Megastigmus specularis Walley, 1932

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 : 198-202

Megastigmus specularis Walley

(figures 26, 42, 63, 81, 101, 119, 139, 157)

Megastigmus specularis Walley, 1932: 187–188 . Holotype X, New Brunswick, Canada (Canadian National Collection, Ottawa [not examined]).

Megastigmus gronblomi Kangas, 1945: 177–180 . Syntypes X and W, Tampere, Finland (Museum Zoologicum Universitatis Helsinki, according to Hussey, 1954 [not examined]). Synonymy by Boucĕk, 1970b: 267.

Female

Body length (without ovipositor) 2.8 mm. Body colour black and tawny yellow. Face, parascrobal area and a circumorbital band interrupted on the middle of inner margin of eye, yellow; remainder of head black. Pilosity pale on lower face, black on remainder of head. Antenna brown except scape and pedicel yellow beneath. Dorsum of thorax mostly black except two transverse, broadly separated yellow spots at posterior margin of pronotum, and a yellow spot on outer surface of lateral lobe of mesoscutum; lateral parts of thorax lighter: lateral panel of pronotum and tegula tawny-yellow; prepectus and upper mesepisternum light brown; acropleuron and mesepimeron dark brown. Pilosity on thoracic dorsum black. Legs mostly brownish yellow except fore legs tawny-yellow and hind coxa black. Propodeum black. Gaster with first apparent tergum entirely black; then terga black on dorsum with the sides yellow; last two terga entirely pale brown. Ovipositor sheaths black.

Head about 1.6× as broad as long in dorsal view. Antennal scape as long as pedicel, anellus and first funicular segment combined; pedicel oval, 0.8× shorter than first funicular segment; first funicular segment 2× as long as wide (figure 26). Pronotum and mesoscutum with coarse cross-striae. Scutellum 1.1× as long as broad, the anterior part weakly reticulate-striate, the frenal area reticulated along the frenal line and the remainder nearly smooth with some shallow areolae (figure 139). Forewing stigma roughly oval, about 1.3× as long as wide; upper part of stigmal vein comparatively elongate, 1.1× as long as stigma width; uncus half as long as upper part of stigmal vein (figure 63). Propodeum without median carina. Ovipositor sheaths 1.9× longer than gaster, 0.9× as long as body. Distal part of dorsal valve of ovipositor with blunt teeth (figure 101).

Male

Body length 2.4 mm. Body colour black and yellow. Head black except face, gena and a circumorbital band yellow. Pilosity pale on lower face, black on remainder of head. Antenna mostly brown; scape except distally above and pedicel beneath, yellow. Dorsum of thorax mostly black except two large, hemispherical spots at posterior margin of pronotum, and outer surface of lateral lobe of mesoscutum yellow. Lateral panel of pronotum, tegula, mesepimeron and mesepisternum yellow; metapleuron with yellowish brown patch on ventral margin. Pilosity dark on thoracic dorsum. Legs yellowish brown except hind coxa brown at base. Propodeum black except callus with yellowish brown patch on ventral margin. Gaster dark brown on dorsum of first apparent tergum, and pale amber at side; dorsum of following terga progressively becoming pale amber at posterior margin, each tergum being separated from the preceding by a narrow, brownish yellow band; last two terga entirely tawny-yellow.

Head 1.4× as broad as long in dorsal view. Antennal scape subequal to combined length of pedicel, anellus and first funicular segment; pedicel ovate, subequal to first funicular segment; distal funicular segments quite subquadrate (figure 42). Pronotum and mesoscutum with coarse cross-striae. Scutellum 1.3× as long as broad, the anterior margin wider than the posterior margin of mid-lobe of mesoscutum. Anterior part of scutellum reticulate-striate, the frenal area reticulated below the frenal line and the remainder nearly smooth with some shallow areolae (figure 157). Stigma broadly oval, 1.2× as long as wide, upper part of stigmal vein 0.8× as long as stigma width; uncus half as long as upper part of stigmal vein (figure 81). Propodeum with a fine irregular median carina on anterior part. Aedeagus large, convex, digitus with three teeth (figure 119; Kangas, 1945).

