma. Submentum (figs. 5, 6). The submentum is represented by a bifid process or median extension of the hypostoma, and is sup- ported by two stout braces rising from the large transverse rostral apodeme beneath the posterior angle of the pregula. THE GENUS DENDROCTOXUS. 19 Labium proper (fiL'- - A . In Demi rod on us and other rhyn- chophorous beetles, the mentum. palpifer. _ and paragL while more or less clearly indicated, are not represented as separate elements of the labium. Mcniuvt: The mentum articulates with the bifid submentum and completely surrounds the basal portion of the labrum. being subcylindrioal, with the anterior ventral area .illy ret use. Palpifrr: The palpifer is represented by the area between the ventral impression of the mentum and the row of palpiferal bristles winch define the anterior limit of the mentum. Palpi: The labial palpi are distinct, 3- jointed, and &s long as the mentum, or longer, with the first joint longer than the other two, or rarely equal. Ligula: The ligula ;ated between the palpi, is thickly set with long lacinial teeth, and occupies the greater part of the dorsal area. It is evident that this ligular area represents - :*? and paraglossa of other insects, and that it is homolo- - with the galea and lacinia of the first maxilla. J/axtfl#(iL: - B, C). The maxilla? (fig. 5, B) have the char- ist ic form of those of all other rhynchophorous beetles and are strikingly different from those of ot her Coleoptera . The form, and relative proportions are shown in the figures. Cardo: The cardo is the stout basal section which articulates with a condyle on FIG .^/)f *drortoL Epistomaia. to / ' D ' " l " pter p to *' D ' t he maxillary process of the hy- inal apodeme. Stipes: The stipes articulates with the cardo and, while it does not appear as a separate piece, it is represented by the posterior ventro-lateral and externo-lateral part of the median section of the maxilla. PaL golf a, subgalea, and lacinia: The palpifer is fused with the stipes and is represented by the anterior part of the median section (fig. 5). The palpifer and stipes are also fused with the subgalea on the exto-lateral area, but on the interno-lateral area the line separating the palpifer from the subgalea is distinct, as is also the suture be- n the latter and the lacinia and galea, which are fused, the latter being represented by a narrow chitinous margin next to the palpus and palpifer. The lacinia is armed on the inner edge with stout lacinial teeth. The length of the base of the subgalea from the apex 20 THE SCOLYTID BEETLES. to the posterior angle is usually greater than the length of the palpifer and stipes, but is sometimes equal and rarely shorter. The ventral FIG. ll.Dendroctonus: Antennae. 1, brevicomis; 3, convexifrons 9; 3a, convexifrons tf; 4,frontalis J 1 ; 5, arizonicus cf; 5a,arizonicus 9; 6 , mexicanus; 7 , parallelocollis; 8,approximatus 9. (Original.) Ia, posteriorface of club when antenna is extended at right angles to head, joints 1, 2, 3; 6, anterior face, joints 1, 2, 3, 4; d, funiculus, joints 1, 2, 3, 4, 5; c, scape. chitinous area of the palpifer and stipes together is always a third or more longer than the combined chitinous parts of the joints of FIG. 12, Dendroctonus: Antennse. 9, monticolse; 10, ponderosse; 12, simplex; 13, pseudotsugx 9 ; perda 9 ; 15, engelmanni; 17, obesus tf; 17a, obesus 9. (Original.) the palpi. Palpi: The palpi are 3-jointed ; the joints connected with each other and with the palpifer by flexible membrane which allows for a certain amount of telescoping, but not adapted for free THE GENUS DENDROCTONUS. 21 lateral movements as in Pterostichus (fig. 7). The relative lengths of the joints vary considerably in the species of the genus, and more or less in the individuals of a species. The first joint is usually longer than the other two together, but is sometimes equal or shorter; the second joint is usually longer than the third, but is sometimes shorter. Mandibles (figs. 4, 14). The mandibles are prominent, stout, triangular, and especially adapted for burrowing in the bark. The inner edges are acute, with a subapical and a median tooth toward the middle and a molar on the basal .angle. The lateral area toward the base has a large impression and there is usually a less evident one on the dorsal area, each bearing one or two bristles. The dorsal FIG. 13.Dendroctonu$: Antennae. 