A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae)

Abstract The Nearctic bark beetle genus Scolytus Geoffroy was revised based in part on a molecular and morphological phylogeny. Monophyly of the native species was tested using mitochondrial (COI) and nuclear (28S, CAD, ArgK) genes and 43 morphological characters in parsimony and Bayesian phylogenetic analyses. Parsimony analyses of molecular and combined datasets provided mixed results while Bayesian analysis recovered most nodes with posterior probabilities >90%. Native hardwood- and conifer-feeding Scolytus species were recovered as paraphyletic. Native Nearctic species were recovered as paraphyletic with hardwood-feeding species sister to Palearctic hardwood-feeding species rather than to native conifer-feeding species. The Nearctic conifer-feeding species were monophyletic. Twenty-five species were recognized. Four new synonyms were discovered: Scolytus praeceps LeConte, 1868 (= Scolytus abietis Blackman, 1934; = Scolytus opacus Blackman, 1934), Scolytus reflexus Blackman, 1934 (= Scolytus virgatus Bright, 1972; = Scolytus wickhami Blackman, 1934). Two species were reinstated: Scolytus fiskei Blackman, 1934 and Scolytus silvaticus Bright, 1972. A diagnosis, description, distribution, host records and images were provided for each species and a key is presented to all species.


Introduction
This monograph presents a revision of the Nearctic Scolytus Geoffroy, 1762 species (Curculionidae: Scolytinae). The Scolytinae is comprised of approximately 6,000 species in 225 genera and 26 tribes (Alonso-Zarazaga and Lyal 2009). Termed 'bark and ambrosia beetles' this weevil subfamily is ubiquitous in forests worldwide. Many species contribute to the decomposition of dead vegetation while others are capable of causing substantial host mortality. True bark beetles, including Scolytus, feed exclusively on phloem and cambium of living, declining, or dead trees and some species specialize on different plant parts from root to fruit and pith (Wood 1982). Beetle feeding on phloem and xylem hastens the decomposition of trees and the introduction of other xylophagous organisms (Stokland 2012). Some bark beetle species kill live trees by passively introducing fungi into otherwise healthy hosts as a by-product of phloem feeding and the galleries may girdle the host causing mortality (Wood 1982). At high density these species cause widespread destruction of economically valuable tree species, giving bark beetles their nefarious reputation as ecologically and economically destructive forest pests (Furniss and Carolin 1977). Other economically important bark beetle genera such as Dendroctonus Erichson, 1836 and Ips DeGeer, 1775 have received considerable attention and therefore have a reasonably solid understanding of the taxonomy (Wood and Bright 1992). Scolytus is also important but has received considerably less attention.

Natural history
Scolytus are distributed in the Holarctic, Oriental (Himalayan) and Neotropical regions and some Palearctic Scolytus species have been introduced around the world to the Nearctic, South Africa, Australia, New Zealand and temperate South America (Rosel and French 1975;Bain 1990;Wood and Bright 1992;Six et al. 2005;Wood 2007;Smith and Cognato 2013). In the Nearctic region, Scolytus species occur from the Atlantic to Pacific oceans and from the boundary of the Neotropical region to the northern limits of tree growth. In the Nearctic, native hardwood-feeders are generally found from the Atlantic coast to Texas and west to the foothills of the Rocky Mountains. With the exception of S. piceae (Swaine, 1910), conifer-feeding Scolytus are restricted to the occurrence of host trees in western mountain ranges including the Rocky Mountains. Scolytus piceae has an expansive range from the east and west coasts of North America and from northern California and Colorado north to beyond the Arctic Circle. Invasive Scolytus species are found throughout the US, northern Mexico and southern Canada (S. mali (Bechstein, 1805), S. multistriatus (Marsham, 1802), S. rugulosus (Müller, 1818), and S. schevyrewi Semenov, 1902).
In the Nearctic region, six Scolytus species have the potential to kill host trees and cause significant mortality of either conifers (Cibrián Tovar et al. 1995) or Carya spp. (Furniss and Carolin 1977). Two of these are the exotic S. multistriatus and S. schevyrewi, both are key vectors of the Dutch elm disease fungi, pathogens that have killed millions of Ulmus L. spp. trees in forest and urban areas across much of the US (Furniss and Carolin 1977). Mortality caused by various Scolytus species is often sporadic and short-term, although some outbreaks locally affect thousands of acres a year (Furniss and Carolin 1977). Damage is most severe in times of environmental stress, which is  (Furniss and Carolin 1977). All Nearctic Scolytus species are monogamous. Females select brood material and begin galley construction. Males walk across the host material in search of females. Mating occurs with the female in the entrance tunnel and the male on the bark. However, mating in twig crotches has been reported for S. multistriatus (Svihra and Clark 1980). The female creates an entrance tunnel at a 45° angle, boring through the bark to the cambium. From the entrance tunnel, she excavates a nuptial chamber and, depending on the species, one or two egg galleries in either direction from the entrance tunnel. The nuptial chamber and galleries are excavated in the cambium but also etch the sapwood. Females excavate egg niches on both sides of the egg galleries and a single egg is deposited in each niche and covered with boring dust. Adult males assist in removing frass and generally stay with the female until egg gallery construction is complete. The male then leaves the gallery and the female dies in the entrance tunnel with her abdomen projecting onto the bark surface. Larval galleries radiate away from the egg tunnels as they feed on phloem, also etching the sapwood. Once larvae mature, the prepupae burrow into the outer sapwood and pupate. The brood overwinters as pupae and adults emerge in the spring (Edson 1967). Upon emergence, S. mali, S. multist- riatus, S. quadrispinosus, S. rugulosus, and S. schevyrewi engage in maturation feeding at twig crotches and/or leaf petioles (Hoffman 1942;Baker 1972;Negrón et al. 2005). Feeding may also occur within small twigs in S. fiskei Blackman, 1934(reported as S. unispinosus LeConte, 1876in McMullen and Atkins 1962. Gallery shape is directly related to the resin system of the host genus. Larix, Picea and Pseudotsuga possess an elaborate system of resin ducts with vertical and radial ducts that are connected to each other (Lieutier 2004). Scolytus galleries in these genera are consistently parallel to the grain of the wood. The vertical ducts are abundant in these tree genera and when Scolytus constructs a vertical egg gallery, both ducts are severed, and as the gallery is elongated, only vertical canals are severed. This minimizes exposure of Scolytus to host resins (Lieutier 2004). Abies and Tsuga lack resin canals and instead possess resin blisters. Galleries in these genera are quite variable and may be transverse, "V" or ("ε") shaped depending on the species because there are no resin canals to avoid (Lieutier 2004).
Conifer-feeding Scolytus species exhibit primary attraction to host volatiles rather than to pheromones produced by conspecifics (Macías-Sámano et al. 1998a). Attraction of hardwood-feeding species is not well understood but primary attraction seems probable for native S. quadrispinosus and the invasive species S. rugulosus and S. schevyrewi (Goeden and Norris 1964a;Kovach and Gorsuch 1985;Lee et al. 2010). Scolytus multistriatus exhibits secondary attraction and to 4-methyl-3-heptanol and multistriatin in combination with alpha-cubenene (Lanier et al. 1977). At endemic population levels, Scolytus infest over mature, unthrifty or weakened standing trees, shaded out branches, recent logging slash, windthrown trees and fallen branches. During outbreaks, vigorous trees may be colonized by more aggressive species, including S. quadrispinosus, S. mundus Wood, 1968and S. ventralis LeConte, 1868(Edson 1967Furniss and Carolin 1977), and the secondary species S. monticolae (Swaine, 1917), S. reflexus Blackman, 1934 [reported as S. monticolae] and S. unispinosus LeConte, 1876 (McMullen andAtkins 1959;USDA 2004). While Scolytus species are generally common in the forest, they are rarely abundant and seldom encountered by collectors. Scolytus species prefer fresh and moist host material. Sun-baked material is not preferred, but Scolytus galleries may be present in cooler, moister areas of the bark that are heavily shaded or on the underside of fallen trees and branches. Infested conifer branches and trees typically bear green needles while infested hardwoods have yellowing leaves (Smith, pers. obs.). The entrance can be identified by peeling off the bark flakes with a knife and searching for white to tan-colored boring dust or by close examination of the lateral and ventral sides of trunks and branches of smooth barked hosts. In Pseudotsuga, the entrance tunnels of Pseudohylesinus Swaine, 1917 can be easily confused with those of Scolytus, but Scolytus entrance tunnels are at a steeper angle and the boring dust is reddish rather than white. Some Scolytus species, including S. piceae, S. monticolae and S. subscaber LeConte, 1876 typically attack shaded out branches on standing trees. Yellowing needles are indicative of an infested tree. Scolytus females typically conceal their entrance tunnels under bark flakes (common in Picea, Pseudotsuga, Tsuga) or in rough patches of bark (Abies, Larix).

Sexual dimorphism
Scolytus species are sexually dimorphic. Sexually dimorphic structures are typically on the frons and epistoma (Fig. 1) and the abdominal ventrites and vary by clade (see clade discussions in results). When viewed laterally, males typically have a flattened, impressed frons and the female frons is always more strongly convex. The male frons is more strongly and coarsely longitudinally aciculate than the female and covered with longer, more abundant and dense erect setae. The epistomal process (when present) is more strongly developed in the male and less developed in the female. With the exception of S. piceae, the spines, tubercles, denticles, carinae and tumescence on the venter are more pronounced in males.
A single apical, unarmed spine-like process that curves toward and extends beyond the process of the inner apical angle of the protibia and by a seven-segmented funicle readily distinguishes the tribe. All display a strongly sexually dimorphic head bearing hair-like setae, with the male frons variously excavated and female frons typically flat to convex. The eye is entire and the posterior area of head is subtruncate. The pronotum is unarmed with a costate lateral margin. In addition, the metapleural suture descends subventrally to the groove, receiving the groove on the costal margin of the elytra, then turns abruptly and parallels the groove near the metacoxal process (Wood 1972(Wood , 1978(Wood , 1982(Wood , 1986. Scolytus is perhaps one of the easiest bark beetle genera to recognize with its distinctive ascendant second abdominal ventrite, the slightly if at all declivous elytra and the depressed basal area of the elytra around the triangular scutellum (Wood 1982).

Taxonomic history
There are currently about 127 recognized Scolytus species in the world (Wood and Bright 1992;Wood 2007;Knížek 2011;Petrov 2013;Smith and Cognato 2013). Twenty-five species occur in the Nearctic region, including four invasive Palearctic species. Several Nearctic Scolytus species were described as the North American continent was explored. General entomologists including Say (1824), Riley (1867) and Walsh (1867) first described the eastern hardwood-feeders. LeConte (1868, 1876) described the most common California species and species native to the interior mountain ranges. The prominent scolytine taxonomists Swaine (1910Swaine ( , 1917, Blackman (1934), Wood (1962Wood ( , 1967Wood ( , 1968 and Bright (1964Bright ( , 1972) also described several Scolytus species. Scolytus californicus LeConte (1868) was described from "California" but Blackman (1934) deemed this species a synonym of S. scolytus (Fabricius, 1775). Blackman also suggested that the specimen given to LeConte might have been incorrectly labeled with the 'California' locality. This species has been intercepted to the United States on numerous occasions but has never become established (Blackman 1934;Wood 1982). Scolytus scolytus was therefore excluded from this monograph. Blackman (1934) and China (1962China ( , 1963 provide a detailed account of the taxonomic history of Scolytus and outline the Scolytus/Eccoptogaster Herbst, 1793 controversy, which occurred from the late 1800's to the early 1900's that resulted from intense debate on whether Geoffroy's (1762) descrip-tion was valid. China (1962China ( , 1963 outlines the International Commission on Zoological Nomenclature ruling that preserved the name Scolytus over Eccoptogaster. Historically, there has been a great deal of uncertainty regarding the status of several Scolytus species, particularly: S. monticolae and S. tsugae (Swaine, 1917); S. abietis Blackman, 1934 andS. opacus Blackman, 1934;S. reflexus and S. wickhami Blackman, 1934;S. fiskei Blackman, 1934 andS. unispinosus. Blackman (1934) and Wood (1982) formally revised the Nearctic Scolytus. A third revision by Edson (1967) was a M.S. thesis but was never published. Wood (1982) synonymized several species described by Blackman including S. abietis, S. wickhami and S. fiskei. However, Edson (1967) recognized these species based on morphological, ecological and geographical differences. One of these species, S. abietis Blackman, was recently removed from synonymy because of such differences (Equihua-Martínez and Furniss 2009). Scolytus species are generally recognized based on differences in male morphology, specifically shape of the venter concavity or lack thereof, ascending angle and protrusion of the basal margin of the second abdominal ventrite, the placement and shape of the spine or lack thereof on the second ventrite, the presence or absence of a spine on the margin of ventrite 2 and 3 and frons aciculation and vestiture. Differences among species are generally subtle and substantial knowledge of the intraspecific variation is needed for accurate identifications. In addition, there is a paucity of diagnostic morphological characters for females; to date diagnostic characters are known only for females of hardwood-feeding species (Smith and Cognato 2010a). Association with a male or comparison to previously identified specimens is needed to determine the species of female specimens of conifer-feeders. Previous keys (LeConte 1876;Swaine 1918;Blackman 1934;Chamberlin 1939Chamberlin , 1958Edson 1967;Bright and Stark 1973;Bright 1976;Wood 1982;Furniss and Johnson 2002) did not address the above deficiencies in species identification. In addition, previous authors were not explicit about their species concepts, raising doubts about species boundaries.
Unlike previous investigations (Blackman 1934;Edson 1967;Bright 1976;Wood 1982), this study incorporates molecular and morphological data in phylogenetic analyses, which provides a basis for assessing species boundaries. This is the first modern taxonomic treatment of any group of Scolytus species and will serve as the basis from which the rest of the genus will be revised. This regional monograph of the Nearctic Scolytus species provides a review of taxonomic characters, an assessment of their phylogenetic utility, an evaluation of intraspecific variation for each species, a key to both sexes and fully illustrates each species and diagnostic characters. We recognize 25 Nearctic Scolytus species.

