﻿The Leptogenys Roger, 1861 (Formicidae, Ponerinae) of Hong Kong SAR with additional records from Guangdong, China

﻿Abstract Leptogenys is the most diverse genus of the ant subfamily Ponerinae and is widely distributed across the world’s tropical and subtropical regions. More than 40 species are known from the Oriental realm displaying a wide range of ecologies, although their life history traits remain poorly understood, and new species are frequently discovered. Here, a faunal review of the genus from Hong Kong SAR, southern China is provided. A total of nine species are recorded, with one new species, Leptogenysgrohli Hamer, Lee & Guénard, sp. nov. described. Ecological and biogeographic information, including new information on reproductive modes for two species are provided with the ergatoids of L.binghamii Forel, 1900 and L.rufidaZhou et al., 2012 described. Additional records for five of these species within the neighbouring province of Guangdong are also provided. Finally, an illustrated key to species known from Hong Kong is presented, as well as notes on each species’ distribution, ecology, and behaviour. An updated provincial distributional checklist of the Leptogenys species of Mainland China and Taiwan is also supplied.


Introduction
The ant genus Leptogenys is currently recognised as the most diverse genus within Ponerinae, comprising 318 species and 14 subspecies (Bolton 2023).The genus is pantropically distributed, with its greatest diversity encountered within tropical regions, and a limited number of species extending to higher latitudes into warm temperature regions (Janicki et al. 2016;Guénard et al. 2017).Based on a molecular phylogenetic study (Schmidt 2013), the genus is hypothesised to have an Old World origin and to confirm this, a broader understanding of its taxonomic and ecological diversity is paramount.Leptogenys species are highly predatory, with epigaeic and leaf-litter foragers that predominantly hunt upon isopods, diplopods, earthworms, termites, earwigs, and other leaf litter invertebrates (Maschwitz et al. 1979;Steghaus-Kovac andMaschwitz 1993, Dejean andEvraerts 1997;Schmidt and Shattuck 2014;Peeters and De Greef 2015;Mizuno et al. 2022).Predatory behaviours range from solitarily foraging, to mass raiding reminiscent of doryline army ants, with a continuum of foraging and recruitment modes between both extremes (Maschwitz et al. 1989;Duncan and Crewe 1994;Janssen et al. 1997;Schmidt and Shattuck 2014;Mizuno et al. 2022).Nests are often ephemeral and typically found within soil, dead wood, or leaf litter, with the whole colony moving to new nest sites frequently (Maschwitz and Mühlenberg 1975;Schmidt and Shattuck 2014), with species of the processionalis group even forming temporary bivouacs (Maschwitz et al. 1989).Colonies are often queenless, with reproductive functions performed by ergatoid individuals, and with some species reproducing via a gamergate system (Peeters 1991;Ito 1997;Schmidt and Shattuck 2014).The high species diversity, wide variety of life histories, including varying forms of predation, foraging and reproduction, make Leptogenys an ideal taxon for the study of evolution, and behavioural ecology (Dejean and Evraerts 1997).
Leptogenys has seen several regional taxonomic treatments in the last few decades, particularly from Asia where Xu and He (2015) provided a revision of the Oriental species and a preliminary regional key.Subsequent work has been produced by Zryanin (2016), Arimoto (2017), Wachkoo et al. (2018), Arimoto and Yamane (2018) for select Oriental species and for species such as the L. chalybaea and L. modiglianii species groups.Numerous species across the Oriental realm, however, remain undescribed (Arimoto 2017;AntWeb 2024), and many regions remain woefully under-sampled and/or lacking contemporary taxonomic revisions.In China specifically, most of the taxonomic studies for the genus are geographically restricted to a few provinces (e.g., Zhou 2001 andZhou et al. 2012 for Guangxi, Xu 2000 for Yunnan, and Chen et al. 2024 for Hainan) with the vast majority of regions and provinces of China still lacking local taxonomic revisions for this genus.
Here we review the Leptogenys of Hong Kong SAR, one of the most densely populated regions of 6,700 people per square kilometre.Hong Kong, though highly urbanised, comprises surprisingly high biodiversity, including many newly recorded and newly described ant species following intensive sampling from early 90s to the present day (Fellowes 1996;Luo and Guénard 2016;Pierce et al. 2019;Tang et al. 2019;Brassard et al. 2020;Wong and Guénard 2021;Hamer et al. 2023a, Hamer et al. 2023b;Silva et al. 2023;Tang and Guénard 2023).Here, a total of nine Leptogenys species are recorded from Hong Kong including four newly recorded species, and one new species to science, Leptogenys grohli sp.nov.Along with the taxonomic accounts, we provide high resolution images, an illustrated dichotomous identification key, and discussions on the morphology as well as the ecology for all species known from Hong Kong.Ergatoid queens of L. binghamii and L. rufida are also described.Records for five of the overall nine species occurring in Hong Kong are provided for the neighbouring Chinese province Guangdong.

