Earwigs are a moderately diversified group of insects which comprise approximately 1,900 species distributed mainly in tropical and subtropical parts of the world (Hopkins et al. 2018). The previous taxonomic study by Srivastava (2013) reported 284 species from India. Although the taxonomy is unstable and unsettled, the genus Diplatys (Diplatyidae), in a broad sense, is species rich with approximately 70 described species from the Ethiopian and Oriental regions (Hopkins et al. 2018). According to the system of Srivastava (1988, 2013), 25 species of Diplatys have been reported from India and Sri Lanka, of which four species are endemic to Sri Lanka (Srivastava 1988, 1989, 2013; Table 1); clearly these two countries represent the centre of Diplatys diversity.

To explore the diversity of earwigs in different agricultural ecosystems of South India, we conducted an extensive taxonomic survey in agricultural and horticultural crop fields. Here we report a new species, D. sahyadriensis sp. nov., based on a male specimen collected from a sugarcane ecosystem. The possible relationships of the new species with other Diplatys recorded from India and Sri Lanka and the diversity of this genus in this region are also discussed.

The specimen was collected by hand from a sugarcane field in Shivamogga District, Karnataka, India, and preserved in 70% ethanol. For the morphological identification, the specimen was examined under a Stemi 508 stereozoom microscope (Carl Zeiss Microscopy GmbH, Jena, Germany). Photographs of the habitus and external body parts were taken under an M205C stereozoom microscope attached with a DFC450 camera (Leica, Wetzlar, Germany). The male genitalia were removed by gently lifting the penultimate abdominal sternite, pulling out from the genital chamber with forceps, and cutting at the site of attachment to the ejaculatory ducts. The genitalia were processed by submerson in 5% KOH for two days for clearing tissues and mounted on a glass slide with glycerol. Photographs of dissected genitalia were taken an M205C stereozoom microscope attached with a DFC450 camera. Based on the photographs, the genitalia were illustrated using Adobe Illustrator CS6. The specimen, with voucher number UAHSE19K, is deposited in the Insect Systematics and Vector Biology Laboratory, Department of Entomology, College of Agriculture, Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, Shivamogga. The terminology of Kamimura (2014) was adopted to describe male genital structures.

In the present study, we follow Srivastava’s (1988, 2013) classification of Diplatyinae, except for the treatment of Haplodiplatys Hincks, 1955, which is considered the sole genus of the family Haplodiplatyidae (Engel et al. 2017). Based mainly on the parameric characters, Steinmann (1974, 1986b) proposed to classify Diplatys sensu Hincks (1955) into four genera (Diplatys, Schizodiplatys Steinmann, 1974, Lobodiplatys Steinmann, 1974, and Circodiplatys Steinmann, 1986). Although Steinmann (1974) placed Diplatys conradti Burr, 1904 in Lobodiplatys, Zacher (1910) erected subgenus Paradiplatys Zacher, 1910, treating this species as its type. According to the Principle of Priority, Sakai (1982) resurrected the subgenus Paradiplatys as a full genus and synonymised Lobodiplatys with it. Engel and Haas (2007), who omitted to cite Sakai (1982), made the same proposal. This view was followed by Srivastava (1988, 2013) in classifying the Indian species of Diplatyinae into three genera: Diplatys, Paradiplatys, and Nannopygia Dohrn, 1863; Srivastava (1993b) considered Nannopygia a senior synonym of Schizodiplatys. Males of Diplatys possess a pair of elongate parameres with unarmed external margins (vs armed with a single movable epimerite in Paradiplatys), but with internal margins armed with one or two teeth, which are sometimes separated by a concavity. Occasionally, a concavity preceding or succeeding the pre-apical tooth is also present but parameres are not divided into two lobes with a cleft (vs cleft in Nannopygia). The elongate parameres of the new species, each with an internal tooth but without deep clefts or articulated structures, clearly indicate that the species is a member of Diplatys.

Steinmann (1986b) proposed a subgeneric classification system for Diplatys (Table 1), mainly based on the relative lengths of virgal regions (paired and unpaird parts), especially those included in the penis lobe. However, some apparently closely related species can be classified into different subgenera according to this system (Gorokhov and Anisyutkin 1994). Therefore, we do not assign D. sahyadriensis sp. nov. to any subgenus, as done for some other Diplatys species described since Steinmann (1986b) (Table 1).