18, rufipennis; 20, punctatus; 21, micans; 22, terebrans; 23, valens J; 23a, valens 9; 23b, valens "Median apodeme PcstscuteUar process LQU etapleural hook. ScutcllutnF Poslplirngma FIG. 2l.Dendroctonus valens: Metatergum, inner aspect, a, Lateral arm of prephragma; 6, dorsal band; c, scapular articulation; d, posterior angle of prescutum; e, posterior arm of postphragma; /, pos- terior apodeme; g, anterior disk; h, posterior margin of scutellum; x, ventral wall of postscutellum. (Original.) with the anterior apodeme (fig. 21), thus defining a large median triangular area which is evidently scutellar. Postscutellum. The postscutellum is the exposed dorsal and lateral area between the clearly defined posterior suture and the line of attachment of the first abdominal tergite. It is firmly connected with the scutellum toward each side at a point near the base of the oblique apodeme of the middle suture, otherwise the connection is membranous. The anterior angles support the metapleural hooks (fig. 20, EjU), which fit into a fold in the dorsal margin of the postepi- merum (fig. 20, p). Postphragma. The postphragma is an invagination of the pos- terior section of the postscutellum and, with the produced posterior disks and arms, serves as important posterior attachments for the longitudinal, tergal, and oblique scutal muscles. 34 THE SCOLYTID BEETLES. METAPLEURA. The metapleurum is well developed and distinctly represented by the two longitudinal sclerites, episternum and epimerum (figs. 3, 20), with their anterior dorsal angles greatly produced to form the pleural clavicula with its clavicle and coracoidal processes. Pleural suture and apodeme. The pleural suture marks the line of division between the episternum and epimerum, and extends from the dorsal angle of the coxse to the apex of the pleural clavicula and between the clavicle and coracoidal process. That this is the true pleural suture is indicated by the corresponding prominent pleural apodeme. It is also quite evident that the episternum corresponds to the hypopleurites and the epimerum to the epipleurites of the abdominal segments (figs. 3, 22). Episternum. The episternum is exposed when the elytra are closed (fig. 2). The suture between it and the sternum is distinct and nearly straight, with the anterior end curved toward the coxa. The posterior ventral angle is oblique and joins the posterior dorsal angle of the sternum; from here the posterior margin is oblique to its acute junction with the epimerum and the dorsal angle of the coxal cavity. From here the dorsal margin is acutely elevated to fit into the anterior lateral groove of the elytron, and is nearly parallel with the ventral margin to the preepisternum. Preepisternum. The preepisternum appears to be represented by the narrow declivous anterior section of the episternum connected with the anterior basal area of the pleural clavicula and is apparently involved in the formation of the clavicle process. The clavicle disk evidently represents one or both of the paraptera of certain other insects and belongs to the prepleura. It is situated immediately anterior to the preepisternum. It is large, prominent, and partially exposed, and is connected by a chitinous tendon to the side of the clavicle process. This disk supports the set of large clavicular or sterno-pleural muscles, the opposite ends of which are attached to the sternum and sternellum. Epimerum. The epimerum is situated between the pleural suture and the tergum. With the exception of the extreme posterior ven- tral angle of the postepimerum it is covered by the elytra. The anterior dorsal angle is strongly produced to form the coracoid pro- cess. The ventral area is chitinous and is joined to the episternum by the pleural suture, while the dorsal area is submembranous tc membranous to its junction with the base of the wing membrane. Postepimerum. The posterior ventral angle and posterior lateral section represent the postepimerum, as is indicated by its articula- tory junction with the poststernellum (fig. 20, p). The posterior THE GENUS DENDROCTONUS. 35 ventral angle or ventral section of the postepimerum, which might be mistaken for a postepisternum, is indicated by the pleural apodeme and pleural suture w r hich here join the dorsal angle of the coxa. It is not impossible, however, that this plate may represent a combined postepisternum and postepimerum. METASTERNA. .e metasterna (figs. 2, 3) form a broad rectangular plate separated to two lateral sections by a median longitudinal line. The pre- sternum and poststernellum are not represented by external parts. ,-Spiracle I -Epipleuritel ~ Epipleurite 2 - -SpiracleS - Epipleurite 3 -Epipleurite 4 -J~*Spirack 5 Epipleurite 5 -/-- Spiracle Q ~ 'Epipleurite 6 ''^Spiracle 7 ^Epipleurite 7 Pygidium 'Stridulating scraper FIG. 22.Dendroctonus valens: Abdominal tergites. a, Anterior arm of epipleurite 7; 6, posterior arm of epipleurite 7; c, membranous lobes. (Original.) Sternum. The sternum is evidently represented by the large con- tinuous area between the mesocoxse and the small median plate and the slightly acclivous area anterior to the metacoxa. Sternellum. The sternellum is evidently represented by the pos- terior median plate and the posterior acclivous areas (fig. 2, a). The relation of the latter to the sterneilar area is indicated by the attach- ment of the posterior pair of clavicular muscles. THE ABDOMEN. The abdominal terga, pleura, and sterna, and their relative pro- portions, are shown in figures 1-3 and 22-25. 