Boloponera ikemkha

Boloponera ikemkha is considered to be extremely rare and is believed to be threatened by current and planned mining activities in the Sekhukhuneland Centre of Plant Endemism.

Identification
Hawkes (2018) - Boloponera ikemkha is readily distinguished from its only known congener by the highly polished torular lobes and lack of standing hairs on the scapes, mesosoma, petiole and first gastral tergite. These distinctions, as well as others, are noted in the following couplet:


 * Torular lobes distinctly longitudinally striate; first gastral tergite with standing hairs and appressed pubescence; subpetiolar process with a strongly developed posteriorly projecting acute tooth; mesosoma dorsum, scapes and femora longitudinally striate between scattered piligerous foveolae (Central African Republic) . . . . . Boloponera vicans


 * Torular lobes smooth and highly polished without striations; first gastral tergite with appressed pubescence only; subpetiolar process terminating in a blunt slightly recurved posteroventral point, but without a strong posteriorly projecting acute tooth; mesosoma dorsum, scapes and femora smooth and shining between scattered piligerous foveolae (South Africa). . . . . Boloponera ikemkha

See Boloponera for features that separate B. ikemkha workers from similar Ponerinae genera.

Distribution based on Regional Taxon Lists
Afrotropical Region: South Africa.

Biology
Boloponera ikemkha specimens were found within the Sekhukhuneland Centre of Plant Endemism, an area recognised for its unique plant diversity, and were limited to a narrow strip of riparian woodland (canopy less than 10 m) in the much drier Sekhukhune Mountain Bushveld. No Boloponera specimens were located during more intensive surveys in this area, which suggests that B. ikemkha prefers the moister riverine fringe which has denser tree cover.

Castes
Hawkes (2018) - Although there is no direct evidence that the Boloponera ikemkha specimens with eyes are ergatoid queens, this seems the most likely explanation for the differences between the two distinct forms collected. In addition to having eyes, the larger specimens also have relatively larger gasters, with the width and length of gastral tergites 1 and 2 averaging 6–13% larger relative to the size of the mesosoma in specimens with eyes than in eyeless specimens. The relatively larger gasters would allow for development of ovaries. The lack of clear differences in the structures of the pronotum and mesonotum, where ergatoid queens normally exhibit distinguishing characters, may be due to the extreme fusion of segments in Boloponera (Christian Peeters, pers. comm.). Additional arguments in favour of the larger specimens being ergatoids rather than large workers are 1) it is very probable that Boloponera forage entirely underground, so there would be no apparent function for eyes in workers of any size, 2) it is also very likely that colony size in Boloponera is small and this would suggest that they could not afford the cost of producing size-variable workers (Christian Peeters, pers. comm.) and 3) analysis of morphological measurements indicates that there are discrete differences in relative proportions of body parts, including leg lengths (the specimens with eyes have relatively longer legs overall as well as differing relative leg lengths), which is different from what would be expected from a simple allometric relationship between leg length and body size within the worker caste. Ideally, dissection of colony samples or observation of live colonies in the laboratory should be carried out to confirm or refute the ergatoid hypothesis. However, given the extreme rarity of Boloponera, the opportunity to do this may not arise for a considerable time. One of the eyeless specimens has thus been designated as the holotype worker and the larger specimens with eyes treated as ergatoid queens, pending further investigation.

Nomenclature

 *  ikemkha. Boloponera ikemkha Hawkes, 2018: 27, figs. 1-4, 24 (w.ergatoid q) SOUTH AFRICA.