The male genitalia of D. sahyadriensis sp. nov. are unique in the genus in having several elaborations: a well-developed flange on the paired part of virgae, three differently shaped sclerites with serration (or denticulation) on the penis lobe, and a filament-like appendage at each virgal tip. Diplatys jawalagiriensis, which has been recorded from Karnataka and Tamil Nadu, also possesses flanged virgae (Kapoor et al. 1971; Srivastava 1988), which indicates a possible relationship with D. sahyadriensis sp. nov. According to the descriptions by Kapoor et al. (1971) and Srivastava (1988), however, no conspicuous associated sclerite is present in the penis lobe of this species.

Diplatys propinquus is a Sri Lankan Diplatys species possibly close to the new species. According to the descriptions and illustrations by Hincks (1955) and Srivastava (1988), each penis lobe includes three different, serrated or denticulated sclerites, which are very similar to those of D. sahyadriensis sp. nov. Little is known of the functions of sclerites observed on the penis lobe of earwigs. However, males of the ovoviviparous spongiphorid Marava arachidis (Yersin, 1860) possess a pair of triangular sclerites (genital hooks) on the penis lobe (Kamimura et al. 2016), and during copulation, the sclerites are firmly pressed against the opening region of the spermatheca, frequently resulting in wounds (Kamimura et al. 2016). At the same time, another spatula-shaped sclerite is shallowly inserted into the spermatheca (female sperm storage organ), supporting the insertion of the narrow (<10 μm in diameter) but highly elongate (ca 20 mm) virga (Kamimura et al. 2016). A similar division of roles among differently shaped accessory sclerites has been reported for another spongiphorid, Paralabellula dorsalis (Burmeister, 1838) (Briceño 1997; Kamimura and Ferreira 2017). Different types of denticulated or serrated accessory sclerites have also been reported for several other diplatyids (Hincks 1955; Sakai 1985; Steinmann 1986a; Srivastava 1988). Males of Diplatys flavicollis Shiraki, 1907 possess three different types of denticulated sclerites (saber-shaped, rod-shaped, and U-shaped) on each penis lobe (Kamimura 2004). During genital coupling, two lateral pockets in the female genital chamber receive the U- and rod-shaped sclerites, while the saber-shaped sclerite contacts the female subgenital plate (Kamimura 2004). The accessory sclerites of D. sahyadriensis sp. nov. may have similar functions in securely holding a female during copulation.

The filament with long spines at each virgal tip represents another characteristic structure of D. sahyadriensis sp. nov. In Diplatys, the Cameroonian D. longipennis Brindle, 1969 also possesses many spines, like barbs, but directly on each tip of the thin, highly elongate paired part of the virgae (Brindle 1969). These barb-like structures may be for the removal of rival sperm from female sperm storage organ(s), as known in several insect groups (Waage 1979). Males of the anisolabidid, Euborellia plebeja (Dohrn, 1863) also use their highly elongate virga, which is usually longer than the entire body, for removing rival sperm from the tubular spermatheca of mates (Kamimura 2000). However, in this species, a recurved flange at the virgal tip is considered responsible for sperm removal (Kamimura 2000). Although males of most earwig species directly insert a virga into the female spermatheca for transferring sperm during copulation (Kamimura 2014; Kamimura et al. 2019), D. flavicollis is an exception: the virgal tips are much wider than the spermathecal openings and ducts, indicating that physical removal of stored sperm by a virga is not feasible (Kamimura 2004). However, as in males, female genitalia are quite variable among diplatyid species (Popham 1965; Klass 2003). Future studies on the female genital structures and reproductive biology are warranted for D. sahyadriensis sp. nov. and other, related species.

Based on temperature and precipitation, India is divided into six regions: highland, humid subtropical, tropical wet and dry, arid, semiarid, and tropical wet zones (Senapati et al. 2013). Diplatys is most species rich in the tropical wet and dry zone (Table 1), which occupies a large part of the southern Indian peninsula. The tropical, rainy climate is responsible for the persistent warm or hot temperature, which normally does not fall below 18°C. India hosts two climatic subtypes, the tropical monsoon climate and the tropical wet and dry climate. The most humid is the tropical monsoon climate, also known as tropical wet climate, which extends over a strip of south-western lowlands abutting the Malabar Coast, the Western Ghats, and southern Assam. These regions are characterised by moderate to high year-round temperatures, even in the foothills, and rainfall which is seasonal but heavy and typically more than 2,000 mm per year (Senapati et al. 2013). Most rainfall occurs between May and November, and this moisture is enough to sustain lush forests and other vegetation for rest of the year. The heavy monsoon rains are responsible for the exceptionally higher biodiversity of earwigs.

The new species of earwig, D. sahyadriensis sp. nov. described from sugarcane ecosystem in Western Ghats gives insight into the possible substantial diversity of this genera in India. There is a need to study its distribution, status, and role in agricultural and horticultural ecosystems.