Megastigmus strobilobius Ratzeburg, 1848

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 : 206-210

Megastigmus strobilobius Ratzeburg

(figures 28, 44, 65, 83, 103, 121, 141, 159)

Megastigmus strobilobius Ratzeburg, 1848: 182 . X, number unknown, Germany (destroyed probably in World War II according to Graham, 1969).

Megastigmus abietis Seitner, 1916: 309–311 . 1 X and 2 W Syntypes, ‘ Fichtensamen’ , Austria (NMW, [examined]). Synonymy by Escherich 1938: 368.

Female

Body length (without ovipositor) 3.7 mm (erroneously estimated at 4.0 mm in the original description; Seitner, 1916). Body colour mostly black. Face yellowish brown connected to a circumorbital yellow band extending to the occipital area, remainder of head black. Pilosity pale on lower face, black on remainder of head. Antenna light brown. Pronotum black with a bright yellow cross-band in front of hind margin, the band being very narrowly interrupted in the middle, remainder of thoracic dorsum black. Lateral panel of pronotum, prepectus and tegula yellow; mesopleuron dark brown, metapleuron black. Pilosity black on thoracic dorsum. Fore coxa brownish yellow at the base, mid- and hind coxa black; remainder of legs yellow. Wings subhyaline, the basal cell of forewing with 12 hairs on the disc. Propodeum entirely black. Dorsum and antero-lateral parts of gaster black, lateroventral parts yellowish brown. Ovipositor sheaths dark brown.

Head 1.4× as broad as long in dorsal view. Antennal scape elongate, as long as combined length of pedicel, anellus and two first funicular segment; pedicel large, 1.1× longer than first funicular segment; second funicular segment and following segments sub-quadrate (figure 28). Pronotum and mesoscutum with coarse crossstriae, very arcuate near the posterior margin of the mid-lobe of mesoscutum. Scutellum 1.2× as long as broad, the anterior part with coarse cross-striation, the frenal area smooth with only a few short carinae expanding from the frenal line (figure 141). Forewing stigma ovale-elongate, about 1.8× as long as wide; upper part of stigmal vein elongate, about as long as stigma width; uncus 0.6× as long as upper part of stigmal vein (figure 65). Propodeum with a median carina. Ovipositor sheaths 0.9× as long as body, 1.1× as long as gaster and thorax combined. Distal part of dorsal valve of ovipositor with a large third median tooth (figure 103).

Male

Body length 3.2 and 3.7 mm (estimated at 3.75–4.0 mm in the original description; Seitner, 1916). Body colour black and yellow. Head mostly yellowish brown except occiput and ocellar area black. Pilosity pale on lower face, black on remainder of head. Scape brown, yellowish beneath; remainder of antenna light brown. Thoracic dorsum black except a bright yellow cross-band on posterior part of pronotum, the band being very narrowly interrupted in the middle, and a brownish, indefinite spot on external side of lateral lobe of mesoscutum. Lateral panel of pronotum, prepectus, lower mesepimeron, lower mesepisternum, tegula and acropleuron yellow. Upper mesepimeron and upper mesepisternum light brown, metapleuron black. Pilosity black on thoracic dorsum. Fore coxa almost entirely yellow except a narrow, indefinite brownish yellow band at the base, mid-coxa yellow, hind coxa black, remainder of legs yellow. Wings subhyaline, the basal cell of forewing with 14 hairs on the disc. Propodeum black except callus light brown. Dorsum and antero-lateral parts of gaster black, latero-ventral and apical parts yellowish brown.

Head about 1.3× as long as broad in dorsal view. Antennal scape elongate, 1.1× as long as pedicel, anellus and first funicular segment combined; second funicular segment and following ones more elongate than in female, about 1.5× as long as wide (figure 44). Pronotum and mesoscutum with coarse cross-striae, very arcuate near the posterior margin of the mid-lobe of mesoscutum. Scutellum 1.2× as long as broad, the anterior part with coarse cross-striation tending to reticulation, the frenal area mostly smooth with short longitudinal carinae forming a limited reticulated area below the frenal line (figure 159). Forewing stigma rounded, about 1.2× as long as wide; upper part of stigmal vein elongate but comparatively smaller than in female, about half as long as stigma width; uncus 0.9× as long as upper part of stigmal vein (figure 83). Propodeum with a median carina. Aedeagus medium-sized, rounded; digitus with four teeth (figure 121).

