Ciao Roberto, da una breve indagine che ho appena concluso, credo non dovrebbe essere difficile determinare questa specie (o queste specie, se sono schiusi due Torymus diversi fra loro, come mi pare di intuire).
Il campo sembra ristretto a due sole possibilità (almeno secondo i dati già noti): Torymus flavipes Walker 1833, che è, a quanto pare, la prima specie di parassitoide di questo genere rinvenuta in Italia fra il 2002 ed il 2004 e Torymus erucarum (Schrank 1781), citato in un recentissimo lavoro (ottobre 2009) per la prima volta, dell'Italia centrale.*
Ho trovato sul web la descrizione in inglese di entrambe le specie, che qui di seguito ti riporto:
Torymus flavipes Walker 1833
The female wasp measures 1.7-3.3mm which averages out at 2.5mm excluding the ovipositor.
The head is coriaceous, metallic green with red/brown tints. The eyes are large and bright red, however the ocelli are almost colourless. The antennae are dark brown with a yellow marked scape and pale sensillae running along the segments. There is one ring and 7 funicular segments which have a slight taper to the continuous club.
The Thorax is metallic gold green and bronze with the notaulices nearly full length. The tegulae are straw coloured which lead on to the wings which are clear and hairy, with pale brown hairs. The veins are yellow brown and although the stigmal vein is only short the stigma and uncus are both well formed. The legs have metallic green coxae with only afew long, pale hairs on the top of the rear pair. The rest of the legs are coloured pale yellow with 5 tarsel segments and darker claws.
The gaster (abdomen) is a shiny brilliant metallic gold green with visible segments that are lightly sculptured and punctured. It is thin from above and from the side view appears triangular. The ovipositor sheaths are hairy, dark above and yellow below, and are mid sized to about just over half of the body length.
The male measures in at 1.6-2.9mm with an average of 2.4mm
The head is slightly different from the female being coriaceous, bright metallic green and hairy. The eyes are large and bright red, however the ocelli are almost colourless, as in the females. The antennae are grey brown in colour, with a glossy pedicel and yellow markings on the scape and longitudinal sensillae. There is one ring and 7 funicular segments. Unlike the female the antennae are not tapered.
The thorax is a bright metallic green with some gold or bronze tinges. It is hairy and the notaulices are deep and full length. The tegulae are straw coloured leading to clear wings with grey brown hairs and pale yellow brown veins. The stigmal vein is short but the stigma is sizable. The legs have metallic green coxae with afew long, pale hairs on the top of the rear pair. The rest is yellow with dark brown or metallic markings on the middle of the femora and tibia, with bright yellow joints. There are 5 tarsel segments and darker claws.
The gaster is bright metallic green at the front, changing to bronze in the rear half with some hairs. It is slender from above but appears to be quite full from the side.
The flight times for this wasp are from march through to october.
Torymus erucarum (Schrank 1781)
The female wasp measures in at 1.9-2.5mm, excluding ovipositor, with an average of 2.1mm.
The head is purple bronze, sculpted and with white hairs. The eyes are mid sized red/brown coloured. The antennae are very dark with a touch of metallic green and a hint of gold between the segments. The scape is yellow and brown. There is one ring and 7 funicular segments.
The thorax is metallic purple with white hairs and sculpted. The notaulices are deep and full length. The wings which are clear and have yellowish veins and hairs, with a very short stigmal and post marginal vein. The legs are pale yellow, with dark metallic purple green coxae. There are 5 tasel segments.
The gaster (abdomen) is a dark bronze/brown at the base, followed by a tesaceous yellow band that extends right round the body with a blob of brown at the top. Triangular from the side with a broad pointed top. The ovipositor sheaths are very long (about 138% body length) and dark brown.
The male is 2.7-3.1mm averaging at 2.8mm in length.
The head is purple bronze, sculpted and with white hairs. The eyes are mid sized red/brown coloured. The antennae are dark brown. The scape is yellow and dark brown. There is one ring and 7 funicular segments and the club is yellow and brown.
The thorax is metallic purple with white hairs and sculpted. The notaulices are deep and full length. The wings which are clear and have yellowish veins and hairs, with a very short stigmal and post marginal vein. The legs are pale yellow, with dark metallic purple green coxae. There are 5 tasel segments.
The bronze/brown gaster has a testaceous band runnign around the body but stopping at the top of the sides, which shows as a constriction in the darker colouring.
The flight time for this wasp is august
* Speranza, S., Stacchiotti, M. and Paparatti, B. 2009. ENDEMIC PARASITOIDS OF DRYOCOSMUS KURIPHILUS YASUMATSU (HYMENOPTERA: CINIPIDAE) IN CENTRAL ITALY. Acta Hort. (ISHS) 844:421-424
Abstract:
The presence of chestnut gall wasp was reported for the first time in Northern Italy in 2002 and has subsequently spread rapidly in Central and Southern Italy. Knowing the harmfulness of this wasp for chestnut growing, we considered essential to inquire the cohort of parasitoids of this new insect for the Italian fauna. This research reports on preliminary results obtained in 2007 on the D. kuriphilus parasitoids in Central Italy. In particular, eight parasitoids species have been found: two Euritomidae [Sycophila biguttata (Swederus) Eurytoma brunniventris (Ratzeburg)], one Pteromalidae [Mosopolobus sericeus (Forster)], three Torymidae [Torymus flavipes (Walker), T. erucarum (Schrank), Megastigmus dorsalis (Fabricius)], one Eupelmidae [Eupelmus urozonus (Dalaman)] and one Ormyridae [Ormyrus pomaceus (Geoffroy)]. We report for the first time the presence of the Torymus erucarum as parasitoid of D. kuriphilus.
Da questa pagina, è possibile scaricare (a pagamento) l'articolo.
P.S. - Il Prof. Paparatti (qui la sua scheda personale con e-mail) cita, per il viterbese, una nona specie di parassitoide di D. kuriphilus: Sicophila variegata (Eurytomidae).
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). Siamo in una situazione completamente diversa da altre aree, col castagno ristretto a pochi kmq e fortemente frammisto a bosco con prevalenza di roverella.