Revision of the cricket genus Nisitrus Saussure (Orthoptera: Gryllidae: Eneopterinae) and descriptions of five new species

Nisitrus Saussure, 1878 is a diurnal and monophyletic group of eneopterine crickets found in parts of Southeast Asia. Species often have vivid colourations which make them charismatic photograph subjects among macro photographers. However, their taxonomy has not been revised since their original descriptions, whereas there are also species awaiting to be discovered and described. A synoptic revision is therefore needed prior to studying the phylogenetic relationships of the genus, and before undertaking more precise studies on biogeography and evolution of traits. By holistically incorporating information about general morphology, male and female genitalia, and bioacoustics, we revise the taxonomy of these crickets and recognise 10 valid species of Nisitrus. Five new species are described: N. crucius Robillard & Tan sp. nov. from Borneo; N. danum Robillard & Tan sp. nov. from Borneo; N. hughtani Robillard & Tan sp. nov. from Sumatra; N. malaya Robillard & Tan sp. nov. from Malay Peninsula; and N. rindu Robillard & Tan sp. nov. from Borneo. We redescribe N. brunnerianus and N. insignis; describe the calls of N. malaya sp. nov., N. musicus and N. vittatus. We consider N. sumatrensis as a junior synonym of N. insignis; and N. marginata as a junior synonym of N. vittatus. Nisitrus hyalinus requires further revision. We also consider N. maculosus as a dubious name.


Introduction
Nisitrus Saussure, 1878 is a monophyletic and morphologically unique group of common eneopterine crickets distributed in Southeast Asia (Fig. 1). It belongs to the tribe Nisitrini Robillard, 2004 along with the apterous genus Paranisitra Chopard, 1925, which was taxonomically reviewed in a recent study (Baroga-Barbecho et al. 2019). Unlike many eneopterines, Nisitrus are slender with long legs, with contrasting vivid colourations (generally black and yellow), with transparent forewings in males, and fully developed hindwings (often with colour patterns) capable of short distance flight. Currently, eight species are known from Borneo, Malay Peninsula and Sumatra, but extinct populations are reported from Java and, probably erroneously, from Maluka (Cigliano et al. 2020).
Nisitrus are diurnal, and males can be heard calling among vegetation throughout daytime (Fig. 2). As these crickets usually stay on the foliage, they tend to feed on fresh leaves and flowers . They can be widely distributed and abundant locally (e.g., Tan et al. 2012Tan et al. , 2013aTan et al. , 2015  2018). As such, they can easily be spotted by macro photographers (thanks to their flamboyant nature, bright colouration and diurnal nature) and they make charismatic photograph subjects and are also often observed by citizen science initiative participants such as iNaturalist, where they add up to at least 700 observations from 265 observers (iNaturalist 2020).
In the context of the study of the evolution of communication systems in crickets, the genus is also often used as a representative member of the eneopterine clades that produce low-frequency acoustic signals, by comparison to species producing high frequencies ter Hofstede et al. 2015;Schneider et al. 2017). As such, and due to the facility to breed them in captivity, they are also excellent candidates for detailed studies on the acoustic communication in crickets, even if these studies focus mainly on a single species only.
Such studies are also possible because Nisitrus has been recognised as a stable monophyletic group (see Robillard & Desutter-Grandcolas 2006;Vicente et al. 2017), having been established to be sister to the clade containing both tribes Xenogryllini Robillard, 2004and Lebinthini Robillard, 2004. While the monophyly of the genus is well supported, the relationships among species of Nisitrus are still unclear, since hitherto four species were represented in the phylogenies. More crucially, this is also attributed to the absence of a systematic revision and species clarification for the genus, and to the fact that several species are potentially awaiting discovery.
The taxonomy of these crickets remains problematic, with species delimitation and identification difficult among many species. In this study, we revise their taxonomy using an integrative approach. By amassing a large collection of ca 450 specimens from numerous natural history collections around the world and citizen science observations and photographs, we examine and evaluate characters of both male and female genitalia, general morphology and colour patterns of both adults and juveniles. We also used acoustics of the crickets to help infer species boundaries and we present a map of the distribution of each species and a key to species.

Acoustics
The basic cricket song terminology follows Ragge & Reynolds (1998). One song unit is called a syllable and corresponds to one opening-closure cycle of the male forewings.
The calls of three species are described (i.e., N. malaya Robillard & Tan sp. nov. and N. musicus Ingrisch, 1987) and redescribed (i.e., N. vittatus (Haan, 1844)) here having been recorded in the field and / or in the laboratory from specimens collected as juveniles or sub-adults. The recordings were made with a  (16 bit). Song features were measured using Avisoft Lite ver. 2.0.0. Power spectra using Fast Fourier Transformation (FFT) were generated using the 'meanspecʼ function at 256 000 sampling frequency, using a Hanning window of window length 512 from the R package ʻseewaveʼ (Sueur et al. 2008). All recording files are deposited in the Sound Library of the MNHN under accession numbers MNHN-SO-2020-2851 to MNHN-SO-2020-2860.
To examine how the call properties of N. malaya sp. nov., N. musicus and N. vittatus differ, the call properties (which were not mutually independent and likely to be highly intercorrelated) were summarised into major gradients of variation by performing a Principal Coordinates Analysis (PCoA) on the scaled call properties using the 'cmdscaleʼ function in R ver. 3.5.1 (R Development Core Team 2018). The nine call properties are: echeme duration, echeme period, downtime between consecutive echemes, first to third syllable durations, fundamental frequency, frequencies of the second and third harmonics. Gower dissimilarity was used as it can be calculated for a set of descriptors containing continuous values bounded by zero.

