Diuncus Hulcr & Cognato
Creators: name: Hulcr, Jiri
name: Cognato, Anthony I.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Curculionidae
Diuncus

description: Genus Diuncus Hulcr & Cognato gen. n.
Type species: Diuncus papatrae (Schedl, 1972).
Diagnosis: Although the overall appearance of Diuncus is unique among Xyleborina, there are rather few characters that unambiguously distinguish the genus. With its bulky, light-colored body, it may resemble some Xylosandrus spp., but can be distinguished by contiguous procoxae. From most other Xyleborina, it can be distinguished by a very robust pronotum usually with two serrations pointing forward on the pronotal anterior edge, by the flattened antennal club of type 1 (obliquely truncated, but unusually thin), slender protibiae (in most species), and most importantly by its short elytral disc and very long, flat, broad, and laterally carinate elytral declivity, usually with one or two pairs of denticles on its summit.
Description: Eyes shallowly emarginate, "bean shaped", upper portion of eyes smaller than lower part. Antennal club more or less circular in shape or slightly asymmetrical, taller than wide, always rather thin. Antennal club type one (truncated, first segment covering posterior side). First segment of club circular around the club, covering the entire posterior face, margin of the first segment clearly costate all around the antenna. Second segment of club narrow, pubescent, visible on the anterior side only. Third segment of club absent from the posterior side of club. First segment of antennal funicle shorter than pedicel, funicle (without pedicel) composed of 4 segments, scapus shape varies from long and slender to short and thick (rare, in the smallest species). Frons above epistoma mostly smooth, alutaceous, with minor punctures. Submentum flat, flush with genae, or slightly impressed, shaped as a very narrow triangle. Anterior edge of pronotum with two distinct flat denticles protruding anteriad. Pronotum from lateral view rounded and robust (type 5). From dorsal view it is rounded (type 1). Pronotal disc shining or smoothly alutaceous, with small punctures, lateral edge of pronotum obliquely costate. Procoxae contiguous, prosternal posterocoxal process short, conical or flat, inconspicuous, or tall and pointed. No sign of mesonotal or elytral mycangial opening. Scutellum flat, flush with elytra. Elytral bases straight, with oblique edge. Punctures on elytral disc in strial lines (which may be difficult to discern). Elytral disc almost always short, often convex, elytral declivity flat, gently sloped, conspicuously broadened and costate along its posterolateral edges, the edges bearing carina, which ends in 7th interstriae. Each of second and third interstriae often bears a tooth or a pointed hook on the summit of declivity, which is the most important diagnostic character of individual species. Elytral declivity with few setae or scales, not conspicuously pubescent, except for small appressed setae in several species. Posterolateral costa ending in 7th interstriae. The inner area of declivity has no tubercles. Striae and interstriae on the upper part of declivity flat and flush, often bearing teeth around the declivity. First interstriae are parallel (sometimes slightly broadened towards elytral summit), or parallel on disc but broadened towards the apex of elytra, where they often bear tubercles. Protibiae sometimes obliquely triangular, broadest at 2/3 of the length, but mostly very slender, slightly broader only at the distal end. Posterior side of protibia flat, smooth, with setae only. Protibial denticles large, distinctly longer than wide, bases of the denticles slightly elevated, or distinctly enlarged, conical, fewer than 6 protibial denticles present. Metatibiae of regular size (not enlarged as in the phylogenetically related Eccoptopterus). Uniformly yellow, orange, light brown or reddish species, pronotum often much lighter (yellow or orange) than elytra. However, some species display a drastic change of color between the lowland and highland populations, with the lowland beetles being yellowish to brown, often bicolored, while the montane forms are typically black. Length: 1.4–3 mm.
Discussion. Morphologically this genus is rather uniform. Within the genus, the main distinguishing feature of many Diuncus spp. is the size and placement of elytral denticles and granules. At the same time, in many cases the size of many of these cuticular processes seems to be correlated, suggesting a single quantitative genetic mechanism. For example, Diuncus haberkorni and Diuncus conidens are both distinguished from other Diuncus spp. by two pairs of equal-sized denticles on the elytral declivity (as opposed to a single pair, or two pairs of unequal size). They differ from each other by the size of the declivital denticles, the size of granules on the apex of elytra, and the size of denticles on the edges of tibiae: all these are larger in D. conidens. However, it is possible that the size of denticles all over the body is driven by a single genetic mechanism, thus all these above mentioned differences are in fact just a single character. It is thus possible that these two species simply occupy different parts of a continuum of morphological change and may eventually be synonymized (as many other Diuncus spp.). Browne (1961) included species of Diuncus into the " mucronatus group".
Etymology: The genus name refers to two spines near the summit of elytra, a distinct character of most Diuncus spp. Gender masculine.
Biology: The genus is mostly of SE Asian and Melanesian distribution, with two species known from Africa. Ecologically, the species are unique in the ability to locate and exploit fungus “gardens” of other ambrosia beetles (Beaver, 1976; Kalshoven, 1960). Browne (1961) provided brief notes on ecology of several Malaysian species, but did not mention any co-occurrence with potential parasitized species. Diuncus spp. are found in all sizes and decay states of wood, from dry twigs to humid trunks.
description: Published as part of Hulcr, Jiri & Cognato, Anthony I., 2009, Three new genera of oriental Xyleborina (Coleoptera: Curculionidae: Scolytinae), pp. 19-36 in Zootaxa 2204 on pages 28-29, DOI: 10.5281/zenodo.189700