Morphology
This revision is based upon examination of 4,996 adult ingroup specimens and 447 outgroup specimens. Specimens were obtained from field collecting events, reared from host material, or borrowed from North American and European collections. Palearctic species Scolytus intricatus (Ratzeburg, 1837), S. laevis Chapuis, 1869, S. mali, S. multistriatus, S. pygmaeus (Fabricius, 1787), S. ratzeburgii E.W. Janson, 1856, S. rugulosus, S. schevyrewi, S. scolytus, S. sinopiceus Tsai, 1962and S. sulcifrons Rey, 1892 were selected as outgroups. Scolytus propinquus Blandford, 1896, a Neotropical species, was selected as the root taxon. These outgroup taxa were chosen based on the results of a large Scolytini phylogenetic analysis (Smith et al. in prep.) which found Neotropical Scolytus sister to Holarctic Scolytus. The following entomological collection abbreviations (most following Arnett et al. 1993) are referenced in the text. Names of the curators that prepared loans are listed in parentheses. ture terminology followed Torre-Bueno (1989). Several highly informative recently described Scolytini characters were also scored (Smith and Cognato 2010b). Provisional morphological homology was assessed by similarity and relative positions of characters.
Characters were scored from both sexes unless otherwise noted. Scolytus exhibits strong sexual dimorphism of the frons and abdominal venter; males display a wide array of morphological features, particularly on the venter, whereas females are more morphologically conserved. Consequently, characters were predominately male based. Male genitalia was found to be autapomorphic or extremely conserved in structure and thus characters were not scored. Characters and character state numbers correspond to data coded in the morphological data matrix for each taxon. The character matrix (Table 3) was constructed and edited using the online database MX (Yoder et al. 2006). Character transformations were evaluated using MacClade 4.0 PPC (Maddison and Maddison 2000) and homology of characters and definitions of characters states were re-examined and modified if necessary.
Forty-three characters were used in this study (19 binary and 24 multistate). Ten morphological characters were coded from the head, two from the thorax, ten from the elytra, one from the metepimeron, and 17 from the venter. Three ecological characters were also coded. Consistency and retention index values from the morphological phylogeny ( Fig. 2) and generated from MacClade are listed next to each character. Characters and states were scored as follows:

Taxa, DNA sequences and alignment
We included 83 specimens (Table 4) representing 32 Scolytus species to reconstruct phylogenies using DNA sequences from mitochondrial and nuclear genes and morphology. The same Palearctic outgroup species used in the morphological analyses were included in the molecular dataset. As many Nearctic species as possible were included in the analysis. We were unable to collect fresh material for S. dentatus, S. hermosus, S. mundus and S. silvaticus, which were therefore excluded from the molecular analyses. Sequences of S. intricatus and S. scolytus were obtained from GenBank and included in the analyses. To assess mitochondrial cytochrome oxidase I (COI) intraspecific variation, we included 89 specimens (Table 4) representing 30 Scolytus species from as many populations as possible. Specimens were included in the four-gene phylogeny only if sequences were available for at least two genes. DNA was extracted from freshly collected specimens preserved in 200 proof ethanol and from pinned specimens killed in sawdust impregnated with ethyl acetate and immediately pinned. Specimens were dissected by removing the head and thorax from the abdomen. DNA extractions were performed on the head and thorax using a Qiagen DNEasy blood and tissue kit (Hilden, Germany) following manufacturer protocols except for the DNA elution procedure, which consisted of a single elution of 100-200 µl of buffer AE depending on the size of the specimen, with specimens measuring less than 5.0 mm in length receiving 100 µl and those greater than 5.0 mm in length receiving 200 µl. After the extraction process was completed, the body parts were rinsed in 70% ethanol, glued onto a mounting board, pinned, labeled and were vouchered in the MSUC. The resulting puri-  fied DNA was used to amplify partial gene regions of COI, D2 region of nuclear ribosomal 28S, CAD, and Argenine Kinase (ArgK) using the PCR primers listed in Table 5. The COI barcoding primers LCO 1490 and HCO 2198 did not consistently amplify scolytine COI sequences, which necessitated the construction of the degenerate scolytine specific primers, 1495b and rev750. These primers worked best for Scolytus specimens and have proven to be effective on a broad array of scolytine taxa (Cognato et al. unpublished). The 1495b and rev750 primers were used to create the Scolytus specific F215 and Rev453 primers, respectively for 5-20 years or older pinned specimens. All PCR cocktails consisted of a total volume of 25 µl and included 14.  Table 5 for specific annealing temperatures), 1 min at 72 °C and a final elongation cycle of 5 min at 72 °C. PCR products were cleaned using ExoSAP-IT (USB Corp., Cleveland, OH, USA) and following the manufacturer protocols. Cleaned PCR products were then prepared for sequencing. Each reaction contained 3.5 µl of cleaned PCR product, 1 µl 33 pM/µl sequencing primers (identical to those used in PCR), and 7.5 µl of ddH 2 O. Samples were sequenced in the Michigan State University Research Technology Support Facility using a Big-Dye Terminator v 1.1 (Applied Biosystems, Foster City, CA, USA) and visualized using an ABI 3730 Genetic Analyzer (Applied Biosystems).
Sequences were received as chromatograms and the sense and antisense strands were compiled using Sequencher (Ann Arbor, MI) to trim sequences, examine for ambiguities and create consensus sequences. Sequences were blasted in GenBank to examine for paralogous copies and other potential problems including contamination and pseudogenes. Sequences for COI, CAD and ArgK were aligned using SE-AL v.2.0a11 Carbon (http://tree.bio.ed.ac.uk/software/seal/). Sequence length variation was only observed in 28S. Sequences of 28S were manually aligned in SE-AL using a scolytine-specific secondary structure model (Jordal et al. 2008). Nexus files are available at http://www.scolytid.msu.edu.

Species concept
Species are hypotheses of unique evolutionary entities, tested by monophyly (sensu Wheeler and Platnick 2000). These monophyletic groups of individuals were named if they were diagnosable by synapomorphies or a unique combination of homoplastic characters. If diagnostic characters were not found, the clade retained the original spe-cies name or was synonymized with the sister clade. Therefore, given our species level morphological and molecular phylogenies, species revisions were based on monophyly of multiple individuals from disjunct populations.

Morphology
Parsimony phylogenetic analysis. A phylogeny was reconstructed using the criterion of parsimony implemented in PAUP*4.0 b10 PPC (Swofford 2002). A heuristic search with 1,000 stepwise random additions with tree bisection-reconnection (TBR) for 37 taxa (25 ingroup, 12 outgroup) was performed. Characters were unordered and equally weighted. Bootstrap values were calculated by performing 1,000 pseudoreplicates with simple additions in PAUP*. Bremer support values were calculated by creating a constraint tree in TreeRot v.2 (Sorenson 1999) and analyzed in PAUP* using a heuristic search with 100 addition-sequence replicates.

Molecular
Likelihood phylogenetic analyses. We analyzed the molecular and morphological datasets using Bayesian estimation of phylogeny with MrBayes 3.2.2 (Ronquist et al. 2012) on the CIPRES Science Gateway (Schwartz 2010). The Bayesian analysis consisted of a combined molecular and morphological dataset (82 taxa). The dataset was divided into 11 partitions by gene and codon position for COI, CAD and ArgK, and one partition each for 28s and morphology. We selected the best model for each data partition using MrModeltest (Nylander 2004). The GTR+I+Γ (general time reversible with a proportion of invariant sites and a gamma-shaped distribution of rate variation across sites) model selected by AIC was found to have the optimal fit for the gene partitions and Γ (gamma) was chosen for the morphology partition. Taxa that were unable to be sequenced were included in the morphology partition of the combined dataset.
Four Metropolis-Coupled Markov Chain Monte Carlo searches (3 heated, 1 cold) were performed for 10 million generations with sampling as described for the molecular dataset. Scolytus dentatus, S. hermosus, S. mundus, and S. silvaticus were included in this analysis with only morphological characters. All parameters reached stability at 500,000 generations and the standard deviation of split frequencies between runs was 0.006983. Bayesian posterior probabilities of clades were calculated by a majority-rule consensus of those trees after the burn-in (75,000 trees).
Parsimony phylogenetic analysis. Intraspecific (Table 6) and interspecific (Table 7) differences for 83 taxa were generated by computing pairwise distances for each gene in PAUP*. A single gene phylogeny was reconstructed using COI using a heuristic search with 100 stepwise random additions with TBR for 89 taxa (79 ingroup, 10 outgroup). Bootstrap values were calculated by performing 1,000 pseudoreplicates with simple Table 6. Intraspecific differences among genes expressed as the proportion of sites differing between sequences.  Table 7. Interspecific differences among genes expressed as the proportion of sites differing among sister taxa. Bremer support values were calculated by creating a constraint tree in TreeRot v.2 and analyzed in PAUP* using a heuristic search with 100 additionsequence replicates.

Distribution mapping
Distribution maps were created in ArcMap (RockWare; Golden, Colorado, USA) by Thomas Atkinson (University of Texas) and are a combination of specimens examined as part of this study (black) and reported material examined by Atkinson and records gleaned from literature (white). A database of Atkinson's localities is available at www. barkbeetles.info.

Terminology
There are some traditionally used terms and characters in Scolytus literature that require clarification. The term 'venter' is regularly utilized. In general, the term refers to the entire ventral surface of an organism. However in Scolytus it only pertains to the abdominal ventral concavity, specifically ventrites 2-5. The length of ventrite 5 compared to ventrite 3 and 4 is another common misleading character in Scolytus literature. Rather than measuring the entire length of segment 5, only the distance from the basal margin to the subapical carinate ridge is measured and compared to the combined lengths of ventrites 3 and 4. The following Glossary (modified from Hopkins 1909;Torre-Bueno 1989;Edson 1967;Harris 1979) summarizes the meanings ascribed to some terms used in this monograph:

General
Apical: referring to a point at or close to the apex or tip. Basal: referring to a point at or closest to the main body. Impressed: a depression in a surface, typically referring the elytral striae or frons. Concave: appearing hollowed out. Convex: appearing rounded. Vestiture: the surface covering composed of setae. In Scolytus the setae are either long or short.

Head (Fig. 3)
Aciculate: referring to longitudinal groves or scratches on the frons that can appear coarse as if made by a knife or fine as if lightly scratched with a needle. Epistomal process: a raised, sinuate process composed of a median and two lateral sections apically fringed with thick, long bristles that cover the median epistomal area just above the mandibles.
Frons: region of the head from just above the epistoma to a point that is just dorsal to the inner apices of the eyes. Inner apices of eyes: the innermost mesal margins of the eyes as viewed frontally. Strigate: having narrow, transverse lines in the cuticle. Vertex: the top of the head, above the eyes.

Elytra (Figs 4-5)
Apex: end of a structure that is distal to the base. Disc: the central upper surface of the elytra between the elytral bases and the sloped declivity. Striae: punctures in rows, which may or may not be impressed to make grooves. Interstriae: longitudinal spaces along the elytra between the striae, which is not as impressed and bear smaller punctures. Corrugated: with alternate ridges and channels, referring to the appearance of the elytral striae and interstriae. Sutural dehiscence: the central notch at the apical margin of the elytra.

Abdomen (Fig. 6)
Carina: a ridge-like or keel-shaped projection of the exoskeleton. Cusp: a slight projection or elevation along a margin; refers to the apical margin of ventrite 1 in a few species. Denticle: a small tooth. Opaque: appearing dull in luster; referring to a surface that reflects little light. Produced: refers to a part of the exoskeleton that is extended, lengthened, or elevated. Punctate: set with fine impressed points appearing as pinpricks. Punctulate: minute punctures. Rugose: appearing wrinkled. Shagreened: covered with a closely set roughness and appearing similar to sharkskin. Shiny: appearing glossy or bright in luster; refers to a surface that appears polished and reflects light well.    Spine: an elongate projection of the exoskeleton that is longer than its basal width. Ventrite: In Scolytus there are five visible ventrites. They are numbered from anterior to posterior with ventrite 1 closest to the head and ventrite 5 closest to the elytral apex. Subapical carinate ridge: a carinate ridge on ventrite 5 occurring just before the apical margin.
Tubercle: a small knob-like or rounded protuberance of the exoskeleton. Tumescence: a swelling of the exoskeleton. Venter: the undersurface of the abdomen, in Scolytus this pertains to the five visible ventrites.
Gallery pattern (Fig. 7) Adult gallery: the composite tunnel produced by the adult female includes 1-2 egg galleries, the egg niches and the nuptial chamber (if present). Egg gallery: a single extension of the adult gallery from the nuptial chamber (if present) along which eggs are deposited in niches. Egg niche: notches along the sides of the egg gallery excavated by females in which a single egg is deposited. Larval mine: the excavation tunnel produced by a larva as it feeds. Nuptial chamber: an enlarged area or short extension of the adult gallery at the base of the entrance tunnel that may be used for mating or as a turning niche. Pupation chamber: an ovoid or circular excavation at the end of a larval mine in which pupation occurs.