Sampling
Most sample collections were performed using leaf litter sampling through Winkler extractors by Dr. John Fellowes between 1993-2002 and members of the Insect Biodiversity and Biogeography Laboratory (IBBL, HKU) between 2014-2023 in Hong Kong.Other sampling methods were conducted during the same periods, including pitfall trapping, baiting and hand collection comprising of nesting locations and general forager collections.

PeL
Petiole length: length of petiole from the anteriormost point of the petiole (including petiole peduncle) to the posteriormost point, measured in lateral view.

PeH
Petiole height: height of petiole from the most ventral margin of the subpetiolar process to the highest point of petiolar dorsal margin, measured in lateral view.

PeW
Petiole width: maximum width of petiole in dorsal view.

Ergatoid description.
With characters of worker but head as wide anteriorly as posteriorly; pronotum wider than remaining mesosoma in dorsal view; mesosoma stout and robust, less elongated as worker; petiole nodiform, distinctly higher than long in lateral view; about as wide as long in dorsal view.Metasomal segments III-VII enlarged, segment III distinctly wider than petiole.Same colour as the worker.
Measurements.Worker (n = 14); HL 1.66-1.84;HLL 1.31-1.47;HLA 0.24-0.3;HW 1.  Ergatoid paratype (n = 1): HL 1. Comparative notes.Leptogenys binghamii is a relatively large, highly sculptured species, with distinctly linear mandibles, small anteriorly positioned eyes and highly angulated lateral clypeal lobes which makes it recognisable within the Leptogenys found in Hong Kong.Within the wider Leptogenys fauna of the Indomalayan region, L. binghamii might be mistaken for L. punctiventris (Mayr, 1879) and L. yandii (Xu & He, 2015).Leptogenys binghamii is distinguishable from L. yandii by antennal flagellomere I longer than antennal flagellomere II, the longer scape, and larger overall size (5.2-5.7 vs 9-10 mm total length for L. yandii and L. binghamii, respectively; Xu and He 2015).Leptogenys binghamii can be differentiated from L. punctiventris by the smaller eyes, the first gastral  tergite being highly punctate, lacking any smooth and shiny regions as well as total size (5-6 vs 9-10 mm total size for L. punctiventris and L. binghamii, respectively; Xu and He 2015).Both L. punctiventris and L. yandii are not recorded from Hong Kong.With these species presenting more meridional and occidental distributions within Asia, respectively.
Distribution.This species is known from Myanmar (type locality), India (Assam and Meghalaya), China (Guangxi, Yunnan, and Hong Kong), and Vietnam (Janicki et al. 2016;Guénard et al. 2017).There are no records from Guangdong, Hainan, or Macao, but its presence is expected in the first two Chinese provinces with more sampling efforts.Its presence in Macao is less likely due to the level of urbanisation and isolation of natural areas for this species to oc-cur.The first record of L. binghamii in Hong Kong was Fellowes (1996), here we provide additional new records across the eastern limits of its range.
Ecology.In Hong Kong, colonies have been found within decaying wood and underneath stones, predominantly within Feng Shui Woods, secondary forests and shrubland.Colonies appear relatively small, with one partial colony collection including 23 workers, 1 male, 5 cocoons, 4 larvae, and 2 eggs (MTH collection code MTH163).One ergatoid queen was extracted from a partial colony collection (MTH268).Specimens are known from pitfall traps, leaf litter, and hand collection events.This species is suspected to be a solitary foraging species, with no group hunting yet observed.However, unless nesting sites are located, L. binghamii is rarely observed diurnally and is therefore suspected to be predominately a nocturnal foraging species.A second colony, kept in captive colony consisted of 24 workers and one ergatoid queen.Workers fed upon isopod prey and showed no interest in cockroaches, millipedes, and termites.In Hong Kong, the species reaches the northern limit of its distribution range with all records found under 500 m a.s.l.. Further sampling is nonetheless required to confirm if the species can colonize higher and cooler elevations.
Morphological variation.Studied specimens showed clear variation in dorsal head sculpturing, with the shape of concentric costulae medially ranging from broadly curved to angulate, and the regularity of costulae varying subtly among specimens.Additionally, we observed the presence of smooth patches in the middle of the head, with varying sizes among certain specimens; when present, these patches were between the concentric costulae.The dorsal margin of the node is completely foveate in most specimens, but fine costulae was observed in the ventral margin of the petiole of one specimen.Fine and faint costulae was also observed on the metapleuron of one specimen, contrary to the general pattern of rugulose sculpture found in other specimens of L. diminuta.Leptogenys diminuta is known to be a highly morphologically variable species, both on a wider geographical scope, as well as within Hong Kong.This is also reflected through the complex taxonomic history of this species and the numerous associated subspecies, either considered as valid or synonyms.Given such morphological diversity, L. diminuta is likely a species complex with numerous cryptic species found across its distribution (Wilson 1958).
Comparative notes.Leptogenys diminuta resembles and is frequently confused with L. kitteli.However, L. diminuta can be readily separated from L. kitteli in Hong Kong based upon the often smooth to finely reticulate pronotum, the presence of a single tooth on the mandibular masticatory margin, as well as its much smaller size relative to L. kitteli.
Distribution.A very wide ranging species, or species complex, known from numerous regions across Asia and Oceania, including the Australasian region (Australia, New Guinea, Solomon Islands), the Indomalayan region (Bangladesh, Borneo, mainland China [Guangdong (additional records provided here), Fujian, Hainan, Guangxi, Hunan, Hong Kong], India, Indonesia, Lanka, Laos, Malaysia, Myanmar, Nepal, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, and Vietnam), as well as the Palaearctic region [part of southwestern China (Sichuan)] (Wilson 1958;Bakhtiar and Chiang 2010;;Xu and He 2015;Bharti et al. 2016Janicki et al. 2016;Guénard et al. 2017).The absence of this species from various countries and provinces (e.g., Cambodia and Guizhou, China) likely reflects lack of sampling efforts.
