Chaloenus gajah, Reid & Beatson, 2013

Reid, C. A. M. & Beatson, M., 2013, Chrysomelid males with enlarged mandibles: three new species and a review of occurrence in the family (Coleoptera: Chrysomelidae), Zootaxa 3619 (1), pp. 79-100 : 81-83

Chaloenus gajah sp. nov.

( Figs 1–6 )

Material examined. Holotype: m/ [ INDONESIA] East Borneo, Balikpapan , Wain River [c. 1°06’S 116°49’E], 50m, xi.1950, A. M. R. Wegner / ( ZMB).

Description [slightly teneral male; female unknown]. Length 6.5mm. Colour: entirely yellowish-brown to orange-brown, except antennomeres 8–11 white, mandibular teeth, lateral edges of buccal cavity, antennomeres 1–7, elytra (but not edges of basal half), tibiae, tarsomeres 1–3 dark brown to almost black (elytra and antennomeres 4–7 darkest). Abdominal ventrites densely and finely setose.

Head ( Figs 1–3 ): impunctate or almost so, vertex shining, not microsculptured, frontoclypeus dull with fine microreticulation; head glabrous, except trichobothrium between postantennal callus and eye, short recumbent setae between antennae and buccal cavity and on upper surface of mandibles; frontoclypeus slightly ridged between antennae, otherwise almost flat with truncate apical margin; antennal cavities large, separated from each other and from eyes by about 0.75x socket diameter; postantennal calli elevated, well-defined, transverse, adjacent for entire length; eyes small, situated dorsally on head not laterally, oval, separated by c. 3x eye length; gena long, equal to eye length; antennae c. 0.75x body length, reaching apical third of elytra if reflexed, all segments elongate but decreasingly so from 3–10, and 8–11 moniliform in shape, antennomere 1 greatly elongated (length 2x eye length) and expanded at apex; relative lengths of antennomeres 1–11, as ratios of the shortest (10): 5, 1.25, 2, 1.9, 1.75, 1.5, 1.35, 1.25, 1.15, 1, 1.35; labrum large, semicircular, with 2 pairs of large setae; mandibles symmetrical, upper surface setose, elongated, laterally swollen at base, with vertical blunt tipped horn in middle of base and three apical teeth (visible ventrally); apical maxillary palpomere elongate-conical, about half length of penultimate.

Thorax: pronotum and hypomera shining, unmicrosculptured, minutely and sparsely punctured, glabrous except trichobothrium in each angle; pronotum transverse, broadest anterior to middle, width c. 2x length, all angles slightly produced; pronotal disc convex but with pair of small circular depressions at sides; anterior edge truncate, not margined, sides strongly margined, sinuate, hind edge strongly margined, shallowly convex; prosternum glabrous, prosternal process reduced to a thin ridge between coxae, triangularly expanded at apex; procoxal cavities closed, by elongate hypopleural lobes reaching apex of prosternal process; scutellum triangular; elytra shining but outer half finely microreticulate, glabrous except 5–6 setae at apices; each transversely depressed a third from base, from suture to slightly more than half width, with groove from this to base at inner margin of humerus; elytra impunctate except: finely punctured sutural striole, 4 short striae of large punctures in transverse depression, the fourth reaching elytral base; epipleura with upper margin elevated, broad at base, narrowing to a single elytral edge before apex; mesoventrite glabrous, other ventral mesothoracic sclerites finely and densely setose; mesoventrite process elongate triangular (but appearing slightly shrivelled); ventral metathoracic sclerites finely and densely setose (metaventrite shrivelled); procoxae globular, strongly projecting; femora glabrous or almost so on basal half, remainder of leg densely and finely setose; pro- and mesofemora almost parallel-sided, metafemora elongate-ovate, width c. 1.5x mesofemur; pro- and mesotibiae externally weakly ridged in basal half, metatibiae expanded at middle and sharply ridged for basal 2/3; length hind tarsus c. 0.5x hind tibia; first metatarsomere slightly shorter than 2+3, fifth as long as first; claws appendiculate, small right-angled basal lobe.

Abdomen ( Figs 5–8 ): ventrites weakly sclerotised, without lateral keels; male: apex of last ventrite weakly medially lobed, shallowly excavate either side of lobe; penis basal foramen circular, thick lipped, shaft cylindrical, sharply reflexed at base then straight, to semi-circular apex; endophallic sclerite thin with poorly defined base; tegmen thin, elongated, Y-shaped.

Notes. Etymology: from the Malay for elephant ( gajah ), a noun in apposition, referring to the two tusk-like mandibular tubercles.

Chaloenus gajah is the only species of Chaloenus with male mandibular horns and therefore easily distinguishable from all other males ( Medvedev 2004; Takizawa 2012). In other Chaloenus species the female has a simple unmodified head and narrower prothorax; this is likely to be true of C. gajah .

Apart from its unique mandibles, Chaloenus gajah is separated from similar Chaloenus species, as keyed and described by Takizawa (2012), as follows: C. brunneus Bryant, 1943 , is small (4.8mm), yellowish with black margins to the elytra, and with flat apex to penis in profile; C. lanjakensis Takizawa, 2012 (female unknown), has black elytra, abdomen and legs, and broadly explanate lateral elytral margins; C. yukikoae Takizawa, 2012 , has more elongate antennae and penis expanded at apex and flattened in lateral view.

The type locality is probably the Wain River Forest Reserve, just north of the city of Balikpapan. This isolated 10,000 hectare reserve of lowland forest (maximum elevation 110m) has been seriously degraded in the last 15 years, with approximately 30% lost to fire, logging and cultivation ( Craven 2002; Cleary & Priadjati 2005; Google Earth, images accessed July 2010).

Some of the larger species of Chaloenus with sexually dimorphic males are known to aggregate at flowers of Araceae subfamily Aroideae ( Kumano-Nomura & Yamaoka 2009; C. Darling pers. com. 2010; Takizawa 2012), and it is possible that C. gajah shows this behaviour. Aroideae are particularly diverse in Borneo ( Mayo, Bogner & Boyce 1997).

Chaloenus gajah appears to be the first record of this genus from Indonesian Borneo (Kalimantan) ( Takizawa 2012), however the senior author has collected an additional 8 species from there.

Figures

FIGURES 1–2. Callidemum cornutum Baly. 1, male head, dorsal; 2, female head, dorsal.

FIGURES 3–8. Chaloenus gajah sp. nov., male holotype. 3, habitus; 4, head, antero-lateral; 5, head, dorsal; 6, apical ventrite; 7, penis lateral, ventral; 8, tegmen dorsal.