Stenamma petiolatum

Identification
Rigato (2011) - An easily recognizable taxon because of its large size, slender body and appendages, and presence of standing hairs on legs and scapes in addition to the usual pubescence.

Distribution
Rigato (2011) - A very rarely collected species, whose occurrence has been ascertained for only a few scattered Italian localities. Records from Switzerland must be referred to Stenamma zanoni. Maltese (Schembri & Collingwood, 1981), Spanish (Martínez & Acosta, 1985) and Corsican (Casevitz-Weulersse, 1990) records await confirmation.

Distribution based on Regional Taxon Lists
Palaearctic Region: Italy, Malta, Slovenia.

Castes
The male caste was described by Kutter (1971) but this material was subsequently assigned to Stenamma zanoni (Rigato 2011). The male caste is currently unknown.

Nomenclature

 *  petiolatum. Stenamma petiolatum Emery, 1897a: 12, fig. (q.) ITALY. Emery, 1915a: 256 (w.); Kutter, 1971: 264 (m.). See also: Emery, 1916b: 128; DuBois, 1998b: 250; Rigato, 2011: 10.

Rigato (2011) - In my opinion the only genuine specimen of petiolatum that DuBois (1998) examined was the holotype gyne (which he labeled as “Lectotype”, despite the fact that Emery (1897) had based his description on a single specimen); all other specimens he referred to S. petiolatum were misidentified. As can be seen from DuBois’ descriptions of worker and gyne, there is at least one striking difference between the holotype and all the other material: he reported all workers and 2 gynes having SI < 100, and stated that the scape was: “almost reaching but not surpassing occipital vertex”. However, the holotype gyne was reported with a SI = 109 (110 in my measurements) and “scape surpassing occipital vertex by an amount slightly greater than the length of first funicular segment”. On the basis of the few specimens I examined the worker and gyne are very similar, as is usual in Stenamma. Therefore, I would expect any genuine S. petiolatum female to have SI distinctly > 100 and with the scape surpassing the posterior margin of the head. DuBois also stated that Corsican workers looked different from those from Mt. Argentario, Italy. He borrowed the latter and two gynes (the only ones available, except for the holotype) from the Museum of Comparative Zoology (Harvard University, USA), but these specimens are reported as having a locality label identical to that of a series of S. debile in MSNM collection. These specimens were originally studied and determined by Finzi (1924), who presumably did not see any genuine S. petiolatum specimens, but merely inferred that it was a common species on Mt. Argentario, because Emery (1915) described petiolatum worker from that locality. I also tried to see the Corsican specimens mentioned in DuBois’ paper. However, Xavier Espadaler, their owner, had lent the specimens to another specialist and could not retrieve them in time for this study.

Kutter (1971) and Della Santa (1988) reported S. petiolatum from the Swiss locality of “Canton Ticino”, a southern region of Switzerland bordering on North Italy. Della Santa (1988) assigned a single worker to S. petiolatum, whose diagnostic features are quite different from what I would expect for petiolatum. I borrowed this worker and realized that it was indistinguishable from my new species Stenamma zanoni. Kutter (1971) described an isolated male he assigned to petiolatum; but I am reasonably certain it also belongs to S. zanoni. In fact, Kutter’s male comes from San Nazzaro, on the Swiss shores of Lake Maggiore, which is very close to the “small island” of Brissago, where Della Santa’s worker originated. Consequently, I am confident that it is a male of S. zanoni. S. petiolatum and S. zanoni are quite different, but share characters of relatively large size and the presence of some raised setae on scapes and tibiae. The occurrence of this feature in Kutter’s male, as well as other distinctive characters different from those of other Stenamma males, led Kutter to assign his specimen to S. petiolatum.

Martinez & Acosta (1985) reported S. petiolatum from several Spanish localities, without any comment about either morphology or taxonomy. DuBois overlooked this paper and I was unable to see any Spanish specimen. Xavier Espadaler (pers. comm.) has not see any Spanish specimen certainly referable to petiolatum and he is strongly uncertain about the reliability of the authors’ identifi cations because Stenamma was poorly known at that time.

Finally, because of lack of reliable data, at present I consider S. petiolatum as a rarely collected Italian endemic.

Worker
Rigato (2011) - TL 4.8–5.0; HL 1.03–1.10; HW 0.85–0.91; CI 83; SL 0.93–0.98; SI 108–109;  PCI 31–33; PnW 0.60–0.67; AL 1.32–1.43; PSI 1.72–2.00; PeL 0.52–0.55; PPL 0.31–0.33; PeH 0.25; PPH 0.24–0.25; PeW 0.19–0.20; PPW 0.27; PI1 57–60; PI2 60–64; MTL 0.82–0.89; TI 96–98 (3 measured).

Mandibles with 9-10 teeth and denticles. Eye with about 10 ommatidia. Scape long, slightly but distinctly surpassing the posterior margin of the head when laid back. Mesosoma, waist and legs slender. Sculpture mostly reticulate-rugose; a longitudinal pattern is present chiefly on the head and waist, Mesosoma, especially dorsally, areolate and with a trace of median carina on the pronotum. Propodeal spines moderately long and apically narrowly blunt. Pilosity mostly as in other European species; but scapes and tibiae also bear some scattered suberect hairs. Colour ferrugineous.

Queen
Rigato (2011) - Holotype. TL 5.4; HL 1.08; HW 0.88; CI 81; SL 0.97; SI 110; PCI 35; AL 1.58; PSI 2.00; ScW 0.76; MnL 1.15; PeL 0.59; PPL 0.36; PeH 0.27; PPH 0.27; PeW 0.20; PPW 0.28; PI1 61; PI2 67; MTL 0.93; TI 106.

TL 5.7; HL 1.08; HW 0.93; CI 86; SL 1.00; SI 108; PCI 36; ScW 0.79; MnL 1.16; AL 1.57; PSI 1.76; PeL 0.59; PPL 0.35; PI1 59; PI2 63; PeH 0.27; PPH 0.27; PeW 0.22; PPW 0.29; MTL 0.93; TI 100 (1 measured).

Main features as in worker except for the usual caste differences.

Type Material
Rigato (2011) - Holotype gyne, ITALY: LAZIO, Isola del Liri, 1896 (Y. Emery) [examined].

[N.B. the handwritten label of the holotype reads: Isoladel Liri 1896 Y. Emery. Emery (1916) reports: Campania, Valle del Liri. Since 1927 “Isola del Liri” and “Valle del Liri” belong to the province of Frosinone of the region Lazio and not to Campania.]