Georeferencing of specimen labels
The description of the localities was manually georeferenced using Google Earth Pro to obtain GPS coordinates. Too imprecise localities were excluded (e.g., only Borneo, Sumatra). Dubious localities were also excluded. For specimens collected during the Midden Oost Borneo Expeditie 1925 in Kalimantan, we georeferenced the localities provided on the map in the book (Buys et al. 1927 (Table 2). We consider N. sumatrensis (Rehn, 1909) as a junior synonym of N. insignis Saussure, 1878;and N. marginatus (Walker, 1869) as a junior synonym of N. vittatus (Table 1). We also consider N. maculosus (Walker, 1871) as a dubious name (Table 2). In total, we recognise 10 species of Nisitrus: N. brunnerianus Saussure, 1878, N. crucius sp. nov., N. danum sp. nov., N. hughtani sp. nov., N. hyalinus Saussure, 1878, N. insignis, N. malaya sp. nov., N. musicus, N. rindu sp. nov. andN. vittatus (Table 2). The distribution of the nine valid species (excluding N. hyalinus) in Southeast Asia is also presented in Fig. 5.
The maximum likelihood tree resulting from the phylogenetic analysis of the mitochondrial gene 12S rRNA marker yielded a largely robust topology within the clade of six species of Nisitrus (Fig. 6)

Remarks on type species
Male genitalia ( Fig. 16) with membranous and setose lophi well individualised; pseudepiphallic parameres including two membranous posterior lobes and a sclerotized anterior lobe oriented anteriorly toward median axis of genitalia and carrying a secondary preapical sclerotized lobe; ectophallic arc transverse, incomplete due to a little-sclerotized median area; ectophallic fold narrowed preapically, its apex narrow, located between anterior apex of pseudepiphallic parameres; dorsal part of fold sclerotized, forming two elongated sclerites connected to the median area of arc; ventral part of ectophallic fold membranous, with two strong rounded lateral sclerites of variable shapes. Membrane of endophallic cavity smooth. Female copulatory papilla (Fig. 17) conical, apex generally sclerotized and pointed. Ovipositor typically longer than FIII; apex thin with both dorsal and ventral edges smooth.

Phylogenetic relationships
Based on previous phylogenetic studies (Robillard & Desutter-Grandcolas 2004c;Nattier et al. 2011;Vicente et al. 2017), Nisitrus is the sister genus of Paranisitra Chopard, 1925(revision in Gorochov 2009and Baroga-Barbecho et al. 2019. The two genera form the Nisitrini tribe (Robillard & Desutter-Grandcolas 2008) and are very close morphologically; Paranisitra is mostly characterised by a lack of wings in both sexes, but except for this, it shares with Nisitrus its general body shape, long thin legs with indented claws, colouration with yellow and black, head shape with large prominent eyes and narrow fastigium, and the general structure of male and female genitalia. Nisitrini are less easy to relate to other clades of Eneopterinae.

Natural history
Species tend to be found at forest edges and gaps in the forest where the vegetation is more exposed. They are also found among shrubs and herbaceous plants (but not grasses). Nisitrus are observed to be generally diurnal, during which the males can be heard calling and individuals are found foraging in the vegetation. It seems as Nisitrus are mostly herbivorous, feeding on leaves, but also on flowers . Nisitrus are also observed to congregate with one another on the same plant, sometimes making up of more than 20 individuals of both adults and nymphs. They can be considered a pest in some parts of Southeast Asia (Willemse 2001 Ingrisch, 1987. G. N. vittatus (Haan, 1844). Scale bar = 1 mm.  (Haan, 1844). Scale bar = 0.5 mm.

Diagnosis
This species differs from all known congeners by the following characters: head nearly completely black (sometimes with yellow patch beneath scapes and eyes). Pronotum lateral lobe either black with small brown spot on postero-ventral corner, or black in dorsal half and yellow in ventral half. Male FW with basal area brown with tint of black, otherwise mostly hyaline; veins mostly yellow. Female FW with dorsal field mostly infumated black, with veins dark brown and lighten towards lateral field and apical areas. Legs red brown; FIII black dorso-basally without bands or stripes on external surface; with a distinct black ring before hind knee; hind knee black. Abdomen with tergites black, sternites mostly black. This species is similar to N. crucius sp. nov. and N. rindu sp. nov. but differs by the combination of these characters: frons nearly completely black (without black cross marking as in N. crucius sp. nov.), dorsum of head completely black (vs with yellow margins in N. crucius sp. nov. or pale with dark patterns in N. rindu sp. nov.) and lateral lobe either with ventral half yellow or with an oval yellow spot at the anterior end (vs with a characteristic dorsal yellow band that extends ventrally in N. rindu sp. nov.).

Redescription
Relatively large and slender (Figs 7A,18). Vertex completely black (Fig. 11A). Fastigium velvety black, with anterior margins yellow. Scapes black, posterior end red brown. Antennae red brown with some segments black and with wide whitish rings. Eyes dark green when alive and red brown when dried. Frons generally black, sometimes with yellow to cream-coloured bands above and beneath antennal cavity and along ventral margins of eyes (Fig. 10A). Mouthparts dark red brown to black. Maxillary palpi creamcoloured; apical segment black apically (Fig. 10A). Head lateral side black (Fig. 12A). Pronotum generally black, covered with white setae; dorsal disk trapezoidal, posterior margin bisinuated (Fig. 11A). Lateral lobes of pronotum with two variants: (1) in lectotype, completely black except for a cream-coloured oblong spot near anterior margin (Fig. 12A); (2) dorsal third black, otherwise completely yellow. Legs red brown. FIIIs dark red brown, sometimes with a dorsal black longitudinal stripe; knees dark brown to black; TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Hindwings hyaline brown, with a rounded transparent window near internal-basal area; longer than FWs, the dark brown tail exceeding FWs more than twice as long as pronotum. Tergites black, in some segments with cream-coloured transverse stripe at anterior end and / or with pale band laterally; sternites pale, their median area red brown. Cerci cream-coloured, short and conical.

