Megastigmus spermotrophus Wachtl

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 : 202-206

Megastigmus spermotrophus Wachtl

(figures 27, 43, 64, 82, 102, 120, 140, 158)

Megastigmus spermotrophus Wachtl, 1893: 26–28 . 3 X and 1 W syntypes, coll. Mayr (NMW [examined]).

Female

Body length (without ovipositor) 3.3, 3.8 and 4.1 mm. Body colour brownish yellow to orange-yellow. Head brownish yellow, with darker, irregular spots as side of clypeus, on gena and around ocelli. Pilosity pale on lower face, black on remainder of head. Antenna brown except scape yellowish and pedicel and anellus brownish yellow beneath. Thorax mostly brownish yellow, with posterior margin of pronotum lighter, and anterior part of mid-lobe of mesoscutum, outer axilla, and median area of scutellum reddish brown; small black spots present at insertion of wings. Pilosity black on thoracic dorsum. Legs brownish yellow. Propodeum brownish yellow with median area reddish brown. Gaster dark orange-yellow. Ovipositor sheaths black.

Head about 1.5× as broad as long in dorsal view. Antennal scape 1.1× as long as pedicel, anellus and first funicular segment combined; first funicular segment elongate (2× as long as wide), 1.1× longer than the following segments (figure 27). Pronotum distinctly wider than long. Pronotum and mesoscutum with dense cross-striae. Scutellum 1.2× as long as broad, the anterior part reticulate-striate, the frenal area nearly smooth with a limited reticulation just below the frenal line and short, weak longitudinal wrinkles (figure 140). Six pairs of bristles on scutellum. Forewing stigma elongate-oval, 1.9× as long as wide; upper part of stigmal vein comparatively elongate, about 0.9× as long as stigma width; uncus very short, 0.3× as long as upper part of stigmal vein (figure 64). Propodeum with a median carina more pronounced anteriorly. Ovipositor sheaths 0.9× as long as body. Distal part of dorsal valve of ovipositor with blunt teeth, except the terminal one (figure 102).

Male

Body length 3.1 mm. Body colour dark lemon yellow. Head lemon yellow except black spots surrounding ocelli, which are partially coalescent. Pilosity pale on lower face, black on remainder of head. Antenna light brown except scape yellowish and pedicel yellowish beneath. Thorax mostly dark lemon yellow with a few black patterns: a transverse band at anterior margin of pronotum; a bilobed, transverse band at anterior margin of mid-lobe of mesoscutum, a spot on outer axilla, and a band on lateral panel of metanotum. Pilosity on thoracic dorsum black. Legs yellowish. Propodeum entirely black. Gaster with the first two apparent terga black on dorsum; remainder of gaster dirty yellow.

Head about 1.5× as broad as long in dorsal view. Scape as long as pedicel, anellus and first funicular segment combined; first funicular segment elongate, twice as long as wide, 1.2× as long as the following segments (figure 43). Pronotum and mesoscutum with dense cross-striae. Scutellum 1.2× as long as broad, the anterior part reticulate-striate, the frenal area nearly smooth with a limited reticulation just below the frenal line and short, weak longitudinal wrinkles (figure 158). Forewing stigma more oval than that of female, only 1.4× as long as wide, with upper part of stigmal vein less elongate, about 0.6× as long as stigma width; uncus 0.4× as long as upper part of stigmal vein (figure 82). Propodeum with a distinct median carina. Penis medium-sized, conical, sinuated at the apex; digitus with four teeth (figure 120).

Variation

The above description corresponds to the type material. In the other specimens we examined, body length varied from 2.8 to 4.3 mm in females, from 2.7 to 3.8 mm in males. Female colour was a little variable. Most specimens from Europe and New Zealand fitted the type description. However, lighter individuals were observed where body was entirely light orange-yellow (e.g. at Vielsaam, Belgium). Specimens darker than the type were not uncommon. The darkest ones presented reddish brown stripes on sides of pronotum and on anterior margin of lateral lobe of mesoscutum, a black band on anterior margin of propodeum, and the black spots at insertion of wings extended in a black line along sutures of tegula and acropleuron (e.g. in France and Finland). Gaster was deep amber, much darker than thorax in these individuals. The relative length of the exserted part of ovipositor varied from 0.9× to 1.1× the body length .

