Neotropical Leaf Litter Beetle Genus Motonerus (Coleoptera: Hydrophilidae): New Species, Distribution Data, and Description of Third Instar Larva

Abstract

Numerous new material of the genus Motonerus Hansen, 1989 (Coleoptera: Hydrophilidae: Sphaeridiinae) was examined over the past decade, resulting in the discovery of several undescribed species as well as new distributional records for most of the previously described species. Three species are here described as new: Motonerus explanatus sp. nov. (Panama), M. inca sp. nov. (Venezuela, Ecuador, Peru, Bolivia) and M. sofiae sp. nov. (Peru). New country records are provided for M. depressus Fikáček & Short (new for Venezuela, Ecuador, Peru and Bolivia), M. hanseni Fikáček & Short (new for Panama) and M. problematicus Fikáček & Short (new for Panama). An updated identification key and distributional maps are provided for all species, along with complete occurrence data in a DarwinCore formatted file. Potential distribution of the genus is modeled using the maximum entropy approach. Wing morphology is examined in detail, which revealed most species are macropterous, with M. andersoni Fikáček & Short being brachypterous, and M. apterus Fikáček & Short, M. oosternoides Fikáček & Short, and M. explanatus sp. nov. micropterous. The third instar of the putative larva of M. obscurus Hansen is briefly described based on larvae collected in association with adults.

Introduction

Motonerus Hansen is a small megasternine genus of terrestrial hydrophilids inhabiting the leaf litter of higher elevation cloud and montane forest areas of Central and South Americas. Hansen (1989) and Fikáček & Short (2006) described eight species occurring from central Mexico to Colombia and western Venezuela. Additional two species from Bolivia were not formally described, pending on the collection of males. Makhan (2009) described two more species of Motonerus from Suriname, but both were recognized as not belonging to the genus and transferred to Oosternum Sharp, 1882 by Short & Fikáček (2011).

Since the publication of the species-level revision of Motonerus by Fikáček & Short (2006), I went through additional material of unidentified Neotropical Megasternini in several North American museums, including newly collected material as well as older holdings. Besides additional specimens of some common Central American species, the examination of this material also revealed additional specimens of species known previously from only a single or very few specimens, including males of one of the species left undescribed by Fikáček & Short (2006). In addition, the material also contains representatives of two previously unknown species, which are newly described here. One sample from Mexico contained larvae collected in association with adults of M. obscurus Hansen 1989, i.e., candidates for larvae of Motonerus. These larvae are briefly described here as well.

Material and Methods

Specimens examined. In total, 240 specimens were examined in this study, deposited in the following collections:

AMNH American Museum of Natural History, New York, USA;

CMN Canadian Natural Museum, Ottawa, Canada (R. Anderson);

FMNH Field Museum of Natural History, Chigaco, USA (C. A. Newton, M. Thayer);

INBio Instituto Nacional de Biodiversidad, Costa Rica (from 2015 transferred to Museo Nacional de Costa Rica, San José, Costa Rica);

SEMC Snow Entomological Museum Collection, University of Kansas, Lawrence, USA (A. Short);

MALUZ Universidad del Zulia, Maracaibo, Venezuela;

MNHW Museum of Natural History, Wroclaw University (P. Jaloszyński);

NHMW Naturhistorisches Museum, Wien, Austria (M. Jäch);

NMPC National Museum, Prague, Czech Republic (M. Fikáček).

Adult morphology. A part of the specimens were dissected, with genitalia embedded in a drop of alcohol-soluble Euparal resin. External morphology of all Motonerus species was examined with a Hitachi S-3700N environmental electron microscope at the Department of Paleontology, National Museum in Prague (using uncoated specimens). Habitus photographs were taken using Canon D-550 digital camera with attached Canon MP-E65mm f/2.8 1–5× macrolens, and subsequently adapted in Adobe Photoshop CS2. Details of genitalia were examined under Olympus BX41 compound light microscope. Drawings were traced from photographs taken using the same equipment. Morphological terminology largely follows Fikáček & Short (2006), with few updates: preepisternal elevation = mesoventral elevation, epipleuron = outer bare part of epipleuron, pseudepipleuron = inner pubescent part of epipleuron. Higher-level classification follows Short & Fikáček (2013).

Larval morphology. Habitus photographs were taken using a Canon D-550 digital camera with attached Canon MP-E65mm f/2.8 1–5× macrolens. Two larvae were cleared of muscle tissue using the proteinase K solution (180 μl of Qiagen ATL buffer and 20 μl of proteinase K, incubated at 56 °C overnight) for detailed examination and subsequently transferred through alcohol to temporary glycerine slides; DNA of these larvae was not extracted as the larvae are likely not in DNA-grade (they were stored in low percentage alcohol and at room temperature for a long time). The head was detached from the body, and mandibles detached from the head; no other disarticulations were done. Larvae were examined using an Olympus BX41 compound microscope; illustrations were made with the aid of an attached drawing tube. Photographs were taken using the Canon EOS 550D digital camera attached to the microscope. Morphological terminology of larvae generally follows Minoshima & Hayashi (2011); for the chaetotaxy of the larval head, we refer to Fikáček et al (2008) and Byttebier & Torres (2009). Since the larval morphology of the Megasternini seems very uniform, I am describing external morphology in detail, but in case of chaetotaxy, I compare the putative larva of Motonerus with that of Cercyon praetextatus (Say, 1825) described by Archangelsky (2016) and only mention differences.

Species distribution data and original photos. All distribution records of Motonerus published here and by Fikáček & Short (2006) were formatted into a DarwinCore (DwC) formatted file; this spreadsheet was also used for the creation of the distribution maps and modeling of potential distribution. The DwC spreadsheet and all original photo-documentation (SEMs of adults of all species, unedited photos of adult habitus, male genitalia and larvae) were uploaded as a .zip file to the Zenodo depository (https://zenodo.org/) under https://doi.org/10.5281/zenodo.2533391. See Arriaga-Varela et al (2017) for details on databasing and archiving strategy.

Potential and known distribution. Distribution maps are based on all records of Motonerus known to the author; they were prepared in QGIS software (https://www.qgis.org/en/site/) using the freely available GLOBE altitude data (https://www.ngdc.noaa.gov/mgg/topo/globe.html) and DIVA-GIS country borders data (http://www.diva-gis.org/). Potential distribution of Motonerus was modeled using maximum entropy algorithm (MaxEnt; Phillips et al2006), considering the genus as a monophyletic clade (see “Discussion”) which seems to be niche conservative (see Wiens & Donoghue 2004, Hadly et al2009) based on known distribution. As environmental variables, I used high-resolution (2.5′, with pixel size roughly corresponding to 5 km2) climate data available in WorldClim database (http://www.worldclim.org/; Fick & Hijmans 2017); lower resolution (10′) was used alternatively to test whether higher-resolution data did not cause over-parametrization (i.e., prediction of excessively small area). All 19 layers summarizing the most important temperature and precipitation data and their seasonality were trimmed for the focal area (34–118°W and 34°S–33°N) and converted to .asc format with − 9999 for no-data pixels, using an R script. Spatial correlation of the environmental variables was measured by Pearson’s correlation coefficient (r) using ENMTools 1.4.4 (Warren et al2010). Layers with r > 0.75 were considered as highly correlated (Šmíd et al2017), and a single variable was kept for each correlated pair or group of variables. Of the six variables selected, BIO18 and BIO19 were excluded as they were shown to bear spatial artifacts (Campbell et al2015). The following four layers were used for the modeling: BIO1 = annual mean temperature; BIO4 = temperature seasonality; BIO12 = annual precipitation; BIO17 = precipitation of driest quarter. Occurrence data included all known occurrences of Motonerus filtered for unique values to eliminate bias from multiple records from the same location (81 unique occurrence points in total, species were not separated). Models were generated using MaxEnt software (Philips et al 2006) with the following settings: (otherwise by default): maximum number of iterations = 5000; replicates = 10; replicated run type = cross-validate, output format = logistic. The average output was used for evaluating the model (using both AUC and partial ROC statistics; Lobo et al2008, Peterson et al2008) and its visualization. Partial receiver operating characteristics (pROC) was calculated using the online NicheToolBox tool (Osorio-Olvera et al2018) available at http://shiny.conabio.gob.mx:3838/nichetoolb2/, with the following setting: proportion of bootstrap points = 50, number of resamplings = 1000, proportion of omission = 0.05. For visualization, I converted the model to a presence-absence map, applying the maximum training sensitivity plus specificity threshold (MTSS), which maximizes the proportions of correctly identified positives and negatives (e.g., Jiménez-Valverde & Lobo 2007, Šmíd et al2017). Final maps of the model were prepared in QGIS software in the same way as distribution maps. Text file with short scripts used to prepare and manipulate data for the analyses is available in the Zenodo depository (https://zenodo.org/) under the doi https://doi.org/10.5281/zenodo.2533391. For the analyses preformed (2.5′ data / 10′ data), the average threshold for maximum training sensitivity plus specificity was 0.1194 / 0.1319. All indicators evaluated both models (2.5′ / 10′) as significantly better than random-training AUC = 0.978 / 0.969; testing AUC = 0.972 / 0.961; AUC standard deviation = 0.014 / 0.019; AUC at 0.95 to AUC at 0.5 ratio (pROC): mean = 1.95 / 1.91; standard deviation = 0.02 / 0.04. Both models (with 2.5′ data and 10′ data) predicted the same areas, and only the 2.5′ model is illustrated in Fig 10A, B.

