Quadrastichus

Fore wing with a single seta on submarginal vein. Postmarginal vein short: usually, less than 1/3 the length of the stigmal vein (STV).
Female funicle 3- and male 4-segmented. Antenna of female with 1 to 3 anelli, the first transverse, the second and third, when present, laminar. Male antenna with 1 or 2 anelli, with scape not swollen and with short to very long ventral plaque, and usually with basal whorls of very long setae present on all the funicular segments. All funicular segments, especially in female antenna, are distinctly longer than wide. Club 3-segmented in both sexes.
Fronto-facial suture near anterior ocellus. Malar sulcus straight and sometimes with fovea below eye, although species living on leafminers usually have a distinctly curved malar sulcus without fovea.
Notauli complete. Midlobe of mesoscutum usually with a single adnotaular seta on each side, placed in posterior half, and with or without median groove. Scutellum with two pairs of longitudinal lines and two pairs of setae. Propodeum without Y-shaped paraspicular carina; propodeal spiracles small to moderate-sized, close or fairly close to metanotum, with their rim exposed. Median carina on propodeum present or absent.
Petiole not distinct. Ovipositor sheaths not or only slightly projecting beyond last tergite of gaster; cercal setae usually unequal in length, with one being distinctly longer than the others.
Colour of the body metallic or non metallic, with or without pale markings; the leafminers parasitoid species, belonging to the “anysis group”, are mainly yellowish.

Species of this genus are known from all continents (Noyes, 2001).

Quadrastichus belongs to the subfamily of Tetrastichinae by having female funicle 3 and male 4-segmented, notauli complete, ventral plaque on male scape and postmarginal vein reduced.
This genus was treated under the name Cecidotetrastichus Kostjukov (Kostjukov, 1977; Graham, 1987), but Boucek (1988: 677) remarked on the similarity between Quadrastichus and Cecidotetrastichus and Graham and La Salle (1991) placed Cecidotetrastichus in synonymy with Quadrastichus.
Quadrastichus is very close to Aprostocetus, Citrostichus Boucek, Mischotetrastichus, Oomyzus Rondani and Tetrastichus Haliday. It may be quite easily distinguished from Aprostocetus by having 1 single dorsal seta on submarginal vein, while Aprostocetus has usually at least 2 setae. However, Citrostichus, Mischotetrastichus and Tetrastichus have 1 single dorsal seta on sumarginal vein as well: Quadrastichus, as Citrostichus, could be distinguished from Tetrastichus by not having Y-shaped paraspicular carina, and from Citrostichus and Mischotetrastichus by not having a distinct petiole. Finally, Oomyzus is very similar to Quadrastichus as well. However, Oomyzus can be recognized by following characters: funicular segments not longer than wide, first female funicular segment often shorter than pedicel and midlobe of mesoscutum with 2-5 adnotaular setae (Graham, 1987; 1991; La Salle, 1994; Schauff et al., 1998).
Keys to Quadrastichus are available only for the European species (Graham, 1991).
Species which might be considered potential biological control agents of agromyzid leafminers were discussed by Hansson & La Salle (1996) and Reina & La Salle (in press).

Diagnosis

Distribution

Biology