Male
Forewings. FW colouration (Fig. 13A): dorsal field cells mostly transparent to pale yellow, veins mostly dark brown to black. Basal area brown with tint of black. R brown, Sc projections brown basally, transparent apically. Lateral field yellow brown, apex more transparent. FW venation (Fig. 13A): 1A somewhat straight. Harp slightly longer than wide, with 3 oblique veins, posterior-most vein bifurcated at base. c1 long and wide, c2 diamond-shaped; mirror (d1) longer than wide, not rounded, generally separated into two parts by a distinct, roundly bent transverse vein, the posterior part hexagonal, shorter than anterior part. Cell d2 narrower than d1. Apical field short and rounded, with 2 wide cell alignments posterior to mirror and a narrow apical alignment; veins yellow. Lateral field with 5-6 projections of Sc. Epiproct black. Subgenital plate pale cream, its median area and anterior and posterior margins black. Genitalia (Fig. 16A). Pseudepiphallus sclerotized, relatively large and broad compared to congeners, anterior margin somewhat broad and straight, posterior margin also straight, lateral margins faintly converging posteriorly. Posterior apex with paired lophi longer than wide (at base), subacute at apex, sclerotized laterally only and covered with strong short setae; spaced apart from one another. Rami swollen preapically, anterior apex somewhat truncated. Pseudepiphallic parameres narrow, divergent posteriorly, their basis membranous, with a sclerotized lobe on anterior apex. Ectophallic arc transverse, complete, with anterior and posterior margins straight. Ectophallic fold strong rounded lateral sclerites appearing bean-shaped. Ectophallic apodemes long and thin, straight and slightly divergent basally. Endophallic sclerite large and sclerotized, its posterior apex with divergent lateral arms and with a short median expansion curved dorsally. Endophallic apodeme with lateral lamellae stout.

Female
Forewings. FW colouration (Fig. 14A): cells on dorsal field mostly infumated black, gradually becoming yellow near CuA, M and R veins; veins generally black or dark brown, also gradually becoming yellow towards CuA, M and R veins; veins near apical area also yellow. Sc projections cream-coloured basally, black apically. Lateral field dark. FW venation: 6-7 strong longitudinal veins on dorsal field, sometimes not smooth; lateral field with 6 projections of Sc. Genitalia. Ovipositor: on average longer than FIII; apex thin with both dorsal and ventral edges smooth. Copulatory papilla conical, slender, more elongated than congeners; apex folded ventrally, long and slender, pointed; dorsal face with a sclerotized area; ventro-anterior end forming a somewhat triangular rim ( Fig. 17A-B).

Juvenile
Unknown.

Measurements
See Table 3.

Ecology
Unknown.

Calling song
Unknown.

Etymology
The species name refers to the dark cross marking on the frons (ʻcrucisʼ = ʻcrossʼ, in Latin).

Description
Average size (Fig. 7B). Colour pattern somewhat intermediate between N. brunnerianus and N. vittatus. Vertex black with cream-coloured margin around eyes (Fig. 11B). Fastigium velvety black with creamcoloured margins. Scapes black dorsally, sometimes reddish ventrally or along dorso-inner margins. Antennae black. Frons yellow, face part of fastigium black between eyes, with a cross-shaped black pattern above mouthparts; clypeus sometimes darkened, mouthparts dark red brown to black (Fig. 10B). Maxillary palpi cream-coloured. Head lateral side generally black. Pronotal disk black with white setae (Fig. 11B). Lateral lobes of pronotum with dorsal third black, cream-coloured ventrally (Fig. 12B). Legs red brown, sometimes internal-basal area black. FIIIs dark red brown, knees dark brown to black; TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Hindwings dark hyaline, with a rounded transparent window near internal-basal area; longer than FWs, the dark brown tail exceeding the FWs about twice as long as pronotum. Tergites black, with a pale band laterally of variable thickness; sternites pale, with a black median area.

Male
Forewings. FW colouration (Fig. 13B): dorsal field cells mostly transparent; veins mostly creamcoloured, sometimes black. Basal area brown, basally cream-coloured, brown towards distal part. R and Sc projections cream-coloured. Lateral field hyaline, with dorsal parts infumated cream-coloured. FW venation (Fig. 13B): 1A somewhat straight. Harp slightly longer than wide, with 2 oblique veins, distal one bifurcate basally. Cell c1 long and wide, c2 diamond-shaped; mirror (d1) longer than wide, not rounded, generally separated into two parts by a distinct straight transverse vein, the posterior part somewhat rectangular, much shorter than anterior part. Cell d2 narrower than d1, usually subdivided by accessory veins. Apical field short and rounded, with 3 wide cell alignments posterior to mirror and a narrow apical alignment; veins cream-coloured. Lateral field with 5 projections of Sc. Epiproct black. Subgenital plate pale cream-coloured with median area and anterior and posterior margins black. Genitalia (Fig. 16B). Pseudepiphallus sclerotized, stout (small but broad) compared to congeners, anterior margin somewhat broad and straight, posterior margin also straight, lateral margins faintly converging posteriorly. Posterior apex with paired lophi slightly longer than wide (at base), obtuse at apex, sclerotized laterally only and covered with short strong setae; narrowly spaced apart from one another. Rami swollen preapically, anterior apex somewhat truncated. Pseudepiphallic parameres narrow, divergent posteriorly, their basis membranous, with a sclerotized lobe on anterior apex. Ectophallic arc transverse, complete, with anterior and posterior margins straight. Ectophallic fold strong rounded lateral sclerites appearing bean-shaped. Ectophallic apodemes long, straight and slightly divergent basally. Endophallic sclerite large and sclerotized, its posterior apex with divergent lateral arms and with a short median expansion curved dorsally. Endophallic apodeme with lateral lamellae stout.

