Rhopalomastix johorensis

Wheeler (1929) - Viehmeyer cites Overbeck as having taken this species from several nests in the dead twigs of mango (Mangifera) and in the bark of durion trees (Durio zibethinus).

Wang, Yong & Jaitrong (2018) - Often found in bark of common relatively large native tree species in secondary or disturbed forests, and abandoned or operational plantations. Colonies have frequently been collected from fruit trees, in particular mango trees (in both Singapore and Thailand).

Wang, Yong & Jaitrong (2021) - Colonies in Thailand are often found in, but not limited to, bark of cultivated mango trees usually on roadsides and/or plantations, close to human dwellings. Actual extent of nests per respective host tree is often unclear, sometimes nest cavities have been uncovered in bark very close to tree base, concurrently with occurrence more than one vertical metre from the base. Nests have also been found near or in the crowns of some mango trees. This species has also been collected in bark of wild Azadirachta excelsa trees, in primary evergreen and peat swamp forests of southern Thailand.

Identification
Wang, Yong & Jaitrong (2021) - There is broad internidal variation in morphology for this species in Thailand, mostly in terms of minor characters that were also observed to vary within different colonies, such as: intensity of striations on posterior half of head, and extent of flatness of anterior clypeal face. Based on COI barcodes, most Thai colonies could be grouped into a large cluster with < 1% uncorrected p distances among individuals (Fig. 1); colonies collected from East Thailand, however, formed a separate cluster divergent from the rest by 4.5 % (Fig. 1). The East Thai specimens are morphologically indistinguishable from other specimens of R. johorensis, despite the relatively high underlying genetic difference between the two clusters. This result may imply that East Thai populations of the species were established via an introduction event different from populations in all other parts of Thailand (Bergsten et al. 2012). Alternatively, there could have been a deep genetic split in Thai R. johorensis in the past for reasons unknown, leading to the development of two separate lineages (i.e., East Thai vs all other parts of Thailand) of the same species. More empirical evidence is required to draw a definite conclusion.

This species is similar to both Rhopalomastix impithuksai and Rhopalomastix javana, but can be distinguished from both mainly by the condition of posterolateral corners of propodeum, in relation to inner posterior propodeal face. In R. johorensis, posterolateral corners of propodeum are bluntly rounded but ill-defined and not distinctly differentiated from the inner posterior propodeal face; whereas in R. impithuksai and R. javana, posterolateral corners of propodeum are bluntly angulate, distinctly projecting posteriorly and differentiated from the inner posterior propodeal face, thus the posterior propodeal margin for the latter two species also appears more distinctly (though still weak) concave in dorsal view.

Previously in Wang et al. (2018b), it was surmised that workers of R. javana and R. johorensis may be differentiated based on strength of sculpture on the posteriormost vertexal strip close to the occiput in posterodorsal view. However, upon examination of additional material from Thailand, it is evident that this character is highly variable within both R. javana and R. johorensis – the posteriormost vertexal strip can range from being finely striate to almost entirely smooth and shining. Thus, in this revision we do not recommend using this character to distinguish between the two species.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Singapore. Oriental Region: Thailand.

Biology
In Singapore, four genera of diaspidid scale insects have been found in the tunnels chewed under bark by this ant (Matile-Ferrero & Foldi 2018, [[Media:Rhopalomastix Yong IS2019 &Supplementary.pdf|Yong et al. 2019]]).

Nomenclature

 *  johorensis. Rhopalomastix rothneyi subsp. johorensis Wheeler, W.M. 1929d: 96 (w.) SINGAPORE.
 * Status as species: Wang, Yong & Jaitrong, 2018: 316.
 * janeti. Rhopalomastix janeti Donisthorpe, 1936a: 55 (w.q.m.) THAILAND.
 * Junior synonym of johorensis: Wang, Yong & Jaitrong, 2018: 316.

Description
Length 2-2. 6 mm.

Distinctly larger than the typical rothneyi, which measures only 1.7- 1.8 mm. Head scarcely longer than broad (l lj6longer than broad in rothneyi) and with somewhat smaller eyes (13 to 15 facets, instead of about 20). Head and thorax rich ferruginous red; appendages, abdomen and sides and declivity of epinotum clear brownish yellow. I have recently received another series of specimens, comprising all three phases of a second subspecies of rothneyi from Java, which may be described as: Rhopalomastix rothneyi subsp. javana subsp. nov.

References based on Global Ant Biodiversity Informatics

 * Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
 * Donisthorpe H. 1936. Rhopalomastix janeti (Hym. Formicidae) a species of ant new to science. Entomologist's Record and Journal of Variation 48: 55-56.
 * Wang W.Y., Yong, G.W.J. & Jaitrong, W. 2018. The ant genus Rhopalomastix (Hymenoptera: Formicidae: Myrmicinae) in Southeast Asia, with descriptions of four new species from Singapore based on morphology and DNA barcoding. Zootaxa 4532: 301-340.