Vollenhovia keralensis

This species is currently only known from Agasthyamalais and Periyar Tiger Reserve in the southern Western Ghats of Peninsular India. It was collected in tropical evergreen forests and mixed forests, ranging from 500–1,200 m. In the west coast tropical evergreen forest, habitat was characterized by Myristica (Myristicaceae) swamp forests and southern sub-tropical hill forests in the southern Western Ghats. Ants were observed moving on fallen tree trunks in shaded regions (Image 16A). On further investigation, the colonies were located inside crevices and under the bark of dead tree trunks. Upon disturbance, workers would disappear into tiny holes and crevices in the dead wood. One full colony was found at 800 m in Agasthyamalai had 52 workers, 20 males, 10 alate gynes, larvae and pupae in various stages of development. Occasionally, solitary gynes were observed under tree bark. No evidence of parasitic behaviour was noticed during our observation, although this needs detailed investigation. Workers were observed preying on beetle larvae and small arthropods nesting on tree bark, dead wood, and bracket fungi (Image 16B).

Identification
Based on descriptive and morphometric data on workers of Vollenhovia from Forel (1911, 1912), Bhart & Kumar (2013), and images of other related species from the AntWeb (2021) (see key below), we found that the workers of Vollenhovia keralensis can be distinguished from other Vollenhovia species reported for the Indian subcontinent and adjoining Indian Ocean Islands by the following combination of characters: body size (TL 3.53– 3.65 mm); convex anterior clypeal margin with a single median tooth; masticatory margin of mandibles with eight teeth, increasing in size from base to apex, and a well-developed subpetiolar process. From V. oblonga subspecies (V. oblonga alluaudi Emery, 1894 from Seychelles and Andaman and Nicobar Islands, as well as V. oblonga levithorax Emery 1889 from Tenasserim hills of Indo-Malaysia), the new species is easily differentiated by having a single median tooth on the clypeal margin, feature absent on V. oblonga and its subspecies. Vollenhovia keralensis can be differentiated from V. penetrans (Smith, 1857) – only known from alate gynes (AntWeb 2021) – based on the petiole length (subequal in the former), and petiole height (higher than long). Vollenhovia escherichi Forel, 1911 from Sri Lanka can be easily differentiated from the new species based on its size (TL ≤2.1 mm) as per Forel (1911), and pale yellowish-brown integumental coloration. With V. piroskae Forel, 1912 (from Seychelles), V. keralensis shares the clypeus with a single median tooth, but the former can be distinguished by its smaller size (TL 2.2– 2.4 mm) and mandible with 6–7 teeth while V. keralensis is larger (TL 3.53–3.65 mm) and worker having eight teeth on the mandible. V. keralensis is distnguished from the Himalayan V. gastropunctata by the workers of the former having masticatory margin with a large apical and preapical teeth and size, and body length (≤2.55 mm in V. gastropunctata). Additonally, the anterior margin of clypeus is convex with a single median tooth in V. keralensis which is concave in V. gastropunctata.

Distribution based on Regional Taxon Lists
Oriental Region: India.

Nomenclature

 * . Vollenhovia keralensis Kripakaran & Sadasivan, 2022: 21381, figs. 12A-C (w.q.m.) INDIA (Kerala).

Type Material

 * Holotype: NRC-AA-3762, 23 March 2011, Worker, Bonaccord, Peppara Wildlife Sanctuary, Trivandrum District, Kerala State, India, at 900 m, coll. Manoj Kripakaran, from under the bark of a dead and fallen tree in a primary evergreen forest, deposited in the insect collection facility of the NCBS (National Centre for Biological Sciences), Tata Institute of Fundamental Research, GKVK, Bellary Road, Bengaluru, Karnataka 560065, India. Earlier, the holotype was with number TARG-1015, mounted for study and preserved in absolute ethanol, currently deposited in the research collections facility at the TNHS, Thiruvananthapuram, Kerala.
 * Paratype workers (n = 3) (Images 13–15):
 * NRCAA-3763, 28 March 2021, Worker, Vallakadavu, Periyar Tiger Reserve, Idukky District, Kerala State, India, at 935 m, coll. Kalesh Sadasivan under the bark of a dead and fallen tree in a primary evergreen forest, deposited in the insect collection facility of the NCBS (National Centre for Biological Sciences), Tata Institute of Fundamental Research, GKVK, Bellary Road, Bengaluru, Karnataka 560065, India. Earlier the paratype was with number TARG-1016, in absolute ethanol, currently deposited in the research collections facility at the TNHS, Thiruvananthapuram, Kerala.
 * Two other paratype workers both with same data as paratype above. TARG-1017 and TARG-1018 to be deposited in the insect collection of the ZSI, Kozhikode, Kerala.

