Revision of the elusive ant genus Rhopalomastix (Hymenoptera, Formicidae, Myrmicinae) in Thailand based on morphology and DNA barcodes, with descriptions of three new species Author Wang, Wendy Y. 41730B76-D515-42D0-A3BE-2788ADFDAA8A Lee Kong Chian Natural History Museum, National University of Singapore, 2 Conservatory Drive, Singapore 117377. Department of Biological Sciences, Faculty of Science, National University of Singapore, 16 Science Drive 4, Singapore 117558. Natural History Museum, National Science Museum, Technopolis, Khlong 5, Khlong Luang, Pathum Thani, 12120 Thailand. nhmwyw@nus.edu.sg-wywang24@gmail.com Author Yong, Gordon W. J. 3D3752DF-3522-4DEE-B4A3-7E85CA774263 gordonyongwj@gmail.com Author Jaitrong, Weeyawat E456F06F-486F-4BD5-AEE6-6DCA639C3E27 polyrhachis@yahoo.com text European Journal of Taxonomy 2021 2021-03-17 739 1 117 157 http://dx.doi.org/10.5852/ejt.2021.739.1271 journal article 7699 10.5852/ejt.2021.739.1271 99f6713d-6ef6-4bee-905b-b987df8832d4 2118-9773 4610565 81383BD5-6040-4156-BD09-A2704E5D9DA7 Rhopalomastix javana Wheeler, 1929 Figs 2c , 5 (worker), 6 (queen), 7 (male), 16b. Also see Wang et al. (2018b : figs 20–23) for male. Rhopalomastix rothneyi subsp. javana Wheeler, 1929: 96 , fig. 1 (w.q.m). Rhopalomastix rothneyi subsp. javana – Chapman & Capco 1951: 111 . — Bolton 1995: 377 . — Xu 1999: 131 (in key). Rhopalomastix javana – Wang et al. 2018b: 310 , figs 8–11 (raised to species, redescription). Diagnosis Worker Workers monomorphic with little size variation ( types : HL 0.48–0.52, HW 0.45–0.48; non-types HL 0.46–0.48, HW 0.41–0.44). Head in full-face view subrectangular, longer than wide, posterior margin with a shallow median concavity ( Fig. 5a ). In profile, clypeus broadly and weakly convex ( Fig. 5c ); dorsum of head finely striate ( Fig. 5a ); striations on posterior half of head generally weaker and more fragmented; ventral face of head largely superficially reticulate. In dorsal view, mesosoma subrectangular with almost parallel sides and weakly concave posterior propodeal margin ( Fig. 5b ); posterolateral corners of propodeum bluntly angulate, slightly projecting posteriorly and distinctly, though shallowly, differentiated from inner posterior propodeal face. Propodeal junction in lateral view roundly obtuse ( Fig. 5d ); posterior propodeal declivitous face weakly marginate and shallowly concave ( Fig. 5b, d ); propodeal dorsum differentiated from posterior face by weakly marginate edge.Anterior face of petiole weakly concave ( Fig. 5d ), with fairly dense appressed and decumbent hairs. Head, mesosoma dorsum and gaster darker brown than rest of body; dorsum of head sometimes with blackish undertones. Queen Small-medium size relative to R. johorensis queen (non-types: HL 0.48–0.49, HW 0.44–0.45), head in full-face view subrectangular and slightly narrower anteriorly ( Fig. 6a ). Anterior clypeal face in profile weakly and broadly convex, sometimes almost flat ( Fig. 6d ). Posterior half and ventral face of head largely smooth and shiny, with feeble striations on frons and vertex. Dorsal outline of mesosoma weakly and broadly convex; propodeal junction roundly obtuse and indistinct ( Fig. 6d ). In dorsal view, anterior margin of pronotal disc broadly convex with roundly obtuse humeral corners; mesoscutum slightly wider than long; propodeum much wider than long; propodeal dorsum weakly convex and rounding into steep posterior declivity at indistinct rounded posterior edge; posterior propodeal face with shallow median concavity ( Fig. 6c ). Dorsum of mesosoma largely finely striate and shiny; lateral-most triangular area of mesoscutum immediately above parascutellar carina mostly smooth and shining ( Fig. 6c ); apicodorsal faces of petiole and postpetiole feebly and superficially reticulate( Fig. 6b, d ), each with a central area that is smooth and shining ( Fig. 6b ). Body largely uniformly dark brown; head, dorsum of mesosoma and gaster slightly darker brown, tibia and tarsus yellowish brown. Male Small size (non-types: HL 0.39–0.41, HW 0.38–0.4). Head in full-face view sub-spherical, posterior margin broadly and strongly rounded ( Wang et al . 