Female
Forewings. FW with cells on dorsal field mostly infumated black, gradually becoming yellow near CuA, M and R veins; veins generally yellow (Fig. 14B). Sc projections cream-coloured. Lateral field transparent, sometimes infumated black apically.

Juvenile
Unknown.

Measurements
See Table 4.

Ecology
Unknown.

Description
Slender and relatively large habitus (Figs 8D, 19). Vertex black with yellow margin around eyes (Fig. 11C). Fastigium velvety black with yellow margins. Scapes dark red brown to black (particularly on the dorsoinner margins). Antennae black with wide whitish rings. Face part of fastigium with a black band across eyes and antennal cavity, otherwise yellow (reddish in preserved specimens); frons almost entirely yellow, including mouthparts, with some black spots (Fig. 10C). Maxillary palpi cream-coloured; apical segment black apically (Fig. 10C). Lateral part of head with a black band posterior to eye (Fig. 12C). Pronotum covered with white setae; dorsal disk dark brown to black (Fig. 11C). Lateral lobes of pronotum dorsal third black, vivid yellow ventrally (cream-coloured in preserved specimens) (Fig. 12C). Legs generally red brown, sometimes dorsally darker. FIIIs brown, knees dark brown to black; TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Tergites red brown, with a pale band laterally; sternites pale, with red brown median area. Cerci red brown, short and conical.

Male
Unknown. Genitalia. Ovipositor: distinctly longer than FIII; apex thin with both dorsal and ventral edges smooth. Copulatory papilla conical, smaller and stout; apex strongly folded (could be due to the preservation of specimen) ventrally, short, pointed; dorsal face with a sclerotized area (Fig. 17E).

Juvenile
Unknown.

Measurements
See Table 5.

Ecology
Unknown.

Calling song
Unknown.

Diagnosis
Large and slender species. Head mostly black, but with cream-coloured margin around eyes in both dorsal and lateral views; frons mostly black, but yellow ventral to eyes and antennal cavity; maxillary palpi white. Pronotum dorsal lobe black, lateral lobe mostly white or yellow, its dorsal margin black. Female  FWs with dorsal field infumated black; lateral field ventrally black; M / R area forming a clearly defined white / yellow stripe. This species is most similar to N. danum sp. nov. from Borneo, but differs by the following characters: larger in size, vertex black with cream-coloured margin around eyes (instead of yellow); frons and mouthparts dark red brown to black; frons black with a cream-coloured band ventral to eyes (instead of completely yellow). This species also differs from the sympatric N. insignis by frons mostly black (instead of yellow); lateral field M / R area forming a clearly defined white stripe (instead of dark); female FW dorsal field with veins black (instead of yellow) and juvenile colouration.

Etymology
The new species is named after Prof. Hugh Tiang Wah Tan

Description
Habitus large and slender, colouration very contrasting with black, white and vivid yellow when alive (Figs 7C, 20A-B). Vertex black with cream-coloured margin around eyes (Fig. 11D). Fastigium velvety black with cream-coloured margins. Scapes dark red brown to black (particularly on the dorso-inner margins). Antennae black with wide white rings. Frons and mouthparts dark red brown to black, frons cream-coloured (whitish when alive) ventral to eyes (Fig. 10D). Maxillary palpi cream-coloured; apical segment black apically (Fig. 10D). Head lateral side dark coloured, with broad cream-coloured band around eyes extending to area behind eyes (Fig. 12D). Pronotum covered with white setae; dorsal disk velvety black (Fig. 11D). Lateral lobes of pronotum with dorsal-third black, cream-coloured ventrally, vivid yellow when alive (Fig. 12D). Legs dark brown. FIII brown, knees dark brown to black; TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Hindwings hyaline brown apically, longer than FWs, the dark brown tail exceeding FW more than twice as long as pronotum. Tergites red brown, with a pale band laterally; sternites pale, with a red brown median area. Cerci red brown.

Male
Forewings. FW colouration (Fig. 13C): dorsal field cells mostly transparent, veins mostly dark brown to black, cream-coloured in apical field. Basal area brown, basally cream-coloured, brown towards distal part. R cream-coloured, Sc projections cream-coloured basally, black apically. Lateral field brown. FW venation (Fig. 13C): 1A curved, slightly angulated. Harp slightly longer than wide, with 3 oblique veins, basal one bifurcate distally, distal one bifurcate basally. c1 long and wide, c2 diamond-shaped; mirror (d1) longer than wide, not rounded, generally separated into two parts by a distinct transverse vein, the posterior part hexagonal, shorter than anterior part. Cell d2 narrower than d1, more or less rectangular. Apical field short and rounded, with 3 wide cell alignments posterior to mirror and a narrow apical alignment. Lateral field with 6 projections of Sc. Epiproct black. Subgenital plate pale cream-coloured with median area, anterior and posterior margins black. Genitalia (Fig. 16C). Pseudepiphallus sclerotized, large and slender, anterior margin narrow and straight, posterior margin also straight, lateral margins distinctly converging posteriorly. Posterior apex with paired lophi longer than wide (at base), subacute at apex, sclerotized laterally only and covered with short strong setae, narrowly spaced apart from each other. Rami swollen preapically, somewhat sinuous. Pseudepiphallic parameres narrow, divergent posteriorly sclerotized arm base to parameres distinctly curved laterally. Ectophallic arc transverse, complete, with anterior and posterior margins straight. Ectophallic fold strong rounded lateral sclerites appearing bean-shaped. Ectophallic apodemes long, straight and slightly divergent. Endophallic sclerite large and sclerotized, its posterior apex with divergent lateral arms and with a short median expansion curved dorsally. Endophallic apodeme with lateral lamellae and dorsal crest only slightly longer than wide.