Morphology
The morphological phylogeny was poorly resolved and few synapomorphic characters were found (Fig. 2). This reflects the morphologically similarity of many taxa.

Mitochondrial COI
The parsimony analysis of mitochondrial COI produced 2,958 most parsimonious trees with a length of 1,434 steps and 606 of 616 characters were parsimony informative (Fig. 8). There was a high degree of synapomorphy and low amount of homoplasy in the phylogeny (CI = 0.356, RI = 0.809).

Combined analyses
Bayesian analysis of the combined dataset recovered the native Nearctic Scolytus as paraphyletic with native species found in two clades: native hardwood and conifer feeders (Fig. 9). Bayesian analysis of the combined dataset ( Fig. 9) recovered the monophyletic groups observed in the morphological phylogeny and the native species were recovered in two clades: native hardwood-feeders (S. fagi, S. muticus and Bremer support values are listed below the node. Non-monophyletic species are indicated in red. Mean intraspecific nucleotide differences (listed next to each taxon) and mean interspecific nucleotide differences (right of solid line) are given. Taxa highlighted in red were not recovered as monophyletic.

Taxonomic treatment
Based on the results of our phylogenetic analyses, 25 species occur in the Nearctic. Several species were not recovered as monophyletic and had less than 1% difference in all genes sequences (Table 6). These species are thus placed in synonymy with the oldest described species. The following synonyms were discovered: S. praeceps (= S. abietis; = S. opacus), S. reflexus (= S. virgatus; = S. wickhami). Scolytus fiskei was recovered as monophyletic and is thus removed from synonymy with S. unispinosus. Further detail regarding taxonomic changes is found in the remarks section for each species.
Description (modified from Wood 1982). Length 1.7-6.0 mm, 1.7-2.9 times as long as wide. Color variable, red-brown to black. Teneral adults are often light brown.
Head visible from above. Frons flattened to convex, sexually dimorphic (discussed below for each species group or clade). Eye elongate, sinuate to shallowly emarginated, finely faceted. Antennal scape club shaped, shorter than four funicle segments; funicle seven-segmented; club larger than funicle, flattened, oval to obovate, minutely pubescent and with 3 strongly procurved sutures, suture 1 partially to completely septate and with or without a surface groove. Pronotum large, wider than long; lateral and basal margins marked by a fine elevated line; disc finely punctate. Scutellum triangular, deeply depressed below elytral surface. Elytra depressed around scutellum and along basal one-fifth to half-length of elytral suture. Elytra wider than pronotum, flattened; striae punctate; interstriate punctate, with or without setae. Venter either gradually ascending from apical margin of ventrite 1 to elytral apex, or ventrite 2 abruptly ascending, sexually dimorphic, with or without tubercules and/or carinae; remaing ventrite usually unarmed, may have various armature or elevated margins, especially in males. Procoxae narrowly separated. Protibia rectangular; sides straight, nearly parallel, without denticles; outer distal angle produced into a curved uncus.
Species descriptions. Species are redescribed and treated alphabetically by clade or group beginning with the introduced group, native hardwood clade and conifer clade. Common names listed are the official common names of the Entomological Society of America and Canada.
Introduced species group. The introduced species group (1.9-4.2 mm long) (S. mali, S. multistriatus, S. rugulosus and S. schevyrewi) is not monophyletic and consists of a morphologically diverse group of Palearctic species that encompasses three formerly recognized subgenera (Butovitsch 1929;Balachowsky 1949). This diversity is reflected in the sexual dimorphism exhibited by the group. Scolytus multistriatus and S. schevyrewi exhibit the typical frons dimorphism as discussed above. The venter lateral teeth are identical in both sexes of S. multistriatus and the spine on ventrite 2 is smaller in the female compared to the male. Sexual dimorphism of S. mali and S. rugulosus is much more subtle and differentiating the sexes can be challenging. Scolytus mali males have the medial area of the frons and epistomal regions impressed and the lateral margins of the epistoma are lightly covered with more abundant erect setae than the female. Scolytus rugulosus males have the medial area of the frons and epistoma slightly more impressed and the frons bears longer and more abundant, erect setae. ( Wood and Bright (1992).

Scolytus mali
Diagnosis. Both sexes of S. mali are distinguished by having ventrite 2 at an oblique angle to ventrite 1, by the aciculate frons, with most setae found just above the epistoma and on the lateral epistomal margins, by the smooth, shining appearance of the pronotum and elytra, and by the weakly rounded and smooth elytral apex.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to weakly rounded, smooth apex; apex weakly emarginate at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae, bearing sparse, long, semi-erect yellow hair-like setae (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron greater than half-length of metanepisternum.
Biology. This species colonizes dying and weakened limbs of its host as well as fresh slash. Typical host material is 15.0-38.0 cm in diameter but branches as small as 8.0 cm are colonized (Pechuman 1938).
Adult galleries are somewhat variable and are either parallel or at a slight oblique angle to the grain of the wood and consisting of a nuptial chamber and a single egg gallery. The adult gallery strongly scores the sapwood and ranges in size from 3.5-6.0 cm in length. Egg niches are constructed along the gallery and score the sapwood. Six to 100 eggs may be laid along the egg galleries with the typical gallery having 40 eggs. Larval mines lightly score the sapwood and radiate perpendicular to the egg gallery. Larval galleries later meander often at an oblique angle to the grain of wood, forming a fan shaped pattern. Pupation occurs within the sapwood and broods overwinter as larvae or adults. The following year, adults emerge and feed at twig crotches before selecting host material (Pechuman 1938;Balachowsky 1949;Baker 1972;Wood 1982). In New York, S. mali has one generation per year although there are two generations per year in Europe (Pechuman 1938).
Collection notes. The senior author collected this species from an 8.0 cm diameter Prunus sp. branch that had broken during a recent windstorm. Females constructed gallery entrances beneath large flakes of bark on the sides and bottom surfaces of the branch. Specimens were infesting the same limbs as Phloeotribus liminaris (Harris, 1852).
Remarks. This species is native to the Palearctic region and was first detected in New York in 1868 when it was described as S. sulcatus LeConte. LeConte (1868) noted in his description that the species most strongly resembled the Palearctic species S. rugulosus and did not mention the collection date of his specimens. Interestingly, Figure 11. Scolytus mali distribution map. no other specimens were collected until 1933, 65 years after the initial discovery from southeastern New York, northern New Jersey and western Connecticut. It is likely that like LeConte's S. californicus (= S. scolytus), S. mali was collected in 1868 but populations never became established. The later collections may be the result of multiple introduction events (Pechuman 1938). Brown (1950) recognized that LeConte's species was morphologically and behaviorally identical to that of S. mali and placed S. sulcatus into synonymy. The native range of S. mali is Europe, Central Asia, Siberia, the Russian Far East, North Africa (Michalski 1973;Knížek 2011). Fig. 12 Ips multistriatus Marsham, 1802: 54. Scolytus multistriatus (Marsham, 1802). Chapuis and Candeze 1853: 577. = Scolytus javanus Chapuis, 1869: 56. Schedl 1954: 137. For complete taxonomic history see Wood and Bright (1992).

Scolytus multistriatus (Marsham, 1802)
Diagnosis. Both sexes of the species are distinguished by the presence of lateral teeth on the apical margins of ventrites 2-4 and by a median conical spine on the basal margin of ventrite 2.
Color not uniform and pronotal and elytral surfaces frequently contain patches of redbrown mixed with dark red-brown. Pronotum typically darker than elytra.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex entire at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae, bearing sparse, long, semi-erect yellow hair-like setae (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron greater than half-length of metanepisternum.
Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate, punctures small, coarse; surface flattened; basal margin armed with a long, smooth, conical spine with it's base extending from basal margin to half length of segment; lateral margins of ventrites 2-4 armed with lateral tooth. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Common names. Smaller European elm bark beetle and the European elm bark beetle.
Mating can occur either as the female is undergoing maturation feeding in twig crotches or within the gallery as described for the genus (Svihra and Clark 1980). The adult gallery is excavated parallel to the grain of the wood and consists of a single egg gallery; a nuptial chamber is not constructed. The adult gallery ranges in size from 2.5-5.0 cm in length. Egg niches are constructed along the gallery and score the sap- wood. Twenty-four to 96 eggs may be laid singly along the egg gallery. Larval mines lightly score the sapwood and radiate perpendicular to the egg gallery. Larval galleries later meander often at an oblique angle to the grain of wood, forming a fan shaped pattern. Larvae construct pupal chambers in the bark (Bright 1976).
There are one to one-half generations per year in Canada and three in the southern US (Furniss and Johnson 2002). In Canada, adults emerge in June and July and feed at twig crotches of healthy trees for 7-10 days before selecting host material (Chamberlin 1958;Baker 1972;Svihra and Clark 1980). The brood from these adults either emerges in August or September or overwinters as larvae.
Scolytus multistriatus is the principal vector of the Dutch elm disease fungus Ophiostoma ulmi (Buisman) Melin & Nannf in North America. This beetle vectored disease killed 50-75% of the elms population in northeastern North America prior to the 1930s (Bloomfield 1979). Adults become covered in fungal spores upon emergence from brood material. Adults inoculate elms with the Dutch elm disease fungus as they feed in twig crotches (Svihra and Clark 1980). This feeding activity leaves wounds in the bark that allow spores to be transferred from the beetle's cuticle to the tree tissues (Bright 1976).
Remarks. This species is native to the Palearctic region and is primarily distributed throughout Europe but also occurs in Iran and Algeria (Knížek 2011). Scolytus multistriatus was first detected in North America in 1909 from elm trees on the Harvard University campus in Massachusetts (Chapman 1910 Wood and Bright (1992).
Diagnosis. Both sexes of S. rugulosus are distinguished by the rounded elytral apices, by the serrate and deeply emarginated elytral apex, and by the oblique ventrite 2.
Head. Epistoma weakly, broadly emarginate; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing convex when viewed laterally, slightly transversely impressed just above epistoma; moderately, finely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures small, coarse; moderately, uniformly covered by long, fine, yellow erect hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two arcuate sutures visible. Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow setae; base weakly bisinuate.
Elytra with sides sub-parallel on basal half, narrowing to strongly rounded, moderately serrate apex; apex strongly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed and equal in width to striae, interstrial punctures uniseriate, equal in size to those of striae, bearing moderately abundant short, semi-erect yellow-brown hair-like setae; striae not impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.
The adult gallery is parallel to the grain of the wood and solely consists of an egg gallery; a nuptial chamber is not constructed. The adult gallery strongly scores the cambium, lightly scores the sapwood and ranges in size from 1.0-5.0 cm in length (Bright and Stark 1976;Furniss and Johnson 2002). Eggs are laid singly in larval niches on both sides of the egg gallery. Larval mines first radiate perpendicular to the egg gallery against the grain of the wood and later turn parallel to the grain (Bright and Stark 1973). The larval stage typically lasts one month. Pupation occurs in the bark for summer emergence. If the brood is unable to complete development during the warmer months, larvae will burrow 1.0-2.0 cm deep within the sapwood to overwinter. The following year, adults emerge and feed at twig crotches before selecting host material (Baker 1972). There are one to four generations per year depending on locality, with more generations occurring in warmer climates (Chittenden 1898;Baker 1972;Wood 1982). Remarks. This species is native to the Palearctic region and was first detected in North America in 1877 from New York (Chittenden 1898). The native range of S. rugulosus encompasses Europe, North Africa, Asia Minor and middle Asia to Zabaikalye (Russia) (Michalski 1973;Knížek 2011). Semenov, 1902 Fig. 16 Scolytus schevyrewi Semenov, 1902: 265. For complete taxonomic history see Wood and Bright (1992).

