Megastigmus rafni Hoffmeyer, 1929

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 : 188-192

Megastigmus rafni Hoffmeyer

(figures 23, 40, 60, 79, 99, 117, 136, 155)

Megastigmus pinus Parfitt, 1857b: 5721 (subsequent description of W, nec X 1857 a).

Megastigmus spermotrophus of Crosby, 1913: 163 and authors (misidentifications in part).

Megastigmus rafni Hoffmeyer, 1929: 331–332 . Holotype X, Colorado, Abies concolor , USA ( ZMUC [examined]). 1 X paratype, same data as holotype ( USNM [examined]) . Allotype W (Hoffmeyer, 1931a: 216–217), Colorado, USA (? ZMUC [not examined]) .

Female

Body length (without ovipositor) 4.0 mm. Body colour mostly brownish yellow with a few brown markings. Head tawny yellow with a brownish triangular spot extending from side of clypeus to malar sulcus, and occiput brown. Pilosity pale on lower face, black on remainder of head. Antennal scape yellow, except distal end, remainder of antenna dark brown to black. Thoracic dorsum predominantly brownish yellow, with pronotum lighter than other parts, except anterior part of mid-lobe of mesoscutum and outer part of axilla dark brown; lateral parts of thorax brownish yellow except tegula and upper mesepisternum darker; metanotum with lateral panel brown, and dorsellum brownish yellow. Pilosity black on thoracic dorsum. Legs mostly brownish yellow except hind coxa dark orange-brown on the ventral side. Propodeum black anteriorly, then brownish yellow. First apparent gastral tergum brown, following terga brownish yellow with lateral oblique dark brown stripes, that are successively narrowing; distal terga mostly brownish yellow. Ovipositor sheaths black.

Head about 1.5× as wide as long in dorsal view. Antennal scape enlarged, 1.1× as long as pedicel, anellus and first funicular segment combined; proximal funicular segments about twice as long as wide but length of funicular segments successively decreasing, the distal ones quite subquadrate (figure 23). Pronotum and mesoscutum irregularly but strongly cross-striated, the striae being very arcuate in the distal part of the mid-lobe of mesoscutum. Scutellum 1.2× as long as broad, the anterior part coarsely cross-striate and the frenal area quite smooth with a shallow reticulation below the frenal line and a few weak wrinkles on the lateral parts (figure 136). Forewing stigma elongate-oval, 1.7× as long as broad, with the upper part of stigmal vein comparatively elongate, about 1.2× as long as stigma width; uncus nearly 0.5× as long as upper part of stigmal vein (figure 60). Propodeum with a weak irregular median carina. Ovipositor sheaths about 1.2× longer than body. Distal part of dorsal valve of ovipositor with a large second median tooth (figure 98).

Male (from Milliron redescription, 1949)

Body length 3.0 mm. Body colour mostly brownish yellow with a few brown to black markings. Head entirely yellow except a narrow circumocellar black line. Pilosity pale on lower face, black on remainder of head. Antenna brownish yellow with scape yellowish. Thoracic dorsum mostly brownish yellow except the following dark brown to black parts: triangular black spot on anterior part of pronotum, large band on anterior margin of mid-lobe of mesoscutum prolongated by light brown infuscation extending towards posterior margin, outer part of axilla, narrow band along frenal line, and lateral panel of metanotum. Lateral parts of thorax entirely yellowish. Pilosity on thoracic dorsum black. Legs yellowish. Propodeum black anteriorly. First apparent tergum of gaster dark brown, the three following terga dark brown on dorsum, orange-yellow laterally, and the last ones entirely orange-yellow.

Head about 1.6× as broad as long in dorsal view. Antennal scape shorter than in female, only 0.8× as long as combined length of pedicel, anellus and first funicular segment; proximal funicular segments about twice as long as wide (figure 40). Pronotum and mesoscutum strongly cross-striated, the striae being very arcuate in the distal part of the mid-lobe of mesoscutum. Scutellum 1.3× as long as broad, the anterior part coarsely cross-striated and the frenal area quite smooth with a limited reticulation below the frenal line (figure 155). Forewing stigma rounded, only 1.1× as long as broad, with a comparatively elongate upper part of stigmal vein, 0.8× as long as stigma width; uncus elongate, 0.6× as long as upper part of stigmal vein (figure 79). Propodeum with an irregular median carina. Aedeagus large, rounded, digitus with three teeth (figure 117).