Ecology.Leptogenys diminuta is a group-hunting species, forming long columns of workers that move through their habitat in search of prey.Colonies are moderately populous with 200-400 individuals per nest and move nesting locations throughout the year (Ito 1997).Nest locations in Hong Kong have included rotting logs, underneath rocks and within leaf litter.The species has ergatoids (Fig. 10D-E) and likely disperses through colonial budding (Ito 1997;Ito and Ohkawara 2000).Records are predominantly known from young to old growth secondary forests, and similar to L. peuqueti, it is one of the most frequently encountered Leptogenys in Hong Kong.
Description.Head.In full face view, head isosceles shaped as trapezoid, longer than wide, widest at mandibular insertion; lateral margin subtly convex and subtly widening beyond eye to posterior margin; posterolateral corner of head blunt; posterior margin of head straight.Mandible linear, basal margin longer than masticatory margin; distinct angle between basal and masticatory margin present; basal margin weakly sinuous and edentate, masticatory margin with one proximal (formed by angle between basal and masticatory margin) and one apical tooth; gap formed between clypeus and mandible when closed.In lateral view, masticatory margin of mandible curves ventrad at apex; mandibular groove present, beginning 1/3 the width of the mandible from base, terminating at ventrolateral mandible apex.Mandalus ovoid, visible at base of mandible when closed.In full face view, anterior clypeal lobe broadly triangular, extending into intermandibular space; 1/5 of head length; terminating in an acute convex point; lateral clypeal margin gradually curving to lateral head margins with inconspicuous lobes; longitudinal clypeal carina present and conspicuous.Frontal lobes small, 2/3 of antennal condyle visible.Frontal groove short, terminating at anterior eye margin.Occipital carina present, extending to ventral surface meeting at an acute angle ventrally.Eye convex, located dorsolaterally in full face view; interrupting lateral head outline; length 1/4 of lateral head length; maximum number of ommatidia across maximum eye length 14 or 15.Antennae with ten flagellar segments; scape long, extending beyond posterior head margin by 3/10 of its length; scape reaching maximum width medially; antennal flagellomere I longer than pedicel and antennal flagellomere II; apical most flagellomere tapering to a point.Hypostomal teeth present; in ventral view, located laterally, adjacent to mandibular base.Palp formula 4:4 (one worker dissected).
Mesosoma.In lateral view, promesonotum feebly to distinctly convex; promesonotum higher than propodeum; propodeal dorsal outline straight to feebly convex; dorsal surface longer than declivitous face; angle between dorsal and declivitous face gradually curving.In dorsal view, pronotum wider than long; pronotum wider than maximum propodeal width.Prosternal process present, anteriorly convex, and posteriorly acutely angled.Promesonotal articulation present but feebly impressed.Mesonotum wider than long.Notopropodeal sulcus present, impressed, with longitudinal cross-ribs.Angle between dorsal and lateral surfaces smoothly curved.Posterolateral propodeum at spiracular height with broadly rounded lobe that extend posteriorly; propodeal declivitous surface concave.In lateral view, mesometapleural suture deeply impressed, with cross-ribs; mesopleural margin of suture distinctly marginated.Mesopleuron not visibly divided into anespiternum and katerpisternum.Propodeal spiracle circular, located above midline of lateral propodeum surface within concave cuticular depression anterodorsally.Metapleural gland bulla circular.Distance between metapleural gland and spiracle greater than spiracle diameter.Legs long and slender; tarsomere one with concave cleaning comb basally.Mesotibia with one pectinate and one simple spur; simple spur 1/2 length of pectinate spur.Metatibia with one long pectinate spur and one simple spur; simple spur ~ 1/3 the length of the pectinate spur.All tarsal claws pectinate.Metasoma.In lateral view, petiole slightly longer than high, trapezoidal in shape with posterior margin higher than anterior margin; dorsum subtly convex, curving anteriorly; anterior face straight, ~ 1/2 as high as of posterior face.Peduncle absent.Spiracle small and circular, located laterally on anteromedial surface.In dorsal view, petiole distinctly longer than wide; posterior width twice the anterior width.Subpetiolar process present, located anteroventrally; process triangular with posterior margin longer than anterior margin, posteroventral angle acute.Semi-circular prora lobe present, pointed ventrally.Angle between anterior and dorsal surface of abdominal tergite III broadly rounded in lateral view.Abdominal tergite III widest posteriorly in dorsal view.Cinctus with numerous short, longitudinal cross-ribs.Sting present.
Sculpture.Mandibular dorsum with faint longitudinal striations across whole length.Clypeal dorsum laterally smooth, coarsely striate medially, with scattered hair-bearing punctae.Head dorsum between eye, clypeus, and frontal lobe with numerous, dense hair-bearing punctulae; punctations become larger and sparse posteriorly; ventrolateral head surface mostly smooth and shining with widely spaced hair-bearing punctations.Antennal segments with numerous, dense punctulae, lacking smooth regions.Mesosomal dorsum mostly smooth with large, sparse punctures; distance between punctures much larger than their diameter.Propodeal declivity with conspicuous transverse striations that do not extend to propodeal dorsum; posterior portion of declivity smooth.Lateral surface of pronotum mostly smooth and shining with large, sparse punctures.Mesopleuron anteroventral and ventral margins with short striations; striations crossing mesopleuron width ventrally; mesopleuron mostly smooth and shining with sparse punctures.Lateral propodeum with striations on ventral margin, around metapleural gland bulla, propodeal spiracle and posteroventral corner.All femora with hair-bearing punctures; punctures progressively denser apically on dorsal surface of profemur.All tibiae smooth and shining with dense punctulae and sparse macro hair-bearing punctures throughout.Petiole dorsum mostly smooth and shining with large hair-bearing punctures; lateral petiole surface smooth.Dorsum of first gastral tergite mostly smooth and shining with large, sparse, hair-bearing macro punctures; anterior face smooth and shining.Presternite IV imbricate.Abdominal segment IV with macro-punctures dorsally; sternite with very sparse macro punctures.Pygidium and hypopygium with sparse, hair-bearing macro punctures only.