Results

New species descriptions

Motonerus explanatus sp. nov.

Type material. Holotype: male (FMNH): “PANAMA: Chiriqui / 81°50′–8°34′, 1856 m / 3.5 km E Escopeta. leg: / Wagner. VI:22:1980 // FM(HD)#80-44. Berlese / conc. floor litter / nr. ridge top. Cerro / Bollo cloud forest”. Paratypes (3): PANAMA: Chiriquí: 1 spec. (FMNH): same data as holotype; 2 spec. (KSEM, NMPC): “PANAMA: Chirique / 81°50′–8°34′, 1856 m / 3.5 km E Escopeta. leg: / Wagner. VI:13:1980 // FM(HD)#80-23. Berlese / floor litter & root / mat. Cerro Bollo / cloud forest”.

Differential diagnosis.Motonerus explanatus sp. nov. closely resembles especially M. oosternoides Fikáček & Short 2006 by linear mesoventral plate (Fig 2A, G), very short metaventrite without median depression (Fig 2A, F), prosternal elevation without large anteromedian emargination (Fig 2C, D) and the median lobe with widened rim just before the apex (Figs 1D and 2I). It can be however easily distinguished from M. oosternoides as well as all other Motonerus species by the explanate lateral margin of elytra (Fig 1A, B) and epipleura very wide throughout, including the elytral apex (Fig 2A).

Fig 1
figure1

General morphology of Motonerus explanatus sp. nov. AB Dorsal and lateral habitus of the paratype. C Aedeagus of the holotype in dorsal view. D Detail of the apex of the median lobe of the holotype

Fig 2
figure2

General morphology of Motonerus explanatus sp. nov., SEM micrographs. A ventral habitus. B Mentum. C Median portion of prosternum in ventrolateral view. D Prosternum in ventral view. E Antennal groove. F Meso- and metathorax in ventral view. G Mesoventral plate. H Denticulation of the lateral margin of the elytra. I Apical part of the aedeagus

Description.Body (Fig 1A, B) widely oval, maximum width in anterior third of elytra; elytra widely rounded at lateral margin; elytra evenly convex but not forming a continuous curve with pronotum in lateral view. Length, 2.1 mm; maximum width, 1.4 mm.

Coloration. Dorsal and ventral sides uniformly reddish brown; legs reddish and antennal club reddish brown; tarsi and antennomeres 1–7 reddish.

Head. Clypeus with very fine and sparse setiferous punctation, interstices without microsculpture; anterior margin arcuate, narrowly rimmed. Lines dividing clypeus from vertex recognizable only as bare areas. Vertex with very coarse and dense setiferous punctation, interstices without microsculpture. Eyes very small, separated by 10× the width of one eye. Mentum (Fig 2B) slightly wider than long; anterior margin deeply emarginated medially; surface with fine, sparsely aggregated setiferous punctures, interstices with very weak mesh-like microsculpture. Maxillary palpomere 2 longer than palpomere 4, swollen apically; palpomere 3 subequal in length to palpomere 2, slightly swollen apically; palpomere 4 spindle-like shaped. Antennae with 9 antennomeres; scapus moderately long and thin, slightly shorter than antennal club; antennomeres 2–6 as long as scapus when combined; antennal club elongate, antennomere 7 as long as antennomere 8; antennomere 9 slightly longer than antennomere 7, distinctly pointed apically and strangulated subapically.

Prothorax. Pronotum strongly arcuately narrowed anteriad, maximum width at posterior corners. Lateral margins slightly explanate; posterior margin bisinuate, with slightly pronounced posterolateral corners. Punctation very coarse and dense, bearing long pale pubescence, interstices without microsculpture. Prosternum (Fig 2C, D) finely carinate medially, with elevated median portion; anteromedian excision very shallow, without tooth-like projection, lateral parts not divided from the median area by a ridge; lateral parts of prosternal elevation with a very small and shallow pit on each side. Antennal grooves minute, not delimited by a ridge laterally (Fig 2E).

Mesothorax. Scutellar shield in the form of equilateral triangle, without punctures. Elytron with 10 punctural series; series 1–6 and 8 reaching elytral base; series 7 and 9–10 arising subbasally, series 10 shortened posteriorly, situated on explanate lateral margin. Intervals convex throughout, no intervals costate; all intervals with one row of very fine punctures on small tubercles bearing long, protruding pubescence; interstices without microsculpture. Elytral margins with strong and dense denticulation throughout (Fig 2H), reaching the elytral apex. Lateral bare part of epipleuron much wider than mesal pubescent part basally, pubescent part reaching posterior margin of metathorax; bare part very wide throughout, reaching the elytral apex. Mesoventral elevation with very narrow plate, ca. 10× longer than wide, without concave median part (Fig 2G).

Metathorax (Fig 2A, F). Metaventrite shorter than mesoventrite, with widely pentagonal elevate median area without median depression; lateral parts of metaventrite with pubescent microsculpture. Anterior margin of metaventrite crenulate (with short ridges arising from postcoxal ridges), postcoxal ridges bent posteriad medially, but median longitudinal ridge very weak and short. Femoral lines absent. Hind wings scale-like (micropterous).

Legs short, femora with fine and sparse setiferous punctures, meso- and metatibiae with sparse pubescence ventrally. Tibiae slightly longer than tarsi. Tarsi densely pubescent ventrally.

Abdomen. Abdominal ventrite 1 bearing strong median longitudinal carina; lateral parts without additional submedian ridges, only finely crenulate on anterior margin. Ventrites 2–5 smooth, without longitudinal ridges.

Male genitalia (Fig 1C, D). Parameres slightly longer than phallobase; strongly narrowing apicad; apices narrowly rounded, with two short apical setae. The median lobe slightly longer than parameres, narrow throughout, slightly widened just before the apex; gonopore present, marginal rim wide, expanded just before the apex.

Variation. Not observed, as only a few specimens are known.

Etymology. The species name refers to the explanate elytral margins of the new species, which are very unusual and unknown in any other Motonerus species (and very rare in Megasternini in general).

Biology. The type series was collected in cloud forest leaf litter and among roots, details are unknown.

Distribution (Fig 10E). Only known from the type locality situated in the mountains of western Panama.

Motonerus inca sp. nov.

Motonerus sp. B: Fikáček & Short (2006).

Type material. Holotype: male (KSEM): BOLIVIA: Cochabamba / Cochabamba, 105 km E / Yungas, nr. Rio Carmen Mayu / (Cochabamba– / Villa Tunari Rd.) / 17°8′51″S, 65°43′50″W, 1750 m / 1–6 FEB 1999; R. Hanley / BOL1H99 024 / ex: flight intercept trap.”

Paratypes (17): BOLIVIA: Cochabamba: 3 spec. (KSEM, NMPC): same data as holotype; 1 spec. (KSEM): “BOLIVIA: Cochabamba / Cochabamba, 105 km E, Yungas / nr. Rio Carmen Mayu (Cochabamba- Villa Tunari Rd.) / 1800 m; 17°8′47″S, / 6 FEB-8 JUN 1999; F. Genier / BOL1G99 033; ex: flight intercept trap”; 1 female (CMN): “BOLIVIA: COCHABAMBA / 109 km E Cochabamba, 1400 m / 17°08′52″S 65°42′54″W/8–12.II.1999, F. Génier, transition mountain forest/cloud forest / ex f.i.t. 99–060”. ECUADOR: Napo: 1 male (NMPC): “ECUADOR, prov. Napo (2) / 1.3 km SW of BAEZA, 2050 m / S00°28′34″W 77°53′47″ / 11.xi.2006, M. Fikáček & / J. Skuhrovec lgt. // dense bush of Chusquea close / to stream with few solitary trees / near pastures & moss and leaves / on slope above road (sifting)”; 1 male, 1 spec. (KSEM, NMPC): “ECUADOR: Napo, Cosanga / 4.2 km S on Baeza-Tena / Road then 1.5 km W on pipeline / access road, 2150 m / 0°37′19″S, 77°50′1″W / 5–7 NOV 1999; Z. H. Falin / ECU1F99 flight intercept trap”; 1 male (MNHW): “ECUADOR: Napo Prov. (11) / Cosanga, Yanayacu station / bamboo leaf litter sifting / 2000–2200 m, / 00°35′S / 77°53′W, / 26.xi.2009, leg. R. Ruta”. PERU: Cuzco: 1 male, 1 spec. (FMNH): “PERU: Cuzco Dept. / Pillahuata, Manu Rd. / km 128, 21-IX-1982 / FMHD #82-270, ex / litter in gravel / gully, L. E. Watrous / & G. Mazurek”; 1 male (KSEM): “PERU: Dept. Cusco: / Cock of the Rock Lodge / NE Paucartambo 13°03.3′S / 71°32.7′W, 1120 m / 4-9-XI-2007 D. Brzoska / ex: flight intercept trap / PER1B07 001”. Paucartambo: 1 female (NMPC): “PERU: Paucartambo / Wayqecha Biological Station / Winkler extraction, sifted / cloud forest litter; 2900m / 16-18.x.2013; 13°10′29.28″S / 71°35′13.92″ W J. Parker”. VENEZUELA: Trujillo: 1 male (KSEM): “VENEZUELA: Trujillo / Laguna Agua Negra, margin / of lagoon w/vegetation / 1840 m, 13.vii.2009 / 9°18.373′N 70°10.516′W, Short et al VZ09-0713-03a / Short lab DNA coll. ABTC-01297”; 4 females (MALUZ): “VENEZUELA: Trujillo / Parc Nac. Guaramacal / Mpio. Boconó, Laguna / de Aquas Negras, 1800 / MSN. 20-25/VIII/1996 // Trampa interceptación / J. Camacho, M. García.”

