Tetramorium tonganum

A widely ranging species that occurs in a variety of forest habitats. Heterick & Kitching (2022) collected this species (or one close to it) in the canopy of a lowland dipterocarp forest in Brunei.

Identification
Bolton (1977) - The distribution of this species in Polynesia has been covered in some detail by Wilson and Taylor (1967) but the range of the species extends from Japan in the north to New Guinea in the south. The east-west distribution is more difficult to ascertain as the species is capable of being transported by human commerce, but it is probably safe to say that Java and Sumba represent the western limits of tonganum. A Malayan record noted below was made in the Botanical Gardens of Kuala Lumpur and I suspect that it may represent an introduction. Similarly with the collection from Sri Lanka which makes up the type-series of the synonymous Tetramorium magitae.

Distribution
Bolton (1977) - The closest relative of tonganum is certainly the species Tetramorium difficile from Nepal and Bhutan, but this is smaller, with relatively shorter antennal scapes. The legs of difficile are shorter and the pronotal corners are more sharply angulate in dorsal view. Also in difficile the propodeum is usually armed with only a pair of minute, acute denticles. A second closely related species, Tetramorium vandalum, occurs in New Guinea, but this is blackish brown in colour and has erect and suberect pubescence upon the dorsal (outer) hind tibial surface. To some extent vandalum may exclude tonganum from New Guinea, as collections of the latter species are rare from that island.

Distribution based on Regional Taxon Lists
Australasian Region: New Caledonia. Indo-Australian Region: Borneo, Cook Islands, Fiji, French Polynesia, Guam, Indonesia, Malaysia, Marshall Islands, Micronesia (Federated States of), New Guinea, Niue, Palau, Philippines, Samoa, Singapore, Solomon Islands, Tokelau, Tonga, Vanuatu, Wallis and Futuna Islands. Oriental Region: Sri Lanka. Palaearctic Region: China, Japan.

Nomenclature

 *  tonganum. Tetramorium tonganum Mayr, 1870b: 976 (w.) TONGA. Santschi, 1928a: 50 (q.); Bharti & Kumar, 2012b: 23 (m.). Senior synonym of magitae: Bolton, 1977: 129.
 * magitae. Tetramorium magitae Forel, 1911i: 224 (w.) SRI LANKA. [Misspelled as mayitae in original.] Junior synonym of tonganum: Bolton, 1977: 129.

Note that all records reported as this species from India by Bharti & Kumar (2012) and Bharti et al. (2016) are based on a misidentification in Bharti & Kumar (2012) and are actually Tetramorium salvatum (Agavekar et al., 2017).

Worker
TL 2.6-3.1, HL 0.62-0.72, HW 0.56-0.64, CI 85-91, SL 0.46-0.54, SI 80-87, PW 0.40-0.48, AL 0.70-0.84 (36 measured).

Mandibles striate; anterior clypeal margin entire and the median portion of the clypeus with a narrow but fairly conspicuous anterior flange or apron. Frontal carinae extending back well beyond the level of the eyes, usually approaching the occipital margin, the carinae themselves not strongly developed but always more conspicuous than any other cephalic sculpture. Scapes relatively long (see SI above), if laid back in the rather shallow scrobes the apex of the scape just fails to reach the occipital corner. Eyes moderate in size, maximum diameter c. 0.14-0.16, about 0.24-0.27 x HW. Pronotum in dorsal view with the anterolateral angles broadly rounded. Propodeal spines relatively short, at most only marginally longer than the broadly triangular metapleural lobes, the spines narrow and acute. In some samples the propodeal armament is reduced to a pair of acute triangular teeth. Petiole in profile with an elongate, narrow peduncle anteriorly which in most is downcurved along its length. In some individuals the curvature appears reduced but the ventral surface of the peduncle always passes through a rounded angle before its junction with the node. Shape of petiole and postpetiole in profile are as shown in figure; in dorsal view the petiole node subglobular. Dorsum of head predominantly longitudinally ruguiose, with few or no cross-meshes before the level of the posterior margins of the eyes; behind this cross-meshes become more conspicuous, and a reticulum is usually present occipitally. Dorsal alitrunk finely reticulate-rugulose. Petiole and postpetiole predominantly smooth, completely unsculptured in some but often with at least traces of sculpture on the petiole, less commonly with traces on postpetiole also. Gaster unsculptured. All dorsal surfaces with numerous fine hairs of varying length but scapes and hind tibiae only with decumbent short pubescence, without erect pilosity of any description. Colour varying from light yellowish brown to mid-brown, often with the gaster somewhat darker than the head and alitrunk.

Type Material
Syntype workers, Tonga: Tongtabu (Godeffroy) [examined].

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