Scolytus schevyrewi
Diagnosis. The S. schevyrewi male most strongly resembles that of S. piceae because in both species the spine on the second ventrite never attains the apical margin. Both sexes can be distinguished from S. piceae by the subapical carina on ventrite 5 located just before end of segment. Males are further differentiated from those of S. piceae by the laterally compressed spine with a bulbous apex, which frequently has a longitudinal groove and by the banded appearance of the elytra. The female is further differentiated from that of S. piceae by the banded pattern of the elytra and by the low median carina (variable and may be absent) that does not touch either margin on the second ventrite.
Description (male). 2.8-3.5 mm long (mean = 3.2 mm; n = 10); 2.0-2.2 times as long as wide. Color red-brown to dark red brown. Elytra of most specimens appears banded with a characteristic dark brown band on reddish colored elytra, but may also be solely dark brown or red-brown without a band. Antennae yellow-brown. Pronotum typically darker than elytra.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger, coarser, deeper and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on basal half, narrowing to moderately rounded, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing small, fine punctures. Scutellar notch densely covered in recumbent white setae (may be abraded). Disc glabrous, smooth, shining; interstriae not impressed, equal in width to striae; interstrial punctures uniseriate, equal in size to those of striae, bearing sparse short, semi-erect yellow hair-like setae; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 flush with base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow; surface convex; densely covered with semi-recumbent, long setae, as long as length of ventrite 3 or less; surface armed with median laterally compressed spine (rarely absent) that has its base close to basal margin but does not touch it; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Female. 2.3-3.6 mm long (mean = 3.2 mm; n = 10); 1.7-2.4 times as long as wide. Similar to male except epistoma feebly emarginated, frons flattened when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed just above epistoma and longitudinally impressed in median area. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Second ventrite armed with low median carina (variable and may be absent) that does not touch either margin. Common name. Banded elm bark beetle.
Biology. This species prefers to attack drought stressed elms (Negrón et al. 2005). Scolytus schevyrewi locate a suitable host via host tree volatiles (Lee et al. 2010).
The adult gallery consists solely of a single egg gallery parallel with grain of the wood; a nuptial chamber is not constructed (Lee et al. 2006). The adult gallery strongly scores the sapwood. Egg niches are constructed along the gallery and score the sapwood. Twenty to 120 eggs are laid along the egg galleries (Lee et al. 2010). Larval mines lightly score the sapwood and radiate perpendicular to the egg gallery. Larval galleries later meander often at an oblique angle to the grain of wood, forming a fan shaped pattern. Pupation occurs in the outer bark and broods overwinter as mature larvae or pupae (Lee et al. 2006). In California, flight occurs from April-September or October. In Nevada, Utah, Wyoming, Colorado, Kansas and Utah, flight occurs from May to September (Lee et al. 2011). There are two to three generations per year (Lee et al. 2011). Development from egg to adult takes 30-45 days (Negrón et al. 2005). Upon emergence, adults feed at twig crotches prior to selecting host material (Negrón et al. 2005). Scolytus schevyrewi is a less effective vector of the Dutch elm disease fungus Ophiostoma ulmi in North America, especially in Rocky Mountain states (Jacobi et al. 2013).
Remarks. This species is native to the Palearctic where it occurs from western Russia and Uzbekistan and east to China, Mongolia and Korea (Michalski 1973). Scolytus schevyrewi was first detected in North America in 2003. The first specimens were collected in Colorado and Utah. By 2005, it was recorded from 21 states suggesting that it had been present for many years before its initial detection (Negrón et al. 2005;LaBonte 2010). Subsequent review of bark beetle survey collections revealed the earlier occurrence of this species in Denver, Colorado in 1994 and Clovis, New Mexico in 1998 (Lee et al. 2006).
In areas where populations of S. schevyrewi and S. multistriatus are both present, the abundance of S. multistriatus is decreasing to the point where this once common species is difficult to find (Negrón et al. 2005;Lee et al. 2010). This competitive displacement of S. multistriatus by S. schevyrewi is likely the result of differences in fecundity, generation time, and emergence. Scolytus schevyrewi produces larger broods that may overwinter as pupae, have a quicker development period, have an earlier flight, and exhibit rapid, strong aggregation to host kairomones as compared to S. multistriatus (Lee et al. 2010).
Scolytus schevyrewi is a highly morphologically variable species. LaBonte (2010) provides an excellent discussion regarding intraspecific variation exhibited within S. schevyrewi. There is considerable variation observed in the shape and appearance of spine on the second ventrite. The male second ventrite spine is typically well developed with a blunt apex that is broader than the base and appears triangular when laterally viewed. In females the spine is variously reduced and may even be absent. In most males, the spine is closest to the apical margin of the second ventrite. In some males the base of the spine is closer to basal margin. Most individuals exhibit the characteristic dark brown band on reddish colored elytra, which is the derivative of the species'.
Common name. Occasionally individuals have been encountered with unicolorous dark brown or reddish elytra. Additional variation was also observed in the coloration of the pronotum. The pronotum can vary from almost entirely dark brown with reddish coloration along the margins (common form) to the entire dorsal surface being reddish with dark brown margins (uncommon form) (LaBonte 2010).

Native Hardwood clade
The native hardwood clade (2.2-5.6 mm long) (S. fagi, S. muticus, and S. quadrispinosus) is monophyletic. The sexual dimorphism of the native hardwood clade differs from the introduced group and the conifer clade as both the males and females have an impressed frons that is strongly longitudinally aciculate, except S. fagi in which the males have a faintly longitudinally aciculate frons and the female frons is granulate punctate. This group arguably has the strongest degree of sexual dimorphism with S. quadrispinosus and S. muticus each possessing a strongly excavated second ventrite numerous spines and teeth or a large setal patch on ventrite 5 respectively. The abdominal venter of S. fagi is identical in both sexes. Diagnosis. Both sexes of S. fagi are distinguished from S. mali and S. muticus by the rugose-reticulate frons that is covered by uniformly distributed setae.
Head. Epistoma weakly, broadly emarginated; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally, slightly transversely impressed just above epistoma and along median line; rugose-reticulate, strongly punctate; punctures small, coarse; moderately, uniformly covered by long, fine, yellow erect hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, thinner on apical half, irregularly ovoid, setose with partial septum, two arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctulate, punctures moderately abundant, larger, coarse and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to weakly rounded, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae, punctures bearing short recumbent yellow setae slightly longer than size of a puncture (may be abraded); striae moderately impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum. Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures large, fine, shallow; surface flattened; setae semi-recumbent, short, about half length of segment 3 or less; apical margin unarmed; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 unarmed; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch absent, median depression present.
Female. 3.9-5.6 mm long (mean = 4.65 mm; n = 20); 1.9-2.8 times as long as wide. Similar to male except epistoma feebly emarginated, epistomal process absent, frons convex when viewed laterally, weakly longitudinally strigate-punctate, setae shorter, less than width of eye and sparse; weakly transversely impressed just above epistoma and between inner apices of eyes. Biology. The gallery has been reported as very confused and undecipherable. Larvae were reported boring in the wood. In addition, the species did not appear to colonize healthy trees (Packard 1890). Smith and Cognato (2010a) summarized all information known about this species.
Remarks. This species is very rarely encountered. Most museum collections occurred in the early 1900's and most recent collections have been from Lindgren funnel traps. There are many gaps in the known distribution of S. fagi but the species likely occurs throughout the eastern US associated with its host trees. Diagnosis. Scolytus muticus are differentiated from other Scolytus species by the presence of long, erect hair-like setae on the elytral interstriae and on the abdominal venter. The male is further distinguished by a pair of strongly elevated areas on the basal two-thirds of ventrite 5, each densely covered with abundant fine, long hair-like setae.
Head. Epistoma moderately, broadly emarginated; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing strongly flattened when viewed laterally; densely, finely, longitudinally aciculate; aciculations converging at epistoma; impunctate; setae on lateral and dorsal margins covered by long, thick, incurved, yellow erect hair-like setae, these longer than width of midpoint of eye, median areas covered with sparse, shorter and thinner setae. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, three very sharply arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; smooth, shining, punctures on disc fine, shallow, moderately abundant, larger, coarser and dense laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex entire at suture. Margin of apical edge bearing small, fine punctures. Disc reticulate, shining; interstriae faintly impressed, equal to width of striae, interstrial punctures large, uniseriate, equal in size to those of striae, bearing moderately abundant, long, semi-erect, yellow hair-like setae (may be abraded); striae moderately impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface reticulate, shining, densely, coarsely punctured; punctures large, coarse; surface flattened; setae moderately abundant, longer than length of ventrite 3; apical margin unarmed; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 unarmed; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; median depression absent; pair of strongly elevated areas on basal two-thirds, each densely covered with abundant fine, long hairlike setae; apical third strongly impressed. frons less strongly flattened when viewed laterally, finely, narrowly longitudinally aciculate, setae shorter, less than width of eye and less abundant; weakly transversely impressed between inner apices of eyes. Second ventrite unarmed. Ventrite 5 without a pair of strongly elevated areas on basal two-thirds or setal patches.   Common name. Hackberry engraver. Biology. Scolytus muticus prefers to colonize dead, dying or felled trees and the broken, dead and dying branches of live hackberry (Blackman 1922;Doane et al. 1936;Bright 1976).
The biology of this species is poorly understood. Adult galleries are parallel to the grain of the wood and consist of a single egg gallery; a nuptial chamber is not constructed. The adult gallery strongly scores the sapwood and ranges in size from 2.5-5.0 cm in length (Blackman 1922). Larval mines first radiate perpendicular to the egg gallery and later meander, giving the galleries a tortuous appearance (Blackman 1922;Bright 1976). Larvae construct pupal chambers in burrows 2.0-3.0 cm deep within the sapwood (Bright 1976;Smith and Cognato, pers. obs.). There are two generations per year in the southeastern US and one generation per year in the northeastern US (Blackman 1922;Baker 1972).
Remarks. The holotype of Scolytus muticus has been lost (Wood 1982), however, Say's (1824) description is unambiguous as to the characteristics of this species. Wood (1982) reports S. muticus as having a transverse gallery that is perpendicular to the grain of the wood. Other authors, including Blackman (1922), Baker (1972), and Bright (1976) report this species as having a longitudinal gallery that is parallel to the grain of the wood. After examining the literature and photographs provided by T.H. Atkinson, it appears that Wood erred in his description and the gallery is parallel to the grain of the wood. Diagnosis. The S. quadrispinosus male is easily distinguished by the autapomorphic features of the abdominal venter which include: the apical margin of ventrite 3 armed by three acute spines (two lateral and one medial), the apical margin of ventrite 4 armed by one median tooth, ventrite 1 apically descending, ventrite 2 deeply concave, with the basal margin produced and bearing a median tubercle. The female is distinguished by the flattened and moderately, finely longitudinally aciculate frons, bearing long, fine, incurved setae on the lateral and dorsal margins.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, golden setae; base weakly bisinuate.
Common name. Hickory bark beetle. Biology. Scolytus quadrispinosus is one of the most destructive pests of hardwoods in the US and the most important pest of hickory (Doane et al. 1936;Baker 1972). The species generally attacks and kills single trees, or solely treetops. However, outbreaks can develop during periods of drought, killing large tracts of hickory. Scolytus quadrispinosus kills its host by mass attack in which a multitude of broods develop in the phloem and cambium, effectively girdling the host tree (Blackman 1922).
Adult galleries are parallel to the grain of the wood and deeply score the sapwood; a nuptial chamber is not constructed. The adult gallery is short (2.5-5.0 cm), and consists of a single egg gallery (Blackman 1922). Eggs are deposited singly in niches on each side of the egg gallery with 20-60 niches per gallery (Blackman 1922). After the eggs have been laid, the female constructs a postovipositional feeding tunnel parallel to the egg gallery (Goeden and Norris 1965b). Larval mines are excavated in the cambium. From the egg gallery, the larval mines are first perpendicular to the grain of the wood and then gradually turn and diverge creating a fan shaped appearance. The larvae bore into the inner bark to overwinter. Larvae pupate the following spring and emerge as adults the following summer (Blackman 1922). Upon emergence, adults feed at twig crotches and leaf petioles before selecting a host (Baker 1972;Goeden and Norris 1964b). There is one generation per year in the north with larvae completing their development in March and April and emergence in May. There may be two generations per year in the south with the brood overwintering as larvae (Doane et al. 1936). See Norris (1964a,b, 1965a,b) for more information regarding the biology of this species.
Remarks. The holotype of Scolytus quadrispinosus is lost (Wood 1982), however Say's (1824) description is unambiguous as to the characteristics of this species. The holotype of S. caryae Walsh was likely deposited in Walsh's type collection, which was housed in the Chicago Academy of Science Museum. This collection burned in the Great Chicago Fire and the holotypes were lost (Sheppard 2004;J. Colby, pers. comm.).

Conifer clade
The conifer clade (1.7-5.9 mm) (S. aztecus, S. dentatus, S. fiskei, S. hermosus, S. laricis, S. monticolae, S. mundus, S. obelus, S. oregoni, S. piceae, S. praeceps, S. reflexus, S. robustus, S. silvaticus, S. subscaber, S. tsugae, S. unispinosus, and S. ventralis) is monophyletic. The sexual dimorphism exhibited by species in the clade follows the general pattern outlined above except for the shape of the frons, which is quite variable. In some species, the frons is convex in both sexes with the female frons more strongly convex than that of the male (S. hermosus, S. obelus, S. praeceps, and S. subscaber). Scolytus laricis males have a flattened and impressed frons when viewed from a lateral profile and that of the female is convex. In the remaining species, the male frons appears flattened when viewed from a lateral profile. Galleries of the conifer clade are in Figures 24 and 25. Wood, 1967 Fig. 26 Scolytus aztecus Wood, 1967: 120. Diagnosis. Scolytus aztecus are distinguished by the characteristics of the elytral apex with the apical margin produced between interstriae 1 and 2, deeply emarginated at interstriae 3, produced on interstriae 4 and deeply emarginated at stria 4.