Differential diagnosis.Motonerus inca sp. nov. forms together with M. problematicus Fikáček & Short 2006 and M. nublado Fikáček & Short 2006 a group of externally very similar species, characterized by medium body size (≥ 1.9 mm), narrow to very narrow mesoventral plate without deep concave area (Fig 4E–F), and metaventrite as long as or longer than mesoventrite, bearing deep median impression (Fig 4D, see also Fikáček & Short 2006: Figs 37, 39). Motonerus inca differs from both above species by simple anteromesal emargination of the prosternum (Fig 4B) (both M. nublado and M. problematicus have a triangular “tooth” in the anterior emargination of prosternal elevation: Fig 5H–G), by evenly arcuate elytra in lateral view (Fig 3B) (abruptly elevated anteriorly in M. nublado, see Fikáček & Short 2006: Fig 24) and by morphology of male genitalia. The median lobe is moderately wide and nearly parallel-sided in M. inca (Figs 3C and 5B), compared to wide and apically narrowing in M. nublado (Fig 5A) and very wide at midlength in M. problematicus (Fig 5C). Apical portion of the median lobe is widely rounded with narrow rim in M. inca (Fig5E) and M. nublado (Fig 5D), but it is narrowly pointed and with very wide subapical rim in M. problematicus (Fig 5F). The proportions of mesoventral plate used as diagnostic by Fikáček & Short (2006) are not reliable for identification, as they vary quite a lot in M. inca.

Fig 3
figure3

General morphology of the new species of Motonerus Hansen 1989. ADM. inca sp. nov. (AB dorsal and lateral habitus of the paratype from Ecuador: Cosanga, C aedeagus of the holotype, D detail of the apex of the median lobe of the holotype). EHM. sofiae sp., nov., holotype (EF dorsal and lateral habitus, G aedeagus, H detail of the apex of the median lobe)

Description.Body (Fig 3A, B) elongate oval, maximum width in anterior fourth of elytra; elytra arcuately narrowing posteriad from ca. anterior fourth, evenly convex in lateral view. Length 1.9–2.1 mm, maximum width 1.1–1.3 mm.

Coloration. Dorsal side dark brown, lateral margins of pronotum slightly paler. Ventral side brown; legs reddish; antennal club slightly darker than antennomeres 1–6.

Head. Clypeus with fine sparse setiferous punctation, interstices without microsculpture; anterior margin arcuate, narrowly rimmed. Lines dividing clypeus from vertex weakly developed. Vertex with coarse and dense setiferous punctation, interstices without microsculpture. Eyes small, separated by 9× the width of one eye. Mentum (Fig 4C) slightly wider than long; anterior margin deeply emarginated medially; surface with moderately large, sparse setiferous punctures, interstices with very weak mesh-like microsculpture. Maxillary palpomere 2 slightly longer than palpomere 4, swollen apically; palpomere 3 shorter than palpomere 2, slightly swollen apically; palpomere 4 long, spindle-like shaped. Antennae with 9 antennomeres; scapus long and thin, ca. as long as antennal club; antennomeres 2–6 shorter than scapus when combined; antennal club elongate, antennomere 7 as long as antennomere 8; antennomere 9 slightly longer than antennomere 7, distinctly pointed apically and strangulated subapically.

Fig 4
figure4

General morphology of the new species of Motonerus Hansen 1989. AFM. inca sp. nov. AE paratype from Ecuador: Cosanga (A ventral habitus, B prosternum, C mentum, D meso- and metathorax in ventral view, E mesoventral plate). F mesoventral plate of the paratype from Peru. GJM. sofiae sp. nov. holotype (G ventral habitus, H prosternum, I mentum, J meso- and metathorax in ventral view)

Prothorax. Pronotum strongly arcuately narrowed anteriad, maximum width in posterior 0.25. Lateral margins slightly explanate; posterior margin weakly bisinuate, with slightly pronounced posterolateral corners. Punctation very coarse and dense, bearing long pale pubescence, interstices without microsculpture. Prosternum (Fig 4B) strongly carinate medially, with elevated median portion; anteromedian excision deep and wide, without anterior tooth-like projection, lateral parts not divided from the median area by a ridge; lateral parts of prosternal elevation with a deep pit on each side. Antennal grooves minute, delimited by arcuate ridge laterally.

Mesothorax. Scutellar shield in form of equilateral triangle, with few minute, setiferous punctures. Elytron with 10 punctural series; series 1–6 and 8 reaching elytral base; series 7 and 9–10 arising subbasally, series 10 shortened posteriad, lying parallel to elytral margin. Intervals moderately convex throughout, all intervals of the same height; all intervals with very fine punctation bearing decumbent pubescence; interstices without microsculpture. Elytral margins with fine blunt denticles basally, becoming slightly finer apicad, reaching nearly the elytral apex. Lateral bare part of epipleuron ca. as wide as mesal pubescent part basally, pubescent part reaching the posterior margin of metathorax; bare part narrowing apicad, reaching the elytral apex. Mesoventral elevation with plate ca. 4.0–8.0× longer than wide (8.0× in the holotype), flat, or only indistinctly concave (Fig 4D–F).

Metathorax (Fig 4D). Metaventrite slightly longer than mesoventrite, with pentagonal elevated median area bearing deep narrow median depression, bottom of the depression with few setiferous punctures; lateral parts of metaventrite with pubescent microsculpture. Postcoxal ridges bent posteriad medially, forming longitudinal ridge reaching anterior 0.25 of metaventrite length; anterior part of metaventrite weakly crenulate (with short ridges arising from postcoxal ridges). Femoral lines absent. Hind wings well-developed (macropterous).

Legs short, femora with fine and sparse setiferous punctures, meso- and metatibiae with sparse pubescence ventrally. Tibiae slightly longer than tarsi. Tarsi densely pubescent ventrally.

Abdomen. Abdominal ventrite 1 bearing strong median longitudinal carina; with strongly developed additional submedian ridges throughout the width (incl. in the holotype) or only laterally. Ventrite 2 with distinct longitudinal ridges throughout its width (incl. in the holotype) or only laterally. Ventrites 3 smooth, or with indistinctly developed additional ridges laterally. Ventrites 4–5 smooth, without longitudinal ridges.

Male genitalia (Fig 3C, D). Parameres ca 1.6× as long as phallobase; narrow basally, weakly narrowing apicad; apices narrow, blunt, bent outwards, each with two apical setae. The median lobe slightly longer than parameres, narrow throughout, weakly narrowing apically; gonopore absent; marginal rim wide at the apex, slightly projecting distally, making the apex weakly bilobate.

Variation. Examined specimens vary slightly in the proportions of the mesoventral plate (very narrow, or slightly widened and in that case sometimes indistinctly concave, compare Fig 4E–F) and in the presence of longitudinal ridges of abdominal ventrite 2 (present throughout the width, or only laterally) and 3 (absent or present laterally). The holotype is characterized by a very narrow mesoventral plate (8× longer than wide) and longitudinal ridges present throughout the width on ventrites 1–2. All examined specimens are constant in all remaining characters including the morphology of male genitalia, and I hence consider the above variation as intraspecific.

Etymology. Originally, when describing the species, I knew about specimens from high altitudes of Bolivia, Peru, and Ecuador, which largely corresponds to the extent of the former Inca Empire, hence the specific name (noun in apposition). Specimens from Venezuela (where the Inca Empire never reached) were discovered shortly before finalizing the paper, when specimens with the holotype/paratype labels were already distributed.

Biology. Specimens were sifted from leaf litter, including bamboo litter and litter at margins of lakes.