Variation

The above description summarizes that given by Milliron (1949) for the American type material. In the European specimens, body length varied from 2.2 to 3.8 mm in females, from 2.1 to 3.0 mm in males. Female colour was highly variable. The circumorbital band could be reduced to a yellow spot adjacent to the eye on its posterior margin (type material of M. gronblomi according to Hussey, 1954b). Milliron (1949) and Boucĕk (1970b) noticed a frequent absence of the yellow spots on pronotum. Most of the specimens we examined from France and Finland did not show any yellow colour on thorax except lateral panel of pronotum. Hind coxa could be entirely black. In addition, the gaster colour pattern largely varied in intensity and definition. The carination of propodeum was variable and often consisted of a complete, fine median carina (type material of M. gronblomi ; Hussey, 1954b). In the European specimens we examined, the relative length of the exserted part of ovipositor varied from 0.9× to 1.1× the body length whilst Boucĕk (1970b) considered that piece as usually longer than body.

Males were also variable in colour. In North America , Milliron (1949) observed specimens much darker than the type material, where most of the yellow markings were absent (especially circumorbital band, spots on pronotum, lateral lobe of mesoscutum and axilla), and mesepimeron, mesepisternum and hind coxa entirely black. However , all the European specimens observed by Boucĕk (1970b) presented large yellow spots on pronotum, as it also appeared in our specimens from France and Finland . Propodeum carination could consist of a complete, but fine, irregular median carina (type material of M. gronblomi ; Hussey, 1954b). The carina was double anteriorly in specimens from France .

Sex ratio Apparently balanced in northern Europe (Annila, 1970).

Hosts

In the native North American areas, develops in seeds of eastern firs, Abies balsamea (Peck, 1963; Grissell, 1979; Hedlin et al., 1980) and A. fraseri (Pursh.) Poir. (Hedlin et al., 1980) (Pinaceae) . In Europe, it was similarly recorded from seeds of exotic fir species introduced from North America: A. amabilis (Annila, 1970) , A. balsamea (Annila, 1970; Ochsner and Jensen, 1998), A. concolor (Annila, 1970; Ochsner and Jensen, 1998) and A. lasiocarpa (Annila, 1970) but damage on A. amabilis and A. concolor was lower in Finland than in the native range (Annila, 1970). It also shifted on to the native A. sibirica (Kangas, 1945; Vikberg, 1966; Annila, 1970; Ochsner and Jensen, 1998) and on to several exotic Asian firs of the balsam fir group, which were heavily attacked: A. nephrolepis (Annila, 1970) , A. sachalinensis (Annila, 1970) , A. veitchii (Annila, 1970; Ochsner and Jensen, 1998; AR). Some other Eurasian fir species were infested but only lightly: A. alba (Annila, 1970) , A. bornmülleriana (Ochsner and Jensen, 1998) , A. holophylla Maxim. (Annila, 1970) , A. homolepis (Ochsner and Jensen, 1998) , A. koreana (Annila, 1970; Ochsner and Jensen, 1998), A. nordmanniana (Annila, 1970; Ochsner and Jensen, 1998) and A. pinsapo (Ochsner and Jensen, 1998) . Annila (1970) assumed that fir species with large cones are less susceptible to colonization by M. specularis because of the shortness of its ovipositor.

Distribution

Probably originates from North America (Boucĕk, 1970b), its present range covering eastern Canada and the eastern USA (Peck, 1963; Grissell, 1979; Hedlin et al., 1980). First introduced into northern Europe and extending to western Siberia, it has been recently recorded from western Europe: Denmark (Ochsner, 1998; Ochsner and Jensen, 1998; Jensen and Ochsner, 1999); Finland (Kangas, 1945; Vikberg, 1966; Annila, 1970); France (AR); Russia (Moscow, Siberia; Vikberg, 1966; Boucĕk, 1970b); Sweden (Hansson, 1991).

Comments

To date, six other species of seed chalcids were observed in seeds of firs in the West Palearctic region: M. milleri , M. pinsapinis , M. pinus , M. rafni , M. schimitscheki and M. suspectus . For separating these species, see the chapter concerning M. milleri .

Material examined

Canada: 4 X, 4 W, ex. A. balsamea , Tourville-l’Islet, Québec, 9 March 1983 (in laboratory) ( GM). Finland: 20 X, 20 W, ex. Abies sibirica Tuusula , 10 July 1974, E. Annila ( AR); 2 X, ex. A. veitchii, Bromaru, 1968 , E. Annila ( MNHN). France: 2 X, 2 W, Les Barres (45), ex. A. veitchii, Les Barres (45), June 1990, R. Ostermeyer ( AR).