Pilosity.Mandibular dorsum with stout erect hairs directed inwards along basal margin, and short, decumbent hairs on dorsum.Anteriormost point clypeal margin with pair of long, stout, tubular peg-like setae and two decumbent hairs adjacent to the peg-like setae; clypeal dorsum with numerous, long erect hairs as well as decumbent short hairs sparsely distributed across surface.Head dorsum, between clypeus, antennal foramen, and eye with dense, semi-decumbent, appressed hairs; hairs posteriorly sparse with suberect hairs only; head dorsolaterally with decumbent hairs directed anteriorly.Scape with numerous subdecumbent and suberect hairs; flagella with numerous suberect and decumbent hairs.Mesosomal dorsum with erect and suberect hairs sparsely distributed.Suberect and decumbent hairs present on lateral surfaces of pronotum and propodeum.Coxae with many decumbent hairs reaching highest density on ventral surface.
Femora with suberect hairs dorsally and subdecumbent hairs ventrally; tibiae with dense, decumbent hairs dorsally, and sparse decumbent hairs ventrally.All tarsi I with stout and apically blunt hairs arranged in a series, surrounded by simple decumbent hairs.Petiolar dorsum with decumbent hairs; lateral petiole surface with sparse decumbent hairs, almost glabrous; subpetiolar process with numerous suberect and erect hairs.Prora with numerous, fine, short, erect hairs directed anteriorly.All abdominal tergites and sternites with sparsely distributed suberect and erect hairs.Pygidium and hypopygium with numerous long erect hairs.
Colour.Dark reddish brown across mesosoma, mandibles and legs distinctly paler red to orange in colour.
Ergatoid description.With characters of worker but: lateral head margin not straight, distinctly widening posteriorly noticeably more so than the worker.Mesosoma stout and robust not as elongated as in worker; promesonotum distinctly convex; propodeum shorter, ~ 1/3 longer than propodeal declivity.Petiole nodiform, distinctly higher than long in lateral view; about as wide as long in dorsal view.Metasomal segments III-VII enlarged, segment III wider than petiole.Same colours as the worker.
Comparative notes.Within Xu and He (2015), specimens of L. grohli will key to the couplet containing both L. peuqueti and L. confucii.Leptogenys grohli is distinguishable from L. peuqueti by the more linear lateral margins of the head than the convex lateral margins of L. peuqueti; the smaller eye (EL 0.22-0.27);and narrower head (HW 0.70-0.75).Sculptural differences also occur, with L. grohli having greater density of punctures across the whole head, scapes, mesosomal, petiole and first two gastral tergites than L. peuqueti.Leptogenys peuqueti is generally larger in all aspects, with L. grohli being a smaller, more gracile species.Leptogenys grohli is also morphologically similar to L. confucii, a species known from Taiwan and Southern Japan, but can be differentiated by the conspicuously defined angle between the basal and masticatory margin of the mandible; a smaller, less conspicuous frontal indentation; more angulated posterior head corner, and the lack of sculpture across the whole mesopleuron and lateral propodeal surfaces.
Distribution.So far L. grohli is only known from Hong Kong and Guangdong This species, however, should be expected from neighbouring Chinese provinces and is likely to have been misidentified previously as L. peuqueti.
Ecology.The type series was collected by sifting and extracting leaf litter within an old growth secondary forest.Specimens were noted during leaf litter sample collection, with the nest located within the soil between the tree trunk and its roots.One ergatoid and 16 workers were obtained, likely representing most of the colony.Solitary foraging individuals have been observed and collected during daytime across Hong Kong, with specimens obtained from tree plantations to secondary forests and Feng Shui Woods.Group hunting behaviour was not observed in this species.
Material examined.Holotype worker.  .Morphological variation.Specimens of L. kitteli show a wide range of variation in sculpture in different parts of the body.In most specimens, the fine costulae on the head run longitudinally across its entire surface; nonetheless, in some other specimens, some of the costulae converge medially, forming a concentric pattern similar to that found in L. diminuta.The mesosomal sculpturing varies even more when compared to the head sculpture; from fine costulae with interspaced foveae to irregular faint costulae throughout the mesosoma.The metanotal groove is deeply incised in the majority of specimens observed, with just a single specimen having a very shallow groove.Similar to L. diminuta, L. kitteli expresses a large degree of morphological variation across its wider geographical range and is likely a complex of species that would require further taxonomic investigation to resolve.
Comparative notes.Leptogenys kitteli is most morphologically similar to L. diminuta within Hong Kong.Both species can be differentiated by the distinctly larger absolute size of L. kitteli, as well as the longitudinally striate pronotum, and absence of a longitudinal carinae on the clypeal dorsum.