Distribution (Fig 10G). Widely distributed along Amazonian slopes of the Andes Mts., from central Bolivia through Peru and Ecuador to western Venezuela. No records are so far known from Colombia.

Motonerus sofiae sp. nov.

Type material. Holotype: male (KSEM): “PERU: Dept. Madre de / Dios: Amazonas Lodge, / N Atalayala, 12°52.2′S / 71°22.6′W, 480m / 10-13-XI-2007 D. Brzoska / ex: flight intercept trap / PER1B07 002”.

Differential diagnosis.Motonerus sofiae sp. nov. differs from all remaining Motonerus species except M. obscurus, M. hanseni Fikáček & Short 2006 and M. andersoni Fikáček & Short 2006 by wide mesoventral plate with deep median depression (Fig 4J) (mesoventral plate is much narrower and without deep depression in the remaining species). Highly elevated alternate elytral intervals (Fig 3E) and deep metaventral depression with small tubercles on the bottom (Fig 4J) are shared with M. hanseni, but easily diagnose M. sofiae from M. obscurus and (in case of elytral intervals only) from M. andersoni; M. andersoni also differs by lateral margin of elytra with denticles usually reaching the elytral apex. Motonerus sofiae may be distinguished from the very similar M. hanseni only on the basis of male genitalia: the median lobe is rather narrow and simple at the apex in M. sofiae (much wider and with deeply bilobate apex in M. hanseni) and parameres are widely cut off in M. sofiae (gradually narrowing into a pointed apex in M. hanseni) (compare Fig 3G, H with Fig. 15–16 in Fikáček & Short 2006).

Description.Body (Fig 3E–F) elongate oval, maximum width at midlength of elytra; elytra nearly parallel-sided in anterior half, arcuately narrowed posteriad, evenly convex in lateral view. Length, 2.6 mm; width, 1.5 mm.

Coloration. Dorsal side dark brown, lateral margins of pronotum slightly paler. Ventral side brown; median part of prosternum, mesoventrite, and metaventrite dark brown; legs reddish; two terminal antennomeres of the antennal club slightly darker than antennomeres 1–7.

Head. Clypeus with fine and dense, setiferous punctation, interstices without microsculpture; anterior margin arcuate, narrowly rimmed. Lines dividing clypeus from vertex weakly developed. Vertex with coarse and dense setiferous punctation, interstices without microsculpture. Eyes small, separated by 11× the width of one eye. Mentum (Fig 4I) slightly wider than long; anterior margin deeply emarginated medially; surface with moderately large, not very densely aggregated setiferous punctures, interstices with very weak mesh-like microsculpture. Maxillary palpomere 2 slightly longer than palpomere 4, swollen apically; palpomere 3 shorter than palpomere 2, slightly swollen apically; palpomere 4 long, spindle-like shaped. Antennae with 9 antennomeres; scapus long and thin, ca. as long as antennal club; antennomeres 2–6 shorter than scapus when combined; antennal club elongate, antennomere 7 as long as antennomere 8; antennomere 9 slightly longer than antennomere 7, distinctly pointed apically and strangulated subapically.

Prothorax. Pronotum strongly arcuately narrowed anteriad, maximum width in posterior 0.25. Lateral margins slightly explanate; posterior margin bisinuate, with slightly pronounced posterolateral corners. Punctation very coarse and dense, bearing long pale pubescence, interstices without microsculpture. Prosternum (Fig 4H) finely carinate medially, with elevated median portion; anteromedian excision deep and wide, with strong triangular tooth-like projection in the middle, lateral parts not divided from the median area by a ridge; lateral parts of prosternal elevation with a deep pit on each side. Antennal grooves minute, delimited by straight ridge laterally.

Mesothorax. Scutellar shield in the form of equilateral triangle, with few minute, setiferous punctures. Elytron with 10 punctural series; series 1–6 reaching elytral base; series 7–9 arising subbasally. Intervals costate posteriorly, weakly costate basally, intervals 2 and 4 highly costate posteriorly, much higher than adjacent intervals; all intervals with very fine punctation bearing long, protruding pubescence; interstices without microsculpture. Elytral margins with fine blunt denticles basally, becoming finer, apicad, reaching only posterior 0.6 of elytra length, posterior part without denticles. Lateral bare part of epipleuron ca. as wide as mesal pubescent part basally, pubescent part reaching posterior margin of metathorax; bare part narrowing apicad, reaching the elytral apex. Mesoventral elevation (Fig 4J) with plate ca. 2.5× longer than wide, bearing elevated narrow lateral edges and strongly concave median part.

Metathorax. Metaventrite (Fig 4J) ca. as long as mesoventrite, with pentagonal elevated median area bearing deep large depression medially, bottom of the depression with setiferous tubercles; lateral parts of metaventrite with pubescent microsculpture. Postcoxal ridges bent posteriad medially, forming longitudinal ridge reaching anterior 0.15 of metaventrite length; anterior part of metaventrite deeply crenulate (with short ridges arising from postcoxal ridges). Femoral lines absent. Hind wings well-developed (macropterous).

Legs short, femora with fine and sparse setiferous punctures, meso- and metatibiae with sparse pubescence ventrally. Tibiae slightly longer than tarsi. Tarsi densely pubescent ventrally.

Abdomen. Abdominal ventrite 1 bearing strong median longitudinal carina; lateral parts with strongly developed additional submedian ridges. Ventrite 2 with indistinct longitudinal ridges laterally. Ventrites 3–5 smooth, without longitudinal ridges.

Male genitalia (Fig 3G, H). Parameres ca. as long as phallobase; weakly narrowing apicad; apices blunt, indistinctly bent outwards, without apical setae. The median lobe ca. as long as parameres, its tip slightly overlapping paremeres, rather narrow basally, slightly widening at midlength, arcuately narrowing into a blunt apex; gonopore absent, marginal rim absent.

Variation. Not observed; single specimen was examined.

Etymology. This Peruvian species which was recognized as new to science in the Czech Republic is dedicated to Sofia, a small Peruvian girl who was born in the Czech Republic few years ago.

Biology. Unknown; the only known specimen was collected in flight intercept trap.

Distribution (Fig 10H). Only known from the type locality at the Amazonian foothills of the Andes Mountains, which also represents the lowest elevation that the genus Motonerus has been recorded to date.

New geographic records

Motonerus andersoni Fikáček & Short 2006

Material examined. COSTA RICA: Cartago: 2 males, 1 spec. (FMNH): 10 km S of Tapanti, Rio Grande de Orosi, mixed floor litter, 1500 m, 9°42′N 83°47′W, 14.vi.1973, leg. J. Wagner, J. Kethley (FM(HD)#73-396). Heredia: 1 male (CMN): 6 km ENE Vara Blanca,, montane forest leaf litter, 2100 m, 10°11′N 84°07′W, 15-22.iv.2002, leg. R. Anderson (2002-004A). Puntarenas-Guanacaste: 2 males (KSEM): Monte Verde, Cerro Amigos, sifted leaf litter, 1780 m, 9.v.1989, leg. J. Ashe, R. Brooks, R. Leschen. PANAMA: Bocas del Toro: 1 male (NMPC): Cerro Colorado cloud forest, “Qda. 3w,” basal sphagnum encased tree, 1490 m, 11.i.1981, leg. W. Suter (FMHD#81-32); 2 females, 1 spec. (FMNH): 25 km NNE San Felix, Quebrada Alicia cloud forest, floor litter on slopes, 81°50′–8°34′, 1500 m, 5.vi.1980, leg. J. Wagner (FM(HD)#80-2); 1 spec. (FMNH): Quebrada Alicia, cloud forest, litter on slopes, 1500 m, 4.vi.1980, leg. J. Wagner (FMHD#80-1). Chiriquí: 1 spec. (FMNH): 3.5 km E Escopelta, Cerro Bollo cloud forest, floor litter & root mat, 81°50′–8°34′, 1856 m, 13.vi.1980, leg. J. Wagner (FM(HD)#80-23); 1 spec. (FMNH): trail to Cerro Colorado peak, 23.i.1981, leg. W. Suter (FMHD#81-64).

Motonerus apterus Fikáček & Short 2006

Material examined. VENEZUELA: Merida: 1 male, 2 spec. (KSEM): ULA Biol. Res. La Carbonerra, 20 km SE Azulita, podocarp forest litter, 28.vi.1989, 2300 m, leg. S & J. Peck (89–240); 2 spec. (KSEM): 34 km NW of Merida, montane forest litter, 8°37′0″N, 71°20′12″W, 2350 m, 22.v.1998, leg. R. Anderson (VEN1A98 027C).