Scolytus aztecus
Description (male). 5.0 mm long (mean = 5.0 mm; n = 2); 2.5 times as long as wide. Body dark red-brown to black, antennae light brown, legs light brown to dark red-brown. Pronotum typically darker than elytra.
Head. Epistoma broadly, deeply emarginated; epistomal process weakly developed, low; median area above mandibles bearing dense patch of long yellow hair-like setae. Frons appearing flattened when viewed laterally, slightly transversely impressed just above epistoma; surface moderately, coarsely longitudinally aciculate-punctate; aciculations converging at epistoma; punctures large, coarse and more dense medially above epistoma; surface moderately and uniformly covered by long, fine, yellow  erect hair-like setae, setae longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, almost subquadrate, setose with partial septum, two arcuate sutures visible.
Pronotum as long as wide; apical margin broadly rounded, area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow and moderately abundant, larger, more abundant laterally and on apical constriction; apical, anterolateral and lateral margins bearing moderately abundant, erect, yellow hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to rounded, serrate apex; apical margin of elytra produced between interstriae 1 and 2, deeply emarginated at interstria 3, produced on interstria 4 and deeply emarginated at stria 4; apical margin of elytral apices bearing large, coarse punctures; apex moderately emarginated at suture. Disc smooth, shining; interstriae bearing short, sparse yellow hair-like setae spaced by length of a setae or less; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae; striae moderately impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface rugose, coarsely, deeply punctate; covered with abundant erect setae that are greater than length of segment 3; surface convex; armed medially with laterally compressed spine with base extending from apical margin to ¾ of segment, apex rounded, shining, impunctate; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to basal margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Specimens examined. 11. Type material. Holotype Scolytus aztecus Wood: female, labeled "27 mi E. Morelia, Mich., VI-4-1965, Mexico, 8, Biology. Scolytus aztecus is an uncommon species and little is known regarding its biology. Scolytus aztecus colonizes both standing trees and felled trees (Wood 1967;Cibrián Tovar et al. 1995). The treetops attacked by S. aztecus exhibit red foliage. Scolytus aztecus has been collected feeding in the cambium of large Abies trees, although it has also been collected from Pseudotsuga. Because of limited host records, it is unknown whether the primary host is Abies or Pseudotsuga. Phylogenetic placement of the species suggests Abies (Fig. 4) because the species belongs to a clade of Abies feeding taxa. The adult gallery is transverse across the grain of the wood with a central nuptial chamber, similar in appearance to that of S. ventralis (see Cibrián Tovar et al. 1995, plate 132). Larval mines are in the cambium and do not score the wood. Pupation occurs in the cambium (Wood 1967;Cibrián Tovar et al. 1995).
Remarks. This is the first description of a male for this species.
Scolytus dentatus Bright, 1964 Figs 28-29 Scolytus dentatus Bright, 1964: 167. Diagnosis. The S. dentatus male is easily distinguished by the endemic distribution in the Santa Lucia range of California, and by the presence of a median denticle on the apical margin of ventrite 4, occasionally median denticles may also be present on the apical margins of ventrites 2 and 3. The female is distinguished by its distribution and differentiated from the S. praeceps female by the presence of a strongly developed and distinct epistomal process and larger size. Description (male). 3.0-4.0 mm long (mean = 3.45 mm; n = 15); 1.7-2.5 times as long as wide. Head, pronotum and abdominal venter dark red-brown, antennae light brown, legs dark red-brown to light brown, elytra light red-brown. Pronotum darker than elytra.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctulate, punctures moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on basal half, narrowing to subquadrate, smooth apex; apex entire at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.

Hosts. Abies bracteata (D. Don) Poit. (bristlecone fir / Santa Lucia fir).
Biology. Little is known regarding the biology of this uncommon and narrowly geographically restricted species. The host, Abies bracteata, is restricted to the Santa Lucia Mountains of California. The tree is distributed in small patches in deep, moist canyon bottoms as well as dry, rocky slopes and ledges within Los Padres National Forest in Monterey County, especially near Cone Peak and Church Creek (Griffin and Critchfield 1972;Sullivan 1993). Scolytus dentatus has been collected feeding in the bole of large standing trees (Bright 1964) but is also reported from larger limbs and fresh slash (Edson 1967).
The adult gallery somewhat resembles an expanded 'E' (Fig. 24). The gallery is parallel to the grain of the wood and consists of a central nuptial chamber and two egg galleries, one below and one above the nuptial chamber. Each egg gallery ends in a pronounced hook. Galleries strongly score the cambium and lightly score the sapwood. The adult gallery averages 2.5-12.0 cm in length (Bright 1964;Edson 1967). Egg niches are closely spaced on both sides of the maternal gallery (Bright and Stark 1973). Larval mines are first perpendicular to the egg gallery and later turn to form a fan shaped pattern before terminating at pupation chambers in the sapwood (Edson 1967).
Remarks. Considerable variation is observed in the presence of median denticles on the apical margins of male ventrites 2 and 3. Frequently males only have a median denticle on the apical margin of ventrite 4 as those on 2 and 3 may or may not be present in the male. This species is related to S. robustus and S. subscaber based on morphological characters (Fig. 2). Both of these species also feed on true firs (Abies spp.) and have the apical margin of male ventrite 1 strongly apically produced.

Scolytus fiskei Blackman, 1934, valid sp. Figs 29, 31
Scolytus fiskei Blackman, 1934: 25. Diagnosis. Scolytus fiskei is very morphologically similar to S. laricis and S. unispinosus. Males of are distinguished from those of S. laricis by the frons flattened when viewed laterally, never deeply impressed, by the moderately abundant frontal setae (compared to dense) and by the host genus, Pseudotsuga. Males are distinguished from those of S. unispinosus by the following combination of characters: abdominal venter shiny in luster, the base of the ventrite 2 spine extends from the apical margin to three-quarters the length of the segment and geographical distribution east of the Rocky Mountains. The female is distinguished from that of both species by the shining luster of ventrite 2.
Head. Epistoma weakly emarginated; epistomal process present, moderately developed, low; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally from epistoma to vertex, slightly transversely impressed just above epistoma to inner apices of eyes; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures large, sparse and coarse; moderately, uniformly covered by long, fine, yellow, erect, hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two broadly arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, twice width of striae, punctures uniseriate, smaller than those of striae; punctures bearing short, sparse, recumbent, yellow setae slightly longer than size of a puncture (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.
Venter. Apical margin of ventrite 1 rounded, 2 marked by weak carina. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; covered with sparse setae less than length of segment 3; surface convex; apical margin armed with laterally compressed, median spine with base extending from apical margin to ¾ length of segment, apex rounded; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge equidistant between basal and apical margins of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Hosts. Pseudotsuga menziesii (Mirb.) Franco (Douglas fir). Biology. Scolytus fiskei colonizes suppressed limbs and branches of Pseudotsuga menziesii as well as fresh slash (Edson 1967;Smith, pers. obs.). The adult gallery is bayonet shaped, parallel to the grain of wood and consists of two egg galleries, one below and one above the nuptial chamber and a turning niche. The female constructs the adult gallery mostly in the cambium and lightly scores the sapwood. Larval mines are perpendicular to the egg gallery and turn to form a fan shaped pattern (Edson 1967;Furniss and Johnson 2002;Smith, pers. obs.) (Fig. 24). The adult gallery measures 3.8-9.0 cm in length (Edson 1967). The following year adults emerge and excavate tunnels within twigs of Douglas fir for maturation feeding causing twig flagging (reported as S. unispinosus McMullen and Atkins 1962).
Like most Scolytus species, there is a very limited amount of information regarding S. fiskei. For many years it was considered a synonym of S. unispinosus and was thus referred to as S. unispinosus in publications. Very little was written about this species in the US (see Wood and Bright 1992) other than host preference and gallery descriptions (Keen 1938;Edson 1967;Bright 1976). McMullen and Atkins (1962) reported some notes on the biology of S. unispinosus in British Columbia and appear to have reported a combined account of S. unispinosus and S. fiskei. The authors noted the gallery of the S. unispinosus studied in their investigations as "in about 15 per cent of the galleries over 20 days of age were the type described by Chamberlin and Keen [S. unispinosus, which has only a single egg gallery]; the majority were of the forked type and were similar to those of S. tsugae [referencing a forked or bayonet shaped gallery that is made by S. fiskei]". Their description matches the gallery description of S. fiskei, which like has two egg galleries as part of a bayonet shaped adult gallery. Because most of the specimens are of S. fiskei, this article does offer some information regarding the biology of the species be used with caution because not all of the findings may apply to S. fiskei.
Remarks. The holotype of S. fiskei does not bear a locality label. Blackman's (1934) description states the holotype was collected at the Capitan Mountains, New Mexico. Furniss and Johnson (2002) report S. unispinosus from Alberta, Canada. These specimens are likely S. fiskei based on the geographic distribution of the species in the Rocky Mountains. Wood (1977: 388) placed S. fiskei in synonymy with S. unispinosus after examining both holotypes and 164 specimens from Arizona to British Columbia and concluded that there was too much intraspecific variation to recognize them as separate species. We assessed the intraspecific and interspecific variation (Tables 6 and 7) for each of the four genes for each species. Scolytus fiskei intraspecific variation for COI was low, 0.0-0.0231, and averaged 0.0183 among all sampled populations. Scolytus unispinosus intraspecific variation was also low, 0.0016-0.0282 and averaged 0.0121. Interspecific variation between S. fiskei and S. unispinosus was much higher, 0.0331-0.0521 and averaged 0.043 among populations. Similar differences were also observed with CAD ( Table 7). The species have separate geographical ranges with S. fiskei occurring primarily in the Rocky Mountains and British Columbia while S. unispinosus occurs in the Cascade and Sierra mountains from California to British Columbia. Both species are sympatric in the Interior Plateau of British Columbia near Merritt. The species are separated by the characters listed in the diagnosis and by the galleries. The galleries of S. fiskei contain two egg galleries; one above and one below the nuptial chamber. The gallery of S. unispinosus only contains a single egg gallery. In addition, the gallery of S. fiskei lightly scores the sapwood while that of S. unispinosus deeply scores the sapwood. After examining the types, 950 specimens of both species and testing the monophyly of each species using four genes, it is apparent that S. fiskei is a distinct lineage and is here removed from synonymy with S. unispinosus. Wood, 1968 Fig. 33 Scolytus hermosus Wood, 1968: 12. Diagnosis. Both sexes resemble the S. silvaticus female. The female is distinguished by having a weakly developed epistomal process and the male is distinguished by having the apical margin of ventrite 1 produced, forming a carinate lip along the basal margin of ventrite 2 that is twice as produced as thick and by the host genus, Abies.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae, punctures bearing sparse, long, erect, yellow hair-like setae (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 produced, forming carinate lip along basal margin of ventrite 2 that is twice as produced as thick, basal margin of ventrite 2 appearing impressed. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow; setae moderately abundant, recumbent, short, about four times length of a puncture; surface weakly concave; apical margin armed with broad median denticle, occasionally absent; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Female. 2.5-3.5 mm long (mean = 3.27 mm; n = 6); 2.1-2.3 times as long as wide. Similar to male except epistoma feebly emarginated, epistomal process absent, frons more strongly convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed just above epistoma. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Second ventrite unarmed. Biology. There is a paucity of information regarding the biology of this uncommon species. Scolytus hermosus has been collected feeding in the cambium of large Abies slash greater than 10.0 cm in diameter (Wood 1967) and weakened and dying large Pseudotsuga menziesii (Cibrián Tovar et al. 1995). The adult galleries are transverse and perpendicular to the grain of the wood (Wood 1967). This species has been reported to colonize the same material as S. mundus (Wood 1968).

Scolytus laricis Blackman, 1934 Figs 29, 35
Scolytus laricis Blackman, 1934: 24. Diagnosis. Scolytus laricis is very morphologically similar to S. fiskei and S. unispinosus. Males are distinguished from those of S. fiskei by the dull appearance of abdominal ventrite 2 and by the frons densely covered by long setae. Males can be distinguished from those of S. unispinosus by the following combination of characters: the base of the ventrite 2 spine extends from the apical margin to three-quarters the length of the segment and host genus. The female is distinguished from that of S. fiskei by the dull luster of ventrite 2 and is distinguished from that of S. unispinosus by the frons moderately and coarsely aciculate-punctate; ventrite 1 rounded over onto surface of ventrite 2, not forming an obtuse angle, and the base of ventrite 2 finely impressed.
Head. Epistoma weakly emarginated; epistomal process present, moderately developed and elevated; median area above mandibles bearing dense patch of long yellow hair-like setae. Frons appearing flattened when viewed laterally from epistoma to vertex, moderately transversely impressed just above epistoma to vertex; strongly, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures sparse, large, coarse; moderately to densely uniformly covered by long, fine, yellow, erect, hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc smooth, shining; interstriae not impressed, twice width of striae, punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae length of interstrial punctures (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect, yellow setae. Metepimeron less than half-length of metanepisternum.
Venter. Apical margin of ventrite 1 rounded, marked by weak carina on ascendant part of venter. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; covered with sparse setae less than length of segment 3; surface convex; apical margin armed with laterally compressed, median spine with base extending from apical margin to ¾ length of segment, apex rounded, rarely a slightly elevated vertical carina (Oregon: Dixie Pass and Frog Lake) instead of spine; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge equidistant between basal and apical margins of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
The adult gallery is parallel to the grain of the wood and consists of two egg galleries and a central nuptial chamber (Fig. 24). The central nuptial chamber extends at a right angle to the rest of the gallery and opposite the nuptial chamber is a rounded turning niche. This gives the central part of the gallery an ovoid appearance that is different from all other Nearctic Scolytus. Egg galleries are extended parallel to the grain of the wood. The adult gallery scores the sapwood more deeply than the cambium, and ranges in length from 6.4-11.5 cm. The female constructs widely spaced egg niches on both sides of each egg gallery. Larval mines extend against the grain of wood and gradually diverge before terminating at pupation chambers that deeply score the sapwood (Edson 1967;Furniss and Johnson 2002). There is one generation per year and broods overwinter as larvae (Furniss and Johnson 2002).
Collection notes. Scolytus laricis was collected four times by the senior author and each time specimens were collected from fresh broken branches that were less than 5.0 cm in diameter with bright green needles. Specimens were also collected from a fallen L. occidentalis of 15.0 cm DBH.
Remarks. Furniss and Johnson (2002) reported that specimens collected from L. lyalli create a different gallery structure than those collected from L. occidentalis (M.M. Furniss pers. comm.). The galleries on L. lyalli are "shorter, less uniform, and with the entrance chamber often extended a short distance to the sides of the gallery" (Furniss and Johnson 2002). Specimens from L. lyalli could not be collected during the coarse of our investigation. We noticed slight morphological variation among some populations but were unable to determine if the differences represent species limits. Further study is needed to address this question. The holotype of S. laricis does not bear a locality label. Blackman's (1934) description states A.D. Hopkins collected the holotype on Cedar Mountain near Moscow, Idaho. Numerous collectors listed in the material examined reported this species as collected from L. lyalli in Oregon. This host species occurs east of the Cascade Range in the Wenatchee Mountains in Washington and is not known to occur in Oregon (Burns and Honkala 1990). It is probable that the host species for these specimens was L. occidentalis.