Ecology.Leptogenys kitteli is known to forage in large groups of workers, preying upon termites, as well as earthworms (Fellowes 1996) Kong SAR, Tai Mo Shan;22.41607, 114.12515;800 m a.s.l.;21 Jun. 2016; R.H.Lee leg.; Grassland, Pitfall trap; IBBL RHL03564.• 1 worker; Hong Kong SAR, Lung Fu Shan;22.27603, 114.14199;400 m a.s.l.;11 Jul. 2016; R.H.Lee leg.; Secondary forest, Bait trap; IBBL RHL-SIA-091.• 1 worker; Hong Kong SAR, Southern Shek O;22.25339, 114.24577;190 m a.s.l.;15 Jul. 2016; M.Pierce leg.; Secondary forest, Bait trap; IBBL ANTWEB1009151.• 1 worker; Hong Kong SAR, Deep Water Bay;22.25483, 114.18338; 107 m a.s.l.; 12 Aug.2016; M.Pierce leg.; Secondary forest, Hand collection; IBBL ANTWEB1009484.• 1 worker; Hong Kong SAR, Nam Fung Road;22.2546, 114.1833;120 m a.s.l.;20 Aug. 2016   Morphological variation.Specimens collected in Hong Kong match well with the description provided by Forel, 1905 of L. kraepelini.However, the sculpture on the propodeum (as 'sloping surface of the metanotum' in Forel 1905) is not entirely 'smooth' (Forel 1905), but instead with transverse striations of varying degrees of pronunciation from few to many striae.Xu and He (2015) utilised this character (among others) to differentiate L. kraepelini from L. chinensis (Mayr, 1870), L. chinensis having transverse striation and L. kraepelini lacking it.Such striations appear absent in the dorsal image of the L. kraepelini (CASENT0281936, antweb.org) studied by Xu and He (2015).However, this specimen (from West Java) could represent a morphological extreme for this character.With a large distribution across Southeast Asia, this species likely shows a high degree of morphological variability similar to L. diminuta and L. kitteli.We suggest that this character should be treated with caution until the holotype specimen and additional material of L. kraepelini can be more closely scrutinised.Within Hong Kong, morphological variation appears to be limited.Most variation is associated with colour, with workers varying from reddish brown to jet-black, to black with a blue iridescent shine.The possibility of cryptic species within L. kraepelini and L. chinensis requires further taxonomic investigation which is not within the scope of this study.As such, despite ergatoids presented here we refrain from describing them.
Comparative notes.This species highly resembles L. peuqueti and L. grohli within Hong Kong.However, L. kraepelini can be separated from both species by its much larger size, the distinctly posteriorly projecting propodeal lobes and the truncated anterior clypeal margin.Leptogenys kraepelini has been confused with L. chinensis in the past (Xu and He 2015).However, L. kraepelini has a rectangular head that does not significantly narrow behind the eyes as in L. chinensis; has punctuate sculpture between the clypeus and eyes which L. chinensis lacks, and a straight anterolateral clypeal margin which is sinuate in L. chinensis.More differing characters will likely be revealed upon closer inspection of type material and the examination of more specimens from across the wider region.Specimens previous determined to be L. chinensis from Guangdong were not examined in this study (Wu et al. 2008;Zhao et al. 2009).Such specimens should be re-examined, especially considering L. kraepelini is now confirmed from Guangdong and Hong Kong (this study), as well as the previously known misidentifications of L. chinensis for L. kraepelini (and L. peuqueti) in the past.
Distribution.Leptogenys kraepelini is widely distributed across Indomalaya, recorded from China (Yunnan and Hong Kong SAR), Vietnam, Laos, Thailand, Malaysia Peninsula, Singapore, Borneo, Sumatra, and Java (Bakhtiar and Chiang 2010;Xu and He 2015;Janicki et al. 2016;Guénard et al. 2017;Khachonpisitsak et al. 2020;Wang et al. 2022).This species is currently absent from many southern Chinese provinces which likely reflects sampling effort in these regions, or has been incorrectly identified as L. chinensis.
Ecology.This species is known to nest within rotting wood in young to old growth secondary and shrublands but is seemingly absent from highly disturbed environments.Specimens have been collected either individually or in small groups (three individuals) during the day, with colonies reproducing through ergatoid queens (Ito 1997).Leptogenys kraepelini appears to have a specialised diet on earwigs (Steghaus-Kovac and Maschwitz 1993) but has been observed preying upon termites in Hong Kong (CYLT pers.obs.).
Morphological variation.Owing to the poor quality and quantity of specimens collected, little is known about the morphological variability of this species.
Comparative notes.Leptogenys laeviterga is superficially similar to L. diminuta owing to similarly shaped triangular mandibles, broad petiole shape, as well as overall body size.However, L. laeviterga is readily differentiated by the distinct and conspicuous median clypeal carina; lack of costulate sculpture on the head, lack of teeth on the mandibular masticatory margin, and longer scapes (SL 1.90-1.99).Within the wider Indomalayan Leptogenys fauna, L. laeviterga is morphologically similar to L. sunzii Xu & He, 2015, but can be differentiated by the truncated clypeal apex in L. laeviterga (pointed and convex in L. sunzii), the smaller eyes (larger in L. sunzii), and the higher than long petiole in L. sunzii whereas the petiole as long as high in L. laeviterga (Xu and He 2015).Distribution.Previously, L. laeviterga was only known from its type locality in Darning Mountain National Nature Reserve, Guangxi (Zhou et al. 2012).Here we provide the first record of the species from Hong Kong, representing the eastern most record for this species thus far.The species should therefore be expected from Guangdong and other neighbouring provinces in China.
Ecology.Very little is known of the ecology of L. laeviterga.Specimens (but not the whole colony) from Hong Kong were obtained from within a decaying log from an old growth secondary forest on the southern slopes of Tai Mo Shan (471 m a.s.l.), Hong Kong.Male specimens were obtained on the day of collection.Considering the sampling effort undertaken in Hong Kong, it is surprising that more L. laeviterga have not been collected, indicating the potential rarity of this species.
Material examined.Workers (n = 3): China • 3 workers; Hong Kong SAR, Tai Mo Shan;22.40403, 114.10691  .Morphological variation.Morphological variation with L. peuqueti specimens collected from Hong Kong consists of overall size variation, with some specimens being larger and more robust than others collected.Such variation can be seen with the dorsal pronotal width and Webers length (PrW 0.6-0.76;WL 2.02-2.2).Additional variation is associated with colour, with workers varying from jet-black, to black with an iridescent blue shine.