Motonerus depressus Fikáček & Short 2006

Material examined. BOLIVIA: Santa Cruz: 1 spec. (KSEM): Comarapa, 32.8 km NW Yungas de Siberia, flight intercept trap, 2400 m, 17°49′24″S 64°42′26″W, 28–30.i.1999, leg. R. Hanley (BOL1H99 020). Cochabamba: 1 spec. (FMNH): Carrasco, Serrania de Siberia, Chua Khocha, cloud forest, baited pitfall trap, 2300 m, 25.viii.-6.ix.1990, P.P. Parrillo, M. Ledezma (FMHD#90–237). ECUADOR: Azuay: 1 female (KSEM): 50 km NW Cuenca, berlesate, 2470 m, 2.ii.1992, leg. C. Carlton & R. Leschen (#94). PERU: Cuzco: 10 spec. (FMNH, KSEM, NMPC, ZMUC): Pillahuata, Manu rd., km 128, litter along stream, 16.ix.1982, leg. L. E. Watrous & G. Mazurek (FMHD#82-240); 4 spec. (FMNH, KSEM, NMPC): same data, but #82-238, litter at seepage area & stream; 1 spec. (FMNH): Pillahuata, Manu rd., km 128, litter along gravel stream, 28.ix.1982, leg. L. E. Watrous & G. Mazurek (FMHD#82–311). VENEZUELA: Trujillo: 1 male, 1 spec. (KSEM): 18.6 km SE Boconó, by stream, 2560 m, 9°14′1″N 70°10′52″W, 19.v.1998, leg. J. Ashe, R. Brooks, R. Hanley (VEN1ABH98 079).

Motonerus hanseni Fikáček & Short 2006

Material examined: COSTA RICA: Heredia: 1 male (KSEM): 16 km SSE La Virgen, 10°16′N 84°05′W, 1070 m, 11–20.iv.2001, INBio-OET-ALAS transect (11/TN/18/008). PANAMA: Chiriquí: 1 male (KSEM): 3.5 km E of Escopelta, Cerro Bollo cloud forest, berlese, 81°50′–8°34′, 1856 m, 18.vi.1980, leg. J. Wagner (FM(HD)#80-30); 1 spec. (FMNH): same locality, but 13.vi.1980, floor litter & root material (FM(HD)#80-23); 2 males, 1 female, 1 spec. (FMNH, NMPC): nr. Nueva California, W. of Finca Palo Santo, floor litter in damp ravine, 4900 ft, 9.iii.1959, leg. H. Dybas (FMNH(HD)#59–239); 1 female (FMNH): same locality, but 6.iii.1959, floor litter in ravine, CNHM Panama Zool. Exped. (1959), leg. H. S. Dybas.

Motonerus obscurus Hansen 1989

Material examined. MEXICO: Hidalgo: 1 spec. (KSEM): 4.4 km N Tlanchinol, Hwy. 105, sifted forest litter, 6.vii.1992, leg. J. Ashe & H. Frania (#07); 1 spec. (NMPC): same locality data, but 1420 m, treefall litter (#9); 1 male, 6 spec. (KSEM): same locality data, but (#11); 3 spec. (KSEM): 3.2 km E Tlanchinol Hwy. 105, treefall litter, 1420 m, 8.vii.1992 leg. J. S. Ashe (#21); 1 spec. (KSEM): same locality and date, but streamside litter, leg. J. S. Ashe, H. Frania (#22); 2 spec. (KSEM): same locality and date, but treefall litter, leg. J. S. Ashe (#28); 1 male (FMNH): 2.5 mi N Tlanchinol, 5200 ft, rotting logs on forest floor, 6–11.vii.1973, leg. A. Newton; 15 spec. (FMNH, NMPC): 2.8 mi N Tlanchinol, berlesate litter under oak chips in fermentation stage, 5200 ft, 9–11.vii.1973, leg. A. Newton; 1 spec. (FMNH): 2.5–3.5 mi N Tlanchinol, 5000–5200 ft, 11.vii.1973, leg. A. Newton; 1 spec. (FMNH): 2.3 mi N Tlachinol, Hwy. 105, sifting litter along stream, cloud forest, 1690 m, 10.v.1977, leg. J. S. Ashe (FMHD#77-419); 3 spec. (NMPC): 3.4 km N of Tlanchinol, Paraje de Montaña, sifting of thin layer and small accummulations of leaf litter in mesophilous Quercus-Liquidambar forest, 1540 m, 21°1.2′N 98°39′W, 15.ix.2016, Cortés-Aguilar, Fikáček & Seidel (2016-MX25); 1 male (NMPC): La Mojonera 4.4 km SE Zacualtipan, lower part of Fagus forest, sifting of thin layer of very wet leaf litter among the hygrophilous vegetation at the sides of a stony stream, 1940 m, 20°38′N 98°37.3′W, 14–16.ix.2016, leg. Cortés, Fikáček & Seidel (2016-MX24); 1 male (NMPC): same locality, but sifting of large accumulations of leaf litter in Fagus forest above small stream. Oaxaca: 1 spec. (KSEM): 32 km SW Valle Nacional, km 85, transition cloud forest, leaf litter, 1650 m, 26.vii.1992, R. S. Anderson (92–030). Veracruz: 2 spec. (NMPC): San Andrés Tlalnehuayacan, Bosque de Chivizcoyo, 2.9 km NWW of Rancho Viejo, under/on rotten wet logs with lots of fungi and fungal mycelia (remnants of a burnt wooden house), partly with many antnests—incl. sifted litter from below the logs, 1630 m, 19°31′N 97°0.3′W, 10–11.ix.2016, leg. Alvarado, Arriaga, Fikáček & Seidel (2016-M18); 1 spec. (NMPC): Aguita Fría, 1.3 km SWW of Rancho Viejo (W of Xalapa), sifting of thin layer of leaf litter: sparse riverside forest with emergent large Platanus and dense understory, 1510 m, 19°31.3′N 96°59.5′W, 9.ix.2016, Alvarado, Arriaga, Fikáček & Seidel (2016-MX14). EL SALVADOR: 1 male, 12 spec. (KSEM, NMPC): Santa Ana, Montecristo, 21.7 km NE Metapan, cloud forest litter, 2100 m, 29.viii.1994, leg. Anderson (#229). HONDURAS: Francisco Morazán: 1 male, 2 spec. (KSEM): 12 km W Zamorano, Cerro Uyuca, 1840 m, 14°02′N 87°05′W, forest litter, 30.vi.1994, leg. Anderson (140C); 1 spec. (KSEM): same data but 6.vi.1994 (#101A); 1 spec. (KSEM): same data but 27.vi.1994 (135B); 1 spec. (KSEM): same data but 1840 m, 9.vi.1994 (#105B); 5 spec. (KSEM): 21.3 km N Teguicigalpa, La Tigra, forest litter berlese, 1950 m, 14°12′N 86°06′W, 29.vi.1994, leg. R. Anderson (#139A); 1 female (CMN): Res. Biol. El Chile, near Guaimaca, upper montane forest litter; 1600 m, 14°21′N 86°52′W, 1600 m, 8.v.2002, leg. R. Anderson (2002-011C). Santa Barbara: 2 females, 8 spec. (KSEM, NMPC): Mt. Santa Barbara, 11.5 km S and 5.6 km W Peña Blanca, cloud forest litter, 1800 m, 14°57′N 88°05′W, 20.vi.1994, leg. R. Anderson (#127). Ocetepeque: 1 male, 6 spec. (KSEM): 24 km E Ocetepeque, El Güisayote, forest berlese, 14°25′N, 89°04′W, 2170 m, 13.vi.1994, leg. R. Anderson (#114C); 6 spec. (KSEM): same locality, but 16.vi.1994 (#119); 10 spec. (KSEM): same locality but 13.vi.1994 (#114); 1 spec. (KSEM): 12.7 km E and 10.6 km S Ocetepeque, lower slopes El Pital, oak berlese litter, 2050 m, 14°25′N, 89°04′W, 15.vi.1994, leg. R. Anderson (#117B). El Paraíso: 2 spec. (KSEM): 6.9 km W Yuscarán, Cerro Monserrat, forest berlese, 13°55′N 86°24′W, 1760 m, 7.viii.1994, leg. Anderson (#108G); 1 spec. (KSEM): same label data but treefall litter, leg. Ashe, Brooks (#020); 2 spec. (KSEM): same label data but ex rotten bolete, 10.vi.1994 (#066); 3 spec. (KSEM): same locality and date but ex: forest berlese, leg. R. Anderson (#107); 14 spec. (KSEM): same locality but (#103); 1 spec. (KSEM): same locality but ex: flower fall litter, 7.vi.1994, leg. Ashe Brooks (#016A); 5 spec. (KSEM, NMPC): 11.1 km SE Zamarano & 11.3 km SE Galeras, “Los Lavaderos”, oak litter, 1700 m, 13°24′N 86°55′W, 11.vi.1994, leg. R. Anderson (#110A). La Paz: 1 male, 5 spec. (CMN): Tutule, Res. Biol. Guajiquiro, cloud forest litter, 2130 m, 14°10′N 87°50′W, 7.v.2002, leg. R. Anderson (2002-010F).