Worker
Measurements (3 measured, holotype in parentheses): TL 3.35–3.42 (3.42), HL 0.76–0.77 (0.77), HW 0.61–0.62 (0.62), HH 0.48–0.49 (0.49), SL 0.43–0.44 (0.44), TLW 0.28–0.29 (0.28), ML 0.46 (0.46), PW 0.45–0.46 (0.45), WL 1.06–1.08 (1.07), PeNH 0.38–0.39 (0.39), PeH 0.43–0.44 (0.43), PeW 0.34–0.35 (0.34), PeNL 0.36–0.37 (0.36), ProTL 0.36–0.38 (0.37), MesTL 0.30–0.32 (0.31), MetTL 0.38–0.39 (0.38), Gt1L 0.56–0.57 (0.57), Gt1W 0.57–0.58 (0.58), Gt2L 0.66–0.68 (0.68), Gt2W 0.57–0.58 (0.58). Indices and estimates: CI 80–82 (81), SI 70–71 (71), HVe 0.117–0.124 (0.124), Gt1WI 53–55 (55), Gt2WI 53–55 (55) (all measurements in mm except HVe, which is presented in mm3).

Head subrectangular, moderately longer than wide (CI 80–82), posterior margin shallowly indented medially, sides almost straight but slightly divergent in anterior half, rounding posteriorly into the broadly convex vertices. Torular lobes extremely large and protruding anteriorly over the clypeus, forcing the medial portion of the posterior margin of the clypeus anterad of, and overhanging, the medially concave anterior clypeal margin. Torular lobes translucent and highly polished, without any trace of striate sculpture except in the median strip between the lobes, a few piligerous foveolae present adjacent to this strip and in the posterior portion of the lobes. A pair of short, weakly diverging setae arise medially at the upper (= posterior) margin of the clypeus, a second similar but more strongly divergent and longer pair arise below these from about the midlength of the clypeus and a third pair of strongly convergent setae arise from the lower (= anterior) clypeal margin. The latter setae cross each other at about their midlength. Lateral portion of clypeus divided into sloping anterior and flat posterior sections by a transverse carina. Clypeus smooth and shining, weakly sculptured posterolaterally and with several weak and incomplete diagonal carinae anteriorly. Frontal carinae are very short, fading out immediately behind the torular lobes and failing to reach the mid-length of the head. Eyes and ocelli absent. Mandibles smooth and shining with scattered piligerous punctures, elongate, curved inward apically and each with an apical and a preapical tooth, with an additional blunt tooth near and another at the base of the masticatory margin. A fine but distinct groove arises dorsally at the base of the basal margin, running diagonally across the outer surface of the mandible, reaching the lateroventral margin at about one third of the length of the mandible and continuing along this margin to the apex, but no dorsal groove parallel to the masticatory margin is present. Antennal scapes short, stout, basally curved and distally thickened; when laid back, scapes fall short of the posterior margin of the head by about half their length. Antennal segment 2 slightly longer than broad, segments 3 to 10 distinctly broader than long. Two-segmented club formed by segment 11, which is slightly broader than long, and the apical (12th) segment, which is twice as long as broad. Scapes with strong sub-appressed pubescence only, lacking erect setae, remaining segments with appressed pubescence and short suberect setae, all segments smooth and shining, unsculptured except for piligerous punctures. Head smooth and shining with scattered piligerous foveolae everywhere apart from a small posterodorsal patch medially, the foveolae irregularly spaced but on average separated by more than their diameter. Hairs arising from the foveolae appressed and medially oriented on dorsum of head. Foveolae weakly longitudinally aligned, spaces between them smooth and shining dorsally and posteriorly but laterally, anteriorly and ventrally undose. Mesosoma: laterally striate, becoming undose dorsolaterally, the sculpture stronger on the pronotum and metapleura, weaker on the mesopleura. All dorsal surfaces smooth and shining medially, weakly undose laterally. Entire dorsal mesosoma with scattered piligerous foveolae which are more widely spaced medially. Promesonotal suture well-defined and flexible, metanotal groove entirely absent dorsally and only faintly discernible laterally. Katepisternum well-defined and isolated by a sharply incised suture, anepisternum also sharply defined dorsally, but not posteriorly, where it is contiguous with the metapleuron. Propodeal spiracles round, situated at about the mid-height of the sides of the propodeum. Propodeal declivity flanked by strongly developed translucent lamellae running from the posterolateral corners of the propodeum to the metapleural lobes, with which they are confluent. In profile the propodeal dorsum meets the declivity in an obtuse angle, the surfaces separated by a weakly defined arched edge that is confluent with the lateral lamellae. Declivity shallowly concave in dorsal view, mostly smooth, but weakly shagreenate in upper half. Metapleural lobes broadly rounded, incurved ventrally. Metapleural gland bulla expanded and protruding posterolaterally, the orifice opening dorsally and obscured posteriorly in lateral view by the upwardly extended ventral flap. Pretarsal claws without preapical teeth. Metafemur dorsally with a strip of thin cuticle slightly more than half its length through which an apparently glandular structure can be seen (see Figure 2D), the surface neither flattened nor indented; mesofemur lacking any such feature. Petiole: node in dorsal view distinctly wider behind than in front, in profile with anterior and posterior faces convergent, the node tapering to the very broadly rounded summit. Subpetiolar process keel-like, slightly recurved and produced posteriorly as a blunt point. Anterior face of node with weakly reticulate sculpture; posterior face smooth, with a few very faint short striae radiating from the posterior petiolar peduncle. Sides of node smooth posterodorsally and with undose sculpture anteroventrally restricted; dorsal surface of node smooth. Lateral and dorsal surfaces of node with scattered piligerous foveolae, which are absent from anterior and posterior faces. Anterior disc of petiole ventrally with a broad C-shaped strip of cuticle around a thinner semicircular patch (see Figure 2F). Gaster with tergites smooth and shining, very weakly undose between scattered piligerous foveolae, pubescence appressed to sub-appressed. Sting present, weakly curved. Pilosity: standing hairs absent from all dorsal surfaces of head and body apart from posterior margin of gastral tergite 2 (A4) and dorsum of subsequent tergites. Meso- and metathoracic tibiae each with a single subapical pectinate spur and a pair of elongate setae located more proximally on the ventral surface. Outer surfaces of femora as well as pro- and metathoracic tibiae with short appressed pubescence, mesothoracic tibiae with longer suberect setae. Colour: medium reddish-brown, legs and apical two antennal segments slightly paler.