Description
Worker

Holotype

Measurements: HL 0.86, HW 0.81, SL 0.51, EL 0.14, Clypeal groove 0.36, DML 1.01, PW 0.52, PeL 0.31, PeW 0.23, PeH 0.30, A3L 0.30, A3W 0.27, A3H including the ventral tubercle 0.24, GL 1.14, Subpetiolar process H 0.10, TL 3.62, CI 94.19, SI 62.96.

Head: Head length and width almost equal, subquadrate (CI 94.19), vertexal margin with mild depression medially (Image 12C); mandibles with eight teeth: a well-developed basal tooth, and masticatory margin of mandibles with large apical and pre-apical teeth followed by six teeth, gradually decreasing in size towards the base of the mandible; anteroclypeal margin convex, with a single median tooth; antennae 12-segmented with inconspicuous three-segmented club; eyes large, placed just below the middle of side margin of head (Images 12A). Lateral head margin weakly convex.

Mesosoma: Pronotum slightly convex in lateral view, mesonotum fat and sloping toward propodeal declivity, promesonotal suture indistinct; metanotal groove distinct and impressed (Images 12A–B); propodeal dorsum convex, posterodorsal corners rounded and unarmed, propodeal lobes developed.

Petiole: In lateral view, the dorsal margin convex, node longer than wide, posterodorsal margin angulate; subpetiolar process well-developed, its free lower edge rounded; on ventral view it diverges in the middle-third and then gently slopes to merge with the petiole at the junction of middle and distal third of the ventral margin of petiole. Subpetolar process lamellar wall distinctly longer than high. Postpetiole: in lateral view, slightly longer than high, dorsal margin convex; in dorsal view, almost spherical; in profile; a well-developed rounded process present on its ventrum almost occupying the anterior half. Gaster: In profile, elliptical, dorsoventrally fat. Sting present, small (Images 12A).

Color, Sculpture and Pilosity: Blackish-brown head and body, gaster shiny blackish-brown. Mandible, antennae and legs brownish (Images 12A–C). Whole body foveolate except the median polished area on the anterior part of mesosoma, dorsolateral aspect of vertex, inferior half of propodeal declivity, the anterior aspect and anterior half of the mid-dorsum of the petiole. Gaster finely punctate, mostly by piligerous punctae, more abundantly on the anterior half of the tergite and across the sternite of the first gastral segment. The distal margin of the tergum and sternum of the first gastral segment reticulate. Surface of the other gastral segments finely reticular on both sides. Body is covered in sparse semierect hairs, brownish white and seen on entre head, body and gaster including petiole and postpetole. Hairs are absent on the lateral aspect of the mesonotum and propodeum. Few long hairs on the lateral margin of the clypeus, a pair of such hairs on each side much longer and prominent. Distal aspect of gaster near the sting bears some long erect hairs. About 15 vertical rows of piligerous foveolae between the anterior margin of the eyes and the midline of the head in fullface view. Opening of metapleural gland guarded by two stout filiform hairs, directed anterodorsally.

Paratype Workers

Measurements: HL 0.84–0.86, HW 0.79–0.81, SL 0.49–0.51, EL 0.14, Clypeal groove 0.35– 0.36, DML 1.00– 1.02, PW 0.51–0.53, PeL 0.29–0.31, PeW 0.22–0.24, PeH 0.30 –0.31, A3L 0.28–0.30, A3W 0.27, A3H including the ventral tubercle 0.23–0.25, GL 1.12– 1.016, Subpetiolar process: H 0.08–0.12. TL 3.53–3.65, CI 94.04–94.18, SI 62.03–62.96.

Variation in workers: Some variation was noted in the body measurements (see above) and surface sculpture. The shiny mid-dorsal area on mesosoma was variable amongst the workers of the same colony. The variation ranged from the polished surface extending across the whole dorsum of mesosoma to the propodeum (Image 15A), to highly reduced to the anterior portion of the pronotum (Image 12B).

Gyne (Images 13A,C, 15D,F)

Measurements (n = 1). HL 0.94, HW 0.90, SL 0.54, Clypeus groove: 0.53, EL 0.21, DML 1.52, PW 0.78, PeL 0.38, PeW 0.32, PeH 0.45 (including the subpetiolar process), A3L 0.46, A3W 0.38, A3H 0.32, GL 1.52, Subpetiolar process H 0.20, TL 4.81, CI 95.74, SI 60.00.

Head blackish-brown, shaped similar to the worker, mandible with eight teeth, antennae 12-segmented. Antennal club not distnct from rest of the antennae. Ocelli present. Mesosoma blackish brown, shaped as in the worker except for the wing sockets. On lateral view, mesoscutum almost fat at the same level as the rest of the thorax. Parapsidal lines running longitudinally extending to almost half of the mesoscutum (Image 15f). Promesonotal and mesometanotal sutures distnct. Inferior half of the anepisternum and the superior higher porton of the katepisternum smooth (Image 15D). Mesoscutellum gently sloping towards the metanotum. Petiole and postpetiole same as worker, with well-developed subpetiolar process. Gaster shiny black, otherwise same as worker. Sculpture of head, mesosoma and first gastral tergite punctate, other gastral tergites fnely reticulate. Body covered in sparse semierect hairs, brownish white in color throughout the entire body, including petiole and postpetiole (Images 15D,F).

