Plagiolepis Mayr, 1861

Phosrithong, N., Rattanachan, K., Satakoune, L. & Jaitrong, W., 2024, Two new species of the ant genus Plagiolepis Mayr, 1861 (Hymenoptera: Formicidae: Fomicinae) from Indochina, Far Eastern Entomologist 492, pp. 1-14 : 3-11

Genus Plagiolepis Mayr, 1861

Plagiolepis Mayr, 1861: 42 . Type-species: Formica pygmaea , by monotypy.

Anacantholepis Santschi, 1914: 36 [as subgenus of Plagiolepis ]. Type-species: Plagiolepis (Anacantholepis) decora , by original designation.

Aporomyrmex Faber, 1969: 52 . Type-species: Aporomyrmex ampeloni , by original designation.

Paraplagiolepis Faber, 1969: 65 [as subgenus of Plagiolepis ]. Type-species: Plagiolepis xene , by monotypy.

DIAGNOSIS OF WORKER. Sharaf et al. (2011) defined the worker of the genus as follows: 1) mandibles armed with five teeth; 2) clypeus large and projecting over basal borders of mandibles; 3) palp formula 6,4; 4) antennae 11-segmented, and eyes well developed; 5) in dorsal view, mesonotum separated from propodeum by a conspicuous transverse groove or impression, therefore metanotum forming distinctly isolated sclerite; 6) propodeum unarmed; and 7) petiole reduced scale, inclined forward and sometimes overhung by first gastral segment.

Plagiolepis chomphuphuangi Phosrithong et Jaitrong sp. n. https://zoobank.org/NomenclaturalActs/ 26617545-983D-440B-A679-CB04B498BBF7

Figs 1–3 , 5

TYPE MATERIAL. Holotype: worker THNHM-I-00018330, THNHM), Laos: Champasak Province, Paksong District, Tad Fane Waterfall , coffee plantation, 15º10'57.96''N, 106º7'37.10''E, 25.VIII.2023, P. Sriranan leg., LAO23-WJT-046 . Paratypes: 2 workers (THNHM-I-00018331 to THNHM-I-00018332, THNHM), same data as holotype .

MEASUREMENTS AND INDICES. Holotype: TL 2.41, HW 0.66, HL 0.63, SL 0.63, EL 0.20, ML 0.73, PRW 0.43, PL 0.30, PW 0.17, CI 95, SI 100.

Paratypes (n = 3): TL 2.41–2.44, HW 0.63–0.66, HL 0.66–0.69, SL 0.63–0.66, EL 0.20, ML 0.73–0.76, PRW 0.43, PL 0.30–0.33, PW 0.17, CI 95, SI 100.

DESCRIPTION (holotype and paratypes). Head: in full face view, subrectangular, almost as long as broad; lateral and posterior margins weakly convex; posterolateral corner of head roundly convex. Mandible subtriangular; masticatory margin with five teeth, including largest apical tooth, followed by medium-sized preapical tooth, a small tooth, medium-sized prebasal tooth, and small basal tooth; basal margin almost straight, without denticles. In dorsal view, clypeus broad, slightly shorter than broad, its anterior margin broadly convex, without denticles, with median keel that fails to reach anterior margin; in profile view, clypeus roundly convex medially. Eye moderately large (130–140 ommatidia), oval, weakly convex, located anterior to med-length of head; with head in full face view outer margin of eye not reaching lateral margin of head. Ocelli present, small; distance between lateral ocelli almost as long as distance between median ocellus to lateral ocellus. Antenna 11-segmented, scape slender, clavate, extending beyond posterolateral corner of head by about one-third of its length; antennal segment II (pedicel) clearly longer than broad, slightly shorter than III– V combined; III as long as each of IV and V; III– V each slightly longer than broad; VI –XI each clearly longer than broad. Frontal lobe narrow, not covering antennal socket; frontal carina relatively short, slightly extending beyond level of anterior margin of eye.