2018b : fig. 21); in lateral view, head with dorsum gently inclined posteriorly; clypeus in profile with distinct dorsal and anterior faces separated by a roundly angulate edge, dorsal face gently sloped downwards and nearly flat, anterior face steep and very weakly convex or flat ( Fig. 7a ). Median ocellus subcircular, less elongate and slightly smaller than lateral ocelli; frontal lobes distinctly raised and differentiated from frontal supraclypeal area; posterior apex of supraclypeal area bluntly rounded ( Wang et al. 2018b : fig. 21). In posterior view, posterior propodeal face indistinctly marginate, weakly differentiated from lateral propodeal face by indistinct rounded lateral margin. In lateral view, petiole short and subtrapezoidal, longer than high, anterior margin long, steep and weakly concave, apical dorsum weakly convex, rounding into short posterior face at indistinct rounded edge ( Wang et al. 2018b : fig. 20). Funiculus of antenna uniformly light brown; legs greyish brown with joints and tarsi pale brownish yellow. Material examined Types INDONESIA • lectotype (top specimen on same pin) and 2 paralectotype workers of R. rothneyi javana ; East Java , Besoeki , Bondowoso ; USNM MCZ.6.9.20783/SNM.595.31. Images generated by the same authors for a previous publication (i.e., Wang et al. 2018b ), examined . Other material SINGAPORE • 18 workers , 1 queen , 2 ♂♂ ; Mandai Track ; 1.40337° N , 103.77824° E ; 4 Jan. 2017 ; G.W. Yong leg.; colony code: GY-SG17-RhoN; ZRC_HYM000576 • 8 workers ; same collection data as for preceding; THNHM • 12 workers , 2 queens ; Bukit Timah Nature Reserve ; 1.35449° N , 103.78211° E ; 21 Jun. 2017 ; C. Peeters leg.; nest in bark of Campnosperma auriculatum (Blume) Hook. f. ; colony code: WW-SG17-015; ZRC_HYM_0001732 . THAILAND – West Thailand • 8 workers ; Kanchanaburi Province , Sai Yok District , Ban Tha Sao ; 14.33389° N , 98.98° E ; 280 m a.s.l. ; 11 Mar.2018 ; W.Jaitrong leg.; mango tree ;colony code:WJT110318- 1; THNHM • 8 workers ; same collection data as for preceding; GenBank: MW267108 to MW267110 (3 barcoded); ZRC_ENT00000931 • 8 workers , 1 ♂ ; same collection data as for preceding; 11 Mar. 2018 ; colony code: WJT110318-2; THNHM • 8 workers , 1 ♂ ; same collection data as for preceding; GenBank: MW267111 to MW267113 (3 barcoded); ZRC_ENT00000932 . – Central Thailand • 8 workers ; Saraburi Province , Phu Khae Botanical Garden ; 14.67056° N , 100.88500° E ; 89 m a.s.l. ; 18 Mar. 2018 ; W. Jaitrong leg.; colony code: WJT180318-2; THNHM • 8 workers ; same collection data as for preceding; GenBank: MW267105 to MW267107 (3 barcoded); ZRC_ENT00000937 • 9 workers ; Khao Yai National Park ; 7 Jul. 2018 ; W. Jaitrong leg.; in bark of mango tree ; colony code: WJT070718- 1; THNHM • 5 workers ; same collection data as for preceding; GenBank: MW267096 to MW267098 (3 barcoded); ZRC_ ENT00007610 . – South Thailand • 8 workers , 2 queens ; Trang Province , Nayong District , Nakhaw Sia Subdistrict ; 7.50833° N , 99.716389° E ; 28 m ; 23 Jan. 2018 ; W. Jaitrong leg.; in bark of Azadirachta excelsa (Jack) Jacobs ; colony code: WJT230118-1; THNHM • 8 workers , 2 queens ; same collection data as for preceding; GenBank: MW267114 to MW267116 (3 barcoded); ZRC_ENT00000942 . – Northern Thailand • 15 workers ; Chiang Rai ; 21 Oct. 2018 ; W. Jaitrong leg; colony code: WJT211018-34; THNHM • 8 workers ; same collection data as for preceding; GenBank: MW267099 to MW267101 (3 barcoded); ZRC_ ENT00007609 . – Northeast Thailand • 18 workers , 1 queen ; Srisa Ket Province , Phanom Dong Rak , Krabau Krabai ; 13 Sep. 2018 ; W. Jaitrong leg.; colony code: WJT130918-17; THNHM • 8 workers , 1 queen ; same collection data as for