Scolytus monticolae (Swaine, 1917) Figs 29, 37
Eccoptogaster monticolae Swaine, 1917: 32. Scolytus monticolae (Swaine, 1917): Keen 1929 Diagnosis. Scolytus monticolae males are easily confused with S. reflexus males, especially those exhibiting the wickhami phenotype. They are easily distinguished by the size of male ventrite 5. In S. monticolae, ventrite 5 is equal in length to width of ventrites 3 and 4 combined. In S. reflexus, ventrite 5 is equal in length to ventrite 4. Scolytus monticolae lacks an epistomal process while S. reflexus typically has a strongly developed epistomal process. Males are distinguished from those of S. tsugae by the following combination of characters: surface of ventrite 2 shining but minutely reticulate; elytral striae not impressed; basal margin of ventrite 2 more pronounced and produced laterally; elytral strial punctures small, spaced 2-3 diameters of a puncture. Females of S. monticolae are distinguished from S. reflexus females by having the apical margin of ventrite 1 weakly produced, never rounded and the surface of ventrite 2 smooth and flat, and are separated from those of S. tsugae by elytral discal striae not impressed and ventrite 2 shining in luster.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on basal half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, twice width of striae, punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae length of interstrial punctures (may be abraded); striae not impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.
Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2, more pronounced and produced laterally forming two cups. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; surface flattened, depressed above basal margin; apical margin unarmed; covered in recumbent setae twice width of a puncture; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Hosts. Pseudotsuga menziesii (Mirb.) Franco (Douglas fir). Biology. Scolytus monticolae commonly infests the bole, suppressed branches and fresh slash of Douglas fir. Scolytus monticolae (as S. tsugae, see remarks below) has been reported to kill drought stressed sapling and pole-sized Douglas fir trees in British Columbia (McMullen and Atkins 1959) and Wyoming (Furniss and Carolin 1977).
Adult galleries strongly resemble those of S. reflexus, parallel to the grain of the wood, bayonet shaped and consist of two egg galleries and a central nuptial chamber (Fig. 24). From the central nuptial chamber, one egg gallery extends with the grain of the wood and the other egg gallery is slightly transversely extended and then is extended parallel to the grain. The nuptial chamber is oblique to the egg galleries. The adult gallery scores the sapwood more than the cambium and averages 5.0-9.0 cm in length. Egg niches are generally placed in pairs along the egg galleries and score the sapwood. Larvae extend their mines perpendicular to the egg gallery before diverging in a fan shaped pattern. Pupation may occur under the bark or in the sapwood. In Idaho, S. monticolae has one generation per year with flight occurring in July (Furniss and Johnson 2002;Smith, pers. obs.). Broods overwinter as larvae and emerge the following summer (Edson 1967;Furniss and Johnson 2002).
Collection notes. The senior author found this species to be common in suppressed limbs and slash in Idaho.
Remarks. The lectotype does not bear a locality label. Swaine's (1917) description states the lectotype was collected at Arrowhead, British Columbia.
In their paper describing the biology of S. tsugae, McMullen and Atkins (1959) considered S. monticolae a synonym of S. tsugae based on correspondence with G.R. Hopping (page 417). Wood (1966: 30) formally synonymized S. monticolae with S. tsugae, and later removed the species from synonymy (Wood 1982;M.M. Furniss, pers. comm.). However, Wood (1982) did not explicitly state that he was the author that recognized the species. These two species are closely related and have subtle morphological differences. This has led to a confusing account of both species in the literature. The majority of which seems to be applicable to S. monticolae rather than S. tsugae. The above diagnostic characters and different biologies readily differentiate the species.  Wood, 1968 Fig. 39 Scolytus mundus Wood, 1968: 13. Diagnosis. This species most strongly resembles S. aztecus and S. ventralis. Both sexes are differentiated by elytral apices slightly emarginated only at interstria 3, by ventrite 3 covered with abundant erect setae that are greater than length of segment 3. The male can also be differentiated by the apical margin of ventrite 2 armed with a broad median denticle; larger size, the geographic distribution.
Pronotum as long as wide; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical, anterolateral and lateral margins bearing abundant, erect, long, dark yellow-brown, hair-like setae; base weakly bisinuate.
Female. 3.3-4.6 mm long (mean = 4.0 mm; n = 13); 1.8-2.6 times as long as wide. Similar to male except epistoma feebly emarginated, epistomal process absent, frons convex when viewed laterally, weakly longitudinally aciculate, setae sparser,    Tovar et al. 1995). Scolytus mundus attacks the tops of mature trees, trunks of recently cut trees and large logging slash greater than 10.0 cm in diameter (Wood 1968;Cibrián Tovar et al. 1995). Trees attacked by S. mundus exhibit red foliage at the tree top. If the population density is high, subsequent generations will colonize the tree from the top down. However, attacks rarely occur at the base and so the host tree typically survives (Cibrián Tovar et al. 1995). Scolytus mundus has been reported to colonize the same material as S. hermosus (Wood 1968).
The female initiates the attack by constructing an entrance in bark crevices at branch nodes. The adult galleries are transverse across the grain of the wood, similar in appearance to S. ventralis and with a central nuptial chamber (see Cibrián Tovar et al. 1995, plates 130-131). Eggs are laid in niches excavated on each side of the central nuptial chamber. The larval mines extend parallel to the grain of wood and are first in the cambium and later penetrate into the sapwood. Pupation occurs in the sapwood and there are two generations per year with the first generation occurring from October to May and the second from June to October (Cibrián Tovar et al. 1995). Wood, 1962 Figs 29, 41 Scolytus obelus Wood, 1962: 81. Diagnosis. Both sexes of S. obelus strongly resemble S. praeceps and are distinguished by the presence of a small median denticle on the apical margin of ventrite 2.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, weakly serrate apex; apex weakly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae not impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 strongly, acutely produced, forming lip along base of ventrite 2, basal margin of ventrite 2 appearing impressed. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow, punctures varying in size, larger and more abundant near basal margin; surface weakly concave; apical margin armed with acute median denticle; setae short, recumbent, about three times that of a puncture in length; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 equal to combined lengths of ventrites 3 and 4; setal patch and median depression absent.
The adult gallery contains two egg galleries that branch from the central nuptial chamber. One egg gallery extends from the nuptial chamber perpendicular to the grain of wood and the second gallery extends at a 45° angle to the grain (Fig. 24). Galleries are frequently initiated near branch crotches and disguised under rough patches of bark. The adult gallery deeply scores the sapwood and lightly scores the cambium. The adult galleries range in size from 1.9-6.5 cm in length. Eggs are laid in niches on both sides of each egg gallery and larval mines radiate perpendicular to the egg gallery forming a fan shaped pattern. The larval mines gradually diverge and lightly etch the sapwood. Pupation occurs in the sapwood (Edson 1967).
Collection notes. The senior author collected specimens from suppressed 2.0-4.0 cm diameter branches of A. lasiocarpa var. arizonica that had been girdled at the base by porcupines. Needles of infested branches were pale green to yellow.
Remarks. This species is sister to S. praeceps and is very similar both in morphology and gallery architecture. Interspecific divergence in COI nucleotide difference between these two taxa is quite large and averages 10.36% (Table 7). Blackman, 1934 Figs 29, 42 Scolytus oregoni Blackman, 1934: 18. Diagnosis. Scolytus oregoni is a rather distinctive species and both sexes are readily distinguished by having the apical margin of ventrite 1 thickened and on the surface of ventrite 2 and by the unarmed ventrite 2.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae weakly impressed. Declivity bearing sparse, short, erect, yellow setae. Metepimeron less than half-length of metanepisternum.
The adult gallery is typically constructed parallel to the grain of the wood and has a central nuptial chamber (Fig. 24). The gallery structure is typically bayonet shaped but may also be longitudinal. Each egg gallery extends in opposite directions to the grain of the wood from the central nuptial chamber. The nuptial chamber is transverse to the egg galleries. The adult gallery deeply scores the sapwood and lightly scores the cambium. The adult gallery averages 6.0-18.0 cm in length. Egg niches are closely spaced and deeply score the sapwood. Larvae extend their mines perpendicular to the egg gallery in a fan shaped pattern before terminating in pupation chambers, which are constructed in the sapwood (Edson 1967).
Remarks. Specimens of S. oregoni are very rarely collected and the species is perhaps the least common of the conifer-feeders in the United States. There are many gaps that occur in its distribution range, particularly between northern and southern California. Considerable variation is observed in the male ventrite 1 and 2 across the geographic range especially between northern California, Oregon and Washington and southern California. Southern California populations colonize Pseudotsuga macrocarpa while individuals from the rest of the range colonize P. menziesii. In addition, S. oregoni males from California and particularly southern California have a greater impression of the second ventrite and thicker margin between ventrite 1 and 2 to specimens from Oregon and Washington.
Head. Epistoma weakly emarginate; epistomal process present, moderately developed, low; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally from epistoma to vertex, slightly transversely impressed just above epistoma to inner apices of eyes; moderately, coarsely longitudinally aciculate-punctate; aciculations converging at epistoma; punctures large, dense, coarse; moderately, uniformly covered by long, fine, yellow, erect, hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate. Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae weakly impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae weakly impressed. Declivity bearing sparse, short, erect, yellow setae. Metepimeron halflength of metanepisternum.
Venter. Apical margin of ventrite 1 rounded, marked by weak carina on ascendant part of venter, more strongly marked laterally. Ventrite 2 nearly perpendicular to ventrite 1; surface reticulate, shagreened, dull, finely punctate; punctures small, fine, shallow punctures; covered with sparse setae that are about twice size of a puncture; surface convex; armed with large conical median spine, apex rounded; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
The adult gallery is parallel to the grain of the wood and bayonet shaped (Fig. 24). From the central nuptial chamber, one egg gallery extends to the grain of the wood and the other egg gallery is slightly transversely extended and then extends parallel to the grain. The nuptial chamber is oblique to the egg galleries. The adult gallery equally scores the sapwood and cambium but in some instances may only lightly score the sapwood. Adult galleries average 5.0-8.0 cm in length. Ten to 30 egg niches are widely spaced and deeply score the sapwood. Larvae extend their mines perpendicular to the egg gallery before diverging in a fan shaped pattern. Pupation may occur under the bark or in the sapwood (Edson 1967;Bright and Stark 1973). There is likely one generation per year (Bright and Stark 1973;Furniss and Johnson 2002).
Remarks. The female paralectotype has been returned to CUIC from the CNCI following the repositories listed in Swaine (1910).
Diagnosis. Scolytus praeceps is a morphologically variable species across its range. Both sexes most closely resemble S. obelus and are differentiated by the absence of a median tubercle on the apical margin of ventrite 2 in both sexes. The female is differentiated from that of S. dentatus by the presence of a weakly developed and almost indistinct epistomal process and smaller size.
Head. Epistoma weakly emarginate; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing convex when viewed laterally, slightly transversely impressed just above epistoma and along median line to upper level of eyes (may not be impressed in some specimens); moderately, coarsely, aciculate-punctate; aciculations converging at epistoma; punctures small, coarse; moderately, uniformly covered by long, fine, yellow, erect, hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, ovoid, setose with partial septum, two arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae not impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 strongly, acutely produced forming lip along base of ventrite 2, basal margin of ventrite 2 appearing impressed. Ventrite 2 nearly perpendicular to ventrite 1; surface glabrous, shagreened, finely punctate (obscurely punctate in some specimens); punctures small, fine, shallow; surface weakly concave; apical margin unarmed or armed with a longitudinal carina and blunt tubercle, appearing keel-shaped or a low median longitudinal carina; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 equal to combined lengths of ventrites 3 and 4; setal patch and median depression absent. Female. 1.7-3.5 mm long (mean = 2.69 mm; n = 20); 2.0-3.0 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, frons more strongly convex when viewed laterally, weakly aciculate, setae sparser, shorter, less than width of eye; entirely convex to weakly transversely impressed just above epistoma. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Apical margin of ventrite 2 unarmed or weakly longitudinally tumescent.   Biology. Scolytus praeceps prefers to colonize fresh slash but is also found in small limbs and tops of small standing trees (Edson 1967;Bright and Stark 1973).
The adult gallery contains two egg galleries that branch from the central nuptial chamber. Typically, one egg gallery extends from the nuptial chamber perpendicular to the grain of wood and the second egg gallery extends at a 45° angle to the grain (Fig. 24). Occasionally both egg galleries are extended obliquely to the grain, at a 45° angle to the grain or perpendicular to the grain (Edson 1967). Galleries are frequently initiated near branch crotches and disguised under rough patches of bark. The adult gallery equally scores the sapwood and cambium. The adult galleries range in size from 2.5-6.4 cm in length. Eggs are laid in niches on both sides of each egg gallery and larval mines radiate perpendicular to the egg gallery. The larval mines gradually diverge forming a fan shaped pattern and lightly etch the sapwood. Pupation occurs in the sapwood (Edson 1967). There is one generation per year and broods overwinter as larvae (Furniss and Johnson 2002).
Remarks. There has been a great deal of historical uncertainty regarding the placement of S. abietis and S. opacus since they were described. The species are extremely morphologically similar and thus difficult to differentiate. This similarity led several authors to treat S. abietis as either a synonym of S. opacus (Wood 1982) or as a subspecies (Bright 1976). Equihua-Martínez and Furniss (2009) removed S. abietis from synonymy with S. opacus based on differences in host use, submentum shape, and striations on the underside of the head and characters of the second ventrite including setae, punctures and spine shape. The species S. abietis, S. opacus and S. praeceps were not recovered as monophyletic in any of our analyses (Figs 2, 8, 9). We observed very low intraspecific COI and ArgK nucleotide differences among populations (COI: 0-0.0049; mean = 0.0032), (ArgK: 0-0.0044; mean = 0.0024) and no differences in 28S or CAD (Table 6). Considerable variation was also observed in the shape of the spine on the male second ventrite, especially within S. praeceps. Scolytus abietis and S. opacus are here placed in synonymy with S. praeceps because they were recovered as polyphyletic (Figs 2,8,9), there are minute molecular difference among populations sampled from California, Oregon, Idaho and Wyoming (Table 6), the species have identical galleries (Edson 1967, Wood 1982 and variability of the spine on male ventrite 2. The lectotype of S. praeceps bears a partial locality label. LeConte's (1868) description states that the lectotype was collected at Calaveras, California by Mr. Crotch. Blackman, 1934 Figs 45, 49-50 Scolytus reflexus Blackman, 1934: 13. = Scolytus virgatus Bright, 1972: 1490. syn. n. = Scolytus wickhami Blackman, 1934: 13. syn. n.