Queen
Ergatoid (2 measured): TL 3.82–3.84, HL 0.84, HW 0.70, HH 0.54–0.55, SL 0.51, OD 0.06, TLW 0.31, ML 0.48–0.49, PW 0.51, WL 1.17– 1.18, PeNH 0.43, PeH 0.48, PeW 0.39–0.40, PeNL 0.40–0.41, ProTL 0.43, MesTL 0.36, MetTL 0.47, Gt1L 0.66, Gt1W 0.70, Gt2L 0.82, Gt2W 0.71–0.72. Indices and estimates: CI 83, SI 72–73, HVe 0.166–0.167, Gt1WI 60, Gt2WI 61, OI 9 (all measurements in mm except HVe, which is presented in mm3).

Matching the description of the worker but differing in the following respects:

1. Larger overall, with head relatively slightly broader and scapes relatively slightly longer.

2. Gastral segments 1 & 2 absolutely and relatively broader and longer.

3. Mesosoma relatively very slightly broader (PW/WL 0.44 vs 0.43), metanotal suture faintly visible in dorsal view in one specimen.

4. Compound eyes present, with 12–17 rather poorly defined ommatidia of varying size and shape, making precise counts difficult.

5. Head somewhat more rounded posterolaterally.

6. Subpetiolar process more bluntly rounded apically, not posteriorly recurved.

7. Legs longer, the difference being more pronounced in the middle and hind legs; in absolute terms the pro-, meso- and metathoracic tibiae of the ergatoid specimens are 14%, 17% and 21% longer respectively than those of the workers and relative to Weber’s length are 4%, 7% and 10% longer.

Larva
Mature (assumed, based on size) larva: white, length through spiracles 4.1 ± 0.7 mm (three measured), elongate pogonomyrmecoid form, weakly curved but distinctly differentiated into head, neck (T1–3 + AI–II) and body (AIII–X).