Mesosoma: in profile view pronotum with convex dorsal outline; mesonotum slightly sloping gradually to metanotal groove; in dorsal view pronotum slightly longer than broad (posterior margin distinctly concave) and clearly broader than mesonotum and propodeum; promesonotal suture weak, medially almost straight; mesonotum small much narrower than pronotum, posteriorly convex; in dorsal view metanotum narrow anteriorly, clearly separated from propodeum by deep groove; in profile view mesothorax reduced; metathoracic spiracle located dorsally, with opening on conical base; mesopleuron clearly demarcated from metapleuron by distinct groove; metapleuron not clearly demarcated from lateral face of propodeum. Propodeum in profile view with weakly convex dorsal outline and sloping evenly; declivity large and flat, bluntly margined laterally.

Petiole in profile sessile, subtriangular, much longer than high, with its anterior slope much shorter than posterior slope. Gaster in dorsal view, elliptical; first tergite anteriorly with shallow concavity to partly receive petiole.

Dorsum of head including clypeus striate, vertex partly reticulate with smooth interspaces; ventral surface of head smooth and shiny; clypeus with smooth area around median keel; antennal scape finely micropunctate; mandible smooth and shiny, with scattered punctures. Dorsum of pronotum, mesonotum, and propodeum entirely smooth and shiny; legs somewhat smooth and shiny. Petiole smooth and shiny. Gastral segments smooth and shiny.

Dorsum of head entirely covered with dense short erect setae; pronotum with sparse suberect setae; dorsum of petiole sparsely with very short setae; gastral tergites I and II with dense short suberect setae (setae on pronotum and gatral tergites I and II shorter than maximum width of antennal scape), except along edges of segments with longer erect setae; mandibles with sparse suberect setae; clypeus anteriorly with two pairs of long suberect setae and long median seta; antenna with dense pubescence. Head and mesosoma dorsally, and entire gaster (mesosoma generally paler than head and gaster) lateral and ventral sides of head, and lateral side of mesosoma reddish brown, somewhat paler than dorsum of the body. Mandible, antenna, and legs reddish brown.

DIAGNOSIS. Plagiolepis chomphuphuangi sp. n. can be easily distinguished from other congeners by the following characteristics 1) body large and dark brown; 2) dorsum of head, pronotum, and gastral tergites with dense short suberect setae; 3) dorsum of head finely and densely striate; 4) mesosomal dorsum entirely smooth and shiny; 5) setae on dorsum of pronotum and gastral tergites relatively short, usually shorter than maximum width of antennal scape.

REMARKS. Plagiolepis chomphuphuangi is most similar to P. silpaarchai sp. n. in having striation on dorsum of head; the differences of both species are discussed below. New species is also similar to P. rogeri (Forel, 1894) and P. jerdonii Forel, 1894 from India; P. adynata Bolton, 1995 and P. demangei Santschi, 1920 from Vietnam; and P. nitida Karavaiev, 1935 from Cambodia in having a dark body colour. However, P. chomphuphuangi sp. n. can be easily separated from them by the head being finely striated (in other species smooth and shiny). New species is similar to P. demangei in having dense erect setae on the body dorsum but differs from latter by 1) head slightly longer than broad (clearly shorter than broad in P. demangei ); 2) head striate (smooth and shiny in P. demangei ); 3) setae on pronotun clearly shorter than those on pronotum and gastral tergite II (distinctly longer in P. demangei ). This new species can be separated from P. jerdonii by the follow: 1) head relatively shorter (CI 95 in new species; CI 88 in P. jerdonii ); 2) mesothorax distinctly reduced, metanotum deep (mesothorax broad and metanotum shallow in P. jerdonii ); 3) pronotum with suberect setae (setae appressed in P. jerdonii ).

ETYMOLOGY. The specific name is dedicated to Dr. Narin Chomphuphuang (Khon Kaen University, Thailand), who invited W. Jaitrong to join a field survey in Laos.

BIONOMICS. This new species inhabits highland (ca. 1000 m a.s.l.). The type series was collected on the ground in a coffee plantation ( Fig. 9 ).

DISTRIBUTION. Laos (Champasak Province, Fig. 21 ).

Plagiolepis silpaarchai Phosrithong et Jaitrong sp. n. https://zoobank.org/NomenclaturalActs/ 914BEB3C-19FF-4A22-B2CE-EC14401709AA

Figs 4 , 6–8

TYPE MATERIAL. Holotype: worker (THNHM-I-27222, THNHM), Thailand: Kamphaeng Phet Province, Kosamphi Nakhon District, Ban Kosomphi, Khlong Wang Chao National Park , mixed deciduous forest, 16°30'16'' N, 99°10'05'' E, 18.XI.2021 . Paratypes: 16 workers (THNHM-I-27223 to THNHM-I-27238, THNHM), same data as holotype .

