Megastigmus pinus Parffit

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 : 181-185

Megastigmus pinus Parffit

(figures 21, 38, 58, 77, 97, 115, 134, 153)

Megastigmus pinus Parfitt, 1857a: 5543–5544 (and 5629–5630). Holotype X, California, USA (BMNH [examined]).

Megastigmus pinus crosbyi Hoffmeyer, 1931a: 215 . Holotype X, Abies concolor , Colorado, USA (ZMUC [examined]).

Megastigmus pinus marginatus Hoffmeyer, 1931a: 215 . Holotype W, Abies grandis , Oregon, USA (ZMUC [examined]).

Female

Body length (without ovipositor) 5.1 mm. Body colour combining black, yellow and orange. Face yellow with a black spot at side of clypeus extending to antennal base; remainder of the head mostly black, with a more or less discontinuous yellow ring around eye. Pilosity pale on lower face, black on remainder of head. Antenna mostly dark brown to black; scape yellow beneath; pedicel and anellus partly brownish yellow beneath. Thoracic dorsum mostly black except a trilobed, orange-yellow transverse band on the posterior margin of pronotum, and a large orange-reddish patch covering posterior margin of mid-lobe of mesoscutum, inner angles of both lateral lobe of mesoscutum and axilla, and scutellum; lateral parts of thorax black except lateral panel of pronotum, a spot on prepectus and tegula orange-yellow. Pilosity on thoracic dorsum pale, even on yellow maculae. Fore and mid-coxa black basally, the latter also on outer surface, hind coxa entirely black; fore femur yellow, mid-femur yellow with limited basal infuscation, hind femur with black patch on anterior and ventral surface; tarsi brownish yellow. Propodeum black. First apparent tergum of gaster black; second tergum with dorsum anteriorly black, posteriorly brownish, and with lateral parts alternating black and yellow spots; yellow colour progressively becoming predominant on the following terga. Ovipositor sheaths black.

Head about 1.5× as broad as long in dorsal view. Scape as long as pedicel, anellus and first funicular segment combined; pedicel oval, 0.9× as long as first funicular segment; first funicular segment twice as long as wide, the rest of funicular segments progressively decreasing in length (figure 21). Pronotum and mesoscutum coarsely cross-striated. Scutellum 1.3× as long as broad, the anterior part with dense cross-striae, the frenal area deeply wrinkled (figure 134). Forewing stigma nearly circular, only 1.1 as long as broad, with a comparatively elongate upper part of stigmal vein, about 0.6× as long as stigma length; uncus short, 0.4× as long as upper part of stigmal vein (figure 58). Propodeum with a more or less distinct median carina (figure 134). Ovipositor sheaths 2.1× longer than gaster, little longer (1.1×) than body. Distal part of the dorsal valve of ovipositor with small teeth, but the second median tooth larger than the others (figure 97).

Male

Body length 4.4 mm. Body colour combining black and yellow. Face yellow, dorsum of head black with a yellow spot extending along outer margin of eye to gena. Pilosity pale on lower face. Thoracic dorsum black except two lateral, irregular spots on posterior margin of pronotum and dorsellum yellow; lateral parts of thorax mostly black except lateral panel of pronotum, tegula, a spot at base of wing. Pilosity on thoracic dorsum mostly pale. Legs mostly yellowish except hind coxa black and a brown patch on dorsum of hind femur. Propodeum black. First apparent tergum of gaster black; next terga black on dorsum with hind margin brown and lateral margin light brown; the lateral margins progressively extend on the following terga, the last tergum being mostly light brown except distal end black.

Head about 1.5× as broad as long in dorsal view. Antennal scape nearly equal (0.98×) to combined length of pedicel, anellus and first funicular segment; funicular segments more elongate than in female (figure 38). Pronotum and mesoscutum coarsely cross-striated. Scutellum nearly 1.3× as long as broad, the anterior part with dense cross-striation, the frenal area deeply wrinkled with distinct fovea (figure 153). Forewing stigma oval, 1.3× as long as broad, with a comparatively elongate upper part of stigmal vein, about 0.6× as long as stigma length; uncus long, 0.9× as long as upper part of stigmal vein (figure 77). Propodeum with a weak median carina and two lateral carinae. First apparent segment of gaster very elongate. Aedeagus conical, medium-sized, larger than that of M. suspectus ; digitus with four teeth (figure 115).

Variation

The above description is based on the type material from North America. In the European specimens, body length varied from 2.8 to 5.6 mm in females, from 2.6 to 4.5 mm in males. The colour pattern was highly variable, especially in females (Hussey and Klingler, 1954), but about half of the examined European specimens fitted the type description. The darkest female specimens showed a thoracic dorsum quite entirely black, with yellow reduced to a narrow band on both posterior margin of pronotum and posterior margin of mid-lobe of mesoscutum, and to a tiny spot at inner angle of axilla. Such specimens were observed on A. procera in Great Britain (Hussey and Klingler, 1954) and on A. grandis in France. The lightest specimens presented a quite continuous circumorbital yellow ring, a pronotum quite entirely orange-yellow with black colour reduced to a narrow band on anterior margin and sides, the mid-lobe of mesoscutum being black only in its proximal third ( variety crosbyi described by Hoffmeyer, 1931a). Such specimens were frequently observed on A. nordmanianna in France and on A. grandis in Belgium. Many intermediary forms were observed, the colour of light parts of thorax varying from greenish yellow (e.g. Laidlaw, 1931, in Scotland) to bright orange (e.g. McNeill, 1946, in Scotland) and orange-reddish (some specimens from France). The relative length of the exserted part of ovipositor female varied from 0.9 to 1.1× the body length. The propodeum carina was often double.