7998009 4 36 THE SCOLYTID BEETLES. ABDOMINAL TERGITES. The eight abdominal tergites are normally covered by the elytra. The apparent difference in the relative proportions, as indicated by figures 3 and 22, is due to the flexible intersegmental membrane and the fact that figure 20 is from a balsam mount. The integument of 1 to 6, inclusive, is more or less membranous, while that of 7 and 8, with the exception of the finely sulcate membranous lobes of 7, is chitinous. In the female, 8 is covered by 7, and forms the so-called FIG. 23. Dendroctonus valens: Male, abdominal tergites 7 and 8. A, Tergite 8 (pygidium), ventral; JB,same, dorsal; C, same, ventral, showing position of sternite 8; D, tergite 7 (propygidium), dorsal; E, same, ventral; a, anterior arm of epipleurite 7; 6, posterior arm of epipleurite 7; c, membranous lobe; d, epipleural process; e, hypopleural arm of sternite 8; /, pleural opening; g, anal space; h, ventral fold; i, rudimentary spiracle 8; j, epipleural disk; k, apical spine; I, stridulating process; m, sensory bristles; n, enlarged section of lateral area; o, enlarged section of membranous lobe; p, stridulating scraper. (Original.) "pygidium," while in the male 8 is distinct and together with 7 forms the so-called "divided pygidium." Pygal tergites of the male. The pygal tergites of the male are shown in figure 23, A, B, C, D, E. Tergite 7 is the propygidium and as a bearer of generic and sexual characters is the most important of the entire series. In the male the posterior margins between the epi- pleurites converge toward the apex, which is produced into a bifid process and supports the stridulating scrapers. The posterior area of the tergite is thickened and strengthened to meet the requirements of stridulation. There is a broad ventral fold (fig. 23 E, 7i) of the integument which may serve a similar function to that of a sounding board. THE GENUS DENDROCTONUS. 37 The median area is triangular in form and covered with bristles and hairs rising from variously formed bases. On its face and some- times on the posterior area there are a few irregularly arranged truncate tubercles (Z), m), each bearing a short, stiff bristle. These may possibly function as sense organs. The membranous lobes are subovate, finely sulcate, and thickly clothed with reclining microscopic spines (o). The exact function of these lobes is not known to the writer. Tergites 4, 5, and 6 have similar lobes. The other dorsal and ventral characters are made sufficiently clear in D and E. FIG. 24,Dendroctonus valens: Female, abdominal tergites 7 and 8. c, Anterior arm of epipleurite 7; 6, membranous area surrounding spiracle; c, membranous lobe; d, epipleural process; e, hypopleural process of steraite 8; /, pleural opening; g, anal space; h, ventral fold; i, rudimentary spiracle; j, epipleural disk; k, median membranous connection of the lateral sections of sternite 8. (Original.) Tergite 8 (A, B) is the pygidium. This, in the male, is always larger and more exposed beyond the margin of tergite 7 than in the female. The relative proportions, as compared with 7, and the dorsal and ventral characters are clearly shown in A and B. The lateral arms serve as attachments for pleural muscles and articulating mem- brane and ligaments. In C the abdominal sternite is added to show its relative position and proportions. Py gal tergites of the female. The pygal tergites of the female are shown in figure 24, A, B, C, D, E, F. Tergite 7 (propygidium) is much more simple in structural details in the female than in the male, and tergite 8 (pygidium) is also more simple and shorter, being almost or entirely covered by 7 when in normal position. The characters of sternite 8 are shown in D t the most important of which is the median membranous area. 38 THE SCOLYTID BEETLES. ABDOMINAL PLEURITES. At the lateral ends of the abdominal tergites and sternites there are well-defined areas (figs. 3, 22, 25), which may be designated as pleurites. Those situated immediately above the pleural suture and bearing the spiracles may be referred to as epipleurites, while those of the sternites which are immediately below the pleural suture may be designated as hypopleurites; both series are well defined in Dendroctonus. In a lateral view (fig. 3) seven epipleurites and five hypopleurites