Polyrhachis flavicornis Smith, 1857

Jaitrong, Weeyawat, Yamane, Seiki & Noon-Anant, Nawee, 2023, The Thai species of the Polyrhachis (Myrmatopa) flavicornis Smith, 1857 species group, with description of a new species (Hymenoptera, Formicidae Formicinae), Zootaxa 5249 (4), pp. 446-464 : 453-458

Polyrhachis flavicornis Smith, 1857

( Figs 4–6 )

Polyrhachis flavicornis Smith, 1857: 63 , worker and queen, Singapore; Donisthorpe, 1932: 446, combination in Polyrhachis (Myrmatopa) : Jaitrong & Nabhitabhata 2005: 38; Pfeiffer et al. 2011: 41; Khachonpisitsak et al. 2020: 64; Yamane et al. 2021: 124; Wang et al. 2022: 10.

Types examined. One syntype worker and one syntype alate queen of Polyrhachis flavicornis from Singapore (A. R. Wallace), deposited in OXUM .

Non-type material examined. LAOS: Vientiane, Naxaythong dist., Sivilay vill., carton nest on leaf, 11.VI.2010, Sk. Yamane, LA10-SKY-077 (workers, SKYC) . THAILAND: W Thailand, Tak Prov., Huai Khaeng , 26.II.2016, Sk. Yamane leg. (workers, SKYC); W Thailand, Phetchaburi Prov., Kaeng Krachan N.P ., 250- 350 m, 30.V.2005, nesting on lower-vegetation, 2.30 m above ground, Colony L, N. Noon-anant leg. (workers, queens, PSUSC, THNHM); NE Thailand, Nakhon Ratchasima Prov., Wang Nam Kheao Dist., Sakaerat Environmental Research Station , 26.IX.2021, W, Jaitrong leg., TH21-WJT-636 (workers, alate queens, THNHM) ; E Thailand, Chacheongsao Prov., Khao Ang Reu Nai W. S., Lamchangwat Stn. , 21.VIII.2003, carton nest on leaf, Sk. Yamane leg., TH03-SKY-18 (workers, SKYC, THNHM) ; same loc., 22.VIII.2003, Sk.Yamane leg., TH03-SKY-61 (workers, male); same data, TH03-SKY-62 (workers, queens, SKYC) ; same loc., 21.III.2003, S. Hasin leg., TH03-SH-004 (workers, males, THNHM) ; same loc., 26.IV.2003, W. Jaitrong leg., WJT03-TH-11 (workers, THNHM) ; same loc., 23.IV.2003, W. Jaitrong leg., WJT03-TH-14 (workers, THNHM) ; same loc., 22.VIII.2003, W. Jaitrong leg., WJT03-TH-256 (workers, alate queen, male, THNHM); E Thailand, Chanthaburi Prov., Pong Nam Ron Dist., Khao Soi Dao , Soi Dao Waterfall , 13.V.2006, W. Jaitrong leg., WJT06-E041 (worker, dealate queen, alate queens, THNHM) ; S Thailand, Songkhla prov., Ton Nga Chang W. S., carton nest, 22.X.2011, Sk. Yamane leg., TH11-SKY-173 (workers, queen, male, SKYC) ; Narathiwat Prov., Bala Forest, Hala-Bala W.S., 50– 300 m, 15.I.2002, on lower vegetation, N. Noon-anant leg. (workers, PSUSC) ; Satun Prov., Ludu Waterfall , Tatutao N.P ., 0– 200 m, 6.III.2005, on lower vegetation, N. Noon-anant leg. (workers, PSUSC) ; Songkhla Prov., Ton Nga Chang W. S., 100– 300 m, 21.I.2002, canopy fogging, S. Tongjerm leg. (workers, PSUSC) ; same loc., 27.III.2004, nesting on lower vegetation, 1.84 m above ground, Colony E, N. Noon-anant leg. (workers, queen, PSUSC) ; Phatthalung Prov., Ton Pra Tong Waterfall 100– 200 m, 19.III.2005, nesting on lower vegetation, 1.63 m above ground, Colony F, N. Noon-anant leg. (workers, PSUSC) ; Nakhon Si Thammarat Prov., Aey Kiew Waterfall , Khao Luang N .P. 100– 300 m, 8.VIII.2005, on lower vegetation, N. Noon-anant leg. (workers, PSUSC) ; Nakhon Si Thammarat Prov., Khao Nun N.P. 100– 500 m, 16.IV.2005, nesting on lower vegetation, 2.35 m above ground, Colony G, N. Noon-anant leg. (workers, queen, PSUSC) ; Surat Thani Prov., inner mainland, Klong Sang W.S. 100– 300 m, 1.V.1994, canopy fogging, L. Lebel leg. (workers, PSUSC) ; Surat Thani Prov., Tai Rom Yen N.P. 400– 500 m, 31.VII.2005, nesting on lower vegetation, 2.25 m above ground, Colony H, N. Noon-anant leg. (workers, PSUSC) ; Ranong Prov., Kuan Mayoy Mom W. S. 190– 250 m, 28.IX.2005, nesting on lower vegetation, 2.20 m above ground, Colony I, N. Noon-anant leg. (workers, queens, PSUSC) ; Prajuab Khiri Khan Prov., Ka Oon Waterfall , 100– 200 m, 10.II.2007, nesting on lower vegetation, 2.05 m above ground, Colony J, N. Noon-anant leg. (workers, queen, PSUSC) ; Prajuab Khiri Khan Prov., Kuy Buri N. P., 100– 300 m, 30.V.2005, nesting on lower vegetation, 1.93 m above ground, Colony K, N. Noon-anant leg. (workers, queen, PSUSC) . INDONESIA: Sumatra, Aceh, P. Simeulue , Babulmakmur , 15.IX.2012, Sk. Yamane leg., SU12-SKY-090 (workers, queen, male, SKYC) ; West Sumatra, Mentawai Is ., P. Siberut , Surisura , 20.II.2007, light-attracted, Sk. Yamane leg. (queen, SKYC) . MALAYSIA: Sabah, Danum Valley , 3–4.III.1999, Sk. Yamane (worker, SKYC) ; Sarawak, Miri, Lambir Hills NP , 21–27.II.2009, Sk. Yamane leg. (worker, SKYC) .