Colour variation was more limited in males. About 20% of the specimens found on A. grandis in Belgium had the pronotum entirely black, without any yellow spot. The lightest males showed a continuous circumorbital yellow ring, large yellow spots on pronotum, and lateral parts of thorax quite entirely yellow except metapleuron black (observed in France on A. alba ). A few (10%) also showed a yellow dorsellum. The colour of light parts of thorax varied from lemon yellow to orange-yellow. Gaster colour was also variable, but usually the terga were black with yellow spots on sides which progressively extended, the last tergum being mostly orange-yellow except distal end black. The light brown colour noticed above on gaster of the examined type material (known as variety marginatus ; Hoffmeyer, 1931a) was not observed in our European specimens as already stated by Hussey and Klingler (1954). The shape of the stigma was also very variable, from nearly circular to oval (1.1–1.3× as long as wide).

Sex ratio

Quite balanced in areas of introduction (45 X:52 W, Ostermeyer, 1990; 135 X:107 X, Tombuyses, 1993; Jensen, in press).

Hosts

Specific to fir seeds ( Abies spp. , Pinaceae ). In native countries, develops in Abies amabilis , A. bracteata , A. concolor , A. grandis , A. lasiocarpa , A. magnifica , A. magnifica shastensis and A. procera (= A. nobilis ) (Keen, 1958; Hedlin, 1974; Hedlin et al., 1980). Usually recorded in Europe from plantations of some of these introduced North American firs: A. concolor (Ostermeyer, 1990; Ochsner and Jensen, 1998), A. grandis (Escherich, 1938; Hussey, 1954a; Jespersen and Lomholdt, 1983; Roques, 1983; Ostermeyer, 1990; Ochsner and Jensen, 1998), A. lasiocarpa (Ochsner and Jensen, 1998) , A. procera (Laidlaw, 1931; McNeill, 1946; Hussey, 1954a; Jespersen and Lomholdt, 1983; Tombuyses, 1993; Iversen and Jensen, 1998; Jensen and Larsen, 1998; Ochsner, 1998; Ochsner and Jensen, 1998; Jensen and Ochsner, 1999; USNM). However, the species was observed to shift on to seeds of A. alba in Denmark (Ochsner and Jensen, 1998), and on to some Mediterranean firs introduced to France and Denmark such as A. cilicica (Roques, 1983) , A. bornmülleriana (Roques, 1983; Ochsner and Jensen, 1998), A. nordmanianna (Ochsner and Jensen, 1998) , A. numidica (Roques, 1983; Ostermeyer, 1990; AR) and A. pinsapo (Roques, 1983; Ostermeyer, 1990; Ochsner and Jensen, 1998; AR). It also shifted on to seeds of an Asian fir introduced to France ( A. veitchii Lindl. ; AR). Biotypes living on A. alba and A. procera were distinguished on the basis of behavioural responses to cone volatiles but cone odours of A. grandis seemed to repel females of M. pinus (Luik et al., 1999) . Records on Picea and Pinus species (e.g. Lessmann, 1962) probably represented misidentifications.

Distribution

Originates from western North America, from British Columbia (Hedlin, 1974) to California (Milliron, 1949; Keen, 1958; Peck, 1963; Grissell, 1979; Hedlin et al., 1980). Introduced to Europe and presently recorded in most of western Europe: Belgium (Tombuyses, 1993); former Czechoslovakia (Wall, 1984); Denmark (Jespersen and Lomholdt, 1983; Iversen and Jensen, 1998; Jensen and Larsen, 1998; Ochsner, 1998; Ochsner and Jensen, 1998; Jensen and Ochsner, 1999); France (Roques, 1983; Ostermeyer, 1990); Germany (Escherich, 1938; Wall, 1984); Great Britain (Laidlaw, 1931; McNeill, 1946; Hussey, 1954a, 1954b; Hussey and Klingler, 1954; Boucĕk, 1970b; USNM); Ireland (O’Connor and O’Connor, 1984); The Netherlands (Oudemans, 1933; AR); Sweden (Hansson, 1991).

Comments

To date, six other species of seed chalcids were observed in fir seeds in the region: M. milleri , M. pinsapinis , M. rafni , M. schimitscheki , M. specularis and M. suspectus . Adults of both sexes of M. pinus are easily differentiated by the pale pilosity dominant on thoracic dorsum, even on the light parts, whereas that of other fir seed chalcids

is predominantly dark. For separating the other species, see the chapter concerning M. milleri .

Material examined

Belgium: 8 X, 9 W, ex. Abies procera, Vielsalm arboretum, 1993, F. Tombuyses ( AR) . Canada: 15 X, 5 W, ex. A. grandis, Cowichan Lake, B.C., 1958 , A. Hedlin ( GM) . France: 7 X, 5 W, ex. A. bornmülleriana, Les Barres (45), May 1981 ( AR) ; 6 X, 3 W, ex. A. cilicica, Les Barres , May 1981, ( AR) ; 6 X, 6 W, ex. A. concolor, Les Barres , May 1990, R. Ostermeyer ( AR) ; 11 X, 12 W, ex. A. grandis, Les Barres , May 1981, R. Ostermeyer ( AR) ; 1 X, 1 W, ex. A. numidica, Les Barres , May 1997 ( AR) ; 4 X, 5 W, ex. A. pinsapo, Les Barres , May 1981 ( AR) ; 1 W, ex. A. veitchii, Les Barres , May 2000, M. Auger-Rozenberg ( AR) . Great Britain: 1 X, ex. A. nobilis , Scotland ( USNM) . USA: 1 X, ex. A. concolor , 8 January 1929, Colorado, Hoffmeyer collection ( ZMUC) ; 1 W, ex. A. grandis , Oregon, 26 December 1928, Hoffmeyer collection ( ZMUC) .