Crematogaster borneensis

A widespread member of a group of Crematogaster species associated with Macaranga plants in Sumatra, Borneo, and Peninsula Malaysia

Identification
Feldhaar et al. (2016) - Worker: Propodeal spines present, scape index (SI) > 0.65, RLEG < 0.7, rarely above. Queen: EL > 0.5 mm (to 0.6mm), REL 0.36 - 0.43, OD1 > OW, Head longer than wide (CI < 0.95).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia, Singapore.

Biology
Crematogaster borneensis André has a large range and occurs in all geographic regions of the Macaranga-Crematogaster association (Malay Peninsula, Sumatra, and Borneo). It is the most generalised species with respect to host plant use. Queens colonize mostly waxy hosts. However, hosts that develop a slight wax-coating only as mature trees will also be colonized secondarily by this species after having been abandoned due to death of the original colony (e.g. Macaranga indistincta). In this case queens of C. borneensis are found in the tip of branches of abandoned mature hosts. Crematogaster borneensis is frequently found on hosts of the section Pachystemon (Macaranga aetheadenia, Macaranga glandibracteolata, Macaranga griffithiana, Macaranga lamellata, Macaranga motleyana, Macaranga hypoleuca, Macaranga indistincta, (in the latter two mainly in larger trees, rarely in saplings) as well as the section Pruinosae (Macaranga hosei, Macaranga pearsonii, Macaranga puberula, Macaranga pruinosa). Virgin alate queens have been found to be parasitized by the phorid fly Trucidophora feldhaarae while still inside the nest within the hollow stem of their host plant on Peninsula Malaysia (Maschwitz et al., 2006).

Nomenclature

 *  borneensis. Crematogaster borneensis André, 1896b: 263 (w.) BORNEO. Forel, 1911d: 386 (m.). Combination in C. (Decacrema): Forel, 1910a: 18. Senior synonym of capax, hosei, macarangae, sembilana: Feldhaar, Maschwitz & Fiala, 2016: 665.
 * capax. Crematogaster (Decacrema) borneensis subsp. capax Forel, 1911a: 37 (w.q.) BORNEO. Junior synonym of borneensis: Feldhaar, Maschwitz & Fiala, 2016: 665.
 * hosei. Crematogaster (Decacrema) borneensis subsp. hosei Forel, 1911a: 35 (w.q.m.) BORNEO. Junior synonym of borneensis: Feldhaar, Maschwitz & Fiala, 2016: 665.
 * macarangae. Crematogaster (Decacrema) borneensis subsp. macarangae Viehmeyer, 1916a: 126 (w.) SINGAPORE. Junior synonym of borneensis: Feldhaar, Maschwitz & Fiala, 2016: 665.
 * sembilana. Crematogaster (Decacrema) borneensis subsp. sembilana Forel, 1911d: 385 (q.m.) WEST MALAYSIA. Junior synonym of borneensis: Feldhaar, Maschwitz & Fiala, 2016: 665.

Worker
Feldhaar et al. (2016) - Lectotype. CI 0.96, DPPW 0.19, DPW 0.19, EL 0.13, HL 0.67, HW 0.64, LHT 0.49, LPS 0.101, MTW 0.4, PI 1.0, REL 0.2, RLEG 0.63, SI 0.71, SL 0.45, (TL 2.8), WL 0.77.

(n=11) CI 0.92-0.97, DPPW 0.18-0.25, DPW 0.19-0.25, EL 0.12- 0.17, HL 0.67-0.97, HW 0.63-0.92, LHT 0.5-0.72, LPS 0.104- 0.169, MTW 0.39-0.51, PI 1.01-1.14, REL 0.17-0.2, RLEG 0.62- 0.71, SI 0.64-0.74, SL 0.46-0.6, (TL 2.8-3.9), WL 0.82-1.03.

Colour light to reddish brown (large workers) with head and gaster being a slightly darker shade than the alitrunk. Workers monomorphic in size. Total body length of workers 2.5 mm to 3.2 mm. Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened. All body parts bear appressed pubescent hairs. Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites. Only few setae on alitrunk and one pair each on petiole and postpetiole.