Male predominant colour varied from lemon-yellow to orange-yellow. In light specimens, the circumocellar spots on head was quite absent, the bilobed band on mid-lobe of mesoscutum reduced to a light brownish, thin stripe extending along the anterior suture, the propodeum was yellow, and the first two apparent terga of gaster showed only narrow brown stripes on dorsum (e.g. specimens from Lavercantière seed orchard, France). In darker specimens, the circumocellar spots were completely coalescent, and a number of black patterns were observed on thorax: a band on anterior margin of pronotum and anterior half of mid-lobe of mesoscutum, a spot on outer axilla and lateral panel of metanotum (e.g. specimens from arboretum of Les Barres, France). The median carina on propodeum could be absent or interrupted.

Sex ratio

Highly variable according to location and year (Milliron, 1949; Hussey, 1955b). Sex ratio was strongly skewed in favour of males in some cases (Roques, 1981).

Hosts

Specific to seeds of Pseudotsuga spp. (Pinaceae) . In the native North American areas, both varieties of Douglas-fir, P. menziesii ( var. glauca [Beissn.] E. Murray and var. menziesii [Mirb.] Franco) are attacked as well as bigcone Douglas-fir, P. macrocarpa (Milliron, 1949; Keen, 1958; Peck, 1963; Grissell, 1979; Hedlin et al., 1980; Niwa and Overhulsen, 1992). Also recorded from P. flahaulti Flous and P. macrolepis Flous in Mexico (Cibrian-Tovar et al., 1995). However, the specimens developing in P. macrocarpa were considered as a distinct subspecies, Megastigmus spermotrophus nigrodorsatus Milliron (Milliron, 1949) .

In the European areas of introduction, records essentially concerned plantations of P. menziesii . In the French arboreta, the typical form of M. spermotrophus was also observed to colonize seeds of several additional exotic species: bigcone Douglasfir, the Japanese P. japonica , and the Mexican P. guinieri and P. rehderi (Ostermeyer, 1990; AR). Earlier records from seeds of Abies spp. (e.g. Hoffmeyer, 1931a; Zacher, 1932; Cĕrmak, 1952; Nikol’skaya, 1952; Lessmann, 1962; Wall, 1984) probably referred to pale specimens of M. rafni and those on Tsuga (e.g. Hoffmeyer, 1931a) to M. tsugae Crosby.

Distribution

Native from western North America, being widespread from British Columbia to California and Mexico (Peck, 1963; Grissell, 1979; Hedlin et al., 1980; Cibrian- Tovar et al., 1995). Introduced with Douglas-fir seeds to New Zealand (Bain, 1977; Commonwealth Institute of Entomology, 1977; Boucĕk, 1988) and Europe. Presently widespread all over Europe, even in Mediterranean countries, being recorded from: Austria (Kapuściński, 1966; AR); Belgium (Jamblinne de Meux and Nanson, 1969; Tombuyses, 1993; AR); former Czechoslovakia (Cĕrmak, 1952; Boucĕk, 1954; Mentberger, 1964; Krístek, 1967, 1968; Krístek et al., 1992); Denmark (Hoffmeyer, 1931b; Jespersen and Lomholdt, 1983; Ochsner, 1998; Jensen and Ochsner, 1999); Estonia (Luik and Voolma, 1988); Finland (Annila, 1982; AR); France (Vayssières, 1931; Roques, 1981, 1983; Rappaport and Roques, 1991; Roques and Raimbault, 1998); Germany (Tubeuf, 1930; Gäbler, 1962; Lessmann, 1974a, 1974b; Sellenschlo, 1984a; Schneider, 1985); Great Britain (Laidlaw, 1931; Hussey, 1954a, 1955); Hungary (Györfii, 1956, 1962); Ireland (Commonwealth Institute of Entomology, 1977), Italy (Sorauer, 1953; Roversi et al., 1993; Da Ros, 1997; AR); Norway (Wall, 1984); The Netherlands (Oudemans, 1933; AR); Poland (Kozikowski, 1949; Madziara, 1955; Kapuściński, 1966; Schnaider, 1970; Szmidt and Banaszak, 1991); Portugal (AR); Romania (Nanu, 1976, 1980; Nanu et al., 1986); Russia (Bekreneva and Tropin, 1975; Nikol’skaya and Zerova, 1978; Stadnickii et al., 1978); Spain (AR); Sweden (Trägårdh, 1917); Switzerland (AR); former Yugoslavia (Boucĕk, 1977).

