Orthostolus Sharp

Ewing, Curtis, 2007, Phylogenetic analysis of the genera of endemic Hawaiian sap beetles (Coleoptera: Nitidulidae) based on morphology with redescription and key to the genera of endemic Hawaiian Nitidulidae, Zootaxa 1427, pp. 1-36 : 22-23

Orthostolus Sharp

TYPE SPECIES: Brachypeplus robustus Sharp 1878: 134 (subs. desig., Sharp in Sharp & Scott, 1908: 452). Brachypeplus: Sharp 1878: 131 (syn. in part).

Orthostolus Sharp in Sharp & Scott, 1908: 452 [n. gen., n. spp.].

Orthostolus : species 5–9 ( Sharp & Scott, 1908: 454–456) removed to Apetasimus .

Diagnosis: Size medium to large, 4.5–7.7 mm L; 1.5–3.0 mm W. Size and color highly variable within species. Males usually dark brown to nearly black, dark markings weakly contrasting; females pale yellow to dark brown often with strongly contrasting dark markings similar to Eupetinus Sharp , most conspicuous on scutellum and abdomen. Pronotum with U-shaped area of anterior directed setae at anterior margin behind head. Antennal club compact, 9th antennomere transverse. Microsculpture of dorsum variable among species and within species, from granulate to fine lines, never obsolete and glabrous.

Description: Eyes small, facets fine; temple short, acute, postgenae forming obtuse angle with occiput. Antennal grooves convergent, medial and lateral margins distinct. Antennal club elongate, antennomere nine transverse. Labrum with two pairs dorsal macrosetae; medial tooth broadly rounded; laterally sinuate to bisinuate, each side with two distinct patches of ventromarginal setae, a smaller patch of short setae adjacent to medial projection and a larger, longer patch before the lateral angle. Mandibles each with two apical teeth and three to six stout subapical teeth. Third labial palpomere subtransvers to weakly elongate, narrowed slightly distally.

Prothorax transverse. Lateral margins smoothly curved or recurved at posterior angle; smooth to weakly crenulate, marginal setae elongate, moderately dense for entire length. Pronotum with area of anterior directed setae behind at anterior margin behind head; remaining setae directed posteriorly. Prosternal process greatly expanded posterad of coxae, 2– 3 x minimum width between coxae; little recurved dorsad posterad of coxae; broadly curved at apex.

Elytra 2x as long as wide or less; lateral margin greater than 2x width of marginal bead, widest near humeral angle. Punctures of elytra coarse, forming distinct striae; striae 1–8 nearly regular, 9 and 10 with punctures reduced, and increasingly more irregular toward elytral margin. Interstices of elytra slightly raised; wide with multiple confused rows of setae; interstices 6 and 7 dilated near middle, often extended distally and/ or proximally. Surface of elytra nearly even to distinctly uneven. Elytra exposing abdominal segments 7, 6, and part of 5.

Tarsomeres 1–3 with ventral lobes progressively dilated and bilobed.

Male pygidium shallowly and broadly or narrowly emarginated to broadly rounded, angles rounded. Anal sclerite broadly rounded, truncate, or shallowly emarginate with angles rounded. Perisac length and form variable, from depressed and sub parallel to narrow proximally with distal 1/3–1/4 expanded; flagellum reduced proximad of junction with sperm duct, flattened and truncate at proximal apex. Female pygidium broadly rounded; gonocoxae elongate. Basal ring of spermatheca weakly sclerotized.

Orthostolus sensu stricto is distributed on Kauai, Oahu, and Maui Nui and contains four described and five undescribed species. Orthostolus sensu lato includes 14 species from all of the high islands ( Sharp & Scott 1908) though five described taxa are herein moved to the genus Apetasimus . The taxonomy of Orthostolus s. s. is in need of revision and examination of the male genitalia suggests there are two lineages with plesiomorphic, undescribed species on Kauai, each of which has colonized Oahu, Molokai, and Maui, with one lineage also present on Lanai. On East Maui three species can be collected sympatrically within a single stick, and dissection of male genitalia is required to distinguish them. Two of these species are present on West Maui. Two species were described from Oahu, Orthostolus nepos Sharp and Orthostolus robustus (Sharp) . Orthostolus robustus is found in both the Waianae and Koolau Mts. on Oahu and specimens from Lanai were included in the Fauna Hawaiiensis redescription ( Sharp 1878; Sharp & Scott 1908). The Lanai specimens previously considered O. robustus represent a distinct species; the male genitalia show it to be allied with Orthostolus germanus Sharp of Molokai. Orthostolus nepos was collected in the southern Koolau Mts. near Honolulu and is known from four male and one female specimen. Based on external morphology they appear to be allied with O. germanus and the Lanai specimens of O. robustus .

All species of Orthostolus s. s. are closely associated with decaying Hawaiian lobelioids in mesic and wet forests. Individuals can be found in actively decaying tissue of stems, droopy leaves, fruit, and flowers. Orthostolus are all fully winged and can be collected occasionally on other plants in areas were their hosts occur. They are often very numerous with large numbers of both adults and larvae found together, and often share the substrate with species of Eupetinus , especially E. impressus (Sharp) . The species exhibit a high degree of intraspecific variability that overlaps that of other closely related species. They are variable in dorsal microsculpture, punctation, evenness of the surface, coloration, and the degree of sinuation at the hind angle of the pronotum.

Orthostolus is similar to Cillaeopeplus ecologically and exhibits the same biogeographic pattern of speciation primarily through colonization from older to younger islands with little within-island differentiation.