preceding; GenBank: MW267117 to MW267119 (3 barcoded); ZRC_ENT00007611 . – North Thailand • 8 workers ; Nan Province , Nan Fa Sai Resort ; 2 Dec. 2018 ; W. Jaitrong leg.; colony code: WJT021218- 7; THNHM • 8 workers ; same collection data as for preceding; GenBank: MW267126 to MW267128 (3 barcoded); ZRC_ENT00007869 • 8 workers , 2 queens ; Nan Province , Puar [sic] District; 4 Dec. 2018 ; W. Jaitrong leg.; colony code: WJT041218-1; THNHM • 8 workers , 2 queens ; same collection data as for preceding; GenBank: MW267120 to MW267122 (3 barcoded); ZRC_ENT00007870 ; ZRC • 13 workers , 1 queen ; Nan Province , Puar [sic] District , Sirapach Waterfall ; 4 Dec. 2018 ; W. Jaitrong leg.; colony code: WJT041218-2; THNHM • 8 workers , 1 queen ; same collection data as for preceding; GenBank: MW267123 to MW267125 (3 barcoded); ZRC_ENT00007871 • 8 workers ; Chiang Rai , Muang district , Huai Chom Koo subdistrict , Khun Korn waterfall ; 21 Oct. 2018 ; W. Jaitrong and Sk. Yamane leg.; colony code: TH18-SKY-169; THNHM • 8 workers ; same collection data as for preceding; GenBank: MW267102 to MW267104 (3 barcoded); ZRC_ENT00007884 . Description Worker Measurements. Lectotype and paralectotype workers (n = 3), measurements from Wang et al. (2018b) : EL 0.08; EW 0.04–0.06; HL 0.48–0.52; HW 0.45–0.48; ML 0.48–0.50; PronW 0.28–0.32; PtH, PtL unavailable; SL 0.18–0.20; TL 1.83–1.98; CI 92–94; REL 17–18; SI 39–42. Non-type workers from Singapore (n = 9): EL 0.08–0.1; EW 0.04–0.06; HL 0.46–0.48; HW 0.41–0.44; ML 0.50–0.54; PronW 0.28–0.32; PtH 0.15–0.18; PtL 0.17–0.20; TL 1.69–2.02; SL 0.18–0.19; CI 89– 93; PtHI 87–90; REL 18–23; SI 41–44. Non-type workers from Thailand (n = 13): EL 0.08–0.12; EW 0.06–0.08; HL 0.46–0.58; HW 0.46–0.56; ML 0.56–0.76; PronW 0.30–0.36; PtH 0.17–0.23; PtL 0.19–0.25; TL 2.02– 2.88; SL 0.20–0.26; CI 92– 96; PtHI 89–92; REL 17–21; SI 44–48. Workers monomorphic with little intranidal variation in size. Head in full-face view subrectangular, longer than wide, posterior margin with a broad but shallow median concavity, posterolateral corners roundly convex, lateral margins of head broadly convex and weakly converging anteriorly, anterior clypeal margin less wide than posterior margin of head, with broadly and weakly convex median section ( Fig. 5a ). Eye with 11–16 ommatidia for types and specimens for Singapore , 13–21 ommatidia for Thai specimens. In lateral view, outline of clypeus evenly and weakly convex, projecting slightly forward from dorsal margin of head ( Fig. 5c ). Mesosoma in lateral view box-shaped or subcylindrical, dorsal outline weakly and broadly convex, propodeal junction roundly obtuse, propodeal declivity steep and shallowly concave ( Fig. 5d ); dorsum of propodeum differentiated from posterior declivitous face by a weak but distinct marginate edge. In dorsal view, mesosoma subrectangular with lateral sides almost parallel to each other; anterior margin of pronotal disc broadly convex, sometimes angulate at its median point, humeral corners rounded and often indistinctly angulate; lateral margins of propodeum broadly convex, transitioning to and differentiated from weakly concave posterior propodeal margin at bluntly angulate posterolateral corners ( Fig. 5b ); posterolateral corners slightly projecting posteriorly and differentiated from inner posterior propodeal face. Posterior face of propodeum weakly marginate, rounding into lateral propodeal face at indistinct angulate edge. In lateral view, petiole inclined posteriorly, slightly longer than high, distinctly narrower at apex than at base, anterior face weakly concave and longer than posterior face; apex roundly convex, apical dorsum rounding smoothly into steeper posterior face at indistinct rounded edge; petiole higher and longer than postpetiole, dorsal margin of postpetiole weakly convex and nearly flat ( Fig. 5d ). In dorsal view, petiole suboval, wider than long; postpetiole globular and less than