Colobopsis howensis

This species, described from Lord Howe Island, is morphologically almost identical to the Australian mainland species Colobopsis macrocephala, and may be conspecific with it. Little has been reported regarding the biology of this species.

Identification
A member of the Camponotus macrocephalus species-group. This group has the following characters:


 * Fore femurs swollen, much greater in diameter than middle and hind femurs, generally more swollen than in most other Camponotus species.
 * Spines or bristles on the lower surfaces of the tibiae lacking, or at most, only one or two (most Camponotus species possess two rows of 5 to 10 spines).
 * Major workers and queens with the anterior of the head is truncated and flattened (phragmotic).
 * Major and minor workers present, but not intermediate-sized workers (worker caste dimorphic).

Within this group, this species can be diangosed as follows:

Mandibles in major workers with distinct rugae superimposed over shallow fovae, rugae covering the entire dorsal surface of mandible. A few long, erect setae on head and gaster, none elsewhere. In lateral view, dorsal surfaces of pronotum, mesonotum and propodeum form a continuous weakly convex surface; posterior propodeal face slightly concave.

Distribution based on Regional Taxon Lists
Australasian Region: Australia, Lord Howe Island.

Nomenclature

 *  howensis. Camponotus (Colobopsis) howensis Wheeler, W.M. 1927i: 152, fig. 12 (w.) AUSTRALIA. Combination in Colobopsis: Ward, et al., 2016: 350. See also: McArthur & Shattuck, 2001: 33.

Taxonomic Notes
McArthur & Shattuck (2001): Wheeler (1927) described Camponotus howensis based on minor workers from Lord Howe Island. His description includes comparisons with a number of species from nearby Pacific islands but makes no reference to mainland Australian species such as C. macrocephalus. A more recent collection from Lord Howe Island by R.W. Taylor includes both major and minor workers, minors of which match Wheeler's types. The specimens from Lord Howe Island are very similar to mainland specimens placed in C. macrocephalus. They differ in having the dorsal surface of the mandibles of major workers sculptured with longitudinal rugae superimposed over shallow fovae. The mandibles in C. macrocephalus are smooth with similar fovae and with, at most, weak rugae along the anterior (the region away from the head capsule) one-half or less. Additionally, the sculpturing on the anterolateral region of the head between the eye and the base of the mandible in major workers of C. howensis tends to be less extensive and weaker than the sculpturing found in C. macrocephalus. Finally, the colour of the Lord Howe Island material (all castes) is consistently dark brown while mainland material varies from yellow-brown to dark brown. No significant differences could be found between the minor workers from these regions. Based on this, these two taxa are treated as distinct with an acknowledgment that they are very closely related and may well prove to be conspecific.

Major worker
In lateral view. Red brown, gaster generally darker, limbs similar in colour but with tarsi and tibiae slightly lighter. Head: Side with no erect setae; posterior glossy, smooth; anterior sharply truncated, anterior striations extending from truncation one/third distance to eye; vertex with few long setae; underside of head without erect setae, with very sparse, short, flat-lying setae. Mesosoma: Without erect setae. Pronotum and Mesonotum: Evenly convex. Metanotum: Wide trough, spiracle well below dorsum. Propodeum: Dorsum evenly curved; angle, rounded; declivity slightly concave, ratio dorsum/declivity approximately 1; spiracle well forward of declivity, closer to coxa than dorsum surrounded by indistinctly reticulate, glossy integument, without pilosity. Node: Without setae, anterior face lower half, straight, upper half evenly convex; summit blunt; posterior face straight. Gaster: Glossy indistinctly striate. Fore femur: Swollen. Mid tibia: Without erect setae, with sparse, flat-lying pubescence, without bristles inside. In dorsal view. Head: Nearly rectangular, sides straight, parallel; vertex straight; angles blunt; scape with very sparse, short, flat-lying setae. Frontal carinae mostly straight, diverging; posterior very wide. Frontal area, very small, depressed. Clypeus sides bordered by sharp ridge, narrow, widest at truncation; sides nearly straight, tapering anteriorly, grossly ridged longitudinally, similar to cheeks; three fourths of clypeus anterior to truncation. Anterior head comprising clypeus, mandibles and cheeks lying on flat circular plane; max HW at eye centre; eyes oval. Clypeus: Without erect setae, carina present, among striations; anterior margin narrow, projecting, evenly convex. In front or rear view. Node: Summit wide, slightly indented, without setae.

