Melophorus microreticulatus Heterick, Castalanelli & Shattuck

Heterick, Brian E., Castalanelli, Mark & Shattuck, Steve O., 2017, Revision of the ant genus Melophorus (Hymenoptera, Formicidae), ZooKeys 700, pp. 1-420 : 179-182

Melophorus microreticulatus Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker from Emu Camp, Victoria Desert, 5 October 1976, P.J. M. Greenslade, (8), h1, [ANIC32-900172] (ANIC). Paratypes: major and media worker from Gawler Range, South Australia, 4 October 1972, P.J. M. Greenslade, (2) [ANIC32-900171] (ANIC); 3 minor workers from Fowlers Gap, New South Wales, 18 November 1979, P.J. M. Greenslade, (4) (ANIC); 2 minor workers from Gawler Ranges, South Australia, 4 October 1972, P.J. M. Greenslade, (2) A (BMNH); 2 minor workers from Brookfield Conservation Park 34°19'S, 139°29'E, South Australia, 29 October 1991, S. Shattuck, # 2525.7 [ANIC32-900098] (MCZ); 2 minor workers from Cunnamulla, Queensland, 17 September 1974, P.J. M. Greenslade, (8), gpt (QM); 2 minor workers from 5 km NE Koonamore HS, South Australia, 26 February 1973, P.J. M. Greenslade, (1) K1/lo(?) 13 (SAM); minor worker from 7 km NE Leinster, Western Australia, 16 September 1988, B. Heterick, soil, native vegetation, rural environment, 451, 8MelBh25 [JDM32-004550] (WAM).

Other material examined.

New South Wales: 40 km NNW Louth, Lake Mere (Greenslade, P.J. M. ), 40 km NNW Louth, Lake Mere (Greenslade, P.J. M. ), Bogan River (Armstrong, J. [ANIC32-900099]), CSIRO Lake Mere Field Station, near Louth (Bryannah, M. ), Fowlers Gap (Greenslade, P.J. M. ), Fowlers Gap (Greenslade, P.J. M. ). Northern Territory: Kunoth Paddock, near Alice Springs (Greenslade, P.J. M. ). Queensland: ‘Merigol’ (Beutel, T.), 10 km E Eulo (Greenslade, P.J. M. ), Cunnamulla (Greenslade, P.J. M. ), Eulo (Greenslade, P.J. M. ). South Australia: 15 km NE Mt Bryan (Greenslade, P.J. M. ), 1 km W Emu Camp, Victoria Desert (Greenslade, P.J. M. ), 50 km E Emu Junction, Victoria Desert (Greenslade, P.J. M. ), 50 km E Vokes Hill, Victoria Desert (Greenslade, P.J. M. ), 7 km NW Morgan (Greenslade, P.J. M. ), 8 km NW Morgan (Greenslade, P.J. M. ), Cambrai (Greenslade, P.J. M. ), Koonamore (Greenslade, P.J. M. ), Koonamore (Greenslade, P.J. M. ), Koonamore, 2 km NE homestead (Greenslade, P.J. M. ), Koonamore (Greenslade, P.J. M. ). Western Australia: 30 km SE Kambalda (Walliss, N. [JDM32-004551]).

Diagnosis.

Melophorus microreticulatus can be placed in the M. biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is placed in the M. biroi species-complex on the basis of a further suite of characters (viz, metatibia of major worker with only one preapical spur [except rarely in the mjobergi clade]; clypeal psammophore placed anteriorly at or just above anterior margin of clypeus in the minor worker and often in the major worker; head dorsoventrally compressed to varying degrees in the minor worker of most species with the eyes placed high on the sides; compact legs, and small body size [excluding mjobergi clade]; HW of smallest minor 0.36 mm, average HW of smallest minors 0.46 mm; HW of largest known major 1.29 mm, average HW of largest majors [where known] 1.05 mm). This species is characterised by having large eyes (EI 40 ≥). The minor worker is of small size (HW 0.40 mm ≥) and lacks erect setae on mesosoma and first gastral tergite. The minor worker can be distinguished from similar size M. biroi , the only species with which it may be confused, by possessing distinct microreticulate sculpture over the mesosoma (this sculpturing may be weaker on the pronotum in some specimens). The major worker has a posterior clypeal margin that is not arched or falling away between the antennal insertion and tentorial pit, and an anterior clypeal margin that is straight and not protuberant. This, and the microreticulate sculpture will serve to distinguish the M. microreticulatus major worker from the major worker of M. biroi .

