Megastigmus atedius Walker, 1851

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 : 153-159

Megastigmus atedius Walker

(figures 13, 34, 50, 71, 89, 109, 126, 147)

Megastigmus atedius Walker, 1851: 214 . Holotype X, England (Oxford University Museum [not examined]).

Megastigmus piceae Rohwer, 1915: 97–98 . Holotype X, Crescent City , California, USA (USNM [examined]). Synonymy by Boucĕk, 1970b: 265.

Megastigmus zwoelferi Scheffer-Immel, 1957: 53–56 . Syntypes X and W, Odenwald , Germany (FIUG [1 X, 2 W examined]). Synonymy by Boucĕk, 1970b: 265.

Female

Body length (without ovipositor) 2.7 mm. Body colour mostly black with yellow markings. Lower face yellow to brownish yellow except a median brown to black spot extending on to supraclypeal area; lower gena and temple light brownish; remainder of the head black except a small, triangular yellow spot above eye. Pilosity pale on lower face, black on remainder of head. Antenna light brown with scape and pedicel yellowish beneath. Thorax entirely black except two slightly transverse dark yellowish spots on posterior part of pronotum, the spots being separated from each other by about their own width at least, and tegula yellowish. Pilosity black on thoracic dorsum. Legs mostly brownish yellow except mid- and hind coxa black. Wings subhyaline; disc of basal cell of forewing bearing eight hairs. Propodeum black with numerous pale bristles on callus. Gaster dark brown to black, with lighter sterna. Ovipositor sheaths dark brown to black.

Head only 1.2× as broad as long in dorsal view. Antennal scape 1.2× as long as pedicel, anellus and first funicular segment combined; funicular segments 2–7 nearly as broad as long (figure 13). Mid-lobe of mesoscutum and anterior part of scutellum finely cross-striated, the frenal area quite entirely smooth with a few short longitudinal grooves extending from the hind margin (figure 126). Scutellum 1.2× as long as broad. Forewing stigma nearly oval, 1.3× as long as broad; upper part of stigmal vein comparatively elongate, 0.8× as long as stigma length; uncus about 0.6× as long as upper part of stigmal vein (figure 50). Propodeum with an irregular median carina (figure 126). Exserted part of ovipositor 0.8× as long as body, nearly equal to combined length of thorax and gaster. Distal part of dorsal valve of ovipositor bearing small, elongate teeth (figure 89).

Male

Body length 2.8 mm. Body colour mostly black with yellow markings. Lower face yellow to brownish-yellow, without brown spots; remainder of head black except a yellow patch extending on gena and temple adjacent to eye margin. Pilosity pale on lower face, black on remainder of head. Thorax black except two yellow rounded spots on posterior part of pronotum. Pilosity black on thoracic dorsum, pale laterally. Legs mostly brownish yellow except mid- and hind coxa black. Wings subhyaline; disc of basal cell of forewing bearing only six hairs. Propodeum black, with numerous pale bristles on callus. Gaster dark brown with yellowish brown spots on sides, expanding on the last terga.

Head 1.3× as broad as long in dorsal view. Antennal scape 1.2× as long as pedicel, anellus and first funicular segment (figure 34). Thorax and propodeum sculpture as in female (figure 147). Forewing stigma wider than that of female, nearly as long as broad; upper part of stigmal vein comparatively elongate, about 0.7× as long as stigma length; uncus very elongate, as long as upper part of stigmal vein (figure 71). Aedeagus short, digitus with four teeth (figure 109).

Variation

The above description is based on the type material of M. piceae for female and M. zwoelferi for male. In the other specimens we examined, body length varied from 1.9 to 4.0 mm in females, from 1.9 to 3.4 mm in males. Females emerging from seeds of Picea spp. were usually smaller (1.9–3.0 mm) than these emerging from Pinus spp. According to Hussey (1967), body length of females from Pinus contorta is longer than that of females from P. strobus (4.0 versus 3.3–3.5 mm). Very few colour variations were recorded. The transverse yellowish spots on pronotum were absent in the darkest female specimens (Boucĕk, 1970b). The basal cell of forewing bore from four to eight hairs in both sexes. Hussey (1967) also noticed a difference in the number of stout bristles on the posterior two-thirds of submarginal vein according to host species (10–12 in females from P. strobus vs eight to nine in these from P. contorta ). However, this number varied from 8 to 12 in our specimens, which emerged from P. strobus and Picea orientalis , and we did not find any definite pattern related to host. In the same specimens, the relative length of the exserted part of female ovipositor varied from 0.8 to 0.9× the body length. Hussey (1967) observed a male specimen with four teeth on the left digitus but five on the right one.

Sex ratio

Quite balanced in most of the European records (Scheffer-Immel, 1957; Lessmann, 1974b). According to Ostermeyer (1990) and Da Ros et al. (1993), male proportion differed with host species in France: 19.2% in Picea orientalis vs 66.6% in Pinus strobus .

