Rhopalomastix javana

Wheeler (1929) - The type specimens were "collected from a sample of bark of a dying Mangifera indica, which was forwarded to our Institute at Buitenzorg by Dr. Loos, the agricultural expert at Bondowoso (Res. Besoeki, Eastern Java). Dr. Loos wrote us that the ants were burrowing in the bark of the dying tree. The bark was riddled by the insects over half the circumference of the tree and at least as high as he could reach. Numerous pupa were seen. The ants, however, were not considered to be the cause of the death of the tree." This note shows that the Rhopalomastix colonies may be very populous.

Wang, Yong & Jaitrong (2018) - Specimens from Singapore were collected from bark of common native trees, e.g. Campnosperma auriculatum (Blume) Hook.f., in secondary forests and nature reserves which used to be abandoned plantations; specimens from Thailand were collected from bark of mango trees. Nests do not appear to occupy large expanses of tree bark.

Wang, Yong & Jaitrong (2021) - As with R. johorensis, colonies can be usually found in (but not limited to) bark of fruit trees such as mango, located close to human dwellings. Populations appear widespread, but more sparsely distributed and less commonplace than those of R. johorensis – this could merely be an artefact of incomplete sampling.

Identification
Wang, Yong & Jaitrong (2021) - This species is most similar to Rhopalomastix impithuksai and Rhopalomastix johorensis, but can be differentiated by characters described in detail under each of these species.

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

Nomenclature

 *  javana. Rhopalomastix rothneyi subsp. javana Wheeler, W.M. 1929d: 96, fig. 1 (w.q.m.) INDONESIA (Java).
 * Status as species: Wang, Yong & Jaitrong, 2018: 310.

Taxonomic Notes
Wang, Yong & Jaitrong (2021) - Thai populations of R. javana appear to be generally larger in size compared to populations from Indonesia (Java) and Singapore (Java and Singapore TL 1.83–2.02; Thailand TL 2.02–2.88). In terms of variation in morphological measurement metrics, Thai populations also seem much more variable relative to the other two countries (e.g., Thai HL 0.46–0.58; Java HL 0.48–0.52; Singapore HL 0.46–0.48), however, this might have arisen from bias in geographic range of sampling. For Thai R. javana, measurements were taken from 13 individuals from seven colonies distributed across Central, North and West Thailand, whereas for Java and Singapore, mostly individuals from 1–2 colonies were measured. A combination of measurements from different countries may be a more accurate representation of actual variation within the species.

Thai colonies that could be morphologically identified as R. javana were extremely variable in terms of COI (313 bp), with internidal divergences spread across multiple different values from 0.0–4.5% (Fig. 1). While sequence divergence between different species existing in sympatry can be as low as 3.8% (average uncorrected p distance) in ants, especially for recently diverged species (Wang et al. 2018a), higher percentage distances (> 4%) between allopatric populations do not necessarily indicate different species. In the latter case, clustering based on barcodes may split allopatric or geographically distant populations of the same species, belonging to older lineages that diverged genetically back in time (Meier et al. 2008). Thus, in light of the two aforementioned possibilities, inferring species boundaries from the clustering pattern of Thai R. javana specimens is complicated. If we define allopatric colonies as those coming from different parts (i.e., North, South, East, West, Central) of Thailand, then possibly the split clusters observed (Fig. 1) mostly represent different lineages of the same species R. javana. However, R. javana colonies considered ‘sympatric’ from North and Central Thailand respectively diverged at 4.5% (Fig. 1), suggesting (but not ascertaining) possible newly diverged species. Taking into account the broad inter- and intranidal variation shown amongst R. javana workers, we were unable to observe any striking morphological differences between specimens from the genetically divergent clusters. Given the lack of more convincing morphological or molecular evidence supporting further species delimitation in this study, we tentatively treat these colonies as conspecific. The possibility remains for this current treatment to be revised in future, when gene flow between R. javana populations are more thoroughly investigated, and the relevant data from other molecular markers are made available.

Worker
Length 1.3-1.8 mm.

Averaging smaller than the typical form of the species. Head not longer than broad; thorax shorter, only 1 2/3 times as long as broad, with the epinotum distinctly narrower than the promesomotum. Median tooth of the anterior clypeal border very indistinct. Eyes smaller, consisting of only 12 to 14 facets. Sculpture finer than in the subsp. johorensis; color similar, but the head and thorax more yellowish ferruginous, the gaster clouded with brown apically.

Queen
(dealated). Length 2.5-2.8 mm.

Antennae 10-jointed as in the worker. Deep castaneous brown; pronotum, thoracic sutures, pedicel and appendages paler, more reddish brown. Sculpture as in the typical rothneyi, the anterior third of the head and the thoracic dorsum very finely longitudinally striated, the posterior portion of the head shining, sparsely and rather coarsely punctate, the gaster shining, with finer, piligerous punctures.

Male
Length 2-2.3 mm.

Black, with brown appendages. Wings clear and hyaline, with dark brown veins and pterostigma, the latter small and subelliptical. The costal vein is absent basal to the pterostigma and there is a distinct indication of a former division of the long cubital cell into two cells and pale indications of former prolongations of the cubitus and discoidal veins towards the tip of the wing. The hind wing is narrow and has only one distinct vein, the media.

Type Material
Described from numerous workers, four females and three males taken at Bondowoso, Besoeki, Eastern Java and received from Dr. L. G. K. Kalshoven. Three syntype workers on 1 pin (USNM, cotype: MCZ.6.9.20783/ SNM.595.31) were examined by Wang, Yong & Jaitrong (2018). One worker (top on pin) was selected as the lectotype.

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
 * Wang W. Y., G. W. J. Yong, and W. Jaitrong. 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.
 * Wheeler W. M. 1929. The ant genus Rhopalomastix. Psyche (Cambridge) 36: 95-101.