NON-TYPE MATERIAL EXAMINED. Laos: 3 workers (THNHM-I-00018333, THNHM), Vientiane Province, Naxaythong District, Sivilay Village , 11.VI.2010, W. Jaitrong leg., general collection .

MEASUREMENTS AND INDICES. Holotype: TL 2.80, HW 0.62, HL 0.66, SL 0.69, EL 0.13, ML 0.50, PRW 0.40, PL 0.17, PW 0.13, CI 94, SI 111.

Paratypes (n = 16): TL 2.34–2.94, HW 0.56–0.69, HL 0.59–0.73, SL 0.53–0.73, EL 0.13–0.17, ML 0.43–0.56, PRW 0.36–0.53, PL 0.13–0.23, PW 0.13–0.20, CI 89–105, SI 95–117.

DESCRIPTION (holotype and paratypes). Head: in full face view, subrectangular, slightly longer than broad; lateral margin weakly convex, and posterior margin almost straight (shallowly emarginate in larger specimens); posterolateral corner of head roundly convex. Mandible subtriangular; masticatory margin with five teeth, including largest apical tooth, followed by medium-sized preapical tooth,

a small tooth, medium-sized prebasal tooth, and small basal tooth; basal margin almost straight, without denticles. In dorsal view, clypeus broad, clearly shorter than broad, its anterior margin broadly and shallowly convex, medially margined with carina, without denticles, with median keel that fails to reach anterior margin; in profile view, clypeus roundly convex medially. Eye moderately large (138–143 ommatidia), oval, weakly convex, located anterior to med-length of head; with head in full face view outer margin of eye not reaching lateral margin of head. Ocelli present, small; distance between lateral ocelli almost as long as distance between median ocellus to lateral ocellus. Antenna 11-segmented, scape slender, clavate, extending beyond posterolateral corner of head by about one-third of its length; antennal segment II (pedicel) clearly longer than broad, almost as long as III– V combined; III as long as IV; III– V each slightly longer than broad; VI –XI each clearly longer than broad. Frontal lobe narrow, not covering antennal socket; frontal carina relatively short, slightly extending beyond level of anterior margin of eye.

Mesosoma: in profile view pronotum with convex dorsal outline; mesonotum slightly sloping gradually to metanotal groove; in dorsal view pronotum almost as long as broad (posterior margin distinctly concave) and clearly broader than mesonotum but only slightly broader than propodeum; promesonotal suture weak, medially almost straight; mesonotum small much narrower than pronotum, posteriorly convex; metanotum (see Bolton’s key book, 1997: p. 45) broad from front to rear, clearly separated from propodeum by deep groove; in profile view mesothorax reduced; metathoracic spiracle located dorsally, with opening on conical base; mesopleuron clearly demarcated from metapleuron by distinct groove; metapleuron not clearly demarcated from lateral face of propodeum. Propodeum in profile view with weakly convex dorsal outline and sloping evenly; declivity large and flat, bluntly margined laterally.

Petiole in profile sessile, subtriangular, much longer than high, with its anterior slope much shorter than posterior slope. Gaster in dorsal view, elliptical; first tergite anteriorly with shallow concavity to partly receive petiole.

Head dorsally including clypeus striate, vertex partly reticulate with smooth interspaces; head ventrally smooth and shiny; clypeus with smooth area around median keel; antennal scape finely micropunctate; mandible smooth and shiny, with scattered punctures. Dorsum of pronotum, mesonotum, and propodeum finely punctate; metanotum more sparsely sculptured and shiny; lateral sides of pronotum, mesopleuron, and metapleuron smooth and shiny; legs somewhat smooth and shiny. Petiole smooth and shiny. Gastral segments superficially shagreened with smooth and shining interspaces.

Dorsal side of head entirely covered with dense short erect setae mixed with two longer erect setae located on vertex; dorsum of mesosoma with sparse erect setae; dorsum of petiole sparsely with very short setae; gaster with dense suberect setae (setae on gaster clearly longer than on head and mesosoma); mandibles with sparse suberect setae; clypeus anteriorly with two pairs of long suberect setae and long median seta; antenna with dense pubescence. Dorsal side of head and mesosoma, and entire gaster (mesosoma generally paler than head and gaster) lateral and ventral sides of head, and lateral side of mesosoma reddish brown, somewhat paler than dorsum of the body. Mandible, antenna, and legs reddish brown.

