Megastigmus transvaalensis (Hussey)

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 : 214-216

Megastigmus transvaalensis (Hussey)

(figures 30, 46, 67, 85, 105, 123, 143, 161) Eumegastigmus transvaalensis Hussey, 1956: 161–162 . Holotype X, Pretoria, Transvaal, South

Africa ( BMNH [examined]); 5 X and 8 W paratypes, same data as holotype ( BMNH,

Hussey collection [2 W examined]). New combination by Boucĕk, 1978: 129.

Female

Body length (without ovipositor) 3.2 mm (according to Hussey, 1956, the abdomen being nowadays absent on the holotype). Body light to dark orange. Head dirty orange with a tiny black spot at clypeus angles and the area around ocelli darker orange-brown. Pilosity pale on lower face, black on remainder of head. Antenna yellowish brown. Thorax predominantly orange-yellow with the pronotum lighter, and with a narrow, darker orange-brown longitudinal band extending centrally on pronotum, mid-lobe of mesoscutum and scutellum. External sutures of lateral lobes of mesoscutum, axilla and metanotum black. Pilosity black on thoracic dorsum, with only three pairs of hairs on scutellum. Legs dirty yellow. Middle part of propodeum with a black, triangular patch, callus orange-yellow. Gaster mostly light orange-brown; first apparent tergum dark brown, following terga (4–7) with a transverse, narrow rectangular dark brown band becoming soon light brown laterally; apical segments paler yellow-brown. Ovipositor sheaths black.

Head about 1.4× as broad as long in dorsal view. Vertex weakly convex with transverse rugae circularly oblique around ocelli; genal area with fine oblique rugae; occipital area relatively weak. Posterior ocellar line 1.7× as long as ocellocular and lateralocellar lines, and 1.4× as long as occelloccipital line; malar space half as wide as compound eye. Antennal scape elongate, 1.2× as long as combined length of pedicel, anellus and first funicular segment; pedicel nearly (0.9×) as long as first funicular segment; funicular segments 2–5 elongate, about twice as long as wide, the two last ones (6 and 7) tending to subquadrate (figure 30). Pronotum and mesoscutum with strong transverse rugae, coarser than on vertex. Scutellum 1.5× as long as wide, with coarse transverse striations. Frenal line weakly marked, the frenal area with strong longitudinal carinae especially on the lateral parts (figure 143). Forewing stigma oval-elongate, 1.4× as long as broad; uncus elongate, 1.2× as long as upper part of stigmal vein (figure 67); basal cell of forewing with 10 hairs. Propodeum with strong oblique carinae. Ovipositor sheaths about 1.4× as long as gaster, but only 0.6× as long as combined length of gaster and thorax, and 0.5× as long as body. Distal part of dorsal valve of ovipositor with a large third median tooth (figure 105).

Male

Body length 2.7 and 2.8 mm. Body mostly pale orange-yellow except gaster. Head light orange with the area around ocelli darker orange-brown. Pilosity pale on lower face, black on remainder of head. Antenna yellowish brown. Thorax predominantly orange-yellow with the pronotum lighter, and with a narrow, darker orange-brown longitudinal band extending centrally on pronotum, mid-lobe of mesoscutum and scutellum. External sutures of lateral lobes of mesoscutum, axilla and metanotum black. Pilosity black on thoracic dorsum, with only three pairs of hairs on scutellum. Legs dirty yellow. Propodeum with a black triangular patch in the middle and callus orange-yellow. Dorsum of gaster entirely dark brown, a few patches extending laterally on terga V–VI, remainder of gaster orange-brown.

Head about 1.4× as broad as long in dorsal view. Antennal scape elongate, 1.1× as long as combined length of pedicel, anellus and first funicular segment; pedicel nearly (0.9×) as long as first funicular segment; following funicular segments elongate, twice as long as wide (figure 46). Pronotum and mesoscutum with strong transverse rugae. Scutellum 1.1× as long as broad, frenal line weakly marked, the frenal area with strong longitudinal carinae especially on the lateral parts (figure 143). Forewing stigma enlarged, little infuscated, about 1.2× as long as wide; uncus slightly smaller (0.9×) than upper part of stigmal vein (figure 85); basal cell of forewing with 10 bristles. Propodeum with oblique carinae. Aedeagus small, rounded, digitus with three teeth (figure 123).

