Rhopalomastix omotoensis

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Rhopalomastix omotoensis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Rhopalomastix
Species: R. omotoensis
Binomial name
Rhopalomastix omotoensis
Terayama, 1996

Rhopalomastix omotoensis F63-65.jpg

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under the bark of living trees in Okinawa, living together with large numbers of diaspidid scale insects (C. Peeters unpublished).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).

Cut-away bark of host tree Castanopsis sieboldii showing the tunnels chewed by R. omotoensis workers. From Okinawa, Japan. Photo by Christian Peeters.
Naked diaspidids inside tunnels of R. omotoensis. From Okinawa, Japan. Photo by Christian Peeters.

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

Distribution based on Regional Taxon Lists

Palaearctic Region: Japan (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Rhopalomastix omotoensis 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.

Bark has been cut away (top) to reveal tunnels chewed by Rhopalomastix ants. Host trees Castanopsis sieboldii are common on Okinawa island. Photo by Christian Peeters.
Ant-associated diaspidids do not build protective shields. Photo by Christian Peeters.

Castes

Dealate queen of Rhopalomastix omotoensis. From Okinawa, Japan. Photo by Christian Peeters.


Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

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

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

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