Diagnosis.
Males exhibiting the reflexus phenotype are readily distinguished by the presence of a strong recurved subapical carinate ridge on ventrite 5 that is medially produced to form a slightly recurved and subrostriform ridge that appears "reflexed". Males of this species exhibiting the wickhami phenotype are easily confused with males of S. monticolae. They are easily distinguished by the size of male ventrite 5. In S. reflexus, ventrite 5 is equal in length to ventrite 4. In S. monticolae, ventrite 5 is equal in length to ventrites 3 and 4 combined. Scolytus monticolae lacks an epistomal process while S. reflexus typically has a strongly developed epistomal process. Females are distinguished from those of S. monticolae by having the apical margin of ventrite 1 rounded and by the ventrite 2 surface rugose, shining, coarsely punctate and convex.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical, anterolateral and lateral margins bearing sparse, erect, yellow, hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae weakly impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae less than length of a puncture; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
The adult gallery consists of two egg galleries and a central nuptial chamber. The adult gallery is parallel to the grain of the wood and bayonet shaped (Fig. 24). From the central nuptial chamber, one egg gallery extends parallel to the grain of the wood and the other egg gallery is slightly transversely extended and then extends parallel to the grain. The nuptial chamber is oblique to the egg galleries. The adult gallery equally scores the sapwood and cambium and averages 3.9-7.6 cm in length. Egg niches are closely spaced and score the sapwood. Larvae extend their mines perpendicular to the egg gallery before diverging in a fan shaped pattern. Pupation may occur under the bark or in the sapwood (Edson 1967).
Collection notes. The senior author has collected S. reflexus in the Chiricahua Mountains, Arizona and Apache Point Observatory, New Mexico killing small (less than 10.0 cm DBH) Douglas fir trees. This species was also reported killing Douglas fir in the Sacramento Mountains and Santa Fe National Forest of New Mexico, and was tentatively and incorrectly identified as S. monticolae (USFS 2004). Scolytus monticolae strongly resembles S. reflexus (see diagnosis) but does not occur in New Mexico.
Remarks. Wood (1977: 388) placed S. reflexus and S. wickhami in synonymy with S. tsugae. Wood (1982) removed S. reflexus from synonymy with S. tsugae. In this publication he also listed S. wickhami as a synonym of S. reflexus and cited Wood (1977) for the synonymy. Wood and Bright (1992: 364) also cite Wood (1977) for the synonymy. However, S. wickhami was never removed from synonymy with S. tsugae and designated as a synonym of S. reflexus.
In his description of S. virgatus, Bright (1972) posited that the species was closely related to S. wickhami or either a subspecies or variety. Wood (1982) considered S. wickhami a synonym of S. reflexus, but as discussed above, never formally placed it in synonymy. All three species are here treated as one slightly morphologically variable species. We assessed intraspecific variation within these three species for four genes (Table 6). It was small for each gene with the average divergence of 1.3% for COI and less than 0.12%, 0.03% and 0.29% for 28S, CAD and ArgK respectively among sampled populations (Table 6). These ranges are consistent with variation observed within other species. There are two main characteristics found that vary among the populations: the male fifth ventrite carina and the male epistomal process. There are two main phenotypes observed in populations: reflexus and wickhami. The reflexus phenotype includes individuals that were previously considered to be S. reflexus with the male ventrite 5 armed with a strong recurved subapical carinate ridge that at its crest is closer to the basal than the apical margin of the segment. The length and height of the subapical carinate ridge is also variable within populations. This character is only found in the Chiricahua Mountains, Arizona and in Mexico. The wickhami phenotype includes individuals that were formerly considered S. wickhami and S. virgatus. In the wickhami phenotype the process on the male fifth ventrite is reduced in the wickhami phenotype and but still forms strong recurved subapical carinate ridge. However it is important to note that both the reflexus and wickhami phenotypes are sympatric in the Chiricahua Mountains. The male epistomal process also varies from a strongly developed and elevated ridge above the epistoma to weakly developed and elevated ridge. In general, the ridge is more strongly developed in the reflexus phenotype but considerable variation is observed especially in the wickhami phenotype. Additional variation is observed in the density of punctures on the male second ventrite and the coarseness of the male frons aciculations. In addition, the gallery structure of S. reflexus and S. wickhami are identical; the gallery of S. virgatus is has not been noted. Scolytus wickhami and S. virgatus are here designated as synonyms of S. reflexus. Blackman, 1934 Figs 52-53 Scolytus robustus Blackman, 1934: 19. Diagnosis. The S. robustus male is quite distinctive with its strongly flattened frons, apical margin of ventrite 1 strongly, acutely produced forming a lip along the base of ventrite 2, basal margin of ventrite 2 appearing impressed and by the unarmed apical margin of ventrite 2. The female is morphologically similar to that of S. ventralis. The S. robustus female is distinguished by having the apical margin of ventrite 1 forming a carinate lip along the basal margin of ventrite 2.
Head. Epistoma moderately emarginate; epistomal process strongly developed and elevated; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally, slightly transversely impressed just above epistoma; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures small, coarse; moderately and uniformly covered by long, fine, yellow erect hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two sharply arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, weakly serrate apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae less than length of a puncture; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Biology. Scolytus robustus is found in the limbs and tops of its host and fresh slash. Galleries are often initiated near limb bases (Edson 1967).
The adult gallery contains two egg galleries that branch from the central nuptial chamber. Gallery shape is quite variable and ranges from 'S' shaped at an oblique angle to the grain to nearly perpendicular against the grain (Fig. 25). Typically one egg gallery obliquely extends from the central nuptial chamber against the grain of wood for a short distance before becoming apically recurved. The second egg gallery is identical to the first but runs in the opposite direction. However galleries may extend perpendicular to the grain of the wood or may not be apically recurved. The adult gallery deeply scores the sapwood and ranges in size from 2.5-7.0 cm in length. Egg niches are distinct, score the sapwood and are closely spaced along the egg galleries. Larval mines rapidly diverge perpendicular to the adult gallery and are parallel to the grain of the wood. Larval mines terminate in pupation chambers that score the sapwood (Edson 1967).
Collection notes. The senior author collected this species from 10.0 cm diameter slash with thick (5.0 mm) bark.
Remarks. A relatively large amount of intraspecific variation (0.0537) was observed in mitochondrial COI sequences from specimens collected from Arizona and New Mexico and low variation observed between the two Arizona populations (Table 6). Scolytus robustus only occurs on Abies. In southeastern Arizona, Abies spp. and S. robustus are confined to high elevation sites on the sky islands. These Arizona populations are isolated from the New Mexico populations by large areas that are unsuitable for Abies. No specific geographic morphological differences were observed among the examined specimens. Bright, 1972, valid sp. Fig. 54 Scolytus silvaticus Bright, 1972Bright, : 1489 Diagnosis. The male is distinguished from other species by having the apical margin of ventrite 4 thickened, forming a broad carina with a blunt median tubercle. The female is distinguished from the morphologically similar male of S. hermosus by having the apical margin of ventrite 1 produced, forming a carinate lip along the basal margin of ventrite 2 that is about half as produced as thick and by the host and is distinguished from the S. hermosus female by having a strongly developed epistomal process.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, dark yellowbrown setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; bearing sparse, recumbent, long, dark yellow-brown setae; striae weakly impressed. Declivity bearing abundant, long, erect dark yellow-brown hair-like setae. Metepimeron half-length of metanepisternum.
Venter. Apical margin of ventrite 1 moderately elevated above base of ventrite 2, ventrite 2 appearing impressed. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; setae small, about two diameters of a puncture in length; surface flattened; lateral margins of ventrites 2-3 unarmed. Apical margin of ventrite 4 thickened forming a broad carina with blunt median tubercle. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Hosts. Pseudotsuga menziesii (Mirb.) Franco (Douglas fir). Biology. Scolytus silvaticus is only known from a single collecting event from broken branches of Pseudotsuga menziesii (Bright 1972). The gallery and biology of this species are unknown but the gallery structure is presumably similar to that of other Pseudotsuga feeding Scolytus, parallel to the grain of the wood.
Remarks. Wood (1975: 22) placed S. silvaticus in synonymy with S. hermosus because it occured on the same mountain as S. silvaticus. Wood reasoned that only one Scolytus species could occur in the same location and that the observed morphological variation was due to intraspecific differences. In addition, he stated that Bright's image of the S. silvaticus male was a normal male of S. hermosus. We here remove S. silvaticus from synonymy with S. hermosus because of the many distinct morphological and host differences originally noted by Bright (1972). In the male of S. silvaticus, the apical margin of ventrite 1 is moderately thickened and weakly produced, the posterior margin of ventrite 3 is slightly medially thickened and the posterior margin of ventrite 4 is in strongly produced and thickened medially, forming a broad carina with a blunt median tubercle. In the male of S. hermosus ventrite 1 apical margin is thickened and strongly produced and ventrites 3-4 are flat and S. hermosus colonizes Abies species rather than Pseudotsuga. It is also not uncommon for multiple Scolytus species to have overlapping distributions.
Diagnosis. The male most closely resembles those of S. obelus and S. praeceps. It is distinguished from that of S. obelus by the sparse, obscure, fine and shallow punctures of ventrite 2, by the dull luster of ventrite 2 and by the geographic distribution. The male can be distinguished from that of S. praeceps by the presence of a median denticle on the apical margin of ventrite 2. Females closely resemble those of S. ventralis and are distinguished by the distinctly, moderately longitudinally aciculate and weakly punctate frons, and by the weakly produced apical margin of ventrite 1 that forms a weak carinate lip along the basal margin of ventrite 2.
Head. Epistoma moderately, very broadly emarginate; epistomal process moderately developed and elevated; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing convex when viewed laterally, slightly transversely impressed just above epistoma; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures minute, fine; moderately and uniformly covered by long, fine, yellow, erect hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, ovoid, setose with partial septum, three arcuate sutures visible.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; punctures bearing short, sparse, recumbent yellow setae slightly longer than size of a puncture (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Female. 3.1-5.0 mm long (mean = 3.85 mm; n = 20); 1.9-2.6 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, frons more strongly convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye. Biology. Furniss and Kegley (2011) provide a detailed and thorough account of the biology of S. subscaber. Adults infest suppressed branches in the crowns of mature trees and are rarely found in slash (Edson 1967;Furniss and Kegley 2011). Scolytus subscaber is also associated with a staining fungus, Spicaria anomala (Corda) Harz. that kills the host cambium (Wright 1938).
Adult galleries are distinct from those of other Scolytus species. They are epsilon ("ε") shaped and deeply excavated in the sapwood (Fig. 25). The gallery consists of a central nuptial chamber and two egg galleries that are recurved around the nuptial chamber (Edson 1967). The adult gallery is 2.0-5.0 cm in length and varies by branch size, with larger branches having larger galleries (Furniss and Kegley 2011). Egg niches lightly score the sapwood. In Oregon 12-30 eggs are laid per gallery and in Idaho the upper limit appears to be 12 (Furniss and Kegley 2011). Larval mines radiate from the egg gallery in all directions, often crossing each other. The larval mines are located in the phloem and cambium for about the first centimeter of their length. After the first centimeter, larval mines lightly score the sapwood. Pupation chambers are formed in the cambium or outer bark. There is one generation per year and the brood overwinters as larvae. In Idaho, flight occurs in July and adults leave the gallery once eggs have been laid (Furniss and Kegley 2011).
Collection notes. Old galleries of this species were observed by the senior author while hiking along the Tuolumne Grove Trail in Yosemite National Park on 23.VII.2010.
Remarks. The lectotype bears a partial locality label. LeConte's (1868) description states the lectotype was collected at Vancouver Island.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, dark yellowbrown, hair-like setae; base weakly bisinuate.
Elytra with sides sub-parallel on basal half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae; striae weakly impressed, elytra with a corrugated appearance. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.
Common name. Hemlock engraver. Biology. Scolytus tsugae attacks fresh slash, the main bole and large branches of hemlock (Edson 1967).
Scolytus tsugae is an uncommon and poorly studied species. The adult galleries are typically perpendicular to the grain of the wood and 4.0-10.0 cm in length (Fig. 25) (Edson 1967;Furniss and Johnson 2002). Adult galleries score the cambium slightly more than the sapwood. However, Edson (1967) reported that specimens from a series in northern California produced an adult gallery that was oriented obliquely to the grain of the wood. Galleries consist of a central nuptial chamber and two egg galleries. Each egg gallery is extended perpendicular to the grain of the wood from the central nuptial chamber. Egg niches are irregularly spaced and faintly score the sapwood. Larval tunnels are extended parallel to the grain of the wood, etching the sapwood lightly at first and deeply near the pupation chamber. There is one generation per year and broods overwinter as larvae (Furniss and Johnson 2002).
Collection notes. The senior author collected this species from fresh logging slash limbs that were 6.0-10.0 cm in diameter in Idaho and Oregon.
For many years S. monticolae was considered a synonym of S. tsugae (see S. monticolae remarks). In their paper describing the biology of S. tsugae, McMullen and Atkins (1959) actually described the biology of S. monticolae. In their investigation the species studied was from Pseudotsuga menziesii rather than Tsuga spp. and created vertical instead of transverse galleries.  Blackman, 1934: 23. Diagnosis. Scolytus unispinosus is very morphologically similar to S. fiskei and S. laricis. Males are distinguished from those of S. laricis by the frons flattened when viewed laterally, never deeply impressed, less moderately abundant frontal setae (compared to dense) and by the host genus, Pseudotsuga. Males are distinguished from those of S. fiskei by the following combination of characters: abdominal venter dull in luster, the base of the ventrite 2 spine extending from the apical margin to half the length of the segment and by the geographical distribution. The female is distinguished from that of S. fiskei by the dull luster of ventrite 2 and is distinguished from that of S. laricis by the finely aciculate-punctate frons; ventrite 1 joining base of ventrite 2 more obtusely, base of ventrite 2 not finely impressed, flush with ventrite 1; epistomal process weakly developed, almost indistinct.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, twice width of striae, punctures uniseriate, smaller than those of striae; bearing short, sparse, recumbent yellow setae slightly longer than size of a puncture (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.
Venter. Apical margin of ventrite 1 rounded, marked by weak carina. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow, nearly obscure; covered with sparse setae that are less than length of segment 3; surface convex; apical margin armed with laterally compressed, median spine with base extending from apical margin to half length of segment, apex rounded; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.
Common name. Douglas-fir engraver. Biology. Scolytus unispinosus is very common (Chamberlin 1939; Smith pers. obs.) and attacks the boles and branches of weakened, injured, dying and recently killed Douglas fir. Populations of this species can build up in windfalls, slash and during drought when the species becomes capable of killing young trees (Keen 1938;Chamberlin 1939;Wood et al. 2003). Outbreaks are sporadic and are of short duration (Keen 1938;Wood et al. 2003).
The adult gallery of this species consists of a single egg gallery that extends with the grain of the wood (Fig. 25). The nuptial chamber includes a short extension at a 45° angle from the egg gallery and is located at one end on the egg gallery. The gallery deeply scores the sapwood and lightly scores the cambium (Chamberlin 1958). The female deposits 40-100 eggs in egg niches on both sides of the egg gallery 0.5-1.0 mm apart (Doane et al. 1936). Larvae extend their mines at a right angle to the egg gallery forming a fan shaped pattern (Chamberlin 1939). There are two generations per year in California and the broods overwinter as either eggs or larvae (Keen 1938;Wood et al. 2003). Adults emerge from late April through July (Keen 1958). In Oregon one generation per year has been observed at high elevations in and two at lower elevations (Chamberlin 1939). McMullen and Atkins (1962) reported some notes on the biology of S. unispinosus in British Columbia and appear to have reported a combined account of S. unispinosus and S. fiskei (see S. fiskei biology for more information). This paper was the main source of information regarding the biology of S. unispinosus and served as the basis for describing the biology of the species in numerous publications (including Bright 1976;Furniss and Carolin 1977;Furniss and Johnson 2002;Wood et al. 2003). Chamberlin (1939Chamberlin ( , 1958 provides the most reliable source of information regarding the biology of the species. Remarks. There are 25 S. sobrinus specimens bearing paratype labels found in the EMEC. These specimens are not designated as such by Blackman (1934) and have been labeled "not Paratype" by the authors. These specimens bear the following Hop- Diagnosis. Males are distinguished from those of other species by having the base of ventrite 2 elevated, the surface of ventrite 2 flat, the apical margin of ventrite 2 often bearing a median denticle, and by the glabrous ventrite 2. Females most closely resemble those of S. robustus and S. subscaber. Females are distinguished from those of both species by the indistinctly and weakly aciculate and strongly punctate frons and by the apical margin of ventrite 1 flush with basal margin of ventrite 2, appearing rounded.
Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow, hairlike setae; base weakly bisinuate.
Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.
Adult galleries are perpendicular to the grain of the wood (Fig. 25), deeply score the sapwood, lightly score the cambium and consist of two egg galleries with a central nuptial chamber (Edson 1967). The nuptial chamber is typically short and at a right angle to the egg galleries but may also extend at an oblique angle. When this occurs, one of the egg galleries is briefly extended at an oblique angle against the grain before becoming perpendicular to the grain (Edson 1967). Eggs are deposited singly in triangular niches spaced 1.0-1.5 mm apart on each side of the egg gallery with 80-300 niches per gallery. Galleries range in size from 8.0-30.0 cm in length (Chamberlin 1958;Edson 1967;Bright and Stark 1973;Furniss and Johnson 2002). Larval mines are perpendicular to the egg gallery and parallel to the grain of the wood. Larval mines are also parallel to each other both above and below the egg gallery, giving the gallery a diamond shaped appearance (Keen 1938;Edson 1967). Larval mines lightly score the sapwood and deeply score the cambium. Larvae construct pupation chambers in the phloem or outer bark (Edson 1967). Broods overwinter as larvae or adults (Bright and Stark 1973). The number of generations per year varies both geographically and with elevation. Development time can range from as little as 41 days at low latitudes and elevations to as many as 380 days at high latitudes and elevations (Bright and Stark 1973). There is typically one generation per year (Bright and Stark 1973). In Idaho pupation occurs from June to July and peak flight occurs in July (Furniss and Johnson 2002).
Remarks. The lectotype does not bear a locality label. LeConte's (1868) description states that George Gibbs collected the lectotype in the Washington Territory.

