A new West African genus of Bostrichidae (Coleoptera), and a key to the Afrotropical genera of tribe Xyloperthini

. A new genus, Plesioxylion Liu & Beaver gen. nov., is described for Amintinus gambianus Borowski, 2018 from West Africa with a more detailed description and new records of both sexes. We also provide a key to the ten Afrotropical genera in the tribe Xyloperthini Lesne, 1921 as the baseline information for a future study.


Introduction
The tribe Xyloperthini Lesne, 1921 is the most genus-rich tribe in the Bostrichidae Latreille, 1802, and currently includes 36 genera (Borowski & Węgrzynowicz 2007;Park et al. 2015;Liu et al. 2016;Liu & Beaver 2017;Liu 2021;Liu & Sittichaya 2022;Zhang et al. 2022). Nine genera of Xyloperthini are distributed throughout the Afrotropical region. The tribe is characterised by the lamelliform intercoxal process of the first abdominal ventrite, which is visible only as a narrow carina, and does not have a distinct ventral face, and by the mandibles which cross at their tips (Lesne 1921;Fisher 1950;Liu & Schönitzer 2011). The species are not major economically important pests, and as a result, there is little information available on their biology. A few species have been studied by Beeson & Bhatia (1937) and Liu et al. (2008). The adults are polyphagous, usually attacking a taxonomically wide variety of host trees, although they may appear to show some host preferences. They bore into twigs and branches, where they construct a short gallery, usually consisting of a circumferential, and one or more longitudinal branches in which the eggs are laid (Liu et al. 2008). The larvae bore through the wood making extensive galleries filled with fine wood particles and excreta. The new generation of adults emerges through the bark, but may reattack the same stem, so that the whole of the sapwood is eventually converted into fine powder (Liu et al. 2008). Borowski (2018) described a new species, Amintinus gambianus, collected from Gambia and provided SEM photos of the antennae and elytral declivities of both sexes. The senior author received two male and one female specimens of this species from Institut royal des Sciences naturelles de Belgique, Brussels, Belgium (RBINS), and one female specimen from Mr Klaus-Ulrich Geis. After examining and comparing them with specimens of eight species (seven described and one undescribed) of Amintinus Anonymous, 1939, and the description of A. sakalavus Lesne, 1939, we considered that the species was sufficiently distinct from all other species of Amintinus to warrant its separation into a new genus. In this paper, we describe the new genus and provide new records from Mali and Senegal, West Africa, photos of both sexes, and illustrate the aedeagus of the male. A key to the ten Afrotropical genera of Xyloperthini is provided.

Material and methods
Specimens of the new genus were loaned from the Institut royale des Sciences naturelles, Brussels and donated by Mr Klaus-Ulrich Geis to the senior author. The generic status of the beetles has been ascertained from studies by the senior author of all available xyloperthine types, and other specimens, in the major European museums. We have examined types or reliably identified specimens of 33 out of 36 genera included in the tribe, and have checked the descriptions of the remaining three genera.

