Megastigmus grewianae Roques & Copeland

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 : 86-90

Taxon classification Animalia Hymenoptera Torymidae

Megastigmus grewianae Roques & Copeland sp. n.

Type material.

Holotype ♀, Kenya, Coast Province, Arabuko-Sokoke forest, 3.2997°S, 39.9869°E, 55 m, 17 Feb 2000, ex. Grewia stuhlmanii fruits, Coll. N° Kip-356, R Copeland leg. (NMKE)

Paratypes: Kenya, 1♀, 1♂, same collection data as holotype (RSC); 2♀♀, 1♂, same collection data as holotype (ARC); 1♀, 7♂♂, Eastern Province, Tsavo, 2.6760°S, 38.3325°E, 638 m, 20 Feb 2000, ex. fruits of Grewia tephrodermis , A&M Coll. N°514, R. Copeland leg. (1♀, 3♂♂ NMKE, 4♂♂ ICIPE); 1♀, Coast Province, Kasigau Mountain, 3.82700°S, 38.64875°E, 1065 m, Malaise trap in campsite clearance, 19 May to 2 Jun 2011, R. Copeland leg. (SAMC); 1♀, Eastern Province, Kasaala area, 2.07486°S, 38.22530°E, 741 m, Malaise trap, 28 Nov. to 4 Dec 2013, leg. J. Bukhebi & R. Copeland (ICIPE).

Additional material in alcohol.

Kenya, 7♀♀, 1♂, same as holotype (ARC); 1♀, Eastern Province, Tsavo, 2.6760°S; 38.3325°E, 638 m, 20 Feb 2000, ex. fruits of Grewia tephrodermis , Coll. #514, R. Copeland leg. (ARC)

Description.

Holotype ♀. Body length (without ovipositor) 4.1mm; length of ovipositor sheaths 3.0 mm. Body colour orange with some darker patterns (Figures 81-83). Head colour orange with a very narrow occipital black line and outer part of ocelli black. Pilosity on face pale, dark on dorsum of head but hairs not strong (Figure 85). Antenna brownish except scape and pedicel yellowish (Figure 85). Pronotum orange with a conspicuous longitudinal black stripe running for 7/8 of the lateral part of the pronotum, interrupted just before the suture with mid-lobe of mesoscutum (Figures 82-83). Remainder of thorax orange except black spots on the posterior part of axilla at wing insertion. Pilosity on thorax black but hairs not strong; a few on pronotum; 5 pairs on latero-posterior part of mid-lobe of mesoscutum; 4 pairs on lateral lobe of mesoscutum along suture with mid-lobe of mesoscutum; 4 pairs on axilla. Scutellum orange with 5 pairs of lateral hairs with conspicuous insertion dots (Figures 83-84).

Legs entirely pale yellow except claws brown, coxae with conspicuous hair dots. Forewing stigma brown without infuscation; basal cell closed, with 13 setae on disc; basal setal line with 6 long setae; costal setal line with 16 small setae, costal cell with 11 setae in 2 rows (Figure 87). Propodeum dark orange, with a small oblique brownish spot around the spiracle; not wrinkled transversally; propodeum hairs dark. Gaster orange with two lateral rows composed of 5 brown elongated spots, one on each of the first five segments, placed latero-medially, the third spot shaped like a comma, larger than the others, followed in size by the 4th one. Ovipositor sheaths black, 1.8 × as long as gaster, 0.7 × as long as body (Figure 82).

Head rounded, width: height ratio: 1.1 × (Figure 85); POL: OOL: 1.3; torulus ca. 1.2 × as long as wide; inter-antennal area much smaller (0.6 ×) than torulus width; scrobe elongate, ca. 3.3 × as long as wide. Scape elongate, 1.2 × as long as combined length of pedicel, anellus and