Megastigmus hypogeus (Hussey, 1956)

Roques, Alain, Copeland, Robert S., Soldati, Laurent, Denux, Olivier & Auger-Rozenberg, Marie-Anne, 2016, Megastigmus seed chalcids (Hymenoptera, Torymidae) radiated much more on Angiosperms than previously considered. I- Description of 8 new species from Kenya, with a key to the females of Eastern and Southern Africa, ZooKeys 585, pp. 51-124 : 96-101

Taxon classification Animalia Hymenoptera Torymidae

Megastigmus hypogeus (Hussey, 1956)

Type material examined.

Holotype ♀ "Bred ex. oil seed, Nairobi; 5-37; Kenya, Corydon Museum; Pres. by Com. Inst. Ent., B.M. 1957-41; B.M. TYPE HYM. 5.1653; NHMUK010263947" (BNHM); Paratypes: 3♀♀, 4♂♂, same collection data as holotype (BNHM);

Additional material.

11♀♀, 14♂♂, Kenya, Coast Province, Shimba Hills, 4°08.096'S, 39°28.082'E, 285m elevation, 25 Nov. 2001, ex. Ozoroa obovata seeds A&M coll. N°1609, R. Copeland leg.; 1♀, Nyanza Province, Sindo-Mbita Road, 0°29.091'S, 34°10.592'E alt 1205m, 11 Dec 2004, ex. Ozoroa insignis ssp reticulata seeds, A&M coll. N°3064, R. Copeland leg.; 11♀♀, 8♂♂, Arabuko-Sokoke forest, 3.3716°S, 39.8949°E, 55m elevation, 18 Feb 2000., coll. N°Kip-372, ex. Ozoroa obovata seeds, R. Copeland leg; 2♀♀, 3♂♂, Arabuko-Sokoke forest, 3.3716°S, 39.8949°E, 55m elevation, 18 Feb 2000, ex. Ozoroa obovata seeds, A&M coll. N°509, R. Copeland leg.; 1♀, Arabuko-Sokoke forest, 3.2030°S, 39.9271°E, 98m elevation, 17 Mar 2001, ex. Ozoroa obovata seeds, A&M coll. N°1103, R. Copeland leg. (all material in RSC except 5♀♀, 5♂♂ from Arabuko-Sokoke forest in ARC)

This species has been first described by Hussey (1956a) under the name of Eumegastigmus hypogea , and erroneously reported to emerge from"Oil seed, probably Helianthus sp." in Nairobi, Kenya. No subsequent records have been published since this original description. In his paper, Hussey mentioned that it is a very variable species. Our collection of a large number of specimens from different hosts, all belonging to the Anacardiaceae genus Ozoroa , allowed us to supplement Hussey’s primary description which was rather limited.

Female. Females range in length from 3.9 to 5.1 mm (without ovipositor), length of ovipositor sheaths from 2.1 to 2.5 mm. Body colour usually yellow and black (Figures 116-118) but some individuals present a dominant orange colour, all the blackish patterns becoming orange-brown. Head yellow with upper part of scrobe black (but interocellar area yellow), and vertex with a brownish infuscation. Pilosity on face, gena and temples pale but with a few long black hairs near clypeus and parascrobal area (Figure 119); vertex with long black hairs. Antenna brownish.

Thorax yellowish-brown with blackish patterns (Figures 116, 118). Pronotum with a large, median dark brown band progressively decreasing in width from anterior to posterior suture (Figure 118) but in a few specimens, the median pronotum line is very light and interrupted at its distal end; mid-lobe of mesoscutum completely black at the anterior part, continuing as a large triangular brown- black band progressively narrowing from anterior to posterior, the sides yellow; lateral lobe of mesoscutum yellow with an orange rectangular band becoming grey posteriorly, continuing on axilla as a similar orange band; a brownish longitudinal line on lower mesepimeron; scutellum with a triangular blackish band increasing in size from the anterior suture to frenal area (but sometimes reduced to a narrow line with an orange-brown infuscation); conspicuous black sutures between the following parts: lateral panel of pronotum and collar, mid-lobe of mesoscutum and lateral lobe of mesoscutum, lateral lobe of mesos cutum and prepectus, axilla and scutellum, callus and metapleuron. In the individuals with a dominant orange colour, the sutures between lateral lobe of mesoscutum and prepectus, wing insertion and middle part of propodeum remain black. Pilosity on thorax with long black hairs; mid-lobe of mesoscutum with five lateral pairs of hairs on the yellow parts; scutellum with 3-4 lateral pairs of hairs on the yellow sides (4 pairs on holotype; 3 pairs on most other specimens). Legs yellow except claws brown; pale hairs on coxa, with conspicuous blackish insertion dots; femora with both pale and black hairs; hairs black at apex of femora; 3 rows of long black hairs on tibia. Forewing stigma brown without infuscation; basal cell indistinct, basal setal line with only 1 seta; costal cell with 3 setae (Figure 121). Propodeum light brown with a large, rectangular longitudinal black band medially. Gaster mostly brown with a narrow yellow line in the middle; T3 black; subsequent terga with transverse brown bands on the dorsum, narrowing progressively towards the lateral sides which are whitish; gaster completely brown on some specimens with only a few whitish dots on sides; in a few others, gaster has an orange T3, with the subsequent tergites having an orange longitudinal band anteriorly, the band becoming yellow posteriorly. The brownish lines on the lateral sides of gaster segments are sometimes absent. Ovipositor sheaths black, Ovipositor sheaths 1.2 × longer than gaster, 0.6 × as long as body (Figure 117).