Variation

The above description is based on the type material from South Africa . In specimens from the West Palearctic , body length varied from 3.0 to 3.5 mm in females, from 2.3 to 3.2 mm in males. Few variations in colour were observed. The central, orange-brown thoracic band completely disappeared in some specimens from Morocco . The black patch on the middle of propodeum could also turn to brown. Gaster dorsum was predominantly black in most specimens from Morocco and Portugal.

Sex ratio Usually balanced in Morocco (e.g. 46 X:42 W at Marrakech, AR).

Hosts

The species is probably an endemic, South African species which has host-shifted from native seeds of Rhus spp. (Anacardiaceae) into the seeds of Schinus spp. , which are Anacardiaceae introduced from South America towards most warm areas of the world (Habeck et al., 1989; Grissell and Hobbs, 2000). It has been reported from S. molle (Hussey, 1956; Boucĕk, 1978; Grissell, 1979; Habeck et al., 1989; AR) and S. terebinthifolius (Habeck et al., 1989; Perioto, 1997 as Megastigmus sp. ; AR) but is still capable of attacking Rhus laevigata under experimental conditions (Grissell and Hobbs, 2000).

Distribution

Probably present in the major part of the introduction range of Schinus spp. , everywhere these trees can flower. Reported from South Africa (Hussey, 1956), La Réunion (AR), the USA (California, Florida, Hawaii; Habeck et al., 1989), Mexico (USNM), the species has recently been observed for the first time in the native South American range of Schinus ( Argentina, Brazil; Perioto, 1997 as Megastigmus sp. ; Grissell and Hobbs, 2000). In the West Palearctic, observed in France (AR), Morocco (AR), Portugal (AR) and Spain (Canary Islands; Grissell, 1979; USNM).

Comments

The pistachio seed chalcid, M. pistaciae , was also reported from seeds of Schinus molle by Rice and Michalides, 1988, but these authors did not supply the original reference of the record. M. pistaciae is morphologically identical to M. transvaalensis except for its larger size (Grissell and Hobbs, 2000). A few specimens closely resembling M. transvaalensis were recently obtained in Morocco by one of us (AR) from seeds of another species of Anacardiaceae , Rhus albida Schousb. (= tripartita D.C.). They may correspond to a closely related South African species, M. rhusi (Hussey) , which was observed there on Rhus lancea L . (Hussey, 1956). Molecular studies are currently under way to determine the degree of genetic relatedness between M. transvaalensis , M. rhusi and M. pistaciae (Grissell and Hobbs, 2000) .

Material examined

France: 1 X, ex. S. molle, Bormes (83), August 2000, G. Rouault ( AR) ; 1 W, ex. S. terebinthifolius, Toulon ; September 2000 ( AR) . Mexico: 1 X, ex. S. molle, PQ US quarantine service ( USNM) . Morocco: 46 X, 42 W, ex. S. molle, Marrakech , February 2000, ( AR) ; 22 X, 18 W, ex. S. molle, Chichaoua , October 2000, G. Rouault ( AR) ; 2 X, 1 W, ex. S. molle , Agadir , October 2000, G. Rouault ( AR) . Portugal: 1 X, 1 W, ex. S. molle, Hortas do Tabual, nr. Sagres , 12 August 2000 ( AR) ; 3 X, 2 W, ex. S. molle, Monsanto (Lisboa) , September 2000 ( AR) . La Réunion Island: 2 X, ex. S. terebinthifolius, St Pierre de la Réunion , 20 December 2000, L. Combes ( AR) . Spain: 1 X, ex. S. molle, Tenerife , Canary Islands, May 1962 ( USNM) . South Africa: 1 X, 3 W, ex. S. molle, Pretoria , 9 May 1919, J. Jooke ( BMNH) ; 1 X, ex. S. molle , 25 October 1919, Riestenburg (Transvaal), J. Jooke ( BMNH) .