Measurements and indices. Worker (10 non-types). TL 3.20–3.35, HL 1.15–1.25, HW 0.95–1.00, SL 1.45– 1.55, PW 0.75–0.80, MTL 1.35–1.45, CI 79–87, SI 150–158. Queen (2 non-types). TL 4.30–4.35, HL 1.40–1.45, HW 1.15–1.20, SL 1.80–1.85, PW 1.15–1.20, MTL 1.75–1.80, CI 82–83, SI 154–157. Male (non-type). TL 4, HL 0.85, HW 0.60, SL 0.95, PW 1.30, MTL 1.55, CI 71, SI 158.

Description of worker ( Fig. 4 A–C , Fig. 5 A–C )

Head in full-face view distinctly longer than broad, with posterior margin evenly and roundly convex, lateral margins distinctly converging anteriad. Frontal carinae distinctly elevated, posteriorly reaching level of mid-length of eye, parallel anteriorly, divergent in middle, parallel posteriorly. Clypeus transverse, trapezoidal, its posteromedian margin straight to very shallowly emarginated; anterior margin slightly convex; anteromedian portion weakly produced, with straight anterior margin and blunt lateral angles. Mandible subtriangular, masticatory margin with 5 distinct teeth. Antennal scape long, ca. 1.37–1.40 times as long as head width including eyes; pedicel more than 2.5 times as long as broad, much longer than first flagellomere that is shortest of all flagellomeres; all flagellomeres longer than broad. Eye in full-face view convex and prominent, in full-face view breaking lateral margin of head, located posterior to mid-length on lateral face of head.