twice as wide as petiole ( Fig. 5b ). Fig. 5. Rhopalomastix javana Wheeler, 1929 , non-type, worker, West Thailand (ZRC_ENT00000932). a . Head in full-face view. b . Body in dorsal view. c. Close-up of clypeus and head in profile. d . Body in lateral view. Dorsum and lateral face of head largely finely striate and shiny, striations on posterior half of head generally weaker and more fragmented; posterolateral corners of head feebly reticulate with interspaces smooth and shining; posteriormost strip of vertexal area just above occiput in posterodorsal view largely unsculptured or with feeble striations, mostly smooth and shiny. Ventral face of posterior half of head mostly superficially reticulate with interspaces smooth and shining. Mandible mostly smooth and shining, area immediately adjacent to masticatory margin punctate ( Fig. 2c ). Median clypeal face with coarse irregular striae, interspaces punctate and weakly shining ( Fig. 5a ), sometimes with a central longitudinal strip more weakly striate or largely smooth and shining. Lateral face of mesosoma largely striate-reticulate with interspaces smooth and shining ( Fig. 5d ); dorsum of mesosoma finely striate ( Fig. 5b ). Lateral face of petiole superficially reticulate with interspaces smooth and shining, petiolar apex finely striate and shiny. Postpetiole and gaster superficially reticulate with interspaces smooth and shining. Dorsum of head with fairly dense though well-spaced short erect and suberect hairs interspersed with sparse long erect hairs, gena with fairly dense short appressed and decumbent hairs. Ventral face of head with fairly dense though well-spaced short suberect, decumbent and appressed hairs. Antennal funiculus mostly with fairly dense appressed and decumbent hairs. Mesosoma dorsum with sparse, scattered short standing hairs that are relatively denser closer to dorsolateral margin, paired long erect hairs sparsely present along dorsolateral margin, with one pair each flanking the anterior margin of pronotal disc, pronotum, mesonotum and propodeum. Anterior rising face of petiole with fairly dense appressed and decumbent hairs, posterior declivity with dense short erect and subdecumbent hairs; apex of petiolar node with few short erect hairs and 1–2 pairs of long erect hairs. Postpetiole with dense short erect and suberect hairs, and one pair of long erect hairs. Gaster pilose, with dense suberect and erect hairs interspersed with sparse long erect hairs. Head, dorsum of mesosoma and gaster generally dark brown, rest of body lighter yellowish brown, dorsum of head and area around eye in some workers with blackish undertones; tips of antennae, first funicular segment and legs pale yellowish brown. Queen Measurements. Non-type queens (n = 3): EL 0.15–0.16; EW 0.09–0.10; HL 0.48–0.49; HW 0.44–0.45; ML 0.70–0.72; MsW 0.36–0.40; PtH 0.21–0.22; PtL 0.25–0.26; SL 0.18–0.20; TL 2.21–2.43; CI 92–94; PtHI 85–88; REL 33–36; SI 40–45. Small-medium size (relative to R. johorensis queen). Head in full-face view subrectangular, slightly longer than wide, slightly narrower anteriorly with anterior clypeal margin distinctly less wide than posterior margin; lateral margins broadly and weakly convex, almost parallel to each other, posterolateral corners rounded, posterior margin nearly straight with a shallow median concavity ( Fig. 6a ). Eye very large (13–18 ommatidia in the longest axis); posteriormost point of eye located slightly below transverse midline of head in full-face view. In profile, clypeus weakly and broadly convex, sometimes almost flat ( Fig. 6d ). Ocelli oval in shape and generally equal in size, roughly equidistant from each other; small area immediately anterior to median ocellus gently depressed ( Fig. 6a–b ). In lateral view, mesosoma subcylindrical, more elongate than that of worker, dorsal outline weakly and broadly convex, propodeal junction roundly obtuse and indistinct ( Fig. 6d ). Propodeal