Tetramorium bessonii, Forel, 1891

Garcia, Francisco Hita & Fisher, Brian L., 2012, The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region — taxonomy of the T. bessonii, T. bonibony, T. dysalum, T. marginatum, T. tsingy, and T. weitzeckeri species groups, Zootaxa 3365, pp. 1-123 : 9-12

Tetramorium bessonii species group

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 welldeveloped 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.

Comments

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.

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, in which all species possess appressed pubescence of varying length.

This species group is based on T. bessonii , which was the only known representative of the group prior to this study, and contains four newly described species, plus one now raised to species status. 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 .

Key to the species of the T. bessonii group (workers)

1. Petiolar node strongly anteroposteriorly compressed, in profile squamiform, anterodorsal margin situated higher than posterodorsal, dorsum tapering backwards posteriorly and comparatively weakly developed, node in dorsal view strongly transverse (LPeI 26–39; DPeI 209–333) ( Fig. 1 )...................................................................... 2

- Petiolar node not strongly anteroposteriorly compressed, in profile high nodiform with well-developed dorsum and approximately parallel anterior and posterior faces, node in dorsal view wider than long but less transverse than above (LPeI 51–63; DPeI 133–165) ( Fig. 2 )................................................................................. 4

2. Cephalic dorsum between frontal carinae with just one strongly developed longitudinal median ruga that diverges at eye level into two rugae leading to posterior clypeal margin ( Fig. 3 ).............................................. T. artemis

- Cephalic dorsum between frontal carinae with one strongly developed longitudinal median ruga that diverges at eye level into two rugae leading to posterior clypeal margin and two to five more irregularly developed longitudinal rugae at each side ( Fig. 4 )...... 3

3. Head always distinctly longer than wide (CI 92–96); first gastral tergite with comparatively long appressed to decumbent pubescence ( Fig. 5 )............................................................................ T. bessonii

- Head approximately as long as wide (CI 98–101); first gastral tergite with very short, appressed pubescence ( Fig. 6 ). T. wardi 4. Promesonotal suture well-developed and conspicuous ( Fig. 7 )........................................... T. orientale

- Promesonotal suture not developed ( Fig 8 ).................................................................. 5

5. Antennal scapes comparatively shorter (SI 71–74); first gastral tergite with very short and strongly appressed pubescence, never with long, standing hairs ( Fig. 9 )............................................................ T. malagasy

- Antennal scapes comparatively longer (SI 76–78); first gastral tergite with comparatively long, dense appressed pubescence, and generally with several long, standing hairs ( Fig. 10 )........................................... T. ryanphelanae

Figures

FIGURES 1 & 2. 1. Waist segments of T. artemis in profile showing the strongly anteroposteriorly compressed and squamiform petiolar node, which tapers distinctly backwards posteriorly—CASENT0481732 (Erin Prado 2010). 2. Waist segments of T. malagasy in profile showing the high rounded nodiform petiolar node with anterodorsal and posterodorsal margins at about the same height—CASENT0449550 (Erin Prado 2010).

FIGURES 3 & 4. 3. Head of T. artemis in full-face view with one strongly developed median ruga between the frontal carinae—CASENT0481732 (Erin Prado 2010). 4. Head of T. bessonii in full-face view with strongly developed longitudinal median ruga and two to five more irregularly developed longitudinal rugae at each side—CASENT0247550 (Estella Ortega 2012).

FIGURES 5 & 6. 5. Head of T. bessonii in full-face view, head shape distinctly longer than wide—CASENT0101298 (April Nobile 2006). 6. Head of T. wardi in full-face view, head shape approximately as long as wide—CASENT0475483 (Erin Prado 2010).

FIGURES 7 & 8. 7. Mesosoma of T. orientale in dorsal view showing the well-developed and conspicuous promesonotal suture—CASENT0101744 (April Nobile 2006). 8. Mesosoma of T. malagasy in dorsal view without a promesonotal suture— CASENT0449550 (Erin Prado 2010).

FIGURES 9 & 10. 9. Gaster of T. malagasy in lateral view with only very short and strongly appressed pubescence on the first gastral tergite—CASENT0449550 (Erin Prado 2010). 10. Gaster of T. ryanphelanae in lateral view, first gastral tergite with comparatively long, dense appressed pubescence, and generally with several long, standing hairs—CASENT0454495 (Erin Prado 2010).