Hosts

In the native North American areas, hosts consist of several spruce species [ Picea spp. , Pinaceae : P. engelmannii , P. glauca Moench. (Boss.) , P. mariana (Mill.) B.S.P., P. pungens and P. sitchensis ; Milliron, 1949; Grissell, 1979; Hedlin et al., 1980; Ruth et al., 1980; Turgeon and de Groot, 1992; Turgeon, 1994] and the eastern white pine (Pinus strobus ; Speers, 1974; Turgeon, 1994). In addition, Hussey (1967) recorded emergence from seeds of lodgepole pine (Pinus contorta Loud. subsp. murrayana ) imported from USA (Washington State) to Great Britain although this tree species was not mentioned as a host in the insect native range (Hedlin et al., 1980). According to Boucĕk (1970b), an earlier record of Hoffmeyer (1931a) in seeds of Abies lasiocarpa var. arizonica Merriam sent from the USA to Denmark is very doubtful. We examined the corresponding slides (forewing, antenna and genitalia of X and W) of the Hoffmeyer collection. Without any doubt, the stigmas, antenna and genitalia are similar to these of M. atedius . Therefore, it is possible that the host seeds were not correctly identified.

Once introduced into Europe, M. atedius was found in the seeds of the introduced Pinus strobus (Gäbler, 1954, 1958; Scheffer-Immel, 1957; Kapuściński, 1966; Boucĕk, 1970b; Lessmann, 1974b; Bekreneva and Tropin, 1975; Nikol’skaya and Zerova, 1978; Ostermeyer, 1990; Da Ros et al., 1993). Infestation was also recorded on two American spruce species introduced to Europe, Picea sitchensis (Hussey, 1954b; Ochsner, 1998; Jensen and Ochsner, 1999) and P. engelmannii (Hussey, 1954b) . However, we did not find this insect in seeds of any of the original American spruce hosts during the extensive survey performed at the Les Barres arboretum in France. The very limited number of filled seeds in these species may, however, have prevented successful chalcid attacks (Da Ros et al., 1993). In western Europe, M. atedius also shifted to oriental spruce, Picea orientalis (Boucĕk, 1970b; Lessmann, 1974b; Krístek et al., 1992; Da Ros et al., 1993; Ochsner, 1998; Jensen and Ochsner, 1999) and Serbian spruce, P. omorica (Ochsner, 1998; Jensen and Ochsner, 1999; AR), but it is not yet recorded from the natural range of these two spruce species in Asia Minor and Yugoslavia, respectively (Çanakçioglü, 1959, 1969; Mihajlović and Glavendekić, 1986). No attack was ever observed on the native Norway spruce, Picea abies , except one infested seed (!) recorded by Lessmann (1974b).

Distribution

Originates from North America, the native range covering northern and western USA (Milliron, 1949; Keen, 1958; Speers, 1974; Grissell, 1979; Hedlin et al., 1980) and Canada (Ruth et al., 1980; Turgeon and de Groot, 1992). Introduced to Europe where it is presently recorded from the western, central and eastern parts: Czech Republic (Krístek et al., 1992); Denmark (Ochsner, 1998; Jensen and Ochsner, 1999); France (Ostermeyer, 1990; Da Ros et al., 1993; AR); Germany (Scheffer- Immel, 1957; Lessmann, 1974b; Boucĕk, 1970b); Great Britain (Hussey, 1954b, 1967; Boucĕk, 1970b); Poland (Kapuściński, 1966); Russia: Northwest (Bekreneva and Tropin, 1975; Nikol’skaya and Zerova, 1978).

Comments

In Europe, spruce seeds are also attacked by a native species, M. strobilobius . Both sexes of M. atedius differ from M. strobilobius by the pilosity on disc of the forewing basal cell (four to eight hairs versus 10–18 hairs), and the sculpture of hind part of mid-lobe of mesoscutum (fine transverse cross-striae vs very arcuate cross-striae). The yellowish patterns on the posterior margin of pronotum (two tranverse spots in M. atedius versus a cross-band very narrowly interrupted in the middle in M. strobilobius ) appear more variable and difficult to be used with certainty, especially for separating males. Forewing stigma is usually more elongate in M. strobilobius (1.8 vs. 1.3× as long as broad in females; 1.3× versus about as long as broad in males).

No other chalcid species has been observed in pine seeds in Europe for the moment.

Material examined

France: 2 X, ex. P. omorica, Arboretum des Barres (45), June 1996 ( AR); 1 X, 2 W, ex. Picea orientalis, Amance Arboretum (54), June 1978; 12 X, 13 W, ex. Picea orientalis, Arboretum des Barres (45), June 1991, R. Ostermeyer ( AR); 3 X, 5 W, ex. Pinus strobus, Arboretum des Barres (45), June 1990, R. Ostermeyer ( AR); 3 X, 1 W, ex. P. strobus, Dampierre en Burly (45), June 1993 ( AR); 2 X, 2 W, ex. P. strobus, Treffor Forest (01), June 1993, J. Castille ( AR). Germany: 1 X, 2 W, ex. Pinus strobus , Hessen, Berfelden Odenwald, 2–17 January 1956, H. Münden ( FIUG); 1 X, ex. P. orientalis, Halzminden Oktib, D. Lessman (MNHN) . USA: 1 X holotype M. piceae, Crescent City, CA , USA ( USNM); one slide with wing and antenna of X, wing, antenna and penis of W, ex. ‘ Abies arizonica ’, Amazona , 6 June 1929, seeds sent to Rafn and Søn (Denmark), Hoffmeyer coll. ( ZMUC); one slide with four wings X, four wings W, January 1929; seeds sent to Rafn and Søn (Denmark), Hoffmeyer coll. ( ZMUC).

