Aprostocetus exertus La Salle
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|Aprostocetus exertus La Salle|
Aprostocetus exertus La Salle sp. nov.
Diagnosis. This species is easily recognized by the exerted part of the ovipositor and postcercale, which are slightly longer than the combined length of the head plus body. This character, coupled with the almost completely white fore and middle coxae, should make it unmistakeable.
Description. Female (Figs 1–3). Body length 1.45 – 1.75 mm from head to base of exerted part of ovipositor and extension of T 7.
Head metallic green to blue, palps yellow. Antenna with scape yellow (may be brownish apically), flagellum yellow to light brown. Mesosoma mainly metallic green to blue; some of the sutures between mesosomal segments may be yellow, particular the mesopleural plates and scapula. Legs white; fore and mid coxae white, with small basal brown spot; hind coxa brown, with white spot apically. Gaster brown with green to blue shine, a yellow spot dorsally on the first gastral tergite, and a white to yellow medial triangle dorsally on the last gastral tergite just anterior to the cerci.
Head (Fig. 7). POL about 3 times as long as OOL; LOL subequal to or slightly longer than OOL. Face with weak frontofacial suture just ventral to median ocellus. Scrobal depression with weak median suture dorsally and median carina or projection ventrally. Torulus located at middle of face; slightly above the lower margin of eye; apex scape not exceeding vertex.
Gena only slightly swollen and malar sulcus straight or very slightly curved. Clypeal margin strongly bidentate. Mouth only slightly wider than length of malar space.
Antenna (Fig. 13) with 3 anelli and 3 funicular segments. Anelli closely appressed, the second anellus smallest, the third anellus subquadrate, and may have setae on external margin. All funicular segments slender and longer than broad. F 1 3.6 –4.0 times longer than wide, F 2 2.6–2.9 times longer than wide; F 3 2.1–2.5 times longer than wide (F 1: F 2: F 3 = 1.0: 0.7–0.8: 0.6–0.7). Clava 3 segmented, 2.0– 2.15 times longer than F 3.
Mesosoma (Figs 8–10). Pronotum short in dorsal view, mainly in vertical plane. Mid lobe of mesoscutum with weak median line; with 2–4 (generally 3) strong, semi-erect adnotaular setae on each side; notaulus quite deep. Scutellum with distinct submedian and sublateral lines; anterior pair of setae located slightly posterior to middle; posterior pair of setae located near posterior margin. Propodeum shorter medially than median length of dorsellum; without distinct median carina; without paraspiracular carina; outer rim of propodeal spiracle partially covered by a raised flap of callus; spiracular depression open to anterior margin of propodeum. Callus with 2 setae.
Gaster (Figs 11–12) with the ultimate gastral segment (T 7) greatly extended so that the length of the postcercale (that region of the last gastral segment posterior to the cerci) is longer than the combined length of the head plus body. What appears to be the exerted part of the ovipositor thus consists of the ovipositor and ovipositor sheaths, plus the extended last gastral tergite. This exerted part of the ovipositor 1.85–2.3 times as long as gaster; 1.15–1.3 times as long as gaster plus mesosoma. Apex of hypopygium extending less than half the length of gaster. Cercus with the longest setae distinctly longer than remaining setae, and slightly curved.
Wing (Fig 15). Submarginal vein with 2 (– 3) dorsal setae; tapering apically and joining parastigma distally to proximal end of parastigma. Marginal vein not swollen. Veins light brown to brown. Wing hyaline, with some light infuscation present near apex of stigmal vein, and at junction of basal and cubital veins. Postmarginal vein less than 0.25 length of stigmal vein. Costal cell apically with 2–4 setae on underside of wing. Marginal vein relatively long in comparison to other veins; costal cell: marginal vein: stigmal vein: postmarginal vein = 0.7–0.85: 1.0: 0.15–0.2: 0.05–0.1. Postmarginal vein 0.3–0.5 length of stigmal vein. Cubital line of setae extending to basal vein or slightly basal to junction with basal vein (speculum closed behind). Subcubital line of setae not extending basal of apical margin of speculum.
Male. Body length 1.0– 1.6 mm.
Body color almost the same as female; although with a larger white to yellow area at the base of the gaster. Antenna (Fig. 14) with 3 anelli; and 4 funicular segments which are all longer than broad; without whorls of long setae. Ventral plaque situated near apex of scape, length less than 0.25 length of scape. Genitalia often distinctly extended, exerted part of genitalia may equal length of gaster (fig. 16).
Type material. Holotype Ƥ: laboratory culture, Hawaii. Originally from TANZANIA, Arusha, Masai Camp Village, 27.i. 2006, M. Ramadan, ex Erythrina abyssinica galls ( ANIC).