Motonerus oosternoides Fikáček & Short 2006

Material examined. PANAMA: Chiriquí: 1 male (KSEM): 5.6 km N Bouquete, La Culebra Trail, cloud forest litter, 8°49′23″N, 82°25′18″W, 1800 m, 15.vi.1996, leg. R. Anderson (PAN2A96 96-131A).

Motonerus problematicus Fikáček & Short 2006.

Material examined. COSTA RICA: Heredia: 1 male, 4 spec. (KSEM): 16 km SSE La Virgen, 10°16′N 84°05′W, 1070 m, 10–21.iv.2001, INBio-OET-ALAS transect, (11/TN/07/022); 3 spec. (KSEM): same data, but 11/TN/07/012; 2 males, 3 spec. (KSEM): same data but 11/TN/16/016; 2 males, 1 spec. (KSEM, NMPC, NHMW): same data but 11/TN/16/006; 2 spec. (KSEM): same data but 11/TN/16/026; 8 spec. (INBio, AMNH, KSEM, NMPC): same data but 11/TN/18/008; 2 spec. (INBio, NMPC): same data but 11/TN/18/018; 2 spec. (KSEM): same data but 11/TN/08/003; 1 spec. (NHMW): same data but 11/TN/023; 1 spec. (INBio): same data but 11/TN/06/001; 1 spec. (INBio): same data but 11/TN/17/007; 1 female, 1 spec. (INBio): same data but 11/TN/09/004; 2 spec. (INBio, KSEM): same data but 11/TN/20/020; 1 spec. (INBio): same data but 11/TN/19/009. PANAMA: Chiriquí: 2 females (FMNH): Cerro Mogla, Quebrada Tufino, litter at cascading stream, 1130 m, 22.i.1981, leg. W. Suter (FMHD#81–74). Cocle: 1 spec. (FMNH): El Valle, trail to Las Minas, ground debris, 2400–2600 ft, 23.ii.1959, leg. H. S. Dybas (#59-220).

Updated identification key

Following identification key is based on that published by Fikáček & Short (2006). Newly described species are incorporated along with some additional characters facilitating the identification.

  1. 1.

    Mesoventral plate narrow to lamellar, without median concave area (as in Figs 2G, 4D). First abdominal ventrite with or without additional longitudinal ridges parallel to median longitudinal carina. Macropterous or micropterous species.………….…….……………………………………………… 2

    • Mesoventral plate wide, with deep median concave area (as in Fig 4J). First abdominal ventrite always with additional ridges parallel to median longitudinal carina (Fig 6B, C). Macropterous or brachypterous species …… 9

  2. 2.

    Elytra widely explanate laterally (Fig 1A, B). Epipleura very wide throughtout the elytral length (Fig 6D).………………………………………………………… M. explanatussp. nov.

    • Elytra not explanate laterally. Epipleura very narrow or reduced in apical half of elytra (Fig 6E, F) .………………… 3

  3. 3.

    Smaller species (1.5–1.8 mm). Hind wings not developed (present as small scales only) (Fig 11C). Metaventrite without median depression (as in Fig 2F, see also Fikáček & Short 2006: Figs 32–33). First abdominal ventrite without additional longitudinal ridges situated laterally of median longitudinal carina (Fikáček & Short 2006: Fig 60) ..….….….….…………………………………………… 4

    • Larger species (≥1.9 mm). Hind wings developed (macropterous species) (Fig 11A). Metaventrite with or without median depression. First abdominal ventrite with or without distinct additional longitudinal ridges situated laterally of median longitudinal carina .……………………… 5

  4. 4.

    Prosternal anteromedian excision deep and wide (Fikáček & Short 2006: Fig 43). Mesoventral elevation in form of narrow plate, 5.0–6.0× longer than wide, ca. as long as metaventrite (Fikáček & Short 2006: Fig 32), usually slightly narrowing posteriad, bearing coarse irregular punctures. Elytral lateral margins without denticles, or with only fine and very distant denticles basally (Fikáček & Short 2006: Fig 54). Eyes very small, separated by 16× width of one eye in dorsal view (Fikáček & Short 2006: Fig 63) …………………………………… M. apterus.

    • Prosternal anteromedian excision very shallow (Fikáček & Short 2006: Fig 46). Mesoventral elevation nearly lamellar, distinctly longer than metaventrite; carina not very distinct posteriorly (Fikáček & Short 2006: Fig 33). Elytral lateral margins with distinct and closely standing denticles basally, denticulation reaching the elytral apex (Fikáček & Short 2006: Fig 55). Eyes larger, separated by 10× width of one eye in dorsal view (Fikáček & Short 2006: Fig 64) …………… M. oosternoides Fikáček & Short.

  5. 5.

    Metaventrite without median depression (Fikáček & Short 2006: Figs 34, 40). Additional longitudinal ridges present only on abdominal ventrite 1 (may be largely reduced even there), never present on abdominal ventrite 2 and 3 ……………………………………………………………… 6

    • Metaventrite with median depression (as in Fig 4D, see also Fikáček & Short 2006: Figs 37, 39, 41). Additional longitudinal ridges present on abdominal ventrites 1 and 2 (Fikáček & Short 2006: Fig 62), sometimes developed also on abdominal ventrite 3 ……………………………………… 7

  6. 6.

    Elytra strongly depressed in lateral view (Fikáček & Short 2006: Fig 23). Prosternal anteromedian excision very shallow, rounded (Fikáček & Short 2006: Fig 44) ……………………………………….… M. depressus Fikáček & Short.

    • Elytra evenly and highly convex in lateral view (Fikáček & Short 2006: Fig 31). Prosternal anteromedian excision deep, more less rectangular (Fikáček & Short 2006> Fig 51) ……………………… Motonerussp. A.

  7. 7.

    Elytra abruptly elevated immediately behind pronotum, then slightly depressed in lateral view (Fikáček & Short 2006: Fig 24). Anterior emargination of prosternal elevation with triangular tooth-like projection (Fig 5H). Denticles on elytral margin becoming gradually more distant apicad, reaching 0.5 of elytral length (Fikáček & Short 2006: Fig 57). The median lobe narrow distally, widened basally (Fig 5A) ………………………………………………………………………………………… M. nublado Fikáček & Short.

    • Elytra not abruptly elevated behind pronotum in lateral view. Anterior emargination of prosternal elevation with or without triangular projection. Denticles on elytral margin fine, equidistant or nearly so, reaching the elytral apex. The median lobe not distinctly wide basally than apically (Fig 5B, C) ……………………………………………………… 8

  8. 8.

    Anterior emargination of prosternal elevation with triangular projection anteromesal (Fig 5G). The median lobe of aedeagus wide, wider than paramere (Fig 5C), gradually narrowing towards the apex (Fig 5F) …………………………………… M. problematicus Fikáček & Short.

    • Anterior emargination of prosternal elevation without triangular projection anteromesal (Fig 4B). The median lobe of aedeagus narrow, ca. as wide as the paramere at midlength (Fig 5B), subparallel throughout except at the apex (Fig 5B, E). ………………………………… M. incasp. nov.

  9. 9.

    Mesoventral plate narrower, ≥ 4.0× longer than wide (Fig 4E, F; Fikáček & Short 2006: Fig 39). Macropterous species ……………………………………………………………………… 8

    • Mesoventral plate wider, 1.6–2.5× longer than wide (Fig 4J; Fikáček & Short 2006: Figs 35, 36, 38). Macropterous or brachypterous species ..……………………………………… 10

  10. 10.

    Elytra highly convex in lateral view (Fikáček & Short 2006: Fig 25), all elytral intervals evenly convex. Lateral margins of elytra with denticles reaching the elytral apex (Fikáček & Short 2006: as in Fig 59). The median lobe with bottle-neck like the apex (Fikáček & Short 2006: Figs 13, 14). Brachypterous species (Fig 11B) …………………………………………… M. andersoni Fikáček & Short.

    • Elytra weakly convex (Fig 3F; Fikáček & Short 2006: Fig 29) or distinctly depressed at midlength in lateral view (Fikáček & Short 2006: Fig 27), alternate elytral intervals at least slightly higher than adjacent ones posteriorly. Lateral margins of elytra without denticles near the apex (Fig 6F). The median lobe without bottle-neck like the apex (Fig 3G; Fikáček & Short 2006: Figs 19–20). Macropterous species …………………………………….. 11

  11. 11.

    Elytral costae only indistinctly alternate. Pronotum sparsely punctate. Abdominal ventrite 2 without or with almost indistinct longitudinal ridges (Fikáček & Short 2006: Fig 61). The median lobe slightly widened subapically, with small excision on the apex (Fikáček & Short 2006: Figs 17–18) …………… M. obscurus Hansen.

    • Elytral costae on intervals 2, 4, 6, and 8 distinctly higher than adjacent ones. Pronotum very densely punctate. Abdominal ventrite 2 with slightly developed longitudinal ridges. The apex of the median lobe either not widened (Fig 3G, H) or with deep apical emargination (Fikáček & Short 2006: Figs 15–16) ….….….….……. 12

  12. 12.