Variation

The above description is based on the type material from North America. In Europe, body length varied from 2.3 to 5.5 mm in females, from 2.3 to 3.7 mm in males. Body colour was highly variable, especially in females. In light specimens, head and thorax were quite entirely orange to golden-yellow except small brown spots on anterior margin of acropleuron and at base of hind wing. Such specimens were found in France on Abies alba and A. nordmanianna . Darker specimens showed a conspicuous dark brown triangular patch on face, and a dark brown coloration extending on anterior margin and suture of lateral panel of pronotum, anterior margin of mid- and lateral lobes of mesoscutum, lower and upper mesepisternum, outer and inner margin of axilla, acropleuron and metanotum. Such specimens were found in France on Abies numidica and A. pinsapo . The median carina on propodeum could be interrupted in the middle.

Body colour was also highly variable in males. The darkest specimens observed in Europe (e.g. on Abies bornmülleriana introduced to France) showed a thoracic dorsum mostly dark brown to black, with the spot on pronotum nearly extending to the posterior margin, the mid-lobe of mesoscutum with only limited oval brownish yellow spots on sides of the posterior half, the axilla with only a small yellowish spot on inner angle, and the band on frenal line of scutellum extending from the centre in the direction of both the anterior and posterior margin of scutellum. In lighter specimens (e.g. from A. alba in France), brown was limited to a narrow band on the anterior margin of mid-lobe of mesoscutum and on the anterior central part of propodeum. Many intermediate forms were observed but the lateral parts of the thorax remained yellow in any case. No strict relationships between colour forms and hosts could be established.

Sex ratio

Apparently balanced in areas of introduction (16 X:14 W in France; Ostermeyer, 1990; cf. above).

Hosts

Specific to fir seeds ( Abies spp. , Pinaceae ). In native areas, recorded from Abies concolor , A. magnifica , A. magnifica shastensis , A. grandis and probably other Abies species (Peck, 1963; Grissell, 1979; Hedlin et al., 1980). Recorded in Europe from three of these introduced American species, A. concolor (Ostermeyer, 1990; Ochsner and Jensen, 1998; AR; USNM), A. grandis (Hussey, 1954a; Ostermeyer, 1990; Ochsner and Jensen, 1998; AR) and A. procera (Hussey, 1952) . It shifted on to the native A. alba in natural stands all other southern France (Mt Ventoux to Pyrénées, AR). It also attacked most of the Mediterranean firs growing in aboreta and plantations of Denmark and France: A. alba (Ochsner and Jensen, 1998) , A. bornmülleriana (Ochsner and Jensen, 1998) , A. cephalonica (Ostermeyer, 1990; AR), A. cilicica (Ostermeyer, 1990; AR), A. equi-trojani (Ochsner and Jensen, 1998) , A. marocana (Ostermeyer, 1990; AR), A. nordmanniana (Ochsner and Jensen, 1998) , A. nebrodensis (AR) , A. numidica (Ostermeyer, 1990; AR) and A. pinsapo (Ostermeyer, 1990; Ochsner and Jensen, 1998; AR). It was also observed on Asian firs introduced to France and Denmark: A. homolepis (Ochsner and Jensen, 1998; AR), A. koreana (AR) , A. pindrow (AR) , A. veitchii (AR) but not on A. procera (Ochsner, 1998; Jensen and Ochsner, 1999). Records referring to M. spermotrophus in seeds of North American firs introduced to Europe (e.g. Cĕrmak, 1952; Lessmann, 1962) are likely to represent misidentifications of light specimens of M. rafni (such as in Hussey, 1955b).

Distribution

Originates from North America, where its range covers Canada (British Columbia; Hedlin, 1974), western and southwestern USA, from Oregon and Idaho to California and New Mexico (Hedlin et al., 1980). Introduced to Europe where it was recorded with certainty only from the western part: Belgium (USNM); Denmark (Ochsner, 1998; Ochsner and Jensen, 1998; Jensen and Ochsner, 1999); France (Ostermeyer, 1990, as Megastigmus aff. suspectus ; Da Ros et al., 1993; AR); Great Britain (Hussey, 1952, 1954a); The Netherlands (AR). However, recent investigations carried out in France showed that the species is now present in most fir stands of the country, especially in the eastern and southern range (M. Auger- Rozenberg and J. P. Fabre, unpublished), and it may soon extend to central Europe if not already done.