Female
Forewings. FW colouration (Fig. 14D): cells black, veins generally black. Longitudinal white stripe around region of CuA, M and R with a distinct margin against black colouration on dorsal field; Sc projections cream-coloured basally, black apically. Lateral field dark. FW venation: 6-7 strong longitudinal veins on dorsal field; lateral field with 6 projections of Sc.
Genitalia. Ovipositor: distinctly longer than FIII. Copulatory papilla conical, large (similar to N. brunnerianus but less slender-possibly due to preservation of specimen); apex folded ventrally, elongated like in N. brunnerianus, pointed; dorsal face with a sclerotized area, but less sclerotized than in congeners; ventro-anterior end forming a somewhat triangular rim (Fig. 17F-G).
Juvenile (Fig. 20C-E) Early instars with a pale colouration with numerous dark stripes all around body. Head generally reddish. Eyes with numerous dark stripes. Pronotum with three thick, dark longitudinal stripes on dorsal disk, one very thick and velvety black stripe between dorsal disk and lateral lobe; another curved stripe on lateral lobe ventral of the thick stripe; stripes never reaching the margins. Fore and middle legs with longitudinal dark stripes. FIII also with longitudinal dark stripes, two dorsally, one on each side; and two ventrally, one on each side. Thoracic (excluding pronotum) and abdominal tergites typically dark or greyish, anterior margin darkest, posterior margin whitish. Cerci whitish with a black stripe.

Measurements
See Table 6.

Ecology
Unknown.

Distribution
Northern Sumatra.

Type locality
Indonesia, northern Sumatra.

Remarks
The syntypes in RMNH are missing. L. Chopardʼs records (Chopard 1929) of this species in Mentawai, North Pagi, Siberut and Padang (all part of or related to Sumatra, Indonesia) correspond to specimens of N. insignis, while N. hyalinus is known only from Borneo. We cannot revise this species owing to the absence of type material and of other specimens from the region of the type locality in the south of Borneo. Nonetheless, we have found images of specimens from Sungai Utik, Embaloh Hulu, Kapuas Hulu Regency, West Kalimantan, albeit not exactly near the type locality in Banjarmasin in South Kalimantan, which could possibly correspond to N. hyalinus. These photographs (Fig. 21) match the description by Saussure (1878)

Diagnosis
Of smaller size but stouter habitus than congeners. Vertex coloration ranging from black with creamcoloured margins around eyes and fastigium to cream-coloured with a strong longitudinal black band and one or two faint transverse black band (forming a T-or a cross-shaped black pattern). FIIIs brown, with a brown longitudinal stripe along external ventral half; sometimes dorsal margin with a paler longitudinal stripe. Dorsal field of male FW always with cream-coloured triangular (sometimes rounded) patch, with very distinctly different venation; harp very small, slightly longer than wide, with one distinct straight oblique vein. This species is similar to N. malaya sp. nov. and N. vittatus but differs by legs with lighter colouration and dorsum of head yellow with variable black pattern (instead of entirely black). This species also differs from the sympatric N. hughtani sp. nov. by smaller size, frons yellow (black in N. hughtani sp. nov.) and vertex colouration pattern; FW lateral field M / R area dark (instead of forming a clearly defined white / yellow stripe), and female FW dorsal field with veins yellow (instead of mostly black).

Redescription
Slightly smaller than other species (Fig. 7D). Vivid yellow, brown and black when alive (Fig. 22A-C). Vertex variable: ranging from black with yellow margins around eyes (mostly in individuals from Sumatra) to cream-coloured with a strong longitudinal black band and one or two faint transverse black bands (forming a T-or cross-shaped black pattern; mostly in individuals from Siberut Islands and Malaysia) (Fig. 11E); dark pattern variable between individuals, some have a narrow pattern appearing more like a longitudinal band. Scapes red brown to black. Antennae red brown (individuals from Siberut) to black (individuals from Sumatra), with wide whitish rings. Frons yellow, cream-coloured to yellow, face part of fastigium brown to dark brown or black between eyes, lighter for individuals from Siberut than from Sumatra (Fig. 10E). Mouthparts dark brown to black in specimens from Sumatra, lighter or sometimes yellow in specimens from Siberut (Fig. 10E). Maxillary palpi cream-coloured; apical segment black apically (Fig. 10E). Head lateral side yellow to cream-coloured, including gena, with a black band posterior to eyes (Fig. 12E). Pronotum dorsal disk black, covered with white setae, rectangular with lateral margin barely widening posteriorly, posterior margin substraight to faintly bisinuous (Fig. 11E). Lateral lobes of pronotum dorsal half black, vivid yellow ventrally (cream-coloured in preserved specimens) (Fig. 12E). Legs generally light grey brown, sometimes with some small dark spots. FIIIs brown, with a brown longitudinal stripe along ventral half (more distinct and darker in individuals from Sumatra); sometimes dorsal margin with a paler longitudinal stripe; knees dark brown to black. TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Hindwings hyaline brown apically; longer than FWs and surpassing cerci, forming a black tail with yellow veins exceeding FWs for less than twice the length of the pronotum. Tergites red brown, with a pale band laterally; sternites pale, sometimes with a dark brown median area. Subgenital plate with a dark median area.