Diagnosis
A member of the tribe Xyloperthini characterized by the antennal club segments elongated, the mandibles crossed at the tips, and the lamelliform intercoxal process of the first abdominal ventrite Fisher 1950;Liu & Schönitzer 2011). The new genus is distinguished from other genera of Xyloperthini by the following combination of characters: frons weakly convex, without long upwardly directed hairs on the head in either sex. Mandibles symmetrical, sharply pointed. Antenna with ten antennomeres, including a 5-segmented funicle and 3-segmented club, antennomeres of club lacking stiff, erect hairs, without clear sensory maculae; antero-lateral angle of pronotum with a moderately strong recurved uncinate tooth, pronotum without a lateral carina; posterior part of elytral disc without costae or teeth, elytral declivity obliquely sloping, simple in male, female with a broadly truncate emargination in middle one-third of posterior margin; 5 th abdominal ventrite of male with pleural pieces swollen towards midline of posterior margin; 4 th abdominal ventrite of female with long, thick, golden hairs on anterior part of median impression, and 5 th abdominal ventrite strongly emarginate in middle.
Coloration. Dark brown to black with the antennae, palps, femora, tibiae except for protibiae yellowishbrown. Coxae and protibiae brown. Posterior part of last abdominal ventrite and pleural pieces yellowishbrown.
Head ( Fig. 1B-C). Moderately convex. Frons longitudinally rugose with sparse, semi-erect, short hairlike setae, except shiny and impunctate in narrow median area, and immediately above fronto-clypeal suture. Clypeus granulate, anterior margin weakly emarginate with short erect hairlike setae. Labrum shiny and punctate. Eyes of moderate size, clearly separated from the genae posteriorly. Antennae 10-segmented, scape elongate, 2 nd antennomere slightly shorter than scape; 3-7 antennomeres together distinctly longer than the last club antennomere in length. Club antennomeres without sensory maculae, with sparse erect hairlike setae on the anterior face of 8 th and 9 th antennomeres. PronotuM ( Fig. 1A-C). As long as wide to slightly wider than long, sides evenly curved in basal twothirds, narrowing anteriorly; anterior angle with a moderately strong recurved uncinate tooth; anterior margin strongly, slightly angularly emarginate between the anterior teeth. Anterior slope rugose above margin without distinct asperities, sparse punctures between the rugosities; upper part of anterior slope to summit with small, slightly transverse asperities more or less concentrically arranged. Posterior angles rounded without lateral carinae. Pronotal disc mostly shiny, smooth; coarsely granulate-punctate in middle behind summit; punctures smaller and sparser posteriorly, fine and very sparse on sides; punctures with short, whitish, semi-appressed hairlike setae.
sCutelluM. Small, tuberculiform. elytra ( Fig. 1A, C-D). 1.8-1.9× as long as wide, slightly narrower than pronotum at base, widening slightly towards apex. Parallel-sided, moderately shiny. Basal margin of elytra with a short carina on each side of scutellum. Disc densely, moderately finely granulate-punctate dorsally, the sides more sparsely punctured except close to elytral declivity. Declivity steep, obliquely truncate, its lateral margin raised and costate except on upper margin, the punctures denser and coarser than on dorsal surface; suture swollen on upper two-thirds of declivity and coarsely punctured; a weak impression on each side of suture. Elytral apices separated by a V-shaped emargination. Vestiture of short, whitish, recumbent hairlike setae, longer, yellower and denser on declivity.
legs. Protibiae parallel-sided without teeth on external side. Long hairlike setae on inner side of all tibiae, and on ventral surface of tarsi.
Head. Generally as in male, but median shiny area above fronto-clypeal suture reduced. PronotuM (Fig. 3A, C). Generally as in male, but emargination of anterior margin between teeth on anterior angles shallower, and more evenly curved; pronotal disc behind summit smoother and more shiny, with sparse punctures, becoming smaller and sparser posteriorly.
sCutelluM. As in male. elytra (Figs 3C, E, 4A). Elytral disc and sides generally as in male. Upper margin of declivity indistinct, slightly longitudinally impressed next to suture, broadly convex on each side beyond the impressions. Declivity very deeply, very widely emarginate (Fig. 4A), its lateral margins raised and costate, the surface shiny, weakly convex, coarsely granulate-punctate on upper part, punctures sparser and finer, and granules weaker towards apex, apical angles moderately acute (Figs 3E, 4A); truncated emargination on middle of posterior margin filled by a pair of spatulate processes ending in very elongate, needle-like tips extending well beyond elytral apices (Figs 3E, 4A). Vestiture of disc similar to male, declivity with longer, yellowish hairs on upper part, shorter and sparse apically; processes glabrous.
legs. Similar to male but protibiae with a row of teeth on the external side.  Damoiseau, 1968. D. Xylion securifer . AbDomEn (Fig. 3B, D). Ventrites 1-3 almost equal in length, posterior margin straight; 4 th ventrite slightly shorter with a strongly concave median area posteriorly; just anterior to this a thick brush of golden hairs (Fig. 3D), more than twice as long as ventrite; 5 th ventrite strongly concave with a broadly concave apical margin fringed by dense golden hairlike setae. Ventrites shiny, finely, rather sparsely punctured with short, recumbent, whitish hairlike setae.
oviPositor. Similar to other genera of bostrichids (Lesne 1924), narrow, very elongate, pointed with a pair of short palpiform appendages at apex, adapted for piercing wood. These new records indicate that the species is distributed more widely in West Africa than its original location in Gambia.  offered the first key to the genera of Xyloperthini. Since that time many new genera have been added to the tribe (see Introduction). Liu & Sittichaya (2022) provided a key to the Oriental genera of the tribe. Here we add a key to the ten genera present in the Afrotropical region (only the three (ex 17) species of Xylopsocus which occur in the region have been included).   Discussion Table 1 compares the characters of the new genus with the three genera that are morphologically closest to it (Amintinus, Mesoxylion Vrydagh, 1955, and Xylion). The four genera listed in Table 1 all have ten antennomeres, lack lateral carinae on the pronotum, and the last visible abdominal ventrite of the male has pleural pieces. They are of similar size and proportions (Table 1). It is clear that Plesioxylion gen. nov. is most similar to Amintinus, the genus in which P. gambianus was originally described. Here we justify the separation of the species into a new genus.
The asymmetrical form of Amintinus was also noted by Damoiseau (1968aDamoiseau ( , 1968b in two additional species of the genus. It is in fact present in all species of the genus (LYL, pers. obs.), although the reasons for its occurrence and persistence over evolutionary time are unknown. Asymmetry is also present in Mesoxylion but affects only the mandibles (Vrydagh 1955). In contrast, the mandibles, head and pronotum of Plesioxylion gen. nov. are symmetrical. Table 1. Comparison of characters of Plesioxylion gen. nov. with selected genera of Xyloperthini Lesne, 1921.