Face subquadrate, width: height ratio in front view: 1.2 ×; POL: OOL 1.6 ×; inter-antennal area as broad as torulus width; scrobe rather short, ca. 2.9 × as long as wide. Scape 1.3 × as long as combined length of pedicel, anellus, and F1 (Figure 120); scape 0.8 × as long as combined length of pedicel, anellus, F1 and F2; anellus subquadrate; F1 1.3 × as long as pedicel, 2.1 × as long as wide; F2 2.1 × as long as wide; following funicular segments elongate tending to subquadrate only from F6, with F7 1.3 × as long as wide. Pronotum with coarse cross- striae, mid- and lateral lobes of mesoscutum, and axilla with finer strong cross- striae (Figure 118). Mid-lobe of mesoscutum 1.4 × as long as scutellum length. Scutellum 1.4 × as long as wide, reticulate; frenum indistinct, 0.4 × as long as scutellum, reticulate in the middle, and with smooth striae on sides. Stigma rectangular, elongate, about 1.9 × as long as wide (Figure 121); upper part of stigmal vein elongate, 0.4 × as long as stigma length; uncus 0.8 × as long as upper part of stigmal vein; marginal vein 0.9 × as long as postmarginal vein. Propodeum with cross- striae becoming reticulate anteriorly, a very weak median carina posteriorly.

Males. They are highly variable in colour, and two extreme forms can be distinguished with intermediates. Paratypes ♂ include three specimens with pale patterns and one with dark patterns whereas our collection included nine specimens of pale form, 13 of dark form, and three of intermediate color.

Pale form. Body length from 4.3 to 5.4 mm. Body colour mostly orange-yellow (Figures 122-124). Head yellow with a black spot covering the interantennal area and the scrobes (Figure 125), extending in a semi-circle to the anterior ocellus, then lengthening in a median irregular line until pronotum insertion. Pilosity on lower face pale, black on the remainder of head; parascrobal area with a line of small setae along the scrobes, and a line of long black bristles along the eye contour; two small setae in the interocellar area; two rows of bristles around pronotum insertion. Antenna yellow.

Thorax mostly yellow- orange with a few black patterns (Figure 124). Pronotum yellow with a triangular black spot (very light in a few specimens) in the middle of pronotum, enlarging apically but not reaching the mid lobe of mesoscutum, and a fuzzy blackish band along the posterior suture; mid lobe of mesoscutum orange with a nar row, median black band extending from anterior to posterior suture (very light in one of the ♂ paratypes); lateral lobes of mesoscutum yellow; axilla yellow with a transparent, rectangular band on the antero-lateral part; scutellum yellow with the anterior suture black prolongating in its middle by a small fuzzy blackish spot surrounded by an orange spot. Posterior sutures of metanotum black. Pilosity on thoracic dorsum black but pale on mesepisternum, mesepimeron and callus; 4 pairs of long black bristles on scutellum (Figure 124). Legs yellow. Forewing stigma of paratype brown with a slight yellowish contour but the specimens we collected did not show such a contour (Figure 128); basal cell only partly closed, the disc with 6 setae; basal line and costal line each with 2 setae; costal cell more than 20 small hairs in 4-5 rows in the apical 1/2 to 2/3. Propodeum yellow with a black, median patch of rombhoid shape, extending from anterior to posterior part; sutures with callus blackish. Gaster petiolate, mostly black with few yellow patterns (Figure 122); T3 elongate, entirely black on dorsum; T4 with a large transvers blackish band on the anterior part and a narrower yellow band on the posterior part, extending on sides; T5 similar; T6 and T7 with the yellow band limited to the sides; last segments yellow. Gaster entirely black on dorsum in a few specimens. A row of long black bristles on the lateral parts of tergites 5, 6, 7 and numerous bristles on T8.