Pronotum in dorsal view much broader than long, anteriorly slightly convex, laterally roundly convex, with straight posterior margin; humerus rounded, weakly angled or produced as very small process; in profile view lateral face of pronotum with shallow furrow along its anterior margin; posteroventral corner broadly rounded. Mesonotum in dorsal view demarcated anteriorly and posteriorly by distinct furrows, much narrower than pronotum, broader than long, trapezoidal, gradually narrowed posteriad; in profile view dorsal margin almost flat but posterior portion of lateral keel of mesonotal dorsum bluntly angled; mesopleuron in profile demarcated from pronotum by deep sinuate furrow but completely fused with metapleuron. Metanotal groove short (‘narrow’) and shallow, continuing down to metathoracic spiracle that has upward-directed small round opening. Propodeum in dorsal view posteriorly as broad as mesonotum; dorsal face rectangular, broader than long, gradually merging with posterior declivity; lateral face not demarcated from metapleuron; propodeal spine short, directed upward; propodeal spiracle located on lateral margin of declivity, prominent, with oblong opening.

Petiole in dorsal view broader than long; dorsal face not clearly differentiated from anterior and posterior slopes, with a pair of long lateral spines that diverge in basal part and are parallel in apical two-thirds, intercalary denticle absent; in profile view anterior slope of node straight, much shorter than posterior slope that is roundly convex; subpetiolar process ventrally with round margin but sometimes with blunt posterior angle.

Head almost entirely puncto-reticulate; area between frontal carinae with much weaker sculpture. Clypeus very densely puncto-reticulate. Mandible in basal half very densely and finely striate with scattered punctures from which setae arise; apical half with much sparser and weaker sculpture and matte or weakly shiny. Antenna densely micropunctate. Pronotum and mesonotum puncto-striate, other parts of mesosoma densely puncto-reticulate to indistinctly puncto-striate. Petiole densely puncto-reticulate; sculpture on posterior face coarser; lateral spines with finer and irregular punctation. Tibiae and tarsi of all legs micropunctate and matte; femora in apical area densely punctate but in other parts superficially and more striated sculptured and shiny; coxae superficially rugulose and shiny. Gastral tergites densely micropunctate and matte; sternites with larger punctures, weakly shiny.

Body with very sparse short appressed pubescence that is absent in some parts, with few long standing hairs; pubescence abundant on gastral tergites and sternites; few standing hairs present on outer margin and along masticatory margin of mandible, clypeus anteriorly, frontal lobe, petiolar sternite anteriorly and venter of gaster. Eye without standing hairs. Head including clypeus, mesosoma, forecoxa and petiole black; mandible, antenna, legs except for forecoxa and gaster yellowish brown to dark reddish brown; antennal scape, mid- and hindcoxae, hindtibia and gaster generally darker than other brownish portions; labial and maxillary palpi yellowish.

Description of queen ( Fig. 5 D–F )

General habitus similar to the worker except for caste-specific structures. Body slightly larger with head width 1.15–1.20 mm (0.95–1.00 mm in the worker). Eye larger and more prominent; ocelli arranged in low triangle. Pronotal humerus round, without any projection. Mesoscutum in dorsal view widest at midlength, with convex lateral margins, with distinct longitudinal median shallow furrow in anterior 1/4 length of scutum, notauli absent, parapsidal line in posterior half of scutum; prescutal carina absent; mesoscutellum narrower than mesoscutum, narrowed posteriorly, with ill-defined posterior face; mesopleuron divided into upper and lower sections by groove, anterior margin of lower section with high acute keel (inconspicuous in the worker). Metanotum in dorsal view short (‘narrow’), indented, sharply demarcated from propodeum by deep furrow; metapleuron barely differentiated from mesopleuron, completely fused with propodeal side; propodeal spines short, blunt. Petiolar spines much thicker and relatively shorter than in the worker; subpetiolar process developed with ventral margin straight. Body slightly hairier than in the worker; in addition to standing hairs mentioned for the worker, queen bears standing hairs as follows: one or two around ocelli, several on mesoscutum, some on mesoscutellum, some on second to fifth gastral tergites. Body color almost identical to the worker.