Male
Forewings. FW colouration (Fig. 13D): dorsal field narrow, cells mostly transparent, veins varying from pale yellow to black. Basal area either infumated brown to black (individuals from Sumatra) or almost transparent (individuals from Siberut), but always with a cream-coloured triangular patch (sometimes more rounded). Chords most often with a white patch, most readily observed in individuals from Sumatra. R black, Sc projections black basally, cream-coloured or transparent apically. Lateral field transparent. FW venation (Fig. 13D): 1A curved, slightly angulated. Harp very small, slightly longer than wide, with one distinct straight oblique vein. c1 long and wide, broader basally; c2 diamond-shaped; mirror (d1) small, longer than wide, not rounded, generally separated into two parts by a transverse vein, the anterior part triangular, about as long as posterior part, posterior part rectangular. Cell d2 about as wide as d1, usually subdivided by accessory veins. Apical field short, including one cell alignment posterior to mirror and a narrow apical alignment; its veins cream-coloured. Lateral field transparent, with 5 or 6 projections of Sc. Epiproct black. Subgenital plate with a dark median area. Cerci red brown. Genitalia (Fig. 16D). Pseudepiphallus sclerotized, stout (medium-sized but broad) compared to congeners, anterior margin somewhat broad and straight, posterior margin also straight, lateral margins faintly converging posteriorly. Posterior apex with paired lophi slightly longer than wide (at base), obtuse at apex, moderately spaced apart from one another. Rami swollen preapically, anterior apex somewhat truncated. Pseudepiphallic parameres narrow. Ectophallic fold rounded lateral sclerites appearing beanshaped to rectangular. Endophallic sclerite wide and rounded laterally, with relatively long lateral arms.

Female
Forewings. FW colouration (Fig. 14E): base of dorsal field with a yellow area; cells black, veins mostly vivid yellow (cream-coloured in preserved specimens). Region of CuA, M and R black, including the veins. Sc projections yellow basally, black apically. Lateral field transparent. FW venation: 6-7 strong longitudinal veins on dorsal field; lateral field with 6 projections of Sc.

Ecology
Habitat and mating behaviour, including multiple mating, male guarding behaviour, female eating spermatophores and male-male competition for females, were described in detail by Preston-Mahfam (2000).

Calling song
Unknown.

Remarks
One syntype of Saussure from Northern Sumatra found in NMW is designated here as the lectotype of the species. Based on comparisons with the type of N. sumatrensis, the latter name is considered as a junior synonym of N. insignis (new synonymy, see below).

Diagnosis
Average size, colouration contrasting with black and yellow, characterised by black vertex, yellow frons and orange brown legs. This new species is very close to N. vittatus from which it differs by adult and juvenile colouration, male and female genitalia and calling song. General colouration darker, particularly among FW cells and veins beneath R; R black (instead of cream-coloured as in N. vittatus); in male venation, anal-most and middle chords narrow and nearly parallel with one another (instead of diverging apically), and basal-most chord extend from basal half of middle chord (instead of at / after midpoint). It differs from N. vittatus by the male genitalia with pseudepiphallus more robust, broad, anterior margin more strongly concave. Female copulatory papilla with truncated lobule at the ventro-anterior end. Juvenile differs strikingly in the body colour pattern. Male calling song also differs by longer echeme period. This species is also similar to N. crucius sp. nov. in size and habitus, but differs by the absence of cross-shaped black pattern on frons and does not occur in Borneo.

Etymology
This specific name is a noun in apposition referring to the speciesʼ distribution in the Malay Peninsula (including Singapore and Peninsular Malaysia).

Male
Forewings. FW colouration (Fig. 13E): dorsal field cells mostly transparent, veins mostly dark brown to black. Basal FW area black (instead of cream-coloured or brown as in N. vittatus), with a relatively small cream-coloured patch basally. R black (instead of cream-coloured as in N. vittatus), Sc projections cream-coloured basally, black apically. Apex of dorsal field somewhat truncated. Lateral field dark. FW venation (Fig. 13E): 1A curved, slightly angulated. Harp slightly longer than wide, with 3 oblique veins, basal one bifurcated distally, distal one bifurcated basally. c1 long and wide, c2 diamond-shaped; mirror (d1) longer than wide, not rounded, generally separated into two parts by a distinct transverse vein, the posterior part nearly rectangular, shorter than anterior part. Cell d2 narrower than d1. Anal-most and middle chords narrow and nearly parallel; basal-most chord extending from basal half of middle chord. Apical field short and rounded, with 3 wide cell alignments posterior to mirror and a narrow apical alignment; veins cream-coloured. Lateral field with 5 projections of Sc. Epiproct black. Subgenital plate pale cream-coloured with median area and anterior and posterior margins black.
Genitalia. Very similar to N. vittatus (Fig. 16E) but differ by pseudepiphallus faintly less robust and broad, anterior margin more strongly concave. Rami more strongly curved. Genitalia. Ovipositor about as long as FIII. Copulatory papilla conical, small and stout; apex folded ventrally, short, pointed; dorsal face with a sclerotized area; ventro-anterior end forming a truncated lobule (Fig. 17J-K).

Juvenile (Fig. 24 A-C)
Differing from that of N. vittatus by darker colouration, usually grey, never as white as N. vittatus. Stripes on head similar to N. vittatus but sometimes very faint; pronotum dorsal disk homogeneously dark grey, without longitudinal stripes; sometimes with a large velvety black spot. Legs grey with dark stripes, but stripes not as distinct as in N. vittatus. Abdominal tergites dark grey, their posterior margins thinly lined with yellow, not forming a pattern of transverse stripes. In some individuals, first and second abdominal tergites with a particularly dark (black), velvety band.

Measurements
See Table 8.