Anonymous, 1939
Mesoxylion Vrydagh, 1955 Plesioxylion gen. nov.  Length of body ( The elytral declivity of both sexes of Amintinus varies with species from convex to concave, with simple or slightly sinuate apical margin. There is no marked sexual dimorphism. This differs greatly from the situation in Plesioxylion gambianus. Here the male elytral declivity is steep and simple, whereas the female declivity is strongly emarginate with a pair of long processes. It may be noted that the female of Mesoxylion collaris (Erichson, 1842) has somewhat similar, but smaller, needle-like spines at the apex of the female elytral declivity to P. gambianus (Fig. 4A-B), but these appear to be a parallel adaptation, the function of which has yet to be determined.

Xylion
The aedeagus of two species of Amintinus (A. lootensi Damoiseau, 1968 andA. minutissimus Damoiseau, 1968) has been illustrated, but not described (Damoiseau 1968a: fig. 10;1968b: fig. 4). The form of the basal pieces and parameres differs considerably between the two species, but in both they appear to be very broad. The basal pieces of Plesioxylion gambianus are much narrower and are sharply pointed apically ( Fig. 2B-C). The parameres are much narrower, and have only a short lateral lobe, unlike the very elongate process seen in A. lootensi (Damoiseau 1968a: fig. 10). The penis of P. gambianus is distinctly expanded at the tip ( Fig. 2C-D), while the penis of the two species of Amintinus is narrowly cylindrical.
The females of Amintinus have the fourth ventrite modified with a pair of processes on the posterior margin in the different species (Lesne 1939). In P. gambianus, the fourth ventrite has no processes, but a long, thick brush of golden hairlike setae projecting over the fifth ventrite.
Plesioxylion gen. nov. is more easily distinguished from the genera Xylion and Mesoxylion, by the absence of sensory maculae on the segments of the antennal club, and the absence of spines on the upper margin of the elytral declivity (Table 1). Xylion also lacks the uncinate pronotal horns present in Plesioxylion.
The tribe Xyloperthini now includes 37 genera, with 10 genera occurring in the Afrotropical region. Following a series of revisions of genera of the tribe Xyloperthini (Liu et al. 2016Liu & Beaver 2017;Liu 2021;Liu & Sittichaya 2022), this study added to knowledge of the Afrotropical fauna, and provided baseline information for a future study, which will revise the tribe Xyloperthini.