    The median lobe widely explanate subapically, deeply excised at the apex (Fikáček & Short 2006: Figs 15–16). Central America …………… M. hanseni Fikáček & Short.

    • The median lobe narrow subapically, without lateral extensions, without apical excision. South America (Fig 3G, H) ………………………………… M. sofiaesp. nov.

Fig 5
figure5

Morphological comparison of Motonerus inca sp. nov., M. nublado (holotype) and M. problematicus.AC aedeagus (AM. nublado, BM. inca from Ecuador: Baeza, CM. problematicus). DF detail of the apex of the median lobe (DM. nublado, EM. inca from Ecuador: Baeza, FM. problematicus). GH prosternal elevation (GM. problematicus, HM. nublado)

Fig 6
figure6

Morphological details of the new species of Motonerus Hansen 1989. AC abdominal ventrites of the holotype (AM. explanatus sp. nov., BM. inca sp. nov., CM. sofiae sp. nov.). DF epipleuron (DM. explanatus sp. nov., EM. inca sp. nov., FM. sofiae sp.nov.). Not to scale

Larval Morphology

Motonerus obscurus

Material examined. 5 third instar larvae, 2 younger larvae (FMNH, NMPC): MEXICO: Hidalgo: 2.8 N of Tlanchinol, 5200 ft, 9–11.vii.1973, berlesate litter under wood chips (oak in fermenting stage), lgt. A. Newton.

Association with adults. Based on the external morphology, examined larvae belong to the Megasternini. They were collected together with 16 adults of Motonerus obscurus, including few teneral specimens; no other representative of Megasternini was collected in this sample. Larvae of Megasternini usually co-occur in the same habitat as adults (e.g., Arriaga-Varela et al2017), and in absence of other megasternines, examined larvae may be hence associated with adults of Motonerus obscurus. The material was not suitable for DNA studies; the association was hence not confirmed by DNA data. If the generic association is correct, the larvae may only belong to M. obscurus, as it is the only species of the genus occurring in central Mexico.

General morphology of third instar larva.Body elongate cylindrical, pale yellowish, scelrotized parts reddish to dark brown (Fig 7A–C).

Fig 7
figure7

General morphology of the putative larva of Motonerus obscurus Hansen 1989. AC habitus (A dorsal, B lateral, C ventral). DI details of the head (D head capsule in dorsal view, E details of microstructure of dorsal surface, F internal crista of gular suture, ventrolateral view, G head capsule in ventral view, H head capsule of larva not treated by proteinase in lateral view, I detail of labium). JO thorax (J detail of microstructure of proscutum, K thorax in ventral view, L prothoracic leg, M mesothoracic leg, N metathoracic leg, O thorax, dorsal view). P tergite on the 8th abdominal segment. hyplob, hypopharyngeal lobe of labium; premen, prementum; spir, mesothoracic spiracle

Head. Head capsule slightly longer than wide (Fig 7D, G); occipital foramen large, angulate on anterior margin; cervical sclerites present, narrowly transverse (Figs 7D and 8C). Dorsal surface with regions covered by spine-like or finger-like projections (in the central part of frons, posteriorly along frontal suture, posteromesally, posterolaterally and dorsolaterally on parietale, Fig 7D, E); frontal lines absent, lateral limits of frontale only recognizable by different microsculpture of the surface. Ventral surface with strongly sclerotized gular sulcus, forming a high ridge internally just before the posterior margin of the head capsule; posterior tentorial pits contiguous with gular sulcus, situated slightly before the midlength of the head. Stemmata aggregated in a single spot, ocular area without thickened cuticle (“lens”). Frontoclypeus slightly asymmetrical, with a cleft on the left side, partly delimited by membranous pubescent lobe (Fig 8A). Antenna with antennomere 1 as long as antennomeres 2 + 3 combined, antennomere 2 the shortest, sensorium longer than antennomere 3 (Fig 9C). Mandibles asymmetrical, right one with single, apically bifid retinacular tooth, angulate subbasally on inner face, left one without retinacular teeth, finely pilose on inner surface, angulate subbasally (Fig 9A, B). Maxillae with cardines largely concealed by projections of the submentum (Fig 8E); stipites slightly asymmetrical: left stipes shorter and wider, with long cuticular projections dorsally on the inner surface and along the complete outer margin; right stipes longer and narrower, with long cuticular projections only dorsally on the distal-outer margin (Fig 9D, E); maxillary palpus with four palpomeres, palpomere 1 (= palpiger) the longest, palpomere 3 the shortest; inner appendage membranous (Fig 9D, E). Labium. The submentum forming nearly the complete ventral anterior margin of the head, laterally projecting into a wide lobe covering maxillary cardines, the lobes slightly asymmetrical, wider on the right side; mentum and prementum short, largely concealed by submentum, hypopharyngeal lobe present, asymmetrical; labial palps situated quite laterally, each with two palpomeres (Fig 9F).

Fig 8
figure8

Morphology and chaetotaxy of the head capsule (dorsal microsculpture omitted) of the putative larva of Motonerus obscurus Hansen 1989. A Frontoclypeus in dorsal view, B head ventrally, C head dorsally, D head laterally, E anterior part of head in ventral view (with bases of maxillae and prementum). FR, frontale; hyplob, hypopharyngeal lobe of labium; LA, labium; MX, maxila; PA, parietale

Fig 9
figure9

Morphology and chaetotaxy of the head appendages of the putative larva of Motonerus obscurus Hansen 1989. AB mandibles in dorsal view (A left, B right); C antenna in dorsal view, DE maxilla in dorsal view (D left, E right); F prementum (only visible part and visible sensilla illustrated), G mesothoracic leg in lateral view

Thorax slightly wider than the head capsule (Fig 7A). Prothorax with large proscutum subdivided by sagittal line, prosternum in form of a pair of narrow transverse sclerites subdivided mesally, situation in front of legs (Fig 7K); mesothorax with a narrow pair of sclerites dorsally, tightly attached to posterior margin of proscutum (Fig 7O); other sclerites absent. Proscutum completely covered by microsculpture consisting of spine-like projections (Fig 7J). Mesothoracic spiracles open, situated on high tubercles (Fig 7K, O). Legs reduced to small bulges bearing a group of long setae (Fig 7K–N and Fig 9G).

Abdomen ten-segmented, with segments IX–X reduced and modified; segments I–VII subequal in size and shape, without distinct sclerites, each segment subdivided in two transverse folds (Fig 7A–C). Segment VIII with a large dorsal plate ca. 1.2× longer than wide, posterior margin weakly sinuate (Fig 7P).

Head chaetotaxy of third instar (only differences from the third instar larva of Cercyon praetextatus listed, see Archangelsky 2016).

Frontale. Nasale (Fig 8A) with 8 short setae in gFR1, 5 of which are situated at the anterior margin. Setae FR8–10 situated in a row, pores FR13 and FR15 not found; setae FR5–6 situated more anteriorly, posteriorly of antennal socket. Pore FR13 not found (Fig 8C). Parietale (Fig 8B, C). Lateral portion with one additional seta between PA8 and PA11, seta PA28 situated more anteriorly, at the level of sensilla PA16–17 and PA26, and pore PA27 situated anteriorly of it; pore PA30 situated ventrally of PA18. Pore PA10 not found. Antenna (Fig 9C). Sensorium ca. 1.5× longer than antennomere 3. Base of antennomere 2 with a cuticular tooth (rather than pore). Mandible (Fig 9A, B). Base of outer margin with single additional seta; sensilla MN6 not found. Maxilla (Figs 8E and 9D, E). Left stipes dorsally with three stout setae basally (MX7 and two setae of gMX2) and 7 shorter setae of gMX2 intermixed with the mesal pubescence on the inner face; right stipes dorsally with two stout setae basally (MX7 and basal seta of gMX1) and 4 long, stout setae (distal setae of gMX2) along the inner surface. Pores MX15, MX17, MX26, and MX27 not found. Labium (Figs 8E and 9F). Setae LA6 rather widely separated from each other, not situated on a distinct sclerite; setae LA5 rather long. Remaining setae of the mentum not examined (concealed by the submentum); sensilla of labial palps not found.

Discussion

Distribution Patterns

At the moment, Motonerus comprises 12 species, 11 described and one undescribed, of which four (M. explanatus, M. nublado, M. sofiae, M. sp. A) are only known from a single locality and were described from a single or few specimens. On the other hand, examination of new material revealed that species previously known from one or few close localities (M. hanseni, M. problematicus and M. depressus) are more widespread than expected (occurring in nearly whole tropical and subtropical Andes Mts. in M. depressus).

