Rhopalomastix omotoensis

Up until 2018, Rhopalomastix omotoensis in the Ryukyu islands (Japan) was classified as "subterranean" since workers had been collected in soil pitfall traps. Nests have now been found under the bark of living trees in Okinawa, living together with large numbers of diaspidid scale insects (C. Peeters, unpublished). Arboreal habits and mutualism with diaspidids were described in Singapore by Yong et al. (2019).

Identification
Terayama (1996) - Separated from the other congeners by the longer head which is slightly longer than wide, yellowish brown head and alitrunk, somewhat larger eyes consisting of 18 facets, much shorter antennal scape, low subpetiolar process, and weaker longitudinal striae on head and alitrunk.

Distribution based on Regional Taxon Lists
Palaearctic Region: Japan.

Biology
 workers chew galleries to accommodate diaspidid scale insects on which they rely for food (secretions, flesh or exuviae). Unlike Melissotarsus, Rhopalomastix workers have normal legs and can walk on the trunk of host trees.

Nomenclature

 *  omotoensis. Rhopalomastix omotoensis Terayama, 1996: 27, figs. 60-65 (w.) JAPAN.

Worker
Holotype. HL 0.48mm; HOW 0.43mm; SL 0.20 mm; CL90; SI47; WL0.58mm; LP 0.18 mm; PH0.24mm; DWP 0.15 mm; TL 1.9 mm.

Head slightly longer than wide, with subparallel sides and almost straight posterior margin in frontal view; frons with numerous thin longitudinal striae. Mandibles triangular with small blunt teeth. Anterior margin of clypeus convex medially. Frontal lobes small, connected to each other. Antennae with 10 segments; scape short, 0.5x as long as head width; 2nd to 9th segments each wider than long; 9th segment 0.47x as long as wide; terminal segment 2.0x as long as wide, and as long as the preceding 7 segments combined. Eyes small, 0.09 mm in length, each consisting of about 18 facets.

Alitrunk with almost straight dorsal margin in lateral view; dorsum with very weakly convex anterior margin and almost parallel sides in dorsal view, surface with numerous fine longitudinal striae; lateral faces weakly microreticulate and subopaque; metanotal groove absent; posterodorsal corner of propodeum rounded, not fornting a distinct angle. Petiole high and short, 1.33 x as long as high; node trapezoidal with broadly convex dorsal margin in lateral view; subpetiolar precess low, with an anterior angle. Postpetiole 0.6 x as long as high in lateral view; whole posterior margin connected to the 1st gastral segment.

Gaster smooth and subopaque. Legs short; trochanters and tibiae incrassate as in Figs. 64 and 65.

Body yellowish brown; antennae, legs and tip of gaster yellow.

Type Material
Holotype. Worker, Mt. Omoto-dake, Ishigaki-ima, Okinawa Pref., 28.VII.1977, H. Takamine leg. Paratype. 1 worker, same data as holotype (mounted on a slide).

References based on Global Ant Biodiversity Informatics

 * Guénard B., and R. R. Dunn. 2012. A checklist of the ants of China. Zootaxa 3558: 1-77.
 * Terayama M. 1996. Taxonomic studies on the Japanese Formicidae, part 2. Seven genera of Ponerinae, Cerapachyinae and Myrmicinae. Nature & Human Activities 1: 9-32.
 * Terayama M. 2009. A synopsis of the family Formicidae of Taiwan (Insecta: Hymenoptera). Research Bulletin of Kanto Gakuen University. Liberal Arts 17:81-266.
 * Terayama M., S. Kubota, and K. Eguchi. 2014. Encyclopedia of Japanese ants. Asakura Shoten: Tokyo, 278 pp.
 * Terayama Mamoru. 2009. A synopsis of the family Formicidae of Taiwan (Insecta, Hymenoptera). The Research Bulletin of Kanto Gakuen University 17: 81-266.
 * Terayama, M. 2009. A synopsis of the family Formicidae of Taiwan (Insecta; Hymenoptera). The Research Bulletin of Kanto Gakuen University 17: 81-266.
 * Yamane S., S. Ikudome, and M. Terayama. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp, 138-317.
 * Yamane S.; Ikudome, S.; Terayama, M. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp138-317.