Tetramorium melleum species group

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Based on Agavekar et al. 2017.

Diagnosis

Twelve-segmented antennae; head shape conspicuously cordate, narrowing anteriorly and broadening posteriorly with strongly concave posterior head margin; anteromedian margin of clypeus arcuate to triangular and conspicuously projecting over mandibles; eyes of moderate size; antennal scapes moderately long; antennal scrobes absent; frontal carinae very short to literally absent; base of first gastral tergite not concave in dorsal view, without tubercles or teeth on each side; pilosity on dorsal surfaces of body erect with long and fine hairs; sting appendage dentiform.

Notes

Due to the very distinctive head modifications, the species of this group were placed, until very recently, together with their Afrotropical relatives in their own genus: Rhoptromyrmex. However, a recent molecular study of the subfamily Myrmicinae provided evidence that Rhoptromyrmex is nested within Tetramorium and consequently not monophyletic (Ward et al., 2015). In spite of the worker and male castes of this group being very similar among species, the queens display an incredible phenotypical variation. This morphological variability is related to divergent lifestyles since it is known that the members of this group demonstrate various stages of social parasitism, ranging from autoparasites through temporary social parasites to workerless inquilines (Bolton, 1976, 1986; Brown, 1964).

At present, only two valid species are known from the region, of which one is found in India. However, on the basis of morphological examinations of material from throughout the whole Indomalayan region, one can observe an astonishing intraspecific variation within Tetramorium wroughtonii, and it is very likely that this species is actually a complex of at least 10 more or less cryptic species.

Additional Resources

References