Tetramorium bessonii

Tetramorium bessonii is a fairly common species in many arid environments in Madagascar. It can be found in the southeastern and southwestern portions of the island, though it seems completely absent from the southern tip. From these southern localities northwards it is also commonly encountered on the High Plateau, especially in the area around Antananarivo and Moramanga. In the northern part of Madagascar, however, T. bessonii seems to be comparatively rare since it is only known from few localities. It was mostly sampled from anthropogenically modified and grassland habitats followed by spiny forests, thickets, and tropical dry forests, while it was only seldom found in montane or littoral rainforests. The preferred foraging microhabitat is very likely the ground and lower vegetation, and nests are constructed directly in the ground or under rocks. (Hita Garcia and Fisher 2012)

Identification
A member of the Tetramorium bessonii-species group / Key to Tetramorium bessonii-group species

Hita Garcia and Fisher (2012) - Tetramorium bessonii can be easily distinguished from other species of the group by the following character set: head distinctly longer than wide (CI 92 - 96); petiolar node squamiform and strongly anteroposteriorly compressed with anterodorsal margin situated higher than posterodorsal margin, dorsum tapering backwards posteriorly, in dorsal view strongly transverse (DPeI 209 - 270).

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  bessonii. Tetramorium (Xiphomyrmex) bessonii Forel, 1891b: 156, pl. 4, fig. 13 (w.) MADAGASCAR. Combination in Xiphomyrmex: Wheeler, W.M. 1922a: 1031; in Tetramorium: Bolton, 1979: 141. See also: Hita Garcia & Fisher, 2012a: 15

Worker
Hita Garcia and Fisher (2012) - HL 0.61 - 0.88 (0.81); HW 0.58 - 0.83 (0.76); SL 0.44 - 0.62 (0.58); EL 0.14 - 0.19 (0.17); PH 0.38 - 0.49 (0.45); PW 0.47 - 0.63 (0.58); WL 0.83 - 1.11 (1.03); PSL 0.17 - 0.26 (0.23); PTL 0.10 - 0.14 (0.12); PTH 0.29 - 0.38 (0.34); PTW 0.23 - 0.30 (0.27); PPL 0.21 - 0.29 (0.26); PPH 0.27 - 0.37 (0.32); PPW 0.27 - 0.38 (0.35); CI 92 - 96 (94); SI 73 - 78 (76); OI 21 - 23 (23); LMI 54 - 60 (57); DMI 54 - 60 (57); PSLI 27 - 30 (28); PeNI 42 - 50 (47); LPeI 29 - 39 (34); DPeI 209 - 270 (237); PpNI 57 - 64 (60); LPpI 77 - 84 (80); DPpI 123 - 146 (135); PPI 117 - 135 (127) (15 measured).

Head distinctly longer than wide (CI 92 - 96). Anterior clypeal margin with distinct median impression. Frontal carinae well-developed, ending shortly before posterior head margin. Antennal scrobes faint and weakly developed, posterior and ventral margins never differentiated. Antennal scapes relatively short, not reaching posterior head margin (SI 73 - 78). Eyes small to moderate (OI 21 - 23). Mesosomal outline in profile convex, dorsally transversely rounded, weakly to moderately marginate from lateral to dorsal mesosoma, promesonotal suture generally absent, sometimes present but shallow, metanotal groove weakly developed to absent; mesosoma comparatively stout and high (LMI 54 - 60). Propodeal spines elongate-triangular to spinose, long, and acute (PSLI 27 - 30); propodeal lobes very small and broadly triangular. Petiolar node strongly squamiform and anteroposteriorly compressed, anterior and posterior faces not parallel, anterodorsal margin higher situated and better developed than weaker posterodorsal margin, dorsum tapering backwards posteriorly; node in dorsal view transverse, between 2.1 to 2.7 times wider than long (DPeI 209 - 270), in lateral view more than 2.5 times higher than long (LPeI 29 - 39). Postpetiole in profile rounded and weakly anteroposteriorly compressed, approximately 1.2 to 1.3 times higher than long (LPpI 77 - 84), in dorsal view approximately 1.3 to 1.4 times wider than long (DPpI 123 - 146). Postpetiole in profile more voluminous than petiolar node, in dorsal view approximately 1.2 to 1.3 times wider than petiolar node (PPI 117 - 135). Mandibles generally striate, sometimes weakly sculptured; clypeus always with strong median longitudinal ruga and one or two weaker rugae at each side; cephalic dorsum between frontal carinae with one well-developed longitudinal median ruga and several irregular longitudinal rugae laterally, median ruga diverging approximately at eye level into two rugae running to posterior clypeal margin, rugae fading out shortly before posterior head margin, median ruga of same length as frontal carinae; scrobal area, lateral and ventral head mostly with irregular longitudinal rugulae. Head with faint punctate ground sculpture. Mesosomal dorsum generally unsculptured, rarely with faint traces of rugulae anteriorly, lateral mesosoma anteriorly almost unsculptured, posteriorly irregularly, longitudinally rugulose. Waist segments and gaster unsculptured and smooth. Mesosoma, waist segments, and first gastral tergite moderately shining due to faint punctate or foveolate ground sculpture. All dorsal surfaces of body generally with numerous fine, long, decumbent to erect hairs, and comparatively long appressed to subdecumbent pubescence. Colouration mostly of uniform brownish colour, sometimes gaster darker, often head, legs, and gaster much darker brown than mesosoma and waist segments.

Type Material
Syntype workers, MADAGASCAR, Fianarantsoa, Pays des Betsileo (Besson) (: CASENT0102347; : CASENT 0101277, CASENT0101278, CASENT0101297, CASENT0101298; : CASENT0101145) [examined].