are clearly defined, with the eighth epipleurite and the second hypo- pleurite indicated, and when the abdomen is removed both the first and second of the latter series are quite distinct. Ilypopleurites . ^ Coxal cavitu Inlercoxal process FIG. 25. Dendroctonus valens: Abdominal sternites, ventral and lateral aspects. A , Lateral; B, ventral; a, sternite 1 , faintly indicated; 6, sternite g, faintly indicated. (Original.) ABDOMINAL STERNITES. The characters of the abdominal sternites are shown in figures 2, 3, and 25. There are eight, corresponding to the eight tergites, but only five are exposed, viz, 3 to 7, which are densely chitinized and clearly defined by four sutures. Sternites 1 and 2 and the anterior portion of 3 are covered and obscured by the large metacoxa and form the posterior wall of the coxal cavity. They are fused, but the sutures are indicated by faint lines. Sternite 3 (first ventral segment of some writers) has the median area produced anteriorly, and with faintly indicated median portions of sternites 2 and 1 it forms the intercoxal process, the apex of which forms a junction with the metasternellar piece. The anterior exposed margin forms the posterior margin of the coxal cavity, but the junction with the preceding segment is but faintly THE GENUS DENDROCTONUS. 39 indicated in the wall of the coxal cavity. Sternites 4, 5, and 6 are nearly of equal length, while sternite 7 is nearly as long as 5 and 6 together, with the posterior margin broadly curved and forming the apex of the exposed series. Sternite 8 (figs. 23, C, and 24, D) is entirely covered by 7, and is represented in the male by a narrow chitinous rim below the anal opening, while in the female the median section of this sternite is membranous. Suture 3, between sternites 3 and 4, is the first visible suture, and is rigid and straight throughout, while sutures 4, 5, and 6 are slightly flexible and are strongly recurved toward and between the hypo- pleurites, thus presenting an important generic character. SPIRACLES. There are 9 well-developed spiracles, 2 thoracic and 7 abdominal, with the rudiments of a tenth. The large mesothoracic spiracle is located in the intersegmental membrane between the prothorax and mesothorax, and lies between the preepisternal process and the anterior ventral angle of the preepisternum. It overlaps the anterior margin of the latter for half its length, but is completely covered and obscured by the epimeral area of the prothorax. The metathoracic spiracle is situated in the intersegmental membrane between the metathorax and mesothorax, and concealed beneath the dorsal margin of the mesepimerum. The abdominal spiracles 1-7 are con- spicuous; 1 is very large and situated in the epipleurite just posterior to the pleural hook of the metapostscutellum; 2-7 are situated in their respective epipleurites, as shown in figures 3, 22, 23, and 24, while 8 is evident, but rudimentary. THE LEGS. The structures and characters of the parts of the legs are so well illustrated in the figures (figs. 3, 26-29) that they do not require detailed description. The procoxae and mesocoxae are large, globose, and prominent, the former subcoritiguous and the latter widely separated by the elevated intercoxal or sternellar piece, while the metacoxae are oblong, oval, and separated by the process of the third abdominal sternite. There is no striking difference in the anterior, middle, and posterior trochanters, femora, tibiae, and tarsi. The trochanters are small; the femora are moderately stout, and each is as long as its tibia, which is dilated toward the apex and armed on its outer lateral margin with stout teeth. The anterior dorsal area has a distinct tarsal groove for the retractile tarsus, as shown in figures 26 to 29. The tarsi are each more than half as long as their tibiae, and have five joints; joint 1 is always longer than 2, but never as long as 2 and 3 together; 3 is distinctly bilobed, the 40 THE SCOLYTID BEETLES. lobes slightly longer than joint 4; joint 5 from tip of lobes of 3 is never as long as the others (1 to 3) together, but sometimes shorter than 1 and rarely equal to 2 and 3. In the males this joint is often longer than in the female. The trochlear articulation of the tibia with the tarsus is shown in figure 26, in which the other more import ant char- acters are shown and named. THE WINGS. Notwithstanding the vast amount of published data on the wings of insects, there is yet much difference of opinion among the leading authors in regard to some of the details, and much confusion exists, due to different interpretations of the homologies of the ele- ments of the wing and its articulatory accessories. A detailed investigation has been made of the basal areas of the wings