Male (Images 13B,D)

Measurements (n = 1). HL 0.61, HW 0.65, SL 0.12, EL 0.22, Clypeal groove: 0.16, DML 1.20, PW 0.65, PeL 0.30, PeW 0.21, PeH 0.18, A3L 0.26, A3W 0.23, A3H 0.22 including tubercle, GL 1.10, TL 3.47, CI 1.06, SI 17.98.

Smaller than conspecific female castes. Head blackishbrown, wider than long, eyes large and occupying the lower half of the lateral head margin. Three large ocelli present. Mandibles highly reduced, masticatory margin toothless. Antennae 12-segmented, scape short, almost equal to other segments of the antennae (Images 13B,D). Frontal margins subparallel, extending from the lower median ocelli downwards. Vertexal margin straight. In lateral view, mesosomal dorsum convex. Propodeal declivity less pronounced than in the workers. Subpetiolar process absent. Postpetiole lacking ventral tubercles. Body shiny (especially gaster) and generally fnely punctate. Pilosity sparse, whole body covered by semierect whitish hairs and longer brownish hairs (Image 13B).

Measurements

EL—Eye length: maximum length of eye measured in lateral view | HL—Head length: maximum measurable distance from the mid-point of the anterior clypeal margin to the mid-point of the posterior margin of head, measured in full-face view | HW—Head width: maximum head width directly behind the eyes, measured in full face view | SL—Scape length: maximum length of scape shaft excluding basal condyle | PH—Pronotal Height: the maximum height of the pronotum in profile | PW— Pronotal Width: the maximum width of the pronotum in dorsal view | DML—Dorsal Mesosoma Length: maximum length of mesosomal dorsum from anterio-dorsal margin of pronotum to dorsal margin of propodeal declivity | WL—Weber’s Length of Mesosoma: the maximum diagonal length of the mesosoma in profile, from the angle at which the pronotum meets the cervix to the posterior basal angle of the metapleuron | HFeL— Metafemur Length: the maximum straight-line length of the metafemur, measured in dorsal view | HTiL—Hind tbia length: maximum length of hind tibia measured on its external face | HBaL—Hind basitarsus length: maximum length of hind basitarsus measured along its external face | PeL—Abdominal Segment II (petiole) Length: the maximum length of abdominal segment II (petiole), measured in dorsal view | PeH—Abdominal Segment II (petiole) Height: the maximum height of the petiolar tergum in profile view, including laterotergite, excluding petiolar sternum | PeW—Abdominal Segment II (petiole) Width: the maximum width of abdominal segment II (petiole), measured in dorsal view | A3L— Abdominal Segment III Length: the maximum length of abdominal segment III, measured in dorsal view | A3W—Abdominal Segment III Width: the maximum width of abdominal segment III, measured in dorsal view | A3H—Postpetole Height: Maximum height of postpetiole in profile | A4L—Abdominal Segment IV Length: the maximum length of abdominal segment IV, measured in dorsal view | A4W—Abdominal Segment IV Width: the maximum width of abdominal segment IV, measured in dorsal view | LS4—Abdominal sternum IV length: maximum length of abdominal sternum IV in lateral view | A5L— Abdominal Segment V Length: the maximum length of abdominal segment V, measured in dorsal view | A5W— Abdominal Segment V Width: the maximum width of abdominal segment V, measured in dorsal view | A6L— Abdominal Segment VI Length: the maximum length of abdominal segment VI, measured in dorsal view | A6W— Abdominal Segment VI Width: the maximum width of abdominal segment VI, measured in dorsal view | WL— Weber’s length: diagonal length of mesosoma in lateral view from the anterior-most point of pronotal slope (excluding neck) to posterioventral margin of propodeal lamella or lobe | TL—Total body length: combined length of HL + ML + PeL + A3L + GL for Myrmicinae.

Indices

CI—Cephalic index: HW / HL × 100 | OI—Ocular index: EL / HW × 100 | SI—Scape index: SL / HL × 100 | DMI —Dorsal Mesosoma Index: PW / WL × 100 | DMI2 —Dorsal Mesosoma Index 2: DML / WL × 100 | LMI — Lateral Mesosoma Index: PH / WL × 100 | DPe (DPI)— Dorsal petole index: PeW / PeL × 100 | LPI —Lateral Petole Index: PeL / PeH × 100 | MFI —Metafemur Index: HFeL / HW × 100 | ASI—Abdominal segment index: A4L /A3L × 100 | IGR—Gastral reflection index: LS4 / A4L.

Etymology
The specific epithet keralensis is feminine, and refers to the state of Kerala, in southern India, where the species was discovered.