Potential distribution of the genus Motonerus modeled on climatic variables (Fig 10A, B) revealed a pattern highly congruent with known distribution: the model indicates climatically suitable habitats at middle to highler altitudes (ca. between 1500 and 3000 m) in the whole Andes Mts. from northern Peru to Venezuela, south of northern Peru their occurrence is only predicted on Amazonian slopes, but not in the antiplano and Pacific slopes. On the Amazonian slope, Motonerus may occur as low as 480 m a.s.l. (see M. sofiae). Two species, M. depressus and M. inca are surprisingly widespread (Fig 10F, G), reaching from central Bolivia to eastern Venezuela, and more local species seem to be so far present only in the north (M. nublado, Merida state of Venezuela, Fig 10F) and in the south of the Andes Mts. (M. sofiae and Motonerus sp. A in southern Peru and northern Bolivia; Fig 10H). In Central America, the model indicated climatically suitable habitats for Motonerus in the mountain system through Costa Rica and central to western Panama (where five species co-occur; Fig 10C–E), in the mountains in northern Nicaragua, Honduras, and southern Mexico, and in the mountains of central Mexico on both Caribbean and Pacific slopes, at altitudes ca. 750–2500 m. Only a single widespread species, M. obscurus, occurs north of Costa Rica (Fig 10C), and its known distribution only partly covers the modeled potential distribution: it was so far not recorded from Guatemala, and in Mexico, it is nearly exclusively recorded from the Caribbean slopes, with a single historical record in the Pacific slopes of Oaxaca. I suppose that it is a result of limited collecting effort. A short recent field work in the states of Veracruz and Hidalgo revealed few previously unknown localities including those in small remnants of riverside forest patches, and the species does not seem rare. On the other hand, intensive collecting effort was recently done in Guatemala (expeditions by R. Anderson), but no Motonerus specimens were found. For summary about known biology of Motonerus species, see Table 1.

Fig 10
figure10

Potential and known distribution of Motonerus Hansen 1989. AB Potential distribution estimated based on ecological niche modeling using climatic data (green) and real known distribution (red dots). CH known distribution of particular Motonerus species

Table 1 Summary of collecting and habitat data available for all available material of Motonerus. Numbers in collecting period column refer to months, question marks indicate no available data

The model of potential distribution also predicts the occurrence of Motonerus in the Greater Antilles, in parts of Guyana shield and in Atlantic rainforests in Brazil (Fig 10A), where the genus was never found and highly probably does not occur. These areas are predicted as climatically suitable, but other abiotic and biotic factors as well as the biology and evolutionary history of the clade (e.g., Soberón & Nakamura 2009) likely excludes the occurrence of Motonerus there.

Adult Morphology

Despite that no formal phylogenetic analysis was performed so far, Motonerus seems to form a well-defined and rather morphologically uniform monophyletic group. Preliminary results based on DNA data of three species (Arriaga-Varela, unpubl. data) do not contradict the monophyly either. Motonerus explanatus described here is morphologically abberant from previously known species in explanate elytral margin (Fig 1A, B) and very wide epipleura (Fig 2A), but in other aspects (extremely short metaventrite, lamelar mesoventral elevation, prosternal elevation with weak anterior emargination and shallow lateral pits only, reduced wings, and rather similar male genitalia; Figs 1 and 2) closely resembles M. oosternoides. Both species moreover occur in mountains of western Panama (Fig 10D, E), and possibly may be closely related. Other groups of morphologically closely similar species are M. problematicus, M. nublado and M. inca (all very similar externally, M. inca and M. nublado also with rather similar male genitalia; Fig 5A, B), and M. obscurus, M. hanseni and M. sofiae (with very wide and deeply concave mesoventral plate). The close similarity of M. hanseni and M. sofiae is especially interesting, as the former occurs in Costa Rica and Panama, and the latter is known from southern Peru only.

Different development of wings in different species was observed already by Fikáček & Short (2006) (Table 2), but partly misinterpreted: M. apterus and M. oosternoides were considered apterous. A more detailed analysis performed here revealed that all “apterous” species have hind wings still present but reduced into small scales (i.e., micropterous, Fig 11C). More surprisingly, Motonerus andersoni was found to be brachypterous (Fig 11B): its wing is ca. half as long and slightly narrower than the usual Motonerus wing (Fig 11A); it lacks the terminal part which is folded in macropterous species, lacks the anal lobe, and has largely reduced cubital and anal veins. Surprisingly, it has well-developed RP vein which is otherwise rudimentary and connected with MP in a form of a “loop” in all macropterous hydrophlids. In macropterous species, the wing venation corresponds completely with that described for other genera of Megasternini (e.g., Fikáček 2010).

Table 2 Size of hind wings in Motonerus species
Fig 11
figure11

Hind wings of Motonerus species. A A representative of macropterous species, Motonerus obscurus Hansen 1989, B the brachypterous species, M. andersoni Fikáček and Short 2006, C a representative of micropterous species, M. apterus Fikáček and Short 2006. AA, anterior anal vein; Cu, cubital vein; MP, posterior media; RA, anterior radius; RP, posterior radius; r4, radial cross vein 4; ScA, anterior subcosta

Larval Morphology

The putative larva of Motonerus was examined, in order to test the assumptions of close morphological similarity of megasternine larvae suggested by Archangelsky (1997, 2016, 2018) and the contrasting observation by Arriaga-Varela et al (2017) about substantial differences in morphology in two different Cercyon groups in Greater Antilles. I also compared it to the larva of Armostus ohymatensis described by Minoshima (2018). The larva is very similar to other known larvae of Megasternini in most external as well as chaetotaxic characters, and most apparent differences are in the external morphology: (1) dorsal surface of the head and prothorax covered with dense spine-like microsculpture (7E, J; smooth in most other Megasternini examined, with fine bulge-like microsculpture in Armostus); (2) the retinacular tooth of right mandible is bifid (Fig 9B; with a single apex in other known Megasternini); (3) antennal sensorium much longer than antennomere 3 (Fig 9C; ca. as long as antennomere 3 in most known Megasternini, shorter in Oosternum costatum); and (4) legs reduced to small tubercles only (Figs 7L–N and 9G, similar to Cercyon quisquilis and Oosternum costatum; reduced but still with one or two segments in Armostus, most Cercyon and Pelosoma: Archangelsky 1997, 2016, 2018; Minoshima 2018). The “lenses” (i.e., areas of thickened cuticle around stemmata, as observed by Arriaga-Varela et al2017) seem to be absent in the examined larva (Fig 7D, H). Another unusual character discovered in the examined larva is the high internal ridge on the base of the gular suture (Fig 7F); additional studies are however necessary to reveal whether this structure is absent in other Megasternini or was just overlooked so far. Maxillary stipites are slightly asymmetrical, with the left one shorter and wider and with more developed dorsal pubescence (Fig 9D) and the right one narrower and longer with less developed setae (Fig 9E), in agreement to the situation found by Archangelsky (2016) in Cercyon, Minoshima (2018) in Armostus, and Archangelsky (2018) in Oosternum. However, in contrast to the latter three genera, the asymmetry also concerns the chaetotaxy of the inner face of stipes of Motonerus, which bears 9 stout setae (interpreted here as MX7 + gMX2 with 8 setae) on left stipes, but 6 stout and long setae (interpreted here as MX7 + gMX2 with 5 setae) on right one. Labium was not examined in detail due to low number of available larvae but seems to be wider (with setae LA5–6 and labial palps more separated than in other known Megasternini).

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Acknowledgments

I am indebted to A. E. Z. Short (KSEM), Al Newton, and Margaret Thayer (FMNH) for hosting me in Lawrence and Chicago in summer 2009 when most of the specimens for this paper were examined; additional loans from KSEM and CMN were able thanks to Andrew Short, Zack Fallin, Robert Anderson, and Francois Genier. Additional material from Mexico was collected thanks to Emmanuel Arriaga-Varela, Fredy Alvarado, and Jesús Cortés Aguilar who allowed me to participate on a field work nicely organized by them. Kristýna Tejmlová (Kladno, Czech Republic) was helping a lot with taking SEM micrographs of previously described Motonerus species. Bruno Clarkson (Brazil) criticized and hence helped to improve the taxonomic part of the manuscript. Jiří Šmíd (NMPC) provided additional advice concerning the use of ENMtools programm; Marianna Simoes (Senckenberg Research Institute, Germany) provided a critique of the ecological niche modeling part of an earlier version of this manuscript which allowed me to perform the analysis more accurately.

Nomenclature

ZooBank registration can be found at: http://zoobank.org/urn:lsid:zoobank.org:pub:E38E8F6F-A63F-43DC-9C7F-B8871338979B

Funding

The study was supported by the Ministry of Culture of the Czech Republic (DKRVO 2019-2023/5.I.a, National Museum, 00023272).

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Fikáček, M. Neotropical Leaf Litter Beetle Genus Motonerus (Coleoptera: Hydrophilidae): New Species, Distribution Data, and Description of Third Instar Larva. Neotrop Entomol 48, 788–808 (2019). https://doi.org/10.1007/s13744-019-00679-4

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Keywords

  • Hydrophiloidea
  • Sphaeridiinae
  • Larval morphology
  • Wing morphology
  • Species distribution modelling