Minor worker description.

Head. Head approximately oval with straight sides; posterior margin of head planar to strongly convex; frons shining with superficial shagreenation or microreticulation only, or matt or with weak sheen, microreticulate or microreticulate-shagreenate; frons consisting exclusively or almost exclusively of well-spaced, appressed setae only (small, erect setae, if present, usually confined to ocular triangle or posterior margin of head). Eye large (eye length ≥ 0.50 × length of side of head capsule); in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight or weakly convex; frontal lobes curved inward in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex and protrusive; clypeal psammophore set below midpoint of clypeus; palp formula 6,4. Five mandibular teeth in minor worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles approximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron matt or with weak sheen and microreticulate throughout, or pronotum smooth and shining, mesonotum shining and superficially microreticulate, mesopleuron densely microreticulate and may be almost matt; anterior mesosoma in profile smoothly rounded anteriad, thereafter pronotum and whole of mesonotum flattened and on same plane as propodeum; erect pronotal setae absent; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum matt or with a weak sheen and microreticulate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 3:2 and 4:3; erect propodeal setae always absent; appressed propodeal setulae long, each reaching setae behind and in front, but not forming pubescence; propodeal spiracle situated on or beside declivitous face of propodeum, and shorter (length <0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node uniformly rounded; node shining and smooth throughout. Gaster. Gaster smooth and glossy; pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour of head and mesosoma dark brown to blackish-brown, mesosoma variably brown-and-orange-tan.

Major worker description.

Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons shining and smooth except for piliferous pits and a few striolae around antennal insertions and Frontal carinae; frons consisting exclusively or almost exclusively of well-spaced, appressed setae only (small, erect setae, if present, usually confined to ocular triangle or posterior margin of head). Eye moderate (eye length 0.20-0.49 length of head capsule); in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical. In full-face view, frontal carinae straight or weakly convex; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in major worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron matt or with weak sheen and microreticulate throughout; anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining, dorsum and declivitous face of propodeum mainly smooth, but with weak to strong vertical striolae arising from metapleuron; propodeum wedge-shaped, tapering dorsad; length ratio of propodeal dorsum to its declivity between 3:2 and 4:3; erect propodeal setae absent; appressed propodeal setae short, separated by more than own length and inconspicuous; propodeal spiracle situated on or beside declivitous face of propodeum, and shorter (length less than 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node uniformly rounded; node shining and smooth with vestigial microreticulation anteriad. Gaster. Gaster smooth and glossy; pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour concolorous light brown or orange tan.

Measurements.

Worker (n = 8): CI 95-111; EI 25-45; EL 0.18-0.19; HL 0.41-0.70; HW 0.40-0.78; ML 0.55-0.90; MTL 0.26-0.44; PpH 0.06-0.09; PpL 0.23-0.39; SI 65-88; SL 0.35-0.50.

Comments.

Melophorus microreticulatus is a reasonably common small Melophorus thus far recorded from arid or semi-arid parts of NSW, NT, QLD, SA and WA, but it undoubtedly also occurs in western Victoria (one record coming from Brookfield Conservation Park near the SA, Vic border). This species is distinctive through its large eye, netted microreticulate mesosoma, protuberant propodeum and small size. As mentioned above, it fits in a clade that includes several other small species that possess a scalloped or otherwise sculptured mesopleuron and distinctive propodeum. The smoother specimens suggest a likely close relationship with M. biroi .

A tiny minor worker (M317) from Canna in the mid north of WA was successfully sequenced for COI. This specimen and the voucher that accompanied it are atypical for M. microreticulatus , with smaller (but still large) eyes, a slightly longer antennal scape and a narrower head capsule, but share with that species the characteristic netted sculpture and narrow, porrect node. The specimens may represent a separate species near to M. microreticulatus , but equally could simply be nanitic workers from a new colony. On the COI tree M317 was sister to the clade that includes M. gracilis , M. mjobergi , and M. postlei . No other specimens were available for sequencing. Specimens collected at Lake Mere were taken from a paddock. The principal author of this work has also collected the species in tall eucalyptus woodland east of Southern Cross, WA. A worker was collected in mulga woodland at Merigol Station, QLD. Apart from these records, ecological data are absent.

Etymology.

Compound of Greek mikros ( ‘small’) plus Latin reticulatus ( ‘netted’); adjective in the nominative singular.