Head subquadratic but slightly elongated, always being longer than wide (CI<0.97) and only slightly rounded on sides. Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly. Occipital margin slightly concavely rounded, occipital lobes rounded. Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus. Denticles increasing continuously in size from most proximate to most distal denticle. Surface of mandibles smooth, covered with short pubescent hairs.

Antennae relatively long in comparison to head width (SI 0.64-0.74; mean 0.68) and covered in short pubescent hair. Terminal three funicular segments form a club, sometimes only the terminal two segments.

Compound eyes elliptically shaped and not protruding over margin of head in full-face view. Pronotum and mesonotum form a convex dome in profile, sometimes slightly flattened dorsally. Anterodorsal surface of pronotum sloping downwards slightly steeper than or as steep as posterodorsal surface of mesonotum. Metanotal groove slightly notched and clearly developed, whereas the promesonotal suture visible but not prominent.

Propodeal spines in lateral view strong and acute. Tip of the spines always protruding over posterior margin of the propodeal spiracle and diverging very slightly. Dorsal face of the propodeum confluent with the horizontal spines or spines bent slightly upwards. Slope of the posterior face of the propodeum similar to posterior slope of mesonotum.

In dorsal view petiole always wider than postpetiole (PI: 1.01-1.14). Node of petiole in dorsal view longer than wide and considerably rounded, dorsal surface flat. In profile the anterior face of the petiolar node shorter than the posterior so that the dorsal surface slopes downwards anteriorly. Dorsal surface of the postpetiolar node in profile rounded. Subpetiolar process usually absent.

In the original description of the worker of Crematogaster borneensis by André (1896) he described the worker as having propodeal spines twice as long as their base. Forel (1911) writes that he has had personal contact with M. André and has been told that this was indeed an error made in the original description as spines are shorter (see above).

Queen
Feldhaar et al. (2016) - (n=27) CI 0.88-0.96, DPPW 0.49-0.61, DPW 0.44-0.57, EL 0.50-0.60, HL 1.31-1.50, HW 1.18-1.42, LHT 1.01-1.18, MTW 0.96-1.21, OD1 0.17-0.23, OD2 0.07-0.10, OW 0.13- 0.17, PI 0.87-1.0, REL 0.36-0.43, RLEG 0.42-0.49, ROD 0.13-0.17, ROD2 0.054-0.077, SI 0.53-0.6, SL 0.7-0.77, (TL 7.0-8.5), WL 2.23-2.7

Queens large, 7.0 to 8.5 mm in total body length and uniformly light to medium brown in colour. Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened. All body parts bear appressed pubescent hairs. Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites. A row of long erect setae pointing anterior present on the clypeus. Mandibles relatively short, capable of closing tightly against the clypeus.

Head elongate, always longer than wide (CI: 0.88-0.96; mean 0.91). Sides of the head only very slightly convex, occipital margin of the head straight to slightly convex. Occipital lobes strongly rounded. Anterior clypeal margin slightly convex. Terminal three segments of funiculus continuously increasing in size forming an antennal club that is not very distinct. Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.

Compound eyes oval-shaped from lateral view and only slightly convex from dorsal view. Compound eyes large relative to head length spanning more than one third of HL. Maximum diameter of compound eyes 0.5 to 0.6 mm. Maximum width of head including compound eyes maximally 10% wider than HW. Ocelli relatively small in diameter. The two lateral ocelli widely spaced and the median ocellus always smaller in diameter than the distance between the two lateral ocelli.

Mesoscutum convexly rounded anterodorsally. Mesoscutellum nearly in horizontal plane in lateral view. Propodeum flattened dorsally and then drops off steeply posterior of the propodeal spiracle. Mesoscutum long, stretching out over approximately half of the alitrunk in lateral view. In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum broadly triangular. Propodeum not armed with spines.

Node of petiole in dorsal view roughly rectangular, anterior side broader than posterior one. Petiolar node quadrangular in shape in dorsal view and not as wide as postpetiolar node (PI<1.0). In lateral view the petiole is anterodorsally flattened and sloping downwards and is slightly longer than the postpetiole. Postpetiole round in dorsal and lateral view without distinct nodes.

Type Material
Lectotype worker and 1 paralectotype worker from Borneo (André) (designated by Feldhaar, Maschwitz & Fiala, 2016: 665).

Determination Clarifications
In former publications we have referred to this species as Crematogaster msp. 1 (Fiala et al. 1999).