Comments

To date, six other species of seed chalcids were observed in fir seeds in the West Palearctic region: M. milleri , M. pinsapinis , M. pinus , M. schimitscheki , M. specularis and M. suspectus . Both sexes of M. rafni are easily differentiated by the light colour predominant on thorax and abdomen, even in the darkest specimens. For separating the other species, see the chapter concerning M. milleri . For lighter specimens, confusion may occur with the Douglas-fir seed chalcid, M. spermotrophus , but the exserted part of female ovipositor is 1.2× longer than body in M. rafni whereas it is never longer than 1.1× body in M. spermotrophus . Stigma shape, especially the relative length of uncus, also allows both sexes of the two species to be differentiated (see chapter concerning M. spermotrophus ).

Material examined

Belgium: 1 X, ex. Abies concolor (USNM) . Canada: 5 X, 6 W, ex. A. grandis, Cowichan Lake , British Columbia, 1958, A. F. Hedlin ( GM) . France: 11 X, 2 W, ex. A. alba, Mt Ventoux (84), May to June 1998 ( JPF) ; 13 X, 8 W, ex. A. alba, Saint André les Alpes (04), June 1998 ( JPF) ; 12 X, 5 W, ex. A. alba, Rialsesse (11), June 1998 ( JPF) ; 5 X, 5 W, ex. A. alba, Gérardmer (88), May 1999, M. Auger-Rozenberg ( AR) ; 5 X, 5 W, ex. A. alba, Le Frézillon (57), May 1999, M. Auger-Rozenberg ( AR) ; 3 X, 1 W, ex. A. alba Freissinières (05), June 2000 ( AR) ; 50 X, 50 W, ex. A. alba, Forest of Lafage (15), June 2000, M. Auger-Rozenberg ( AR) ; 1 X, ex. A. bornmülleriana, Les Barres (45), May 1981 ( AR) ; 2 X, 2 W, ex. A. cephalonica, Les Barres , May 1990, R. Ostermeyer ( AR) ; 12 X, 6 W, ex. A. cephalonica, Marcelly (11), June 1998 ( JPF) ; 3 X, ex. A. cilicica, Les Barres , May 1990, R. Ostermeyer ( AR) ; 12 X, 14 W, ex. A. concolor, Les Barres , May 1990, R. Ostermeyer ( AR) ; 1 X, 1 W, ex. A. grandis, Les Barres , May 1990, R. Ostermeyer ( AR) ; 3 X, 3 W, ex. A. grandis, Forest of Der (52), June 2000, M. Auger-Rozenberg ( AR) ; 1 X, ex. A. homolepis, Les Barres , May to June 1999, M. Auger-Rozenberg ( AR) ; 1 X, ex. A. koreana, Les Barres , May 2000, M. Auger-Rozenberg ( AR) ; 2 X, 2 W, ex. A. marocana, Les Barres , May 1990, R. Ostermeyer ( AR) ; 4 X, 3 W, ex. A. nebrodensis, Les Barres , May to June 1999, M. Auger-Rozenberg ( AR) ; 6 X, 4 W, ex. A. nordmanniana, Les Barres , May 1990, R. Ostermeyer ( AR) ; 3 X, ex. A. numidica, Les Barres , May 1995 ( AR) ; 1 X, ex. A. pindrow, Les Barres , May 2000, M. Auger-Rozenberg ( AR) ; 9 X, 8 W, ex. A. pinsapo, Les Barres , May 1990, R. Ostermeyer ( AR) ; 54 X, 22 W, ex. A. pinsapo, Rialsesse (11), June 1998 ( JPF) ; 1 W, ex. A. veitchii, Les Barres , May 2000, M. Auger- Rozenberg ( AR) . The Netherlands: 7 X, 10 W, ex. A. grandis, Sleenerzand , May 1989, P. Grijpma ( AR) . USA: 12 X, holotype and paratypes, ex. A. concolor , Colorado, 12–21 July 1928, Hoffmeyer collection ( ZMUC, USNM) .