Minor worker
Head: Red-brown to dark brown, limbs and antennae slightly lighter colour, anterior of head yellow brown, vertex with few setae; underside of head without erect setae. Mesosoma: Glossy, microscopically reticulate without pilosity. Pronotum: Anterior and posterior thirds straight, centre third convex. Mesonotum: Mostly straight, slightly raised above pronotum and propodeum. Metanotum: Slight ridge, spiracle near middle of side. Propodeum: Dorsum straight to flatly convex; angle abrupt; declivity concave; ratio dorsum/ declivity about 1.5; spiracle situated midway between dorsum and coxa surrounded by glossy microscopically reticulate integument. Node: Without pilosity; anterior face lower half straight, convex above; summit sharp; posterior face straight. Gaster: Finely striate. Fore femur: Swollen. Mid tibia: With indistinct sparse, short, flat-lying setae, without bristles inside. In dorsal view. Head: Sides straight, slightly tapering to the front, vertex and angles forming an even convexity; scape with indistinct, sparse, short, flat setae; frontal carinae diverging widely; frontal area indistinct, diamond shaped; max HW just posterior to eye centre. Clypeus: Glossy, finely reticulate, few sparse, erect setae; carina feeble; anterior margin convex, wide, projecting. In front or rear view. Node: Summit wide, sometimes indented, without setae.

Measurements
PW 0.90-1.06 mm, HT 1.06-1.28 mm, EL 0.44- 0.45 mm, HW 1.31-1.64 mm, HL 1.48-1.82 mm, CAR W 0.63-0.89 mm, CLY W 0.60-0.63 mm, TL 0.95-1.15 mm, NW 0.48-0.55 mm.

Worker minor. Length 4.5-5 mm. Head about one-sixth longer than broad, slightly narrower in front than behind, broadest through the eyes, with broadly rounded posterior corners and nearly straight sides. Eyes large, moderately convex, a little more than half again as long as their distance from the anterior corners of the head. Mandibles short and rather convex, their somewhat oblique apical border with 5 subequal teeth. Clypeus broader than long, subcarinate, its anterior border slightly reflected, forming a short, broadly rounded lobe. Frontal area and groove indistinct; frontal carinae rather straight, diverging posteriorly. Antennae slender; scapes extending about 2/5 their length beyond the posterior border of the head. Thorax long, laterally compressed, especially in the epinotal region; promesonotal and mesoepinotal sutures impressed, the former more strongly than the latter. Thoracic dorsum in profile nearly straight, except for the sutural impressions and a slight elevation of the mesonotum anteriorly; pronotum feebly rounded in front. The compression of the epinotum reduces its dorsal surface to a roof-like ridge with terminates behind in a blunt point from which the triangular declivity falls nearly perpendicularly in profile; the base being nearly straight and horizontal, the somewhat shorter declivity distinctly concave. Petiole node rather high, its anterior surface convex above, its posterior surface flat, the superior border very sharp. Seen from behind the node is rectangular, somewhat narrowed above, the superior border straight and entire, with distinct lateral corners, more rarely somewhat emarginate in the middle. Gaster elongate elliptical; legs somewhat flattened, the fore femora distinctly enlarged. Shining and very finely and evenly shagreened; mandibles finely striate-punctate; cheeks sparsely but not deeply punctate. Hairs yellow, very sparse, present only on the clypeus, front, vertex and gaster. Pubescence short, sparse and appressed, distinct only on the gaster, appendages and head. Black; mandibles, clypeus, cheeks and antennae castaneous; palpi yellow; insertions and tips of antennal scapes, first funicular joint, knees, and tarsi brownish yellow; tibiae brown. Described from numerous specimens from Lord Howe Island. This species is related to C. sommeri Forel of New Caledonia, but is quite distinct in color, and has a narrower head, more angulate epinotum, etc. The thorax of howensis is more like that of several Fijian species (mayrellus, mandella and janus) recently described by Mann, but all these forms have a differently shaped head and coloration. C. conithorax Emery of the New Hebrides is also related to howensis but is somewhat smaller, has 6-toothed mandibles, is more opaque, and the thorax and petiole have a different shape.

References based on Global Ant Biodiversity Informatics

 * CSIRO Collection
 * Hoffmann, B. D., R. Graham, and D. Smith. 2017. Ant species accumulation on Lord Howe Island highlights the increasing need for effective biosecurity on islands. NeoBiota 34:41-52.
 * McArthur A.J., and S. O. Shattuck. 2001. A taxonomic revision of the Camponotus macrocephalus species group (Hymenoptera: Formicidae) in Australia. Trans. R. Soc. S. Aust. 125: 25-43.
 * Taylor R. W. 1987. A checklist of the ants of Australia, New Caledonia and New Zealand (Hymenoptera: Formicidae). CSIRO (Commonwealth Scientific and Industrial Research Organization) Division of Entomology Report 41: 1-92.
 * Taylor R. W., and D. R. Brown. 1985. Formicoidea. Zoological Catalogue of Australia 2: 1-149.
 * Wheeler W.M. 1935. Check list of the ants of Oceania. Occasional Papers of the Bernice Pauahi Bishop Museum 11(11):1-56.
 * Wheeler WM. 1927. Ants of Lord Howe and Norfolk Islands. Proceedings of the American Academy of Arts and Sciences. 62.4: 120-153.
 * Wheeler, W. M. 1927. The ants of Lord Howe Island and Norfolk Island. Proc. Am. Acad. Arts Sci. 62: 121-153