Tetramorium mixtum species group

Bolton (1977) defined and included 4 species in this Oriental group. Roncin (2002), describing two new species, abandoned this group and transferred the species to other groups.

Roncin (2002) - Bolton defined this group by the combination of the following characters: 12-segmented antennae; frontal carinae extending back beyond the eyes; eyes of moderate size; and especially the development of a pair of anterolateral tubercles (gastral horns) on the first tergite of the gaster which surround the posterior portion of the postpetiole in dorsal view. This structure is also visible in profile as a tooth protruding forward above the anterodorsal limit of the sternite. This last character that led Bolton to create the mixtum-group, is also shared with the the inglebyi group. But species of this latter group differ by their reduced frontal carinae and eyes, smaller node of petiole, shorter propodeal spines, and are more related to the palaearctic caespitum group. Some African species of the solidum group also exhibit a similar development of the anterior part of the first gastral tergite as figured by Prins (1973) for Tetramorium peringueryi dichroum (presently Tetramorium dichroum) and Tetramorium rutilum (a junior synonym of Tetramorium glabratum). However this group is not related to the Asiatic groups discussed in this paper.

Well-developed gastral horns are one of the defining features of the mixtum-group, as defined by Bolton (1977). There are large specific differences in the degree of development of these structures in the mixtum-group. The most developed tubercles occur in the largest species: Tetramorium rugigaster and Tetramorium mixtum, and the less developed ones, in the smallest species: Tetramorium transversarium and in the two new species described here (Tetramorium kieti and Tetramorium securis). In fact, the state of development of this character in transversarium, kieti and securis is transitional with that observed in species of the tonganum- or of the scabrosum group. Bolton (1977) already stated the close proximity of these latter groups to the mixtum-group. Tetramorium seneb of the tonganum group has indeed the anterolateral parts of its gaster angled/slightly dentate, as clearly as transversarium of the mixtum-group; this character is a little less marked but still present in T. kraepelini of the scabrosum group. The anterolateral gastral margin varies from regularly curved to angled and at the extreme markedly tuberculate in each of these groups, and cannot be used as a supra-specific diagnostic character. We therefore propose to abandon the mixtum-group and to transfer its species into the scabrosum and the tonganum groups, both groups being defined according to Bolton (1977), except for the gaster morphology. Even so, as already stated by this author, the tonganum and scabrosum groups remain weakly defined and are more taxonomically practical groups than monophyletic units.