Ecology
This species can be found among shrubs and herbaceous plants (but not grasses) (Fig. 27). The adults and nymphs from Singapore and Malaysia (previously reported as N. vittatus) have been reported to feed on the flower parts of a varieties of native (e.g., Dillenia suffruticosa (Griff.) Martelli) and exotic weedy (e.g., Lantana camara L.) plant species . They also feed on the foliages of understory plants such as Piper sarmentosum Roxb. (Fig. 27). In Singapore, N. malaya sp. nov. can be found abundantly in the understory where Piper sarmentosum dominates.

Distribution
Malay Peninsula (Singapore and Peninsular Malaysia [northern limit at the state of Penang]) (Fig. 5).

Type locality
Singapore.

Remarks
We split the species previously recognised as N. vittatus into two distinct species after integrating evidence from general and nymphal colouration, female genitalia morphology, acoustics, DNA (12S sequence) and distribution. In terms of adult morphology, the new species is very similar to N. vittatus in habitus, other than being darker in colouration. The male genitalia are not always distinguishable between these  (Haan, 1844), N. malaya Robillard & Tan sp. nov. and N. musicus Ingrisch, 1987. species; but the sclerotization of the female genitalia can be differentiated. However, the colour patterns in the nymphs are drastically different. Likewise, a multivariate analysis of the call properties also showed distinct calling songs. The 12S gene tree also demonstrates that the two species form distinct clades. Lastly, the new species occurs in Malay Peninsula whereas N. vittatus occurs in Borneo and Sumatra.
Integrating these pieces of evidence indicates that N. vittatus and N. malaya sp. nov. are indeed separate species having probably diverged recently, despite the similarities in adult habitus and male genitalia.

Type details
Male, not located.

Remarks
According to the uninformative original description, the type of the species is from Seram Island, while no species of Nisitrus has ever been recorded in the region of Maluku Archipelago (Indonesia). In addition, the description mentions that the eyes are little prominent, and that the FWs extend beyond the abdomen, which is not compatible with any other species of Nisitrus. With the type missing, we consider this species as nomen dubium (new status). Walker, 1869 junior synonym of Nisitrus vittatus (Haan, 1944), syn. reinstated

Nisitrus musicus
Diagnosis (revised from Ingrisch, 1987) Frons whitish with a black stripe between eyes and black mouthparts; femora reddish brown with a black stripe dorsally; male genitalia with pseudepiphallus slenderer than in congeners. This species is most similar to N. danum sp. nov., also from Borneo, from which it differs by mouthparts black (instead of yellow), FIIIs black dorsally and female papilla. While this species is restricted to the highlands in the Kinabalu range, N. danum sp. nov. occurs in the Danum Valley and Tawau Hill areas at the east of Sabah. It is also similar to N. vittatus, N. crucius sp. nov. and N. malaya sp. nov., from which it differs by slightly larger and slenderer habitus, frons whitish with black front head and mouthparts, FIIIs with a black pattern dorsally, and slenderer pseudepiphallus.  The calling song consists of long homogeneous bouts formed of very short echemes consisting of doublets of syllables; echeme duration is 29.7 ± 1.1 ms (28.4-31.3 ms); echeme period is 72.2 ± 2.1 ms (69. 8-76.8 ms); downtime between consecutive echemes is 42.5 ± 2.2 ms (39.4-45.9 ms). Duration for first and second syllables of the doublets are as follows: 7.5 ± 0.6 ms (6.6-8.1 ms) and 18.7 ± 1.5 ms (15.8-20.5 ms); with second syllable usually with greater amplitude than the first. The song spectrum consists of a series of harmonics, with two main peaks in the first two harmonics: first harmonic (fundamental frequency) which is also the dominant frequency peaks at 5.46 ± 0.03 (5.42-5.51) kHz; second harmonic peaking at 10.93 ± 0.04 (10.88-11.02) kHz.  Table 9. Measurements of Nisitrus musicus Ingrisch, 1987 (in mm, means in brackets).

Nisitrus rindu
European Journal of Taxonomy 761: 1-75 (2021) and Indonesian. This new species is dedicated to the front-liners fighting against the COVID-19 pandemic who were far from their homes and loved ones during the early phase of the global pandemic (when the speciesʼ name was chosen).

Description
Relatively large for the genus, colouration contrasted ( Fig. 9C-D). Vertex cream-coloured with a variable longitudinal black band and one or two faint transverse black bands forming a T- or ʻ+ʼ-shaped black pattern (Fig. 11H). Scapes black, posterior end red brown. Antennae red brown with some segments black. Frons and face part of fastigium completely black, without yellow spots or bands (Fig. 10H). Mouthparts dark red brown to black. Maxillary palpi cream-coloured (Fig. 10H). Head lateral side black, sometimes with a small yellow spot at the ventro-posterior margin of eye (Fig. 12H). Pronotal disk generally black with lateral and posterior margins yellow (Fig. 11H); pronotal lateral lobe yellow, its ventro-anterior corner black (Fig. 12H). Legs red brown. FIIIs dark red brown, their inner basal area black; knees dark brown to black; TIIIs brown with black spines and spurs, dark brown to black near distal end; tarsomeres dark brown to black. Hindwings hyaline brown, with a longitudinal transparent window near external-basal area; longer than FWs, forming a dark brown tail exceeding FWs more than twice as long as pronotum. Abdomen generally black.

Male
Unknown.

Female
Forewings. FW dorsal field with cells almost completely black; veins almost always yellow (Fig. 14H). Lateral field with M and R cream-coloured, sometimes with a cream-coloured patch at base; otherwise transparent or dark. FW venation: longitudinal veins on dorsal field with many cross-veins, creating a thin net-like mosaic.

Measurements
See Table 10.

Ecology
Unknown.