Variation

The above description corresponds to the type material of M. abietis . In the other examined specimens, body length varied from 2.3 to 3.7 mm in females, from 2.2 to 3.7 mm in males. Female colour was a little variable. The yellow band on pronotum could be continuous, without interruption in the middle ( Boucĕk , 1970b; a few specimens we examined from France). The band could also vary in size (large to tiny) and colour (bright to dirty yellow). In a few male specimens of Poland, the lateral parts of thorax and legs were entirely yellow except hind coxa. In both sexes, the number of hairs on the disc of forewing basal cell varied from 10 to 18 (Boucĕk, 1970b). In both sexes, the median carina on propodeum was often interrupted in the middle .

Sex ratio

Balanced. Seitner (1916) noticed 43.3% of males (161 W:211 X) in Austria whilst this proportion varied from 38 to 66% in the populations observed by Skrzypczyńska and Roques (1987) in France.

Hosts

Develops primarily in seeds of spruces ( Picea spp. , Pinaceae ) native to northern Eurasia, Norway spruce, P. abies (among others, Seitner, 1916; Kapuściński, 1966; Cankov, 1974; Del Favero and Masutti, 1974; Nanu, 1976, 1980; Stadnickii et al., 1978; Roques, 1983; Skrzypczyńska and Roques, 1987) and Siberian spruce, P. obovata (Stadnickii et al., 1978) . The chalcid extensively colonized plantations outside the natural range of these species (Roques, 1983). In addition, it shifted to closely related Asian spruce species planted in French arboreta: the Caucasian P. orientalis (Roques, 1983) , P. asperata and P. montigena from western China, and P. glehnii from the islands of northeastern Asia (Da Ros et al., 1993), the latter species being also attacked by M. ezomatsuanus in its native range (Kamijo, 1962). M. strobilobius was also observed in seeds of the North American Picea pungens planted in Denmark (USNM). Earlier records on Abies spp. (e.g. Sorauer, 1953; Lessmann, 1962; Edomskii, 1965; Gusev, 1984; Wall, 1984; Krístek et al., 1992), Pseudotsuga and Tsuga (Krístek et al., 1992) are likely to represent misidentifications.

Distribution

Western Europe to Lake Baïkal, at least: Austria (Seitner, 1916); Belgium (AR); Bulgaria (Cankov, 1974); former Czechoslovakia (Cĕrmak, 1952; Boucĕk, 1970b; Krístek et al., 1992); Denmark (Hoffmeyer, 1929, 1931b; Jespersen and Lomholdt, 1983; Ochsner, 1998; Jensen and Ochsner, 1999; USNM); Estonia (Luik and Voolma, 1988); Finland (Kangas, 1940; Annila, 1966, 1984); France (Roques, 1983; Trosset and Roques, 1986; Skrzypczyńska and Roques, 1987; Ostermeyer, 1990; Da Ros et al., 1993; AR); Germany (Holste, 1922); Great Britain (Hussey, 1954a; Boucĕk, 1970b); Hungary (Wall, 1984); Italy (Del Favero and Masutti, 1974); Lithuania (Milishaukas, 1976; Saksons, 1976; Dumchius, 1984; AR); Norway (Wiersma, 1978); Poland (Szmidt, 1953; Madziara-Borusiewicz, 1961, 1965; Kapuściński, 1966; Skrzypczyńska, 1982, 1986, 1989a; Skrzypczyńska and Roques, 1987; but rare in the 1990s, Witteczek, 1998); Romania (Tudor et al., 1973; Istrate and Ceianu, 1975; Nanu, 1980; Nanu et al., 1986); Russia: from Arkhangelsk and European part to Altaï Mts, Irkutsk and Tiumen (Nikol’skaya, 1952; Jakovlev, 1961; Edomskii, 1965; Stadnickii, 1971; Golutvina et al., 1972; Voroncov, 1975; Nikol’skaya and Zerova, 1978; Stadnickii et al., 1978 as M. abietis ; Edomskii, 1980; Zerova and Seryogina, 1994); Sweden (Wiersma, 1978); Slovakia (Kelbel, 1997); Ukraine (Padii, 1974; Stadnickii et al., 1978); Yugoslavia: Bosnia (Fitze, 1959).