Paratypes: 58 Ƥ, 553. Same data as Holotype (3 Ƥ, 73 ANIC; 2 Ƥ, 23 BMNH, 2 Ƥ, 23 SANC, 2 Ƥ, 23 USNM). South Africa, KwaZulu-Natal Prov., Pietermaritzburg, University Botanic Gardens, 29 ° 36 ’S 30 ° 22 ’E, xi. 2008, D.J. Brothers or B. Muller, ex leaf galls on Erythrina latissima (39 Ƥ, 323 ANIC; 2 Ƥ, 23 BMNH, 2 Ƥ, 23 USNM, 2 Ƥ, 23 SANC, 2 Ƥ, 23 BPBM, 2 Ƥ, 23 NMK)
PLATE 1. Aprostocetus exertus La Salle. Fig. 1. Ƥ Habitus. Figs 2–3. Female wasp searching for galls. Fig. 4. A. exertus egg on EGW pupa. Fig. 5. A. exertus larva feeding externally on EGW larva. Fig. 6. A. exertus pupae: female (above) and male (below).
Biology. Foreign exploration work searching for EGW parasitoids in East Africa was undertaken by one of us (MR), and revealed that Aprostocetus exertus is one of three main parasitoids in Tanzania reducing the populations of the gall wasps of Erythrina species. The other two species are Eurytoma erythrinae Gates & Delvare (Gates & Delvare 2008) , and an Aprostocetus species being described in a companion paper by Prinsloo & Kelly (2009). Field observations showed that A. exertus was not the dominant parasitoid at any surveyed locality in Tanzania; however it is an important component of the parasitoid guild because it is present at very low population levels of the gall wasps, and under a very harsh environmental condition.
Because of its exerted long ovipositor, it has the ability to reach for galls deep in the stems of Erythrina that other parasitoids can not reach. Also, it is known to attack EGW under native conditions, as it was found attacking Quadrastichus erythrinae in Erythrina abyssinica in the Morogoro province in Tanzania.
Biological studies undertaken by the Hawaii Department of Agriculture have shown that this species is ectoparasitic, and will attack both larvae and pupae (Figs 4–5). Specimens from South Africa emerged from leaf galls on Erythrina latissima (see Prinsloo & Kelly 2009).
PLATE 2. Aprostocetus exertus La Salle ♀. Fig. 7. Head, frontal view. Fig. 8. Mesosoma, dorsal view. Fig. 9. Mesoscutum, dorsal view. Fig. 10. Scutellum and propodeum, dorsal view. Fig. 11. Gaster and ovipositor, lateral view. Fig. 12. Apex of gaster, base of postcercale, lateral view.
PLATE 3. Aprostocetus exertus La Salle. Fig 13. Ƥ Antenna. Fig 14. 3 Antenna. Fig. 15. Ƥ Forewing. Fig. 16. 3 Habitus (wings removed), showing exerted genitalia.
Distribution. Africa: Tanzania, South Africa.
Etymology. The species name exertus is indicative of the extremely long and exerted ovipositor in this species.
Discussion. Aprostocetus is the largest genus in the Tetrastichinae (indeed, one of the largest genera in the Chalcidoidea), and it is biologically and morphologically diverse. Its identity in a modern sense was established by Graham (1987, 1991), and this interpretation of the genus has been followed by subsequent authors (e.g. Bouček 1988, La Salle 1994, Schauff et al. 1997). Currently the genus contains 6 subgenera ( Graham 1987, La Salle 1994).
Aprostocetus exertus is treated in this paper as belonging to the subgenus Aprostocetus , but it does not completely agree with previous definitions of this group, and appears to share some characters with the subgenus Ootetrastichus . Graham (1987) distinguished Ootetrastichus from Aprostocetus s.s. as follows: midlobe of mesoscutum usually without a median line; subcubital line of setae reaching or nearly reaching basal vein; speculum small; propodeal spiracle generally small, with or without their outer rim partially covered by a raised flap on the callus; ovipositor sheaths slightly to greatly exerted; always with one of the cercal setae distinctly longer than the others; usually with 3 or more setae on the SMV, but occasionally with 2 (or even 1); generally elongate, brightly metallic species. A. exertus displays a combination of these characters, so that it does not comfortably fit in either Ootetrastichus or Aprostocetus ss. Clearly, there are some research opportunities remaining in African tetrastichines.
Biologically, Ootetrastichus seem to form a distinct group in that species are egg parasitoids of Hemiptera ( Delphacidae , Cicadellidae ), Orthoptera ( Gryllidae ), Odonata and Coleoptera ( Dytiscidae ), and some species can parasitize eggs in aquatic situations. There is, however, one exception: the African Aprostocetus (Ootetrastichus) theionerus (Masi) is a hyperparasitoid on stem borers ( La Salle 1993).
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