Tetraponera nigra species group

Based on Ward 2001.

Worker diagnosis

In this group the worker caste is characterised by the following traits. (I) The mandible is short and robust, with the masticatory margin being as long as, or longer than, the basal margin, and bearing four teeth; the basal margin has 0-1 small teeth or denticles. (2) The clypeus is short and lacks a strongly protruding median lobe, its anterior margin being flat or broadly convex. (3) The mesopropodeal impression varies from elongate and open at the sides to short, transverse and pit-shaped; a metanotal plate is always absent. (4) The metabasitarsal sulcus is well developed and usually lies in a conspicuously darkened strip of cuticle, subtended by a low ridge. (5) Except at the edges, the mesosternum is largely smooth and shining and lacks the dense pubescence seen in allaborans-group workers. (6) Abdominal tergite IV usually has a moderate to high density of appressed pubescence, the hairs being separated by their lengths or less (exceptions occur). The known queens of the nigra-group exhibit features (4), (5) and (6), but are more variable with respect to mandible and clypeus shape. In both males and queens, the forewing has two cubital cells, with rare (and apparently aberrant) exceptions. The male genitalia and associated structures (i.e. sternite IX) are distinctive: see description and comparison in the discussion of the allaborans-group. Recent anatomical investigations by Billen and Buschinger (2001) have revealed the existence of a novel gut structure-termed the bacterial pouch-in workers of several Tetraponera species, all members of the nigra-group. This structure is apparently absent in other Tetraponera species and in Pseudomyrmex.

At present the nigra-group contains 20 recognised species and is distributed throughout most of the Indo-Australian region. Several clusters of related species can be identified, based on similarities in the worker and queen castes and features of the male genitalia:

1. difficilis-complex (Tetraponera difficilis, Tetraponera inversinodis)

2. laeviceps-complex (Tetraponera atra, Tetraponera laeviceps, Tetraponera mimula, Tetraponera punctulata, Tetraponera rotula, Tetraponera tucurua)

3. nigra-complex (Tetraponera attenuata, Tetraponera binghami, Tetraponera buops, Tetraponera nigra)

4. nitida-complex (Tetraponera nitida, Tetraponera nixa, Tetraponera nodosa, Tetraponera notabilis)

Left unassigned to these complexes are four taxonomically peculiar and apparently uncommon species, two known primarily from the worker caste (Tetraponera aitkenii, Tetraponera polita) and two based on queens only (Tetraponera vivax and Tetraponera volucris).

Distribution

Indo-Australian

Notes

The nesting habits of most nigra-group species appear to be generalised, with colonies occupying dead twigs or branches of unspecialised plants. But T. tucurua and T. binghami are obligate inhabitants of live plant cavities (domatia) of Cupaniopsis and bamboos, respectively, in which they keep scale insects (Coccoidea) (Ward 1991; Klein et al. 1992). In addition, some individual colonies of T. nigra and T. punctulata have been found occupying live plant cavities (Ward 1991; D. McKey personal communication), so there appears to be a propensity to develop habits along these lines.

Valid Species

Related pages

References

Ward, P. S. 2001. Taxonomy, phylogeny and biogeography of the ant genus Tetraponera (Hymenoptera: Formicidae) in the Oriental and Australian regions. Invertebrate Taxonomy. 15:589-665.