Comparative notes.Leptogenys peuqueti is most similar to L. grohli and L. kraepelini within Hong Kong and Macao, being distinguishable from L. grohli by the smooth head dorsum, larger eyes, shorter tubular setae on the anterior clypeal margin, and convex lateral head margins.Leptogenys peuqueti highly resembles L. kraepelini, but lacks the truncated anterior clypeal margin found in L. kraepelini, the posteriorly projecting propodeal lobes and is overall smaller.Within the wider Indomalayan Leptogenys species, L. peuqueti is most similar to L. confucii, as well as other members of the L. chinensis group.Leptogenys peuqueti can be differentiated by the smooth head dorsum, meso-and metathorax, and propodeum, as well as its black colour.Distribution.A very wide-ranging species in Indomalaya, L. peuqueti is recorded from several Chinese provinces including Fujian, Guangdong, Guangxi, Hainan, Hong Kong Hubei, Hunan, Macao, Yunnan, and Zhejiang (Guénard and Dunn 2012;Xu and He 2015;Janicki et al. 2016;Guénard et al. 2017;Brassard et al. 2021).Other countries include Bangladesh, Bhutan, India (Andaman Islands, Kerala, Meghalaya, Sikkim, and West Bengal), Indonesia (Java), Malaysia (Peninsular and Bornean parts), Myanmar, The Philippines, Singapore, Sri Lanka, and Vietnam (Bakhtiar and Chiang 2010;Janicki et al. 2016;Guénard et al. 2017;Wang et al. 2022).Further sampling effort across the Oriental region will likely produce new country level records of this species (e.g., Cambodia, Laos, Thailand).
Ecology.Leptogenys peuqueti is the most common Leptogenys recorded from Hong Kong, collected from a wide variety of habitats including forests, shrubland as well as disturbed urban sites.Workers are known to foraging individually but will recruit small numbers of workers to tackle larger prey items (Janssen et al. 1997;MTH pers. obs.).Workers have been noted to feed upon isopods in Hong Kong.Nests have been found within rotting logs, under rocks and within soil (often underneath objects).Colonies are queenless, instead reproducing through gamergates (Ito 1997).One colony collection contained 67 workers, 20 cocoons and four larvae (MTH271), correlating with Ito (1997) who found the number of workers in L. peuqueti colonies to range from 5 and 97.
Material examined.Workers (n = 134):   Morphology.Little to no variation is detected with the specimens examined, other than subtle differences in the development of the longitudinal ribbing across the mesonotal notch, however in no specimens was this character absent.
Comparative notes.Leptogenys rufida is the smallest Leptogenys known from Hong ) and is further recognisable by the following combined morphological characters; subquadrate petiole with a broadly rounded anterodorsal corner, rugose meso-and metapleural, head dorsum punctate, with relatively small eyes (EL 0.16-0.18).This species could be mistaken for L. grohli due to the ribbing across the notopropodeal sulcus, punctate head dorsum and small eyes, but L. rufida is smaller, with a more sculptured meso-and metapleural, and flagellomere segment I is as long as flagellomere segment II, shorter clypeal median lobe length (CML 0.19-0.21),and a petiole that is as high as long in lateral view , and as wide as long in dorsal view .
Across the Indochinese Leptogenys fauna, L. rufida is most similar to members of the L. zhuangzii species group (L.mengzii Xu, 2000, L. laozii Xu, 2000, and L. zhuangzii Xu, 2000), and can be differentiated by the following combined characters; petiole in lateral view as long as high, anterodorsal margin distinctly convex, sculptured meso-and metapleural, and red colour.Leptogenys rufida and L. confucii can be differentiated by the triangular shaped petiole of L. confucii, the smaller eyes in L. rufida and the densely sculptured meso-and metapleural of L. confucii.
Distribution.Leptogenys rufida is known from China only, including the Chinese provinces of Guangxi, Yunnan, Zhejiang and now Hong Kong SAR (Zhou et al. 2012;Xu and He 2015).To our knowledge, this species is not reported from other southern Chinese provinces but considering the gap in records between Yunnan, Guangxi and Zhejiang, it seems likely to be found in Guangdong and Fujian.
Ecology.Records for L. rufida in Hong Kong are sparse, but when collected it has occurred predominantly within pitfall traps, leaf litter samples and hand collection events (predominantly within leaf litter or soil) from secondary forest habitats.Two colony collections are known from Hong Kong  .
Morphological variation.Upon examination of five specimens from the only collection locality in Hong Kong, it was noted that the number of teeth on the masticatory margin are not consistent but were always between three and five.Teeth were either conspicuous or barely discernible from the mandible margin, suggesting these teeth might be worn down and, or broken.A distinct diastema between the basal tooth and fourth tooth was, however, always present.The utility of teeth count as a differentiable and diagnosable character should likely be treated with caution unless combined with additional less variable characters.
Comparative notes.Leptogenys strena is immediately recognisable within the Leptogenys of Hong Kong by the combined characters of small anteriorly positioned eyes, a subquadrate head, triangular mandibles with 3-5 teeth on the masticatory margin, and a distinctly red body colouration.Within the wider Leptogenys fauna of China, L. strena is most similar to L. lucidula Emery, 1895 and can be differentiated by the rounded posteroventral corner of the subpetiolar process, fewer teeth on the masticatory margin and the species overall larger size.
Distribution.This species is so far only known from China, including Guangxi (type locality), Hunan, and Guangdong, and Hong Kong SAR (Zhou et al. 2012;Xu and He 2015).Absence from other southern Chinese provinces is likely attributable to sampling effort.
Ecology.Next to nothing is known about the ecology of L. strena.Specimens from Hong Kong are known only from Sunset Peak, Lantau Island.One collection was by J. R. Fellowes in 1992, and another in 2023 by A. Reshchikov using a ground SLAM trap, which was positioned in a tiny fragment of forest near the top of the mountain which yielded one further specimen.Further sampling efforts by members of Insect Biodiversity and Biogeography Laboratory have yet to collect additional specimens from this locality and from Hong Kong at large.The species' small eyes might suggest leaf litter and/or nocturnal foraging.