Tubercles yellowish-white, very numerous (708 on CASENT0257322), conoid with 0–2 simple hairs (0–2 on T1–T3, 0–1 on AI–AX) and surmounted by an elongate slender cone with spinulose integument (= conoid with spine sensu Wheeler and Wheeler 1976a). Tubercles absent ventrally on T1–T3.

Anus ventral, a weakly recurved transverse slit approximately 0.1 mm across, with a very fine anterior and much larger posterior lip (Figure 4E), four tubercles (conoid with a spine and two setae) arranged in a semicircle just behind the anus. Spiracles visible on T2–T3 and A1–A8, all ten of similar diameter (3.5–4.0μm); each set in a short cone-like peg set in a slight depression and with spinules on the inner surface of the atrium (Figure 4D). Thoracic segments and first eight abdominal segments distinct; abdominal segments nine and ten difficult to distinguish. Spinules abundant, in scattered short transverse rows of 2–7 posteriorly, longer rows ventrally on thoracic segments.

Head small (0.32 mm, ca. 8% of body length) subquadrate, clypeus arcuate, antennae high on head, at about the upper third, each an elongate oval with stronger lateral but weak anterior and posterior demarcation, the three weakly defined sensilla each with a small blunt subglobular spinule. Hairs on head very sparse (ca. 16–20) and short (approximately 5 μm): two on each side near the anterolateral margin of median portion of clypeus, two on each side near posterolateral margin of clypeus, one on the side of head behind the mandibular insertion, a short longitudinal row of 2–3 hairs on sides near posterolateral corners of head and a single hair on each side between these rows, behind the level of the antennae. Labrum subrectangular, slightly wider than long, with a row of four hairs on the anterior margin, a few rows of elongate spinules posteriorly on the ventral border and numerous rows on the posterior margin. Mandible pogonomyrmecoid, with a sharp-edged, strongly inwardly curved apical tooth and two very blunt preapical teeth. Maxillae paraboloidal, anterior and interior surfaces of the lacinia with rows of spinules, stipes without spinules, but with 3–4 hairs on the outer surface; the paxilliform maxillary palp stouter and sub-equal in length to the digitiform galea, both with apical and subapical sensilla. Anterior surface of labium with short rows of elongate spinules, labial palps paxilliform and ventrolaterally situated, with one subapical and three apical sensilla. Hypopharynx densely spinulose, the spinules arranged similarly to those on the posterior margin of the labrum.

Larval morphology is similar to that described for Plectroctena cryptica by Wheeler and Wheeler (1976b) and Plectroctena mandibularis (listed as Plectroctena conjugata in Wheeler and Wheeler (1989). The number of tubercles in Boloponera ikhemka (ca. 700) is intermediate between that reported for Plectroctena mandibularis (ca. 1600) and Plectroctena cryptica (ca. 350), the latter being similar to the 300 reported for Streblognathus aethiopicus (Smith) by Wheeler and Wheeler (1989). The spiracle structure in Boloponera most closely matches that described by Wheeler & Wheeler (1976a) for Paraponera and Thaumatomyrmex. Although the spiracle form in Plectroctena was not explicitly described for either Plectroctena mandibularis or Plectroctena cryptica, inspection of a Plectroctena mandibularis larva at 230× magnification suggests that the structure is similar in this genus; SEM examination would be required to confirm this.

Type Material
Holotype worker. SOUTH AFRICA, Limpopo, Sekhukhune, De Grooteboom 373 KT portion 1, 1025 ±10m, -24.93625, 30.14494 ±5m, P. Hawkes, J. Fisher, S. Pillay, 08.xii.2016, TRP2016b-TSF-131, Riverine fringe forest (in Sekhukhune Mountain Bushveld), hand collected 10–15 cm deep in soil at base of tree, CASENT0254322. Paratype workers. 2 specimens, same data as holotype, CASENT0254323, CASENT0254324. Paratype ergatoid queens. 2 specimens, same data as holotype worker, CASENT0254320, CASENT0254321.

Etymology
ikemkha is derived from Ancient Egyptian (ikem = shield; kha = shining) and refers to the very large, highly polished torular lobes. The specific epithet is a noun in apposition and is thus invariant.