Tetramorium bessonii species group


 * Tetramorium artemis
 * Tetramorium bessonii
 * Tetramorium malagasy
 * Tetramorium orientale
 * Tetramorium ryanphelanae
 * Tetramorium wardi

Key to Tetramorium bessonii-group workers

Based on Hita Garcia and Fisher 2011, 2012

The species of this group are distributed throughout Madagascar but completely absent from the surrounding island systems. All prefer more arid habitats such as grasslands, spiny thicket or woodlands, and dry tropical or gallery forests. However, they can also be found in disturbed montane or littoral rain forest, but only very rarely. Furthermore, all species seem to live and forage on the ground and on low vegetation.

All six species are relatively similar to each other morphologically indicating a close relationship. For convenience they can be separated into three species with a strongly anteroposteriorly compressed petiolar node in which the dorsum tapers backwards posteriorly: T. artemis, T. bessonii, and T. wardi; and the remaining three species with a high nodiform petiolar node with approximately parallel anterior and posterior faces, and a much better developed petiolar dorsum: T. malagasy, T. orientale, and T. ryanphelanae.

The group is well distinguished from others with 11-segmented antennae by the highly reduced sculpture on head, mesosoma, and waist segments, the distinctly rounded mesosoma without any distinct margination between sides and dorsum, the unsculptured waist segments, and a petiolar node that is always much higher and wider than long. The other two species groups with 11-segmented antennae and highly reduced sculpture, the T. marginatum and T. tsingy groups, cannot be mistaken for any member of the T. bessonii group. Both species of the T. tsingy group differ strongly in petiolar node shape since it is nodiform in profile and longer than wide in dorsal view, whereas it is always much wider than long in the T. bessonii group. The species of the T. marginatum group are not likely to be confused with the T. bessonii group since the mesosoma of the latter is only weakly or not marginate between lateral and dorsal mesosoma while the mesosoma of all of the T. marginatum group species is moderately to strongly marginate. Additionally, both groups differ strongly in pilosity. In the T. marginatum group pubescence is rare and not well-developed, and abundant, erect pilosity is typical on mesosoma, waist segments, and the first gastral tergite, whereas standing hairs are more of an exception in the T. bessonii group, which possesses appressed pubescence of varying length in all species.

Diagnosis
Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae well-developed and usually ending between posterior eye margin and posterior head margin; anterior face of mesosoma not well-developed and no distinct anterodorsal angle present; mesosomal profile generally moderately rounded and convex, no distinct margination between lateral and dorsal mesosoma, instead sides of mesosoma smoothly rounding onto dorsum; mesosoma comparatively high (LMI 42 - 49); propodeal spines medium-sized to long, elongate-triangular to spinose; propodeal lobes only weakly developed, broadly triangular but usually very short; petiolar node either squamiform and anteroposteriorly compressed or rounded high nodiform, in profile always much higher than long, in dorsal view distinctly wider than long, anterior and posterior faces either parallel or almost so, anterodorsal angle either better developed than posterodorsal angle and dorsum tapering backwards posteriorly, or both angles at about same height; postpetiole weakly anteroposteriorly compressed and approximately rounded; mandibles generally sculptured; cephalic sculpture often reduced to a large extent; mesosoma usually unsculptured, in one species with superficial weak sculpture; waist segments and gaster unsculptured, smooth, and shiny, sometimes weak to moderate foveolate ground sculpture present on petiole; pilosity on dorsal surfaces of head, mesosoma, and waist segments variable; first gastral tergite either without any standing hairs at all, only with short to relatively long, appressed to decumbent pubescence, or with medium-sized appressed to decumbent pubescence intermixed with relatively few erect hairs; sting appendage spatulate.