Crostis Casey, 1922

Prena, Jens & Anderson, Robert S., 2022, The genus Crostis Casey (Coleoptera: Curculionidae: Baridinae) in North America, Zootaxa 5162 (2), pp. 153-162 : 154-155

Crostis Casey, 1922

Nomenclature. Genus name feminine, made available on page 166 in Casey (1922). Type species C. subexplanata Casey, 1922 by original designation (as subplanata in key on page 105, alternative spelling subexplanata used in description on page 167 and fixed as the correct original spelling on page 507).

Diagnosis. The genus includes 1.8–3.2 mm long species with decussate mandibles, divergent claws, and an anteriorly tubulate prothorax. Characteristic are (i) the angular transition between pronotal disc and flank, (ii) the pair of long, ventrodistal setae on the rostrum, (iii) the deep, variously shaped impression in front of the procoxae, (iv) the prominent lateral ridge on the prosternum with a bare or squamulose fovea (modified to a ventrally directed spine in one species), and (v) the in repose deeply recessed abdomen with distally protruding elytral apices.

Species of similar size and color, with obtusely margined pronotum and exposed elytral apices, occur also in Buchananius Kissinger , Diorymerus Schönherr in the widest sense, Microcholus LeConte , and Zaglyptoides Champion. At least some Diorymerus and Zaglyptoides have similar prosternal depressions with laterally raised margins but all of the above-named genera lack the laterally directed fovea typical for most Crostis .

Redescription. Length 1.8–3.2 mm. Body oblong-ovate, pyriform [termed lyrate in Casey (1922)], or subtriangular; integument glabrous or with widely spaced elongate white scales. Head with widely spaced small punctures, in lateral view with transition to rostrum forming broadly obtuse angle, eyes dorsally separated by width of rostrum; rostrum cylindrical to slightly compressed, as thick as femora and slightly longer than pronotum, arched (more strongly basally, less so apically), dorsally smooth, middle section with ventrolateral edge, ventrodistally with pair of long setae. Antenna with 7 funicular articles, inserted at more or less distal third (both sexes), scape not reaching head in repose, funicle with first article subequal in length to next 2–3 combined, elongate in species with ovate club to compressed in species with cylindrical club, not sexually dimorphic. Pronotum with front abruptly tubulate; flanks generally meeting disc at angle, not transitioning smoothly; disc and flanks variously striate, punctate or uniformly glabrous, glossy; postocular lobe subtle. Mesoscutellum small, quadrate, flat, emarginate behind, upper surface feebly convex. Elytra with 10 complete striae; distal margins protruding beyond abdominal apex, apicoventral ridge sharply produced in steep angle. Hind wings developed. Prosternum with variously sized median excavation (fovea), with anterior margin modified to lamellar rim and projected variously across anterior part of fovea; fovea usually limited at each side by strong longitudinal ridge forming ventral margin of characteristic single, large, laterally-directed fovea (rarely visible only internally on the inner face of the ridge; in one species modified to a ventrally directed spine); procoxae separated by 1/3 their own width. Mesanepisternum and mesepimeron with 5–9 very large punctures on each, metasternum similarly punctate, metanepisternum very narrow, slightly wider posteriorly, with single row of small contiguous punctures, punctures larger posteriorly; sclerolepidia digitate, much reduced in numbers, those present widely spaced. Legs with femora feebly clavate, tibiae not sexually dimorphic, premucro absent, tarsi rather small, narrow, with third article only slightly dilated, tarsal claws small, curved, basally separate. Abdomen with ventrites coarsely punctate to smooth, glossy, suture between ventrites I and II more or less effaced medially, ventrites I and II subequal in length, III and IV subequal in length, together slightly longer than II, V at middle about as long as III and IV together; tergite VII without plectra. Penis asetose, apodemes basally hyaline and fused, endophallus distally with elongate endophallite; duct attached to endophallite either asymmetrically (at one rod or its associated sclerite) or symmetrically (medially); tegmen with basal apodeme long, parameroidal lobes developed.

Natural history. Most specimens were extracted from leaf litter [“hojarasca” or “HR” on some labels] or collected in flight intercept traps. The species occur from the lowlands up to elevations of more than 3000 m. Host associations are presently unknown.

Diversity. We have seen approximately 15 unnamed species from Argentina, Bolivia, Brazil, Costa Rica, Ecuador, El Salvador, Guatemala, Mexico, Nicaragua, Panama, Peru, U.S.A., and Venezuela. The type species, C. subexplanata , is known only from a single specimen collected in Santarém, Pará by H.H. Smith [images available at https://collections.si.edu/search/results.htm?q= Crostis ], probably around 1874/75 ( Kunzler et al. 2011). The specimen is doubtfully distinct from Lamprobaris thoracica (Kirsch, 1875) and might be a junior synonym of the latter. Because of insufficient material and Kirsch’s damaged type, we refrained from dissections and defer the issue to a later revision of the genus with more inclusive material. Baridius thoracicus Kirsch is transferred here from Lamprobaris (placement by Hustache 1938) to Crostis as Crostis thoracica (Kirsch) (new combination).

Most species of Crostis have pyriform or subtriangular elytra, i.e., they are widest in the posthumeral region and rapidly converge from there towards the apex. Oblong-ovate specimens, even though known for decades from the U.S.A. and Mexico, have never been assigned to any known genus because of their unusual habitus among members of the North American barids and the confounded taxonomy of the subfamily. Among those oblong-ovate specimens, which we here call the Crostis boreas species group, we recognize three morphologically similar species and describe them herein. Aside from the more ovate body shape in dorsal view, specimens of the group are also less deep in lateral view, the pronotum is proportionally longer compared to elytral length, elytra have their greatest width more posterior to the posthumeral region, elytral interstriae are wider and flatter than in most pyriform and subtriangular species and have two types of widely spaced white scales/setae (often abraded), the prosternal fovea is more extensively covered by the anterior lamellar projection, and males have medially depressed basal abdominal ventrites. The sexually dimorphic median depression on abdominal ventrites I and II is absent in most (but not all) pyriform and subtriangular species we have seen and none of them (save for an aberrant species from Ecuador) have any punctures on the pronotal flanks, which are glossy. We have seen specimens of multiple pyriform species from Mexico south as far as Argentina; but species of the Crostis boreas species group appear limited to the U.S.A. and Mexico. A complete description of the Crostis boreas species group follows herein.