Description of male ( Fig. 6 )

With general characteristics of Polyrhachis males ( Wong and Guénard, 2020). Body with weak cuticle, often deformed in dry-mounted specimens. Head in full-face longer than broad, but if including eyes, then distinctly broader than long. Clypeus transverse, posteriorly clearly demarcated from frons with posteromedian margin shallowly emarginate medially, anteriorly broadly convex, with anterior margin entire. Mandible weakly sclerotized, spatulate, twice as long as broad with outer margin curved; masticatory margin short and edentate with apex bluntly pointed. Eye large, positioned at mid-length of lateral face of head; distance between mandibular base and anterior margin of eye (malar space) half as long as maximum diameter of eye; ocelli large, arranged in very low triangle; distance between median ocellus and lateral ocelli equal to diameter of median ocellus; distance between lateral ocelli twice as long as diameter of median ocellus. Antennal scape moderately long, as long as head width including eyes.

Mesosoma in dorsal view much broader than head including eyes. Pronotum short (‘narrow’), almost entirely concealed by inflated mesoscutum; prescutal furrow complete. Mesoscutum with faint longitudinal median line, without notauli; parapsidal line present in posterior half of scutum; scuto-scutellar sulcus prominent; mesoscutellum much narrower than mesoscutum, distinctly narrowed posteriad. Metanotum short (‘narrow’), deeply indented, clearly defined from propodeum with deep furrow. Propodeum without distinct separation of dorsum from declivity; spines absent. Petiole low and globular, in dorsal view as broad as long. Gaster rather weakly sclerotized, easily deformed after drying.

Entire body superficially and finely sculptured, weakly shiny. Short appressed hairs present over body surface but often indistinct; standing hairs confined to following parts: clypeus with pair of standing hairs along posterior margin and two to three long hairs anteriorly; mandible with some long hairs of varying length on outer surface; standing hairs on maxillary and labial palpi numerous; mesoscutum with few or no standing hairs; mesoscutellum with several standing hairs and sparse appressed hairs that are longer than standing hairs; a few standing hairs present in posterolateral area of propodeum and around propodeal spiracle; petiole with ca. 20 fine standing hairs dorsally, pair of standing hairs on its sternite ventroposteriorly, and thick golden hairs on anterior face of petiolar node. Gastral tergites generally lacking standing hairs except on apical tergites; gastral sternites with more standing hairs; coxae of all legs with sparse standing hairs. Eye bearing microscopic hairs that can be recognized under high magnification (>100x). Body brown to dark brown; mandible, legs and genitalia yellowish or light brown; maxillary and labial palpi yellowish.

Habitat. Carton nests of P. flavicornis were found on the underside of plant leaves or between leaves in lowland evergreen forest and dry evergreen forest.

Distribution. Laos, Cambodia, Thailand, Singapore, Malaysia, and Indonesia ( Fig. 10 B ).

Remarks. Polyrhachis flavicornis is most similar to P. varicolor . For the worker caste, the head and mesosoma are clearly black in P. flavicornis , but reddish brown in P. varicolor . For body size, P. flavicornis (HW 0.95–1.00 mm in worker, 1.15–1.20 mm in queen, 0.60 mm in male) is on average smaller than P. varicolor (HW 1.00– 1.25 mm in worker, 1.25 mm in queen, 0.65 mm in male).

Figures

FIGURE 4. Polyrhachis flavicornis (non-type worker, WJT08-E068). A, Body in profile view; B, head in full-face view; C, body in dorsal view.

FIGURE 5. Polyrhachis flavicornis. A–C, Syntype worker of Polyrhachis flaviconis (ANRWEB CASENT 0901857); D–F, non-type dealate queen of Polyrhachis flavicornis(TH21-WJT-636); A, E, body in profile view; C, D, head in full-face view; B, F, body in dorsal view.

FIGURE 6. Polyrhachis flavicornis (non-type male, TH03-SH005). A, Body in profile view; B, head in full-face view; C, body in dorsal view.

FIGURE 10. Distribution map of Polyrhachis flavicornis species group. A) P. constructor and P. longipilosa sp. nov. B) P. flavicornis and P. varicolor.