Melophorus laticeps

The ant has been taken in mulga and arid woodland and is absent from wetter areas. The only edaphic note is that a specimen from near the Capricorn Roadhouse in WA was collected from red soil. The appearance of the mandible suggests a granivorous diet, but there are no data at present to confirm this. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus laticeps can be placed in the Melophorus biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is also placed in the Melophorus wheeleri species-complex because it agrees with the following apomorphies possessed by the complex: the minor worker often has more than five teeth, the largest major worker has a short, massive, elbowed mandible directed posteriad; in profile, the maxillary palps are short in the major and generally short in minor workers (in the minor worker, usually only attaining the neck sclerite at their maximum extent when the head is moderately inclined) and, in full-face view, the anterior margin of the clypeus in the large major worker is usually planar or weakly concave (variable in other subcastes but planar or narrowly protuberant anterior clypeal margins predominate). In full-face view, the broad head capsule of the minor worker of M. laticeps is expanded towards the mandibular insertions, giving it a slight to strongly accentuated trapezoidal shape, and the basal margin of the major worker mandible is a carinate ledge set at 90° to the rest of the mandible throughout its length, with the (slightly) offset basal tooth horizontal and the sub-basal tooth with a horizontal and a vertical plane. A mandibular carina is present to varying degrees in media and minor workers. All workers have a glabrous mesosoma. These characters will distinguish M. laticeps from all other Melophorus except for its close relation, Melophorus pelorocephalus. The heads of minor and media workers of M. pelorocephalus, however, are even more exaggeratedly trapezoidal and the upper head of this species is distinctly darker in colour than the lower head and the mesosoma (all are uniformly coloured in M. laticeps).

Melophorus laticeps has a massive, carinate mandible that distinguishes it from all other Melophorus except for its close relative, Melophorus pelorocephalus. Seen in full-face view, the latter has a trapezoidal head shape compared with a square shape in M. laticeps. Only one WA specimen of M. laticeps has been sequenced, but this is sufficient to reveal a sister relationship with M. pelorocephalus.

Distribution
This common species is found in all mainland states except the ACT.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  laticeps. Melophorus laticeps Wheeler, W.M. 1915g: 813, pl. 66, fig. 2 (q.) AUSTRALIA. Combination in M. (Erimelophorus): Wheeler, W.M. 1935c: 71.

Heterick et al. (2017) - The species was described by Wheeler from a queen. This specimen, although damaged, exhibits the characteristic mandible that enables it to be associated easily with the worker (the head capsule is not splayed outwards near the mandibular insertions as would almost certainly be the case in the [as yet unknown] queen of Melophorus pelorocephalus, the only alternative assignment).

Worker
Heterick et al. (2017) - (n = 8): CI 128–134; EI 11–19; EL 0.22–0.37; HL 0.89–2.56; HW 1.14–3.43; ML 1.49–2.64; MTL 1.13–1.95; PpH 0.16–0.27; PpL 0.57–1.08; SI 49–99; SL 1.13–1.69.

Minor. Head. Head square or rectangular, tending to trapezoid; posterior margin of head planar or weakly convex; frons shining with superficial shagreenation or microreticulation only; 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 side of head capsule); in full-face view, eyes set above 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 distinctly concave; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin straight; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five to six 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 moderately shining and shagreenate throughout; anterior mesosoma in profile convex anteriad, mesonotum often slightly overlapping pronotum, mesosoma planar or slightly sinuate posteriad; erect pronotal setae absent; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and shagreenate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and shorter (length < than 0.50 × height of propodeum). Petiole. In profile, petiolar node narrowly conical, vertex blunt, directed posteriad; in full-face view, shape of petiolar node tapered with blunt vertex; node shining and smooth with vestigial sculpture. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae, erect setae (present in at least some workers) confined to margin of sclerite. General characters. Colour of foreparts tan or reddish (legs may be darker) gaster dark brown to black.

Major. Head. Head horizontally rectangular, broader than wide; posterior margin of head weakly concave; cuticle of frons shining and smooth except for piliferous pits; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. Eye small (eye length less than 0.2 × length of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical. In full-face view, frontal carinae distinctly concave; frontal lobes curved toward antennal insertion. Anterior clypeal margin straight; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Mandibular teeth in major worker always 4; mandibles strongly incurved, apical sector uniformly carinate and forming a bifurcate, horizontal ledge that terminates in the basal and pre-basal teeth; third mandibular tooth distinctly shorter than apical tooth, but equivalent in length to remaining teeth; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron shining and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; anterior mesosoma in profile broadly convex; erect pronotal setae long (i.e., longer than length of eye) and unmodified, or erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle and metathoracic spiracles; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae absent; appressed propodeal setae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and shorter (length less than 0.50 × height of propodeum), or situated at least twice its width from the 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, or tapered with blunt vertex; node shining and smooth throughout. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae, or consisting of well-spaced short, inconspicuous, appressed setae, erect setae (present in at least some workers) confined to margin of the sclerite. General characters. Colour of foreparts reddish (legs light reddish-brown to brown), gaster black.