Tetramorium diomedeum

Very little is known about the biology of of this species other than it is a host for the workerless inquiline  (Sanetra et al., 1999; Seifert, 2018).

Identification
A member of the Tetramorium ferox species complex in the Tetramorium caespitum species group. Csösz and Schulz (2010) - In general the smooth and shiny sculpture separates T. diomedeum gynes from those of Tetramorium ferox and Tetramorium densopilosum. Ventral part of katepisternum is always smooth and shiny in T. diomedeum gynes. These characters can also help to distinguish them from the gynes of T. ferox, where the katepisternum is always finely rugulose or microreticulate. Gynes of T. diomedeum can be confused with those of Tetramorium feroxoides by the feeble sculpture of head and mesosoma. However, gynes and workers of T. feroxoides have long C-haped setae on the ventral surface of head. Those of T. diomedeum have only short setae on the ventral surface of head. The colour can also be a good characteristic for the separation between the gynes of the latter two species: T. diomedeum is light brown or sometimes (though not frequently) yellow. The gynes of T. feroxoides are usually dark brown or black.

Tetramorium diomedeum workers cannot be confused with those of T. ferox or T. densopilosum. The general appearance of the head of T. diomedeum workers are always shiny, and usually smooth at least in part, these body parts of T. ferox or T. densopilosum are rugulose and microreticulate.

In a few cases larger T. diomedeum workers can be confused with those of T. feroxoides by sculpture. However, in the eastern populations (in Turkey where these two species co-occur) sculpture of diomedeum workers is usually very feeble. These characters and the lack of C-shaped setae of T. diomedeum workers (in contrast to those of T. feroxoides) result in clear separation without morphometry.

Workers of T. diomedeum can also be confused with those of T. aegeum on the basis of external characters. The sculpture of these species is similar to each other; head and mesosoma are frequently smooth and shiny. For best separation a discriminant D(4a) function has been provided (see differential diagnosis of T. aegeum).

Along the wide, decisively east–west geographical range, including small islands, workers of T. diomedeum display a rather strong gradient of morphological variation in characters such as body size, colour and sculpture. Body size indicators (CS) of individuals show moderate correlation with longitude (Spearman r = -0.391, p<0.01), i.e. eastern populations are smaller. Average CS values of nest means do not correlate significantly (Spearman r = -0.304, p=0.06).

In the eastern populations workers are paler, body sculpture feebler, and the post-ocular surface of head in particular is smooth and shiny. Smaller workers often bear one pair of standing hairs on genae. This combination of characters is more frequent in the eastern populations and rare in the western ones. Some workers in nest series from Calabria and Syracusa (Italy) also bear this combination of characters, especially in the case of small workers.

A discriminant function using various morphological measurements has also been defined and can be used to make determinations in this species group.

Distribution
Eastern part of the Mediterranean basin: Italy, Croatia, Bulgaria, Turkey and Greece – including the islands of Rhodos and Crete. (Csösz and Schulz 2010)

Distribution based on Regional Taxon Lists
Palaearctic Region: Bulgaria, China, Croatia, Greece, Italy, Malta, Montenegro, Turkey.

Nomenclature

 *  diomedeum. Tetramorium caespitum var. diomedea Emery, 1908d: 24 (w.q.) ITALY. Subspecies of ferox: Grandi, 1935: 102; Baroni Urbani, 1971c: 138. Raised to species: Schembri & Collingwood, 1981: 435; Agosti & Collingwood, 1987a: 56. Junior synonym of ferox: Bernard, 1967: 235; Dlussky, Soyunov & Zabelin, 1990: 201; Radchenko, 1992b: 55. Revived status as species: Sanetra, Güsten & Schulz, 1999: 324. Senior synonym of bariensis: Emery, 1916b: 194; Sanetra, Güsten & Schulz, 1999: 324; of laevior: Csösz & Schulz, 2010: 17.
 * bariensis. Tetramorium caespitum var. bariensis Forel, 1911d: 331 (w.) ITALY. Junior synonym of diomedeum: Emery, 1916b: 194; of ferox: Bernard, 1967: 235. Revived from synonymy and raised to species: Baroni Urbani, 1971c: 134. Junior synonym of ferox: Radchenko, 1992b: 55; of diomedeum: Sanetra, Güsten & Schulz, 1999: 324.
 * laevior. Tetramorium ferox var. laevior Menozzi, 1936d: 292 (w.) TURKEY. [First available use of Tetramorium caespitum subsp. ferox var. laevior Forel, 1911d: 333; unavailable name.] Finzi, 1939c: 157 (m.). Junior synonym of diomedeum: Csösz & Schulz, 2010: 17.