dorsum weakly convex ( Fig. 6d ), rounding into steep posterior declivity at indistinct rounded posterior edge; posterior propodeal face with shallow median concavity. In dorsal view, mesosoma subcylindrical, anterior margin of pronotal disc broadly convex, humeral corners obtusely angulate, mesoscutum slightly wider than long, propodeum much wider than long, posterior margin weakly concave and indistinct, lateral margin of propodeum rounding into posterior margin at indistinct rounded edge ( Fig. 6c ). In lateral view, petiole inclined posteriorly, longer than high, anterior margin weakly concave and steep; petiolar node bell-shaped with bluntly rounded apex, apical face rounding smoothly into and not distinctly differentiated from posterior face, posterior face shorter and steeper than anterior face ( Fig. 6d ). In lateral view, postpetiole not as long as petiole, dorsal margin broadly convex ( Fig. 6d ). In dorsal view, petiole suboval, less than twice as wide as long; postpetiole globular, much larger and wider than petiole ( Fig. 6b ). Anterior half of head dorsum largely finely striate and shiny, posterior half mostly smooth and shining with scattered punctures, frons and vertex with feeble striations; clypeus coarsely striate but with a median longitudinal strip that is smooth and shining. Ventral face of head mostly smooth and shining. Mandible mostly smooth and shining, area next to masticatory margin slightly striate-punctate. Lateral face of mesosoma weakly substriate-reticulate, interspaces smooth and shining. Dorsum of mesosoma mostly finely striate and shining, median section of pronotum superficially reticulate with interspaces smooth and shining ( Fig. 6c ); lateral-most triangular area of mesoscutum immediately above parascutellar carina mostly smooth and shining or more weakly striate than rest of mesoscutum ( Fig. 6c ); posterior face of propodeum mostly smooth and shining. Lateral faces of petiole and postpetiole superficially reticulate with interspaces smooth and shining; apicodorsal faces of petiole and postpetiole feebly and superficially reticulate with a central area that is smooth and shining. Gaster largely smooth and shining, area near anterior margin of tergite superficially reticulate. Fig. 6. Rhopalomastix javana Wheeler, 1929 , non-type, queen, Northeast Thailand (THNHM-I-21751). a . Head in full-face view. b . Body in dorsal view. c . Close-up of mesosoma in dorsal view. d . Body in lateral view. Dorsum of head with fairly dense short suberect and decumbent hairs, interspersed with very sparse long erect hairs, including one pair on median section of clypeus; lateral and ventral faces with fairly dense short appressed and decumbent hairs. Antennal scape with uniform short standing hairs and a long erect hair on basal and median points respectively. Dorsum of mesosoma with sparse short standing hairs ( Fig. 6c ); paired long erect hairs sparsely present along dorsolateral margin, with one pair each flanking the anterior margin of pronotal disc, pronotum, mesoscutum, and propodeum; mesoscutum and mesoscutal disc each one pair of long erect hairs. Anterior face of petiole with dense short appressed and/or decumbent hairs, posterior face with dense short erect hairs, apex with sparse short erect hairs, 1–2 pairs of long erect hairs. Postpetiole with dense short decumbent or standing hairs and two pairs of long erect hairs. Gaster pilose, with dense short appressed and/or decumbent hairs, scattered short standing hairs, and long erect hairs sparsely distributed along posterior margins of tergites. Body generally uniform dark brown; head, dorsum of mesosoma and gaster slightly darker brown; tibia and tarsus paler and yellowish brown. Male Measurements. Thai male specimens unavailable. Non-type males from Singapore (n = 2): EL 0.18–0.20; EW 0.14; HL 0.39–0.41; HW 0.38–0.40; ML 0.66–0.70; MsW 0.40–0.44; PtH 0.17–0.18; PtL 0.21– 0.22; SL 0.06; TL 