A first faunistic study on the tribe Oniticellini Kolbe, 1905 (Coleoptera: Scarabaeidae) of Baikunthapur Tropical Forest of the Himalayan foothills, West Bengal, India

Abstract Background Oniticellini Kolbe, 1905 is a paucispecific tribe of the scarab beetle subfamily Scarabaeinae. The tribe is composed of 256 described species worldwide, while from India, 26 species were recorded to date. Beetles belonging to this tribe are commonly known as paracoprid dung beetles and perform some remarkable ecological functions. Nevertheless, there is a dearth of knowledge on the occurrence of these beetles in the mega diverse tropical forests of the Himalayan foothills located in the north of the West Bengal state of India. New information A first faunistic account of the tribe Oniticellini Kolbe, 1905 from Baikunthapur Forest, located at the Himalayan foothills of the West Bengal state of India is presented. A total of five species of the tribe distributed over two genera Tiniocellus and Liatongus were recorded during multiple surveys of the scarab fauna of the Forest. All taxa were recorded for the first time from the area, while Tiniocellus spinipes (Roth, 1851) is a new record for the West Bengal State of India. Additionally, a preliminary checklist of Indian species of the tribe is also provided.

Beetles of this tribe perform some indispensible ecological functions to the forest ecosystem. According to their nesting strategies and ecological role, they are called tunnellers and belong to the paracoprid functional guild of coprophagous beetles (Halffter and Edmonds 1982). These beetles, while feeding and nesting, enhance nitrogen volatilisation and mineralisation rates by altering the microorganism fauna present in dung pats and brood balls (Yokoyama et al. 1991). Adults and larvae of these beetles also control the abundance of dung breeding detrivorous flies and dung dispersed nematodes and protozoa (Nichols et al. 2008). These ecological functions have immense implications for livestock, wildlife and human health (Miller 1954, Byford et al. 1992. Considering all these functions, the paracoprid beetles form an extremely important component of tropical forest ecosystems. From the Oriental Region, the first ever comprehensive work on the taxonomy of Scarabaeidae was that of Arrow (1910), Arrow (1917), Arrow (1931). Later, monographic works from the Oriental and Palaearctic Regions were presented by Balthasar (1963a), Balthasar (1963b), Balthasar (1963c), Oppenheimer (1977, Micsik (1982), Lumaret and Lobo (1996) and Löbl and Löbl (2016). From India, data on the occurrence of these beetles are chiefly based on the publications of the Zoological Survey of India and the works carried out regionally from different parts of India. Some of the noteworthy works are of Biswas and Chatterjee (1985), Chatterjee and Biswas (2000), Chandra (2005), Sewak (2006), Sewak (2009), Chandra and Ahirwar (2007), Karimbumkara and Priyadarsanan (2013), Sathiandran et al. (2015) and Gajendra and Prasad (2016). On the contrary, from the West Bengal State of India major contributions are of Sarkar et al. (2010) , Sarkar et al. (2014) , Sarkar et al. (2015) and Kharel et al. (2020). However, a concise taxonomic account of these beetles from India is still lacking.
The Baikunthapur Forest, although exhibiting the tropical forests of the Himalayan foothills and being a mega biodiversity zone, has never been assessed for its scarab fauna. The Forest is located at the south of the outer foothills of the Himalayas in the alluvial flood plains of the West Bengal State of India. The Forest stands as an excellent example of the tropical forest ecosystem of the Himalayan foothills and harbours an array of unique flora and fauna.
It is with this background that a project has been taken up to explore the scarab fauna of the Forest. Multiple surveys were carried out in different parts of the Forest, based on vegetation pattern and distribution of mammals. The surveys resulted in the recognition of approximately 78 scarab species, of which five belong to the tribe Oniticellini Kolbe, 1905 and are presented here in this paper. The five species belong to two genera Liatongus Reitter, 1893 andTiniocellus Péringuey, 1901. Liatongus Reitter, 1893 is composed of 62 species worldwide, whereas Tiniocellus Péringuey, 1901 is a species-poor genus and has only seven species throughout the world (Schoolmeesters 2020). From India, the genus Liatongus is known by 10 species and Tiniocellus by two species.
Here, we compile a preliminary checklist of the Oniticellini species recorded from India to date (Table 1). The list is based on the distributional data published in past literature, including the publications of the Zoological Survey of India. Until now, 24 species were recorded from India, of which Oniticellus cinctus seems to be the most abundant species of the tribe across the country.

