Megastigmus brevicaudis Ratzeburg, 1852

Roques, A. & Skrzypczyńska, M., 2003, Seed-infesting chalcids of the genus Megastigmus Dalman, 1820 (Hymenoptera: Torymidae) native and introduced to the West Palearctic region: taxonomy, host specificity and distribution, Journal of Natural History 37 (2), pp. 127-238 : 163-166

Megastigmus brevicaudis Ratzeburg

(figures 16, 53, 92, 129)

Megastigmus brevicaudis Ratzeburg, 1852: 225 . Holotype X, Germany (destroyed probably in World War II; Grissell, 1999).

Neotype X here designated, ex. Sorbus aucuparia , 4 May 1995, Ojców, Poland, M. Skrzypczyńska leg., deposited at NHMK.

Female

Body length (without ovipositor) 1.8 mm. Colour mainly brownish yellow and black. Face brownish yellow, vertex including ocelli and occiput dark brown to black; eye surrounded with yellowish; temple mainly dark brown. Antenna brownish yellow, scape yellowish beneath. Pilosity pale on lower face, dark on remainder of head. Pronotum mainly yellow with dark brown spots on the middle and a dark band on the posterior margin. Remainder of the thorax black, including mesoscutum, scutellum, axilla, metanotum, mesopleuron and metapleuron. Pilosity on thorax pale. Legs brownish yellow except hind coxa black. Wings subhyaline, with a narrow infuscation around the forewing stigma; venation brown. Propodeum black. Gaster dark dorsally dark brown with weakly marked band on the anterior part. Ovipositor sheaths black.

Head about 1.2× as broad as long in dorsal view. Eye hardly protruding. Postocellar distance about 2× as long as ocellocular distance. Relative measurements: eye 11:8, malar space about 5, width of head 20, width of frons 12. Scape much longer (1.2×) than combined length of pedicel, anellus and first funicular segment, but nearly equal (0.9×) to combined length of pedicel, anellus and the first two funicular segments; funicular segments 2–6 progressively becoming wider than long (figure 16). Flagellum about as long as head width. Pronotum 2.3× wider than long. Pronotum and mesoscutum with fine arcuate cross-striae. Scutellum 1.2× as long as broad, the anterior part striate-reticulate, the frenal area smooth with a few short longitudinal carinae extending from the anterior margin (figure 129). Forewing stigma densely hairy; basal cell closed by complete cubital and basal setal lines; marginal vein about half as long as costal cell; postmarginal vein not clearly defined apically but slightly longer than marginal vein; stigma oblong, 1.4× as long as broad; uncus elongate, as long as upper part of stigmal vein, about half as long as stigma length (figure 53). Propodeum irregularly reticulate in the middle, with a more or less distinct median carina in the anterior part. Ovipositor sheaths much smaller (0.3×) than body, about 0.9× as long as gaster. Distal part of dorsal valve of ovipositor with blunt teeth, the second median tooth being a bit larger than others (figure 92).

Male

No specimen observed during the study. Zerova and Seryogina (1994) described it as follows. Body length: 2 mm; thorax brighter than in female, sternum, head and abdomen darker; legs including coxae yellow; stigma wider than in female. The description given by Crosby (1913) refers to another species attacking Sorbus seeds in North America, M. americanus Mill. (Milliron, 1949) .

Variation

Females other than type ranged in length from 1.7 to 2.7 mm. Body colour was stable. Vikberg (1966) noticed that the length of upper part of stigmal vein is highly variable.

Sex ratio

Most studies revealed only females (Vikberg, 1966; AR) but Lessmann (1974b) reared 1 W for 127 X.

Hosts

Seeds of Sorbus spp. and Amelanchier spp. (Rosaceae) : Sorbus aucuparia (Seitner, 1916; Hoffmeyer, 1931a; Laidlaw, 1931; Kapuściński, 1948, 1966; Vikberg, 1966; Lessmann, 1974b; Nikol’skaya and Zerova, 1978; Krístek et al., 1992; Zerova and Seryogina, 1994; Ochsner, 1998; Jensen and Ochsner, 1999; AR), S. aria (Crantz) (AR) , Sorbus sp. (Hoffmeyer, 1931a; Cĕrmak, 1952; Boucĕk, 1954), Amelanchier ovalis (Seitner, 1916; Zacher, 1932), Amelanchier spicata (Vikberg, 1966) and Amelanchier sp. (Hoffmeyer, 1931a) . However, we did not find any chalcid on Amelanchier ovalis although we reared a large number of seeds from the Southern French Alps.

Distribution

Observed in western, central and northern Europe, extending eastwards to Siberia (Komi, Irkustk, Zerova and Seryogina, 1994). Recorded from the Czech Republic (Cĕrmak, 1952; Boucĕk, 1954; Krístek et al., 1992); Denmark (Hoffmeyer, 1931b; Jespersen and Lomholdt, 1983; Ochsner, 1998; Jensen and Ochsner, 1999); Finland (Vikberg, 1966); France (AR); Germany (Milliron, 1949; Lessmann, 1974b); Great Britain (Askew and Shaw, 1979); Poland (Kapuściński, 1948, 1966; MS); Sweden (Lessmann, 1974b); Russia (Kniazheckii, 1949; Nikol’skaya, 1952; Shtakel’berg, 1955; Vikberg, 1966; Nikol’skaya and Zerova, 1978; Zerova and Seryogina, 1994); Ukraine (Zacher, 1932).

Comments

It is the only species infesting seeds of Sorbus and Amelanchier in the West Palearctic.

Material examined

France: 11 X, ex. Sorbus aria, Briançon (05) elev. 1200 m, July 1992 ( AR) ; 18 X, ex. S. aucuparia, Marcillac (12), elev. 400 m, July 1991 ( AR) . Poland: 5 X, ex. S. aucuparia, Las Wolski , 27 July 1972 ( MS) ; 1 X neotype, 3 X, ex. S. aucuparia, Ojców National Park , 4 May 1995 ( MS) .