Remarks
Based on the study of the type from Sumatra, we consider N. sumatrensis as a junior synonym of N. insignis, even though the colour pattern of the types of both species is slightly different. After the examination of the material from Sumatra identified "N. sumatrensis" and "N. insignis", we observed that the colour patterns form a continuum between a lighter version in N. insignis and the darker, more contrasting specimens previously identified as in the type of N. sumatrensis. There are also little diagnostic differences in the male and female genitalia for both series.  Female Genitalia. Copulatory papilla conical, smaller and stout; apex folded ventrally, elongated, pointed; dorsal face with a sclerotized area; ventro-anterior end with an oblong rim, without truncated lobule ( Fig. 17P-Q).
Juvenile (Fig. 24D-F) Characterised by pale white or yellow colouration with numerous dark stripes all around body. Dorsum of head with three transverse black stripes that extends to gena. Eyes with numerous dark stripes. Fastigium with margin black; antennal black with pale rings; frons with a few black spots; palpal segments white with apices black. Pronotum with three thick, dark longitudinal stripes on dorsal disk, one very thick velvety black stripe between dorsal disk and lateral lobe; another curved stripe on lateral lobe ventral of the thick stripe; these stripes not reaching margins. Fore and middle legs with longitudinal dark stripes, two on each face, usually one dorsal and one ventral. FIII with longitudinal dark stripes, two dorsally, and two ventrally. Thoracic (excluding pronotum) and abdominal tergites typically dark or greyish, anterior margin dark, their posterior margin whitish forming a homogeneous light / dark striped pattern. Cerci whitish with a black stripe.

Measurements
See Table 11.

Ecology
This species can be found among shrubs and herbaceous plants (but not grasses) at the forest edge (Fig. 27A). Similar to N. malaya sp. nov., the adults and nymphs of this species have been observed in Brunei Darussalam to feed on the flower parts of a varieties of native and exotic plant species .

Type locality
Indonesia: Sumatra: Lampongs, Wai Lima. of N. marginatus from Sumatra resembles N. vittatus, we consider the species described by Walker (1869) as a junior synonym of N. vittatus.

Discussion
This extensive taxonomic revision of the genus Nisitrus allowed us to assess the validity of most of the existing species, to redefine the genus and to describe five new species from Malay Peninsula and Borneo. We consider N. sumatrensis (Rehn, 1909) as a junior synonym of N. insignis Saussure, 1878;and N. marginatus (Walker, 1869) as a junior synonym of N. vittatus, and N. maculosus (Walker, 1871) as a dubious name (Table 2). In total, we recognise 10 valid species in the genus.
We observed that unlike typical crickets and other eneopterines recently revised taxonomically (e.g., Jaiswara et al. 2018Jaiswara et al. , 2019Robillard et al. 2014), male genitalia may not always be useful for differentiating species in Nisitrus. Male genitalia can be variable within species of Nisitrus, partly due to their more membranous nature, which can be deformed due to preservation or state of specimens (e.g., age of specimen at collection date, method of preservation and / or age of specimen). Female genitalia can be more useful than male genitalia in some instances, as for example to differentiate N. vittatus and N. malaya sp. nov. In general, species were more accurately differentiated by colour patterns, especially those on the face, pronotum lateral lobes and wings. However, colouration of the head and lateral lobe of pronotum can also be variable within species (e.g., in N. insignis and N. brunnerianus), making their use as specific characters uneasy. For example, in N. insignis, there are two clear variants from Sumatra and the smaller neighbouring Mentawai Islands, which made us hesitate whether there were one or two distinct species. Likewise, we observed that lateral lobe of pronotum in N. brunnerianus can range from completely black, with a small yellow spot, to bicolour, with ventral half yellow. Surprisingly, juveniles of Nisitrus can be distinctly different in their live colour patterns in species which have very similar adult morphology. This is particularly the case of N. vittatus and N. malaya sp. nov. However, juveniles are unknown for most species other than from anecdotal observations. Lastly, male call properties (both time and frequency domains) can also be used as evidence for species delimitation, but recordings are also rare for most species.
Although the phylogenetic tree obtained from the 12S mitochondrial marker probably does not reflect robust evolutionary relationships of the species of Nisitrus, this molecular marker allowed us to test species delimitation for the well-sampled species. It strongly supported the fact that N. malaya sp. nov. was a distinct species from N. vittatus, adding to the evidence from juvenile colouration and acoustics. To reconstruct a robust phylogeny, multigene or genomic data should be used, in particular to include   (Haan, 1844) in mm, means in brackets).
species only known by old specimens. A study on the phylogeny and evolution of Nisitrus was previously impossible because the taxonomy of this genus still warranted a revision to describe unknown species and to identify diagnostic characters to delineate species. Nonetheless, based on this first taxonomic revision of this genus, it is now possible to follow up with a new study to investigate questions on the evolution, speciation and biogeography of these crickets.
The distribution map (Fig. 5) based on this study shows that Nisitrus can be found in Malay Peninsula, Sumatra, Borneo and Java. Two species are found in Malay Peninsula, three in Sumatra and six in Borneo.
We also found that in many parts of the distribution of Nisitrus, two or more species can coexist. This is the case for N. insignis and N. hughtani sp. nov. in Sumatra as well as N. vittatus, N. crucius sp. nov. and N. rindu sp. nov. in parts of Borneo. However, we postulate that samplings in Borneo and Java are probably insufficient and the current map does not represent the true diversity and species distribution in these islands.
Lastly, there is still very little known about the ecology of most species as most natural history notes are anecdotal. This taxonomic study allows for future investigations on ecological questions, such as what predicts the activity, abundance and diversity of Nisitrus, and what the microhabitat, habitat and dietary preferences are (Fig. 28). Given that species of this genus can be locally abundant and charismatic, Nisitrus can potentially be used as flagship and indicator species when a better understanding of their ecology and behaviour is available.