of rep- resent atives of different orders of insects, to deter- mine facts relating to the fundamental plan of devel- opment and modification, and the system of orgaiii- zation of the elements as represented in Dendroc- tonus. Nomenclature. W h i 1 e FIG. 2Q.Dendroctonus valens: Tibia and tarsus, articulation, etc. A, 4-44. tibia, ventral view; B, teff tibia, dorsal view; femora, ental view; D, iatftibia, dextral view of base; E, tdft tibia, sinistral view of base; F, tarsus; a, apical tooth; 6, subapical tooth; c, tarsal groove; d, subapical ridge; e, marginal teeth; /, ciuii'ti^4 margin; g, deKtooi margin; h, median fossa; i, lateral condyle of tibia; j, anterior fossa; k, lateral condyj ties it has not been sufficient to warrant a detailed discussion in this connection. 7998009 5 52 THE SCOLYTID BEETLES. DIGESTIVE SYSTEM. The general character of the digestive system is shown in figure 35, and no further explanation is necessary in this connection than that given in the legend under figures 35 and 36. In figure 36 some of the details of the internal anatomy of the fore intestine are shown, and especially the structures and elements of the proventriculus and hypopharynx. , SECONDARY SEXUAL CHARAC- TERS. While there are certain clearly defined secondary sexual characters in these beetles, they have not been recognized by other writers, and they were not found by the present writer until after much detailed study of the genus. When they were determined it was surprising how such prominent characters could have been overlooked. Thus we have another example of how thoroughly familiar one must be with a given group in order to rec- ognize and properly interpret the significance of characters in struc- ture, sculpture, vestiture, etc. In the first subdivision of the genus the females are distinguished by at transverse ridge across the anterior area of the pronotum, while the ; males are distinguished by the ab- sence of this ridge and by more prominent frontal tubercles which are separated by a deeper frontal; groove. In the second subdivision the females are distinguished by thei smoother and more shining ely tral I declivity. In the third subdivision the females have the elytral declivity distinctly more rugose, while that of the males is smooth and shining. Thus we have a reversal of the secondary sexual characters within the same genus, which is an unusual occurrence. Rectum FIG. 35.Dendroctonus valens: Digestive organs of adult. A, Fore intestine; B, mid intestine; C, hind intestine; a, anterior section of mid in- testine; b, median section of mid intestine; c, posterior section of mid intestine; d, coacal glands; e, ileum or small intestine; /, base of 4 malpighian tubes; g, base of 2malpighian tubes. (Original.) THE GENUS DENDROCTOX I'S. 53 In the fourth subdivision the sexes are more difficult to recognize, but the males are distinguished by stouter, more opaque mandibles, broader front, and by a narrower and more elongate antennal club. Whenever there is doubt as to the sex of an individual it can be settled by examining the pygal segments for the characters shown in figures 2:5 and 24. Fi<;. W.Dtndroctonus valens: Fore intestine, showing details. A, Fore intestine; B, transverse section ofproventriculus; C, longitudinal section of same; D, single plate; E, teeth; F, plates; O, hypopharynx; o, muscles; b, proventricular teeth; c, posterior condyle of mandibular articulation; d, median fossa of same; e, anterior condyle of same; /, hypopharyngealbracon; g, anterior margin; h, hypopharyngeal papilli. (Original.) PUPA. The general structure, proportions, and anatomical details of the Dendroctonus pupa are shown in figures 37 and 38. Among the distinctive generic characters are the large prominent head and broad pronotum, while among the divisional and specific characters are the sculpture, armatures, etc., of the head, pronotum, elytra, and abdominal segments, as shown in the figures and defined in the synoptic tables and descriptions. 54 THE SCOLYTID BEETLES. Head. The elements of the adult head recognizable in the young pupa are the antennae, mandibles, maxillae, labium, and what appears to be a well-developed labrum, which extends to the middle of the man- dibles. Evidently, however, this does not represent the labrum or even the clypeus, but is a pad to accommodate the development of the long epistomal bristles. The frontal spines in examples repre- senting different divisions and species are variable in size and position and are of considerable taxonomic importance. The antennae do not extend to the base of the pronotum or scarcely beyond the mouth parts, and the club does not extend beyond the lateral margins of the pronotum. TIIK GENUS DENDROCTONUS. 55 J'rotln>r