1.98–1.99; CI 97–98; REL 45–53; SI 15–16. Small size (relative to R. johorensis male). Head in full-face view sub-spherical, posterior margin broadly and strongly rounded ( Wang et al. 2018b : fig. 21). Eye very large (20–25 ommatidia in the longest axis); posteriormost point of eye only slightly exceeding transverse midline of head, outline of eye bulging from lateral margin of head by a little ( Wang et al. 2018b : fig. 21). Median ocellus subcircular, less elongate and slightly smaller than lateral ocelli; small area of head dorsum immediately anterior to median ocellus weakly depressed, continuous with weak median furrow separating frontal lobes; frontal lobes strongly raised and differentiated from supraclypeal area ( Wang et al. 2018b : fig. 21). Posterior apex of supraclypeal area bluntly rounded. In lateral view, head broad-ovate with dorsum gently inclined posteriorly, posterodorsal outline broadly rounded with differentiation between dorsal and posterior faces indistinct, posterior margin rounding into broadly convex ventral margin forming a continuous curve with no distinct posteroventral angle ( Fig. 7a ). In the same view, clypeus strongly projecting from dorsum of head, with distinct dorsal and anterior faces separated by a roundly angulate edge, dorsal face gently sloped downwards and nearly flat, anterior face steep and very weakly convex or flat ( Fig. 7a ). In lateral view, mesosoma sub-oblong, dorsal margin almost completely straight or very weakly and broadly convex, propodeal junction roundly obtuse; anterior face of pronotum about as high as anterodorsal face of mesoscutum ( Wang et al. 2018b : fig. 20); propodeal dorsum weakly convex, rounding into steep and short posterior declivity at indistinct rounded posterior edge. In posterior view, posterior propodeal face indistinctly marginate, weakly differentiated from lateral propodeal face by indistinct rounded lateral margin. In dorsal view, mesosoma obovate, notauli absent, parapsidal line weakly present ( Wang et al. 2018b : figs 22–23). In lateral view, petiole inclined posteriorly, short and subtrapezoidal, longer than high, anterior margin long, steep and weakly concave, apical dorsum weakly convex, rounding into short posterior face at indistinct rounded edge; anteroventral extension of subpetiolar process shallow and subtriangular, longer at base than apex ( Wang et al. 2018b : fig. 20). Dorsal outline of postpetiole weakly convex, differentiated from gaster by a weak but distinct cinctus ( Wang et al. 2018b : fig. 20). Head mostly superficially substriate-reticulate with interspaces smooth and shining, and scattered punctures ( Wang et al. 2018b : fig. 21); area of head dorsum enclosed by and around ocelli rugulose and weakly shining; median area immediately anterior to median ocellus largely smooth and shining; frontal lobes coarsely rugulose-reticulate and weakly shining; clypeus coarsely rugulose with interspaces punctate and weakly shining. Lateral face of mesosoma weakly striate-reticulate with interspaces smooth and shining ( Wang et al. 2018b : fig. 20). In dorsal view, mesoscutum largely weakly substriate with interspaces smooth and shining, lateralmost area of mesoscutum in between parapsidal line and parascutellar carina unsculptured, largely smooth and shining; mesoscutal disc largely smooth and shining with feeble superficial striations; propodeum superficially reticulate with interspaces smooth and shining ( Wang et al. 2018b : fig. 23). Petiole, postpetiole mostly reticulate with interspaces smooth and shining, apices smooth and shining. Dorsum of head with dense short standing hairs; lateral, ventral and posterior faces with dense short decumbent and appressed hairs ( Fig. 7a ). Dorsum of pronotum and mesoscutum with fairly dense short standing hairs; posterolateral margins of propodeum with sparse short erect hairs. Anterior rising face of petiole with few or no hairs, apicodorsal