Face rounded, width: height ratio in front view: 1.0 × (Figure 125); POL: OOL 1.4 ×. Scape 1.2 × as long as combined length of pedicel, anellus, and F1 (Figure 126); scape 0.9 × as long as combined length of pedicel, anellus, F1 and F2; anellus subquadrate; F1 elongate, 1.5 × as long as pedicel, 2.1 × as long as wide; F2 and following funicular segments similarly elongate, with F7 1.4 × as long as wide.. Pronotum with strong transverse cross-striae; mid lobe of mesoscutum with finer, very irregular cross-striae (Figure 124); mid-lobe of mesoscutum 1.1 × as long as scutellum length; scutellum 1.2 × as long as wide, irregularly reticulate; frenum 0.4 × as long as scutellum length, reticulate as scutellum in its middle but with longitudinal carinae on the sides. Forewing stigma nearly rectangular, 1.4 × as long as wide (Figure 128); upper part of stigmal vein short, 0.2 × as long as stigma length; uncus short, 0.6 × as long as upper part of stigmal vein; marginal vein 0.8 × as long as postmarginal vein. Propodeum with coarse, irregular carinae extending laterally but no median carina. Genitalia with short aedeagus, its part above digitus about 1.2 × as long as digitus length; digitus compressed, about 2.3 × longer than its maximum width, with three teeth (Figure 127).

Dark form. Body length slightly longer than in pale form, from 5.0 to 5.5 mm. Body substantially black (Figures 129-132). Head entirely black (Figure 132) but antenna yellow with scape brownish (Figure 133). Pronotum dark-yellowish with a large median black extending from head insertion to mid lobe of mesososcutum, a large black rectangular patch on the sides, and a larger fuzzy blackish band along the posterior suture (Figure 131); mid lobe of mesoscutum with a large median, dark orange brown band covering most of the surface; lateral lobes of mesoscutum and axilla dark orange; scutellum with a large brown- black median band from anterior to posterior suture. Lateral parts of the thorax (mesepisternum, mesepimeron and callus) entirely black except acropleuron dark orange. Legs mostly black; coxae black; femora black on the apical 2/3 in fore- and mid- femur, and quite completely in hind femur; tibiae and tarsi yellow. Forewing stigma brown with a large, triangular infuscation (Figure 135); basal cell with 16 strong setae on disc; basal line with 3 strong setae; costal line with 26 small setae; costal cell with more than 100 small hairs in a number of rows. Pilosity of thorax similar to that in pale form. Propodeum entirely black (Figure 131). Gaster conspicuously petiolate, entirely black (Figure 129-130).

Relative dimensions of head and antenna similar as in pale form; sculpture of thorax and propodeum same as in pale form. Forewing stigma nearly rectangular, 1.3 × as long as wide (Figure 135); upper part of stigmal vein very short, only 0.2 × as long as stigma length; uncus as long as upper part of stigmal vein; marginal vein 0.8 × as long as postmarginal vein. Aedeagus similar to pale form but one digitus with four teeth, the other one with three teeth (Figure 134).

Intermediates.

Body length as in pale form, from 4.6 to 5.4 mm. Some specimens with infuscate stigma show lighter coloration patterns than in the extreme dark form, with the median band on pronotum smaller, the lateral lobes of mesoscutum and axilla yellow, the scutellum with the median band limited to the anterior part, and the gaster with narrow yellow bands from T4 to T6.

Host plants.

Ozoroa obovata , Ozoroa insignis ssp reticulata ( Anacardiaceae ). Probably a seed feeder, based on its place in the molecular phylogeny of Megastigmus spp. where it clusters with the other species developing in seeds of Anacardiaceae (Figure 14), such as Megastigmus ozoroae and Megastigmus lanneae , and despite the presence of numts in the short COI fragment.

Distribution.

Mixed bush-/grassland in western Kenya near Lake Victoria and in similar habitat in coastal areas. Adults emerged from up to 2.8% of the fruits in some collections (Table 3).

Diagnosis.

The key from Hussey (1956a) distinguished the females of Megastigmus hypogeus by their large body (>5 mm), the ocelli surrounded with black, and the thoracic dorsum with longitudinal black stripe. Actually, it does not allow one to separate females of this species from those of some other species associated with fruits of Anacardiaceae , which are also large and present a thoracic dorsum with a longitudinal dark band; i.e., Megastigmus lanneae , Megastigmus ozoroae , and Megastigmus smithi . Megastigmus hypogeus differs from these species by the relative length of its ovipositor being 1.2-1.3 × longer than gaster length whereas it is shorter than gaster length in Megastigmus ozoroae (Figure 43), and Megastigmus smithi (Figure 31), and much longer in Megastigmus lanneae (1.8 ×; Figure 97).

Genitalic characters also allow separation of Megastigmus hypogeus males from those of other species developing in seeds of Anacardiaceae , the aedeagus part above digitus being significantly less elongated (1.2 × as long as digitus length) than in Megastigmus ozoroae (1.8 ×; Figures 53, 60) and Megastigmus lanneae (1.8 ×; Figures 107, 115) but much longer than in Megastigmus pistaciae (0.8 ×; Figure 148) and Megastigmus transvaalensis (0. 5 ×; Figure 162).