DIAGNOSIS. Plagiolepis silpaarchai sp. n. can be easily distinguished from other congeners by the following characteristics 1) body large and dark brown; 2) dorsa of head and gastral tergites with dense erect setae; 3) dorsum of head finely and densely striate; 4) dorsum of mesosoma densely punctate; 5) setae on dorsa of pronotum and gastral tergites relatively long, usually longer than maximum width of antennal scape.

REMARKS. Plagiolepis silpaarchai sp. n. is similar to P. rogeri (Forel, 1894) and P. jerdonii Forel, 1894 from India; P. adynata Bolton, 1995 and P. demangei Santschi, 1920 from Vietnam; and P. nitida Karavaiev, 1935 from Cambodia in having a dark body colour. However, this new species can be easily separated from them by the head being finely striated (in other species smooth and shiny). Plagiolepis silpaarchai sp. n. is similar to P. demangei and P. jerdonii in having dense erect setae on the body dorsum. This species can be distinguished from P. demangei by 1) head slightly longer than broad (clearly shorter than broad in P. demangei ); 2) head striate (smooth and shiny in P. demangei ); 3) setae on pronotun clearly shorter than those on gastral tergite II (distinctly longer in P. demangei ). The new species can be separated from P. jerdonii by the following characteristics: 1) head relatively shorter (CI 89-105 in new species; CI 88 in P. jerdonii ); 2) mesothorax distinctly reduced, metanotum deep (mesothorax broad and metanotum shallow in P. jerdonii ); 3) pronotum with erect setae (setae appressed in P. jerdonii ).

Plagiolepis silpaarchai sp. n. is also similar to P. chomphuphuangi sp. n. in having dense striation on dorsum of head. However, P. silpaarchai sp. n. can be separated from P. chomphuphuangi sp. n. by 1) dorsum of mesosoma entirely punctate (smooth and shiny in P. chomphuphuangi sp. n., see Figs. 5 and 6 for comparison); 2) setae on dorsa of pronotum and gastral tergites relatively long, usually longer than maximum width of antennal scape (usually shorter than maximum width of antennal scape); 3) pronotum and first gastral tergite with erect setae (suberect setae in P. chomphuphuangi sp. n., see Figs. 1 and 7 for comparison); 4) posterior margin of head almost straight or feebly concave (weakly convex in P. chomphuphuangi sp. n., see Figs. 3 and 4 for comparison).

ETYMOLOGY. The specific name is dedicated to Mr. Varawut Silpa-archa, the former Minister of Natural Resources and Environment (from July 2019 – September 2023) and his family who supported the conservation of natural resources in Thailand.

BIONOMICS. This species inhabits lowland (ca. 250 m a.s.l.). The type series was collected with a pitfall trap in a disturbed area near a mixed deciduous forest ( Fig. 10 ) during the dry season.

DISTRIBUTION. Laos (Vientiane Province) and Thailand (Kamphaeng Phet Province, Fig. 21 ).

Key to the Southeast Asian species of the genus Plagiolepis

Figures

Fig 21. Distributions of the new species of Plagiolepis in Indochina.

Figs 1–2. Plagiolepis chomphuphuangi sp. n., holotype worker (THNHM-I-00018330). 1 – body in profile view; 2 – body in dorsal view.

Figs 3–4. Plagiolepis workers, head in full-face view. 3 – P. chomphuphuangi sp. n. (holotype, THNHM-I-00018330); 4 – P. silpaarchai sp. n. (holotype, THNHM-I-27222).

Figs 5–6. Plagiolepis workers, Mesosoma in dorsal view. 5 – P. chomphuphuangi sp. n. (holotype, THNHM-I-00018330); 6 – P. silpaarchai sp. n. (holotype, THNHM-I-27222).

Figs 9–10. Type localities of the new species. 9 – type locality of Plagiolepis chomphuphuangi; 10 – type locality of Plagiolepis silpaarchai.

Figs 7–8. Plagiolepis silpaarchai sp. n., holotype worker (THNHM-I-27222). 8 – body in profile view; 9 – body in dorsal view.