Megastigmus atlanticus Roques and Skrzypczyńska , sp. nov. (figures 6, 14, 51, 90, 127)

Holotype female

Body length (without ovipositor) 2.5 mm; length of exserted part of ovipositor 1.6 mm. Body colour dark orange. Head light orange except occelli and occipital carina surrounded with black. Pilosity mostly pale on head. Antenna with scape, pedicel and anellus yellowish, the funicular segments brownish yellow. Pronotum light orange; remainder of thorax quite entirely dark orange except transscutal articulation, suture of prepectus, and sublateral grooves black, anterior suture of mid-lobe of mesoscutum brownish, and an elongate black spot on lateral panel of metanotum. Pilosity pale on thoracic dorsum. Legs yellowish orange, with claws darker. Wings subhyaline; forewing stigma light brown. Propodeum dark brown in the middle part, the anterior suture black; callus yellowish with pale hairs extending from conspicuous black dots. First apparent segment of gaster blackish; remainder of gaster mostly yellowish brown with darker bands on distal part of terga, which extend laterally. Ovipositor sheaths black.

Head about 1.2× as broad as long in dorsal view. Eyes little protruding. Scape elongate, reaching level of clypeus, 0.9× as long as combined length of pedicel, anellus, first and second funicular segments (figure 14); pedicel elongate, nearly twice as long as wide; anellus subquadrate; first funicular segment 1.3× as long as pedicel, nearly twice as long as wide, the following funicular segments progressively tending to subquadrate. Thorax about 1.6× as long as width of mesoscutum. Pronotum, mid- and lateral lobes of mesoscutum, and axilla with strong cross-striae (figure 6). Scutellum 1.2× as long as wide, with coarse transverse carinae on the anterior part; frenal area mostly smooth with a few longitudinal carinae on the lateral parts (figure 127). Stigma elongate, about 2× as long as wide; upper part of stigmal vein comparatively short, ca 4× as small as stigma length; uncus 0.8× as long upper part of stigmal vein (figure 51). Propodeum without median carina (figure 6). Ovipositor sheaths 0.7× as long as body, nearly (0.8×) as long as thorax and gaster combined, 2.1× as long as gaster. Distal end of dorsal valve of ovipositor bearing strong first and second median teeth (figure 90).

Male Not known. Variation

Females ranged in length from 2.4 to 2.8 mm, with length of exserted part of ovipositor varying from 1.6 to 1.8 mm. Body colour was little variable, except head which could be dark orange and propodeum light brown with a black anterior suture. Material examined

Type material. H   X, Amizmiz, Morocco, ex. 20 September 1995 from seeds of Cupressus atlantica (Cupressaceae) collected in summer 1995 (A. El Hassani), deposited at MNHN. P    : 3 X, with same rearing data as holotype, deposited at MNHN; 5 X, Marakkech, Morocco, ex. 14 October 1998 from seeds of C. atlantica collected August 1998 (A. El Alaoui El Fels), deposited at Faculty of Sciences Semlalia, Marrakech, Morocco; 8 X, Idni, Morocco, ex. 5 October 1999 from seeds of C. atlantica (A. El Alaoui El Fels) deposited in AR collection.

Non-type material. Algeria: 1 X, Chréa, ex. 12 April 1993 from seeds of Cupressus macrocarpa, K. Bouaziz leg. ( AR). Morroco: 2 X, Marakkech, ex. 10 October 1998 from seeds of C. sempervirens, A. El Alaoui El Fels leg. ( AR).

Etymology Named from the host species, Cupressus atlantica .

Hosts

Develops specifically in seeds of cypresses, Cupressus spp. (Cupressaceae) . It probably originates from C. atlantica in Morocco but it has shifted on some exotic species of cypress introduced to north Africa: the East Mediterannean C. sempervirens and the American C. macrocarpa . Megastigmus emergence holes were observed on another cypress species native of Algeria, C. dupreziana (Bouaziz, 1993) , but the species could not be ascertained yet.

Distribution North Africa: Algeria, Morocco.

Comments

Two other species, M. amicorum and M. wachtli , attack seeds of cypresses within the Mediterranean range. The relative length of the exserted part of female ovipositor allows an easy differentiation of M. wachtli . In that species, the ovipositor sheaths are nearly 3.0× longer than gaster and 1.2–1.3× longer than body whereas they are smaller than gaster and thorax combined in M. atlanticus and M. amicorum . Females of M. atlanticus differ from these of M. amicorum (as well as from these of M. wachtli ) by the pale pilosity of the thoracic dorsum.