Key to the Nearctic adults of Scolytus
This is the first key to both sexes of Nearctic Scolytus adults. Unlike previous keys (e.g. Edson 1967;Wood 1982) apriori knowledge of the gender is not required. Only one sex is necessary to identify the specimen and host species or gallery types are not needed. Because the sexual dimorphic characters are not consistent for the Nearctic species (see sexual dimorphism discussion above), the sexes could not be evenly split. In general, males and females of native hardwood-feeding species will key out beginning at couplet 3 and both sexes of some Abies feeding species beginning at couplet 23. The key lists the gender of the identified specimen. If no gender is specified, the identification applies to both sexes. The length of frons setae is measured relative to the width of the midpoint of the eye.

1
Elytral apices narrowly rounded (Fig. 60A)  Apical margin of ventrite 4 armed by an acute median denticle; apical margins of ventrites 2 and 3 may also each bear a smaller median denticle (variable Apical margin of elytra produced between interstriae 1 and 2, deeply emarginate at interstria 3, produced on interstria 4 and deeply emarginate at stria 4; ventrite 2 armed with a laterally compressed tubercle that extends from the apical margin of ventrite 2 to approximately ¾ the length of ventrite; frons weakly longitudinally aciculate, strongly punctate; epistoma strongly emarginate .. Apical margin of ventrite 1 thickened or produced on the ventral and/or lateral margins, forming a carinate lip along the basal margin of ventrite 2, often weakly produced in S. monticolae and S. tsugae; surface of ventrite 2 flat to impressed (Fig. 61B)  Spine on ventrite 2 extending from apical margin to three-fourths length of ventrite; ventrite 2 surface shining (Fig. 62A)

Discussion
Morphology failed to resolve the Scolytus phylogeny and very few synapomorphic characters were found (Fig. 2). Unique combinations of homoplastic characters define species limits. Characters that are among the most informative are sexually dimorphic and male including: male fifth ventrite carina (character 36), size and coarseness of frons punctures (character 7), first ventrite apical margin (character 27), second ventrite surface (character 29) and presence of an epistomal process (character 2). Other nondimorphic informative characters included elytral apex emargination (character 20), host (character 43), and strial impression (character 18). The lack of phylogenetically informative characters necessitated the need for further investigation using molecular characters to illuminate species boundaries. As in other phylogenetic studies, COI data failed to recover many species as monophyletic ( Fig. 3) (Cognato et al. 2005;Jordal and Hewitt 2004). Several relationships found in this phylogeny did not agree with the topologies obtained from different analyses. For example a hardwood-feeder, S. rugulosus, was found to be sister to the conifer clade in the Bayesian analysis and S. ventralis was found to be sister to the Nearctic conifer clade. In addition, the hardwood clade was paraphyletic with S. fagi and S. muticus forming one lineage and S. quadrispinosus as sister to S. multistriatus. Saturation of nucleotide substitutions and a lack of lineage sorting are potential reasons for the discordance among these mitochondrial and nuclear phylogenies (Sota and Vogler 2001;Funk and Ohmland 2003;Lin and Danforth 2004). The mitochondrial phylogeny may suffer from both phenomena because of the observed poor resolution and support for deeper nodes and short-branch lengths among the conifer-feeding species (Fig. 3). As with other studies, concatenating the COI dataset with multiple genes and morphology remedied its deficiency and elucidated the relationships among the Scolytus species (Jordal and Hewitt 2004). When analyzed together, the genes used in this study (COI,28S,CAD,ArgK) were useful in resolving the Scolytus phylogeny and species limits. These genes have demonstrated similar phylogenetic utility in other scolytine studies (Cognato and Sperling 2000;Farrell et al. 2001;Jordal et al. 2002;Jordal and Hewitt 2004;Cognato et al. 2005;Cognato and Sun 2007;Jordal et al. 2008;Dole et al. 2010;Jordal et al. 2011;Jordal and Cognato 2012). Overall, the model-based rates of nucleotide evolution utilized in Bayesian analysis combined with all four genes and morphology allowed us to recover a well-supported and sufficiently resolved phylogeny which enabled the revision of Scolytus (Fig. 4).
Nearctic Scolytus were recovered as paraphyletic in two clades, native hardwood and conifer (Fig. 4). A group of introduced Palearctic species was also found. Members of the native hardwood clade are sister to the Scolytus scolytus subgenus sensu Butovitsch (1929) rather than the native conifer clade. This is supported by morphological similarities between the two groups. The clade containing the S. scolytus subgenus sensu Butovitsch and the native hardwood-feeders share a median impression on male ventrite 5 (except S. laevis and S. quadrispinosus) and a setal patch on ventrite 5 (except S. laevis and S. quadrispinosus). Several species in these groups also share the absence of a carina on male ventrite 5 (S. laevis, S. mali, S. ratzeburgii, S. fagi and S. muticus).
the American Museum of Natural History Theodore Roosevelt Memorial Grant, Entomological Society of America Systematics and Evolutionary Biology student travel grant, Museum of Comparative Zoology Ernst Mayr Travel Grant in Animal System-