Stenamma striatulum

Identification
Rigato (2011) - This is the smallest (especially the gyne) West European Stenamma, characterised, in both the female castes and the male, by finer and more longitudinally arranged rugulation on head (especially on frons and vertex) and promesonotum; the integument in females looks also somewhat shinier than in other species. Furthermore, the worker has moderately long propodeal spines (PSI nearly always > 1.6 and sometimes even > 2.00), and both female castes have scapes almost reaching the posterior margin of the head when laid back. The waist appears somewhat stocky and with petiolar sternite straight and postpetiolar sternite shorter than usual. Males have relatively weakly developed mandibles and a peculiar propodeal dorsum sculpturation: strongly finely reticulate-punctate with several transverse rugulae.

A quite distinctive species because of its small size, more regular longitudinal sculpturation, propodeal spines length and waist structure. The workers may be superficially confused with small specimens of Stenamma debile.

After the examination of dozens of S. striatulum workers, I discovered that in profile the short, shallow, somewhat rectangular prominence of the postpetiolar sternite in S. striatulum is about 40% of PPH; whereas the same structure in other species is > 50% of PPH. This feature seems consistent and allows the recognition of S. striatulum female castes at a glance.

Males of S. striatulum are easily recognizable by their combination of strongly sculptured propodeal dorsum and slightly reduced 4-  to 5-toothed mandibles, and by their low SI (< 45) and TI (< 135).

Distribution based on Regional Taxon Lists
Palaearctic Region: Andorra, Croatia, Greece, Iberian Peninsula, Italy, Malta, Russian Federation, Slovenia, Spain, Switzerland, Turkey.

Nomenclature

 *  striatulum. Stenamma westwoodi var. striatulum Emery, 1895c: 300 (footnote) (w.q.) ITALY. Kutter, 1971: 259 (m.). Raised to species: Müller, 1923: 46. Senior synonym of tscherkessicum: Arnol'di, 1975: 1822. See also: Kutter, 1971: 263; Kutter, 1977c: 74; DuBois, 1998b: 259; Rigato, 2011: 13.
 * tscherkessicum. Stenamma westwoodi var. tscherkessicum Arnol'di, 1928b: 214 (q.) RUSSIA. Junior synonym of striatulum: Arnol'di, 1975: 1822.

Worker
Rigato (2011) - TL 2.9–3.4; HL 0.67–0.78; HW 0.57–0.67; CI 83–89; SL 0.53–0.62; SI 89–97; PCI 26–34; PnW 0.38–0.46; AL 0.77–0.97; PSI 1.59–2.00; PeL 0.28–0.35; PPL 0.18–0.21; PeH 0.18–0.22; PPH 0.18–0.23; PeW 0.14–0.17; PPW 0.19–0.23; PI1 57–67; PI2 46–55; MTL 0.43–0.52; TI 73–81 (24 measured).

Queen
Rigato (2011) - TL 3.5–3.8; HL 0.75–0.80; HW 0.65–0.71; CI 85–90; SL 0.59–0.62; SI 86–91; PCI 24–32; AL 1.02–1.11; PSI 1.61–2.08; ScW 0.52–0.56; MnL 0.70–0.79; PeL 0.32–0.37; PPL 0.20–0.23; PeH 0.23–0.25; PPH 0.24–0.25; PeW 0.16–0.19; PPW 0.23–0.27; PI1 58–66; PI2 49–54; MTL 0.50–0.57; TI 77–82 (9 measured).

Male
Rigato (2011) - TL 3.1–3.4; HL 0.55–0.56; HW 0.47–0.48; CI 85–86; SL 0.17–0.20; SI 36–42; AL 1.05–1.12; ScW 0.50–0.54; MnL 0.74–0.77; PeL 0.31–0.34; PPL 0.19–0.20; PeH 0.20–0.21; PPH 0.19–0.20; PeW 0.16–0.17; PPW 0.21–0.23; PI1 59–62; PI2 66–71; MTL 0.60–0.64; TI 128–133 (3 measured).

Type Material
Rigato (2011) - 2 syntype workers and 1 dealate gyne, ITALY: Capodimonte [Naples], 30.iii.[18]72 (C. Emery) [not examined]. 1 syntype alate gyne, ITALY: PIEMONTE “776” [handwritten by Gribodo] (Gribodo) [not examined].