Discussion
Considering the relatively small geographical size (1100 km 2 ), the genus Leptogenys is surprisingly rich in Hong Kong.Nine species are now recorded, including one new species, L. grohli sp.nov.Hong Kong is now the third most diverse region for this genus across Mainland China and Taiwan even with additional species provided for Guangdong, a considerably larger Mainland Chinese province (Table 1).Such low diversity for Guangdong, as well as Fujian and the more tropical Chinese Province of Hainan (Table 1), is undoubtedly attributable to limited sampling and taxonomic efforts, and is unlikely to reflect true biodiversity patterns.The lack of regional knowledge, especially for a large, mostly epigaeic, genus such as Leptogenys, indicates our lack of knowledge regarding the biodiversity of this region, a pattern also observed in other recently reviewed ant genera (e.g., Species of Leptogenys are predominately collected via pitfall trapping and hand collection, with fewer known from Winkler samples, at least from Hong Kong.This is likely a result of their more epigaeic, nomadic, and nocturnal nature, at least for a few species.Some species seem to be locally rare, including L. rufida, L. strena, and L. laeviterga, which are known from just a few localities.Leptogenys strena and L. laeviterga are known from a single locality from Sunset Peak, Lantau Island, and Tai Mo Shan, New Territories.Considering the sampling effort carried out across Hong Kong, comprising thousands of pitfall traps, Win- kler samples and hand searching events, it is surprising that more material from more localities has not been collected, suggesting that both species are scarce. Although Xu and He (2015) provided a comprehensive review of the genus in the Oriental region, much is yet to be understood about the taxonomy of the genus in Asia.For example, several species groups have been proposed, based upon limited morphological evidence (but see Arimoto 2017; Arimoto and Yamane 2018).Moreover, several species complexes (e.g., those of L. diminuta, L. kitteli, and L. kraepelini) exist within the region (Wilson 1958;Xu and He 2015).In addition, many regions lack sampling efforts including West and East Malaysia, Vietnam, Laos, and Cambodia.Thus, with known uncertain species groups, new species to science, unsorted species complexes, and lack of regional revisions, the Leptogenys is clearly in desperate need of greater taxonomic attention.
Dorsal petiole length: length of petiole in dorsal view, from anteriormost point of the petiole (including peduncle) to the posteriormost point, measured in dorsal view.CI Cephalic index: HW / HL × 100 CLI Clypeus index: CML / HL × 100 SI Scape index: SL / HW × 100 OI Ocular index: EL / HLL × 100 LPI Lateral petiole index: PeH / PeL × 100 DPI Dorsal petiole index: PeW / DpeL × 100 Depository institution abbreviations HKBM Hong Kong Biodiversity Museum, University of Hong Kong.IBBL Insect Biodiversity and Biogeography Laboratory, The University of Hong Kong.SKYC Seiki Yamane Collection, Kitakyushu Museum of Natural History and Human History, Kitakyushu, Fukuoka, Japan ZRC Zoological Reference Collection, Lee Kong Chian Natural History Museum, Singapore.

Figure 1 .Figure 2 .Figure 3 .Figure 4 .Figure 5 . 7 Figure 6 .7Figure 7 .8
Figure 1.Schematic diagram of the linear measurements used within this study A head measurements B eye diameter C lateral mesosomal and petiole measurements D dorsal mesosomal and petiole measurements.

Figure 9 .
Figure 9. Leptogenys binghamii (ANTWEB1010110) and ergatoid (ANTWEB1010225) A worker in lateral view B worker in dorsal view C worker in head in full face view D ergatoid in lateral view E ergatoid in lateral view and F ergatoid in dorsal view.

Figure 10 .
Figure 10.Leptogenys diminuta worker (ANTWEB1010183) and L. diminuta ergatoid (ANTWEB1010180) A worker specimen in lateral view B worker specimen in dorsal view C worker specimen in full face view D ergatoid in lateral view E ergatoid in lateral view and F ergatoid in dorsal view.

Figure 11 .
Figure 11.Leptogenys grohli holotype (ANTWEB1010093) A lateral view B dorsal view C head in full face view.

Figure 12 .
Figure 12.Leptogenys grohli sp.nov holotype (all images are ANTWEB1010093, other than C ANTWEB1010092) close up sections A close up of head and mesosoma in lateral view B close up of right hand mandible in full face view C close up of right antennal scape in full anteroventral view D close up of petiole in lateral view E close up of propodeum, petiole and first gastral tergite in dorsal view.

Figure 13 .
Figure 13.Leptogenys grohli ergatoid queen (ANTWEB1010094) A lateral view B dorsal view C head in full face view.

Figure 14 .
Figure 14.Leptogenys kitteli (PFL1T2W3-1) A lateral view B dorsal view C head in full face view.

Figure 15 .
Figure 15.Leptogenys kraepelini (RHL00392) and ergatoid (ANTWEB1010172) A worker in lateral view B worker in dorsal view C worker in head in full face view D ergatoid in lateral view E ergatoid in lateral view and F ergatoid in dorsal view.

Figure 17 .
Figure 17.Leptogenys peuqueti (FK1T2W5-1) A lateral view B dorsal view C head in full face view.

Figure 18 .
Figure 18.Leptogenys rufida (RHL01259) and ergatoid (ANTWEB1010234) A worker in lateral view B worker in dorsal view C worker in head in full face view D ergatoid in lateral view E ergatoid in lateral view and F ergatoid in dorsal view.

Figure 19 .
Figure 19.Leptogenys strena (ANTWEB1010114) A lateral view B dorsal view C head in full face view.

Figure 20 .
Figure 20.Distribution maps of Leptogenys species recorded from Hong Kong A L. binghamii B L. diminuta C L. grohli D L. kitteli.The base map displayed shows tree canopy cover with the darker green areas indicating greater tree cover.

Figure 21 .
Figure 21.Further distribution maps of Leptogenys species recorded from Hong Kong A L. kraepelini B L. laeviterga C L. peuqueti D L. rufida E L. strena.The base map displayed shows tree canopy cover with the darker green areas indicating greater tree cover.
Little to no variation, other than morphometric values, were detected in the specimens examined from Hong Kong.
. Similar to L. diminuta, colonies are known to move nesting locations and include up to several hundred individuals.

Table 1 .
Distributional checklist of the Leptogenys species for the provinces of Mainland China and Taiwan.NR indicates new records presented in this study.