Comments

No other chalcid species was observed in the seeds of Pseudotsuga spp. in the West Palearctic. M. spermotrophus nigrodorsatus Milliron , identified in the seeds of P. macrocarpa in southern California (Milliron, 1949), was not apparently introduced with the seeds of that species in Europe. According to Milliron (1949), the male differs from that of M. spermotrophus by predominantly black patterns on head dorsum (a quadrilateral spot extending from occipital carina to antennal scrobe) and thorax (a large median spot on pronotum; the mid-lobe of mesoscutum mostly black except a narrow yellow stripe along notuli; an oblique spot on lateral lobe of mesoscutum; the frenal line and a complete median longitudinal line on scutellum). No reliable characters were identified for differentiating females, yet.

Confusion may occur between darker specimens of M. spermotrophus and lighter specimens of a fir seed chalcid, M. rafni . Female can be differentiated by the relative length of the exserted part of ovipositor (1.2× longer than body in M. rafni versus 0.9–1.1× as long as body in M. spermotrophus ) and the shape of forewing stigma (uncus comparatively more elongate in M. rafni ; figures 64, 69). In males of M. spermotrophus , stigma is less rounded (1.4× versus 1.1× as long as wide in M. rafni ) and uncus is much less elongate (figures 79, 82). To separate males, Milliron (1949) also used presumed differences in colour patterns (black coloration never extensive on axilla in darker forms of M. spermotrophus ) but lighter forms of M. rafni may present axilla entirely yellow.

Material examined

Austria: 1 X, ‘seeds from Austria, 1941’ ( MNHN) . Belgium: 6 X, 5 W, ex. Pseudotsuga menziesii, Fenffe , May 1993, F. Tombuyses ( AR) . Finland: 3 X, 2 W, ex. P. menziesii, Kirkkunomi, Båtvik , January 1994 (in laboratory), M. Pulkinnen ( AR) .

France: 35 X, 30 W, ex. P. menziesii, Lavercantière (46), May 1986 ( AR) ; 11 X, 15 W, ex. P. menziesii, Les Barres (45), May 1981 ( AR) ; 4 X, 3 W, ex. P. macrocarpa, Les Barres , May 1981 ( AR) ; 1 X, 2 W, ex. P. guinieri, Les Barres , May 1990, R. Ostermeyer ( AR) ; 3 X, 2 W, ex. P. rehderi, Les Barres , May 1990, R. Ostermeyer ( AR) ; 8 X, 12 W, ex. P. japonica, Angers (49), May 1989 ( AR) . Germany: 11 X, 5 W, ex. P. menziesii, Bergach , May 1993 ( AR) . Italy: 10 X, 9 W, ex. P. menziesii, Amborzasco (Liguria) , May 1993, A. Battisti ( AR) ; 6 X, 5 W, ex. P. menziesii, Vallombrosa (Toscana) , May 1992, A. Battisti ( AR) ; 6 X, 5 W, ex. P. menziesii, Acquerino (Toscana) , May 1992, A. Battisti ( AR) ; 2 X, 3 W, ex. P. menziesii, Etroubles (Aosta) , May 1992, M. Kenis ( AR) ; 10 X, 12 W, ex. P. menziesii, Sila (Calabria) , May 1993, A. Battisti ( AR) ; 1 X, ex. P. menziesii, Paluzza (Friul) , May 1993, A. Battisti ( AR) . The Netherlands: 2 X, 4 W, ex. P. menziesii, Ede , May 1991 ( AR) ; 2 X, 3 W, ex. P. menziesii, Vaals (LI) , May 1991 ( AR) . New Zealand: 3 X, 2 W, ex. P. menziesii, Roturoa , September 1993, N. Kay ( AR) . Poland: 2 X, 2 W, ex. P. menziesii, Beskid Żywiecki, Nadleśnictwo Ujsoły , June 1987 ( MS) . Portugal: 15 X, 13 W, ex. P. menziesii, Amarante , May 2000, ( AR) . Spain: 22 X, 23 W, S. Breixo, Guitiriz , ex. P. menziesii , May 1992, G. Vega ( AR) . Switzerland: 23 X, 15 W, ex. P. menziesii, Birmensdorf (ZU) , May 1993 ( AR) . USA: 12 X, 10 W, ex. P. menziesii , California, 1994, N. Rappaport ( AR) .