Study site
The Baikunthapur Forest is located in the northern part of the West Bengal State of India ( Fig. 1). It is a Terai forested area, situated at the Himalayan foothills in the Dooars Region of theState. The forested area forms an extremely important ecological zone and provides habitat for many wild animals, such as Elephant, Royal Bengal Tiger, One horned Rhinoceros, Barking Deer, Hog Deer, Bison, Chital, Wild Boar etc. The Forest, spread over an area of 257.13 km , lies between 26°30' and 27°00' north latitude and 88°20' and 88°40' east longitude and has an annual rainfall of 382 cm. The altitude of the forested area ranges from 100 m to 165 m above mean sea level. The Mahananda River flows to its west, while the River Teesta to its east. The entire Forest is subdivided into six different forest ranges namely Ambari, Sarugara, Apalchand, Targhera, Belacoba, and Dabgram. The vegetation pattern of the Forest is characterised as riverine grassland and moist deciduous forest. The grassland comprises mainly of tall grasses, namely Kasia (Saccharum spontaneum), Dhadda ( Saccharum arundinaceum), Nal (Arundo donax), Khagra (Phragmites karka) etc. Locally, these grasses are known as 'elephant grass' and can grow up to the height of 6 m. Some of the dominant tree species of the Forest are Sal 2 (Shorea robusta), Kadam (Anthocephalus cadamba), Siris (Albizzia procera), Simul (Bombax ceiba), Khair (Acacia catechu), Chalta (Dellenia indica) etc.

Specimen collection and identification
Several faunistic surveys were carried out at all of the six Forest ranges of the study area during March 2018-February 2020. Insect specimens were collected in every month from each range during the period of surveys. Random sampling, hand picking from dung pats and pitfall traps were utilised for the collection of beetles. The pitfall traps were made of plastic containers (210 mm in diameter and 150 mm in depth) and buried into the soil up to their rims. The traps contained water-formalin-liquid soap mixture, a wire grid above the mixture and about one litre of animal dung over the wire grid. The traps were placed in four replicates at all of the six ranges during our survey. Beetle specimens were collected from the traps after every 5-6 days of exposure in the field. After collection, the specimens were placed in a jar containing chloroform-dipped cotton and then transferred to 70% alcohol in glass vials. The male genitalia (aedeagus) was dissected out and cleaned in 10% potassium hydroxide (KOH) solution and the remaining muscles and fats were removed further in glycerine. Species identification was done following the keys of Arrow (1931) and Branco (2010). The photographs of adult habitus and genitalia were taken with the camera (MAGCAM DC 5) attached to the Stereozoom Trinocular Microscope (OLYMPUS SZX7). For measurements, the apex of clypeus to the tip of elytra and maximum width of the elytral base were taken for length and breadth, respectively. The map of the study area showing collection points was created online at simplemappr.com and compiled in Adobe Photoshop CS3.