Worker
Csösz and Schulz (2010) - Small to large size, CS 753 [647, 930]. Whole body and appendages yellow to brown. Head slightly longer than broad, CL/CW 1.02 [0.97, 1.08], with feebly convex sides, straight posterior margin with widely rounded corners. Eyes small, or medium sized, EYE 0.165 [0.144, 0.185]. Frons moderately wide, FR/CS 0.38 [0.35, 0.41], frontal lobes usually as wide as the frons, rarely slightly broader, FL/FR 1.0 [1.00, 1.04]. Scape moderately long, SL/CS 0.76 [0.73, 0.79], without a dorsal-basal carina, surface smooth and shiny. Promesonotal dorsum slightly convex, metanotal groove shallow. Propodeal denticles moderately long. Petiolar node trapezoid seen in profile, higher than long NOH/NOL 1.12 [0.96, 1.39].

Head longitudinally rugulose and feebly microreticulate, in eastern populations rarely the head can be shiny, posterior surface reticulate, ground surface very feebly microreticulate, appears shiny. Mesosoma dorsum and mesopleura finely ruguloso-reticulate, ground surface feebly microreticulate, or smooth. Dorsolateral part of petiolar node ruguloso-reticulate, ground surface microreticulate, median part smooth. Dorsum of postpetiole rugulose and microreticulate. First gastral tergite smooth, appears shiny. Ventral surface of head with a row of short setae only (without long C-shape hairs).

Queen
Csösz and Schulz (20101) - Medium size, CS 955 [857, 1012]. Head distinctly broader than long, CL/CW 0.88 [0.85, 0.93], with straight, sub-parallel sides, straight posterior margin with widely rounded corners. Frons wide, FR/CS 0.42 [0.39, 0.46]. Scape short to moderately long, SL/CS 0.72 [0.67, 0.76]. Head as wide as scutum, MW/CS 1.01 [0.92, 1.12]. Propodeal denticles short. Petiole and postpetiole wide, CS/PEW 1.68 [1.53, 2.09], CS/PPW 1.33 [1.24, 1.42].

Whole body and appendages yellow to brown. Frons and genae with very fine longitudinal rugulae, or completely smooth, rest of head smooth. Scutum, scutellum, and anepisternum smooth and shiny, very fine rugulae can occure, ventral part of katepisternum always smooth and shiny. Petiolar node and postpetiole feebly microreticulate, or smooth and shiny. First gastral tergite smooth, appears shiny. Ventral surface of head with a row of short setae only, without long C-shape hairs.

Male
Csösz and Schulz (2010) - Head sides feebly convex, posterior margin widely rounded. Scutum much broader than head. Propodeal denticles reduced, propodeum rounded in profile. Dorsum of petiolar node without a transverse crest, dorsolaterally sharp and angulate. Whole body and appendages brownish black. Head finely rugulo-reticulate, between main sculpturation microreticulate. Scutum, scutellum, anepi- and katepisternum finely rugulose, and smooth in part. Petiole and postpetiole finely rugulo-reticulate, between main sculpturation microreticulate.

Type Material
Csösz and Schulz (2010) - Syntype workers, gynes, males (9w, 6q, 1m): Italy, Tremiti, Caproni (J. Domino Cecioni) [labels: Tremiti, caproni; T. caespitum, ferox, var. diomedea n.] (examined).

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