Comments

In the West Palearctic, seeds of some spruce species (e.g. P. orientalis ) were also infested by an exotic chalcid introduced from North America, M. atedius . Diagnostic characters to separate the two species are given in the chapter concerning M. atedius . Another species, M. ezomatsuanus Hussey and Kamijo , was recognized in the Far East and its western limit is not precisely known. We examined specimens from northeastern China (1 X from Picea koraiensis Nakai, Moershan , Heilongjiang, 4 June 1993, AR) and Japan (1 W from P. jezoensis, Teshio , Hokkaido, 17 May 1956, K. Kamijo leg.; 1 X from P. ghlenii, Teshio , Hokkaido, 27 May 1956, K. Kamijo leg.). Females of M. ezomatsuanus are distinguished by a smooth frenal area and a comparatively shorter exserted part of ovipositor, which is as long as thorax and gaster combined and only 0.8× as long as body whereas these values reach 1.1 and 0.9 in M. strobilobius , respectively. Males have a more elongate antennal scape, as long as the combined length of the first two funicular segments, according to Kamijo’s observations (1962). Another species from southwestern China, M. likiangensis Roques et Sun , is easily differentiated by the presence of extended yellow patterns on thorax (posterior and lateral margins of pronotum, latero-posterior margin of mid-lobe and outer surface of lateral lobes of mesoscutum, antero-lateral parts of scutellum, and inner angle of axilla, and dorsellum; Roques et al., 1996).

Material examined

Austria: 1 X, 2 W syntypes M. abietis , ex. Picea abies, Seitner (NMW) . Belgium: 6 X, 3 W, ex. P. abies, Gilbuschheck , May 1993, Belgium Forestry Office ( AR); 1 X, 1 W, ex. P. abies , Cote des Forges, May 1993, Belgium Forestry Office ( AR). Denmark: 1 X, ex. P. pungens , 13 May 1974 ( USNM). France: 7 X, 4 W, ex. P. abies, Névache (05), elev. 1550 m, July 1981, ( AR); 4 X, 4 W, ex. P. abies, Amance (54), July 1980 ( AR); 6 X, 5 W, ex. P. abies, Meygal Forest (43), July 1980, ( AR); 2 X, 2 W, ex. P. abies, Les Barres (45), July 1991, R. Ostermeyer ( AR); 1 X, 1 W, ex. P. abies, Malbuisson Forest (25), May 1993, French National Forestry Office ( AR); 2 X, 3 W, ex. P. asperata, Les Barres June 1990 , R. Ostermeyer ( AR); 2 X, 3 W, ex. P. glehnii, Les Barres , June 1991, R. Ostermeyer ( AR); 6 X, 5 W, ex. P. montigena, Les Barres , June 1991, R. Ostermeyer ( AR); 5 X, 4 W, ex. P. obovata, Les Barres , June 1990, R. Ostermeyer ( AR). Lithuania: 2 X, 2 W, ex. P. abies , Kaunas, 27 May 1982; 6 X, 6 W, ex. P. abies , Kaunas, May 1993, O. Dumchius ( AR). Poland: 1 W ex. P. abies, Powroźnik Forest , 7 March 1980 (laboratory conditions) ( MS); 15 X, 5 W, ex. P. abies, Beskid Sąndecki Mts , June 1987 ( MS); 1 W, ex. P. abies, Wisła, Beskid Sląski Mts , April 1997 (cone coll. October 1995), M. Kozioł ( MS).