Material deposition
The collected beetle specimens were deposited in the Entomology Laboratory of the Department of Zoology, University of Kalyani, West Bengal, India (ZE-KU). surface dark and moderately shining; head bears a broad transverse carina on the vertex with its angles forming a pair of sharp pointed divergent processes; clypeus bilobed at front and nearly straight at sides, moderately punctured and bears a curved carina posteriorly; pronotum dark brown on the disc, laterally testaceous, strongly and closely punctured, with a mid-longitudinal groove near the base and a slight vertical declivity in the middle anteriorly; elytra deeply striate, irregularly punctured, intervals slightly convex; metasternal shield finely punctured, mid-longitudinally grooved; pygidium coarsely punctured, surface coriaceous. Genitalia: Phallobase elongate, broad at base, heavily sclerotised (Fig. 3a); parameres broad, ventrally curved with the apex extended into a hook-like process (Fig. 3b).  . 2b): Length 9 mm, breadth 5.5 mm; upper surface dark brown and opaque; head finely punctured with the sides round, forehead bears a strong, basally flat and backwardly curved, erect horn, with its tip diverged into two slender and sharply pointed processes; clypeus finely punctured and separated from the forehead by a feebly curved carina; pronotum very deeply and broadly excavated in its anterior part with the cavity smooth, shining and posteriorly elevated into a strong, straight and compressed, blade-like horn, with its tip rounded; elytra deeply striate and strongly punctured, intervals slightly convex; metasternal shield very smooth and bears a mid-longitudinal groove; pygidium minutely punctured. Genitalia: Phallobase elongate, broad at base and heavily sclerotised (Fig. 3c); parameres ventrally curved, broad and round at base, laterally extended into a hook-like process, apically sinuate with the tips round and blunt (Fig. 3d).   Diagnosis: This species can be distinguished from other Liatongus species by the following combination of characters (Fig. 2c): Length 7 mm, breadth 3.5 mm; upper surface dark; head broad, angulate at sides, finely punctured; pronotum coarsely and densely punctured, with a mid-longitudinal groove at the base and a curved declivity just behind the front margin, the edge of the declivity raised and forming a pair of strong tubercles on each side; elytra shallowly striate, closely punctured, with the intervals flat; metasternal shield smooth in the middle and bears a large depression upon the posterior part; pygidium densely setose and closely punctured. Diagnosis: This species can be distinguished from other Tiniocellus species by the following combination of characters ( Fig. 2d): Length 6.5 mm, breadth 3 mm; upper surface dark brown; head short and broad, both coarsely and finely punctured with the large punctures setiferous, with the genae protruding from sides of clypeus at clypeogenal junction and the vertex bears two sinuate carina basally; clypeus rugosely punctured, anteriorly reflexed and feebly excised in the middle; pronotum coarsely and closely punctured, disc without testaceous patches and bears a shallow median basal furrow occupying approximately half of its length; elytra not completely covering the abdomen and met-episterna at the sides, shallowly striate, interstriae flat, wide and fringed before the hind margin, 1 interstria with four and 5 with three long erect setae, 3 and 7 without long erect setae other than the tuft on apical declivity; metasternal shield smooth, with a spoon shaped concavity at the end of impunctate and shining mid-line; pygidium wider at base than the 1 to 5 elytral interstriae of the two elytra taken together; hind femur devoid of setae on postero-inferior edge. Diagnosis: This species can be distinguished from other Tiniocellus species by the following combination of characters ( Fig. 2e): Length 6 mm, breadth 2.5 mm; upper surface dark; head short and broad, gently rounded at sides, with the vertex bearing two sinuate carina basally and the genae not protruding from sides of clypeus at clypeo-genal junction; clypeus anteriorly reflexed and deeply bilobed in the middle; pronotum coarsely and rugosely punctured, very dark on disc and testaceous at sides and bears a mid-longitudinal groove at the base; elytra shallowly striate and not completely covering the abdomen and metepisterna at the sides, interstriae flat, narrow and fringed before the hind margin, 1 interstria with 4, 5 with 2 and 7 with 1 long erect setae, 3 without long erect setae, other than the tuft on apical declivity; metasternal shield smooth, with a very indistinct depression medially; pygidium narrower at base than the 1 to 5 elytral interstriae of the two elytra taken together; hind femur devoid of setae on postero-inferior edge.

Discussion
Beetles of the subfamily Scarabaeinae, commonly known as coprophagous or dung beetles, are broadly classified on the basis of their feeding and nesting strategies into three categories, namely paracoprid (tunnellers), endocoprid (dwellers) and telecoprid (rollers) dung beetles (Halffter and Edmonds 1982). The paracoprids bury their brood balls in vertical chambers (tunnels) near the original deposition site, the endocoprids brood their young inside the dung mass itself and the telecoprids transport and roll dung balls horizontally to some distance before their burial into the soil (Halffter and Edmonds 1982). By consuming and burying dung, these beetles play a significant role in various ecological functions, such as nutrient recycling, seed dispersal, bioturbation, pollination and parasite suppression (Yokoyama et al. 1991, Mittal 1993, Nichols et al. 2008. Moreover, these beetles, by altering the micro-organism fauna in dung pats, brood balls and associated soils, also stimulate the aerobic conditions and reduce methane production (Yokoyama et al. 1991, Mittal 1993, Nichols et al. 2008. Dung beetles show their highest diversity in tropical forests and savannahs (Hanski and Cambefort 1991) and the ecological functions performed by them are considered extremely important for the maintenance of biodiversity in these mega biodiversity zones.
During our survey, we have recorded 78 scarab species, of which 32 are dung beetles and belong to the subfamily Scarabaeinae. Of these, five included within the tribe Oniticellini, are paracoprid dung beetles and are presented here in this paper. All the five species were recorded for the first time from the area, while Tiniocellus spinipes is a new record for the West Bengal State of India. Amongst all recorded species, Tiniocellus imbellis seems to be the dominant species of the Forest as it shows maximum abundance and was recorded from maximum ranges of the Forest and is widely distrtibuted throughout the study area, followed by Tiniocellus spinipes.