and posterior petiolar faces with short standing hairs; dorsum of postpetiole with short standing hairs. Gaster pilose with dense standing, decumbent and subdecumbent hairs. Body generally dark greyish-brown; head, dorsum of mesosoma and gaster dark blackish-brown; funiculus of antenna uniformly light brown; legs greyish brown with joints and tarsi pale brownish yellow. Distribution and binomics Indonesia ( Java ), Singapore , Thailand ( Fig. 16b ). As with R. johorensis , colonies can be usually found in (but not limited to) bark of fruit trees such as mango, located close to human dwellings. Populations appear widespread, but more sparsely distributed and less commonplace than those of R. johorensis – this could merely be an artefact of incomplete sampling. Fig. 7. Rhopalomastix javana Wheeler, 1929 , non-type, ♂, Singapore (ZRC_HYM_0000576). a . Head and clypeus in profile. b . Close-up of genitalia in profile. Remarks Thai populations of R. javana appear to be generally larger in size compared to populations from Indonesia ( Java ) and Singapore (Java and Singapore TL 1.83–2.02; Thailand TL 2.02–2.88). In terms of variation in morphological measurement metrics, Thai populations also seem much more variable relative to the other two countries (e.g., Thai HL 0.46–0.58; Java HL 0.48–0.52; Singapore HL 0.46– 0.48), however, this might have arisen from bias in geographic range of sampling. For Thai R. javana , measurements were taken from 13 individuals from seven colonies distributed across Central, North and West Thailand , whereas for Java and Singapore , mostly individuals from 1–2 colonies were measured. A combination of measurements from different countries may be a more accurate representation of actual variation within the species. Thai colonies that could be morphologically identified as R. javana were extremely variable in terms of COI (313 bp), with internidal divergences spread across multiple different values from 0.0–4.5% ( Fig. 1 ). While sequence divergence between different species existing in sympatry can be as low as 3.8% (average uncorrected p distance) in ants, especially for recently diverged species ( Wang et al. 2018a ), higher percentage distances (> 4%) between allopatric populations do not necessarily indicate different species. In the latter case, clustering based on barcodes may split allopatric or geographically distant populations of the same species, belonging to older lineages that diverged genetically back in time ( Meier et al. 2008 ). Thus, in light of the two aforementioned possibilities, inferring species boundaries from the clustering pattern of Thai R. javana specimens is complicated. If we define allopatric colonies as those coming from different parts (i.e., North, South, East, West, Central) of Thailand , then possibly the split clusters observed ( Fig. 1 ) mostly represent different lineages of the same species R. javana . However, R. javana colonies considered ‘sympatric’ from North and Central Thailand respectively diverged at 4.5% ( Fig. 1 ), suggesting (but not ascertaining) possible newly diverged species. Taking into account the broad inter- and intranidal variation shown amongst R. javana workers, we were unable to observe any striking morphological differences between specimens from the genetically divergent clusters. Given the lack of more convincing morphological or molecular evidence supporting further species delimitation in this study, we tentatively treat these colonies as conspecific. The possibility remains for this current treatment to be revised in future, when gene flow between R. javana populations are more thoroughly investigated, and the relevant data from other molecular markers are made available. This species is most similar to R. impithuksai Wang & Jaitrong sp. nov. and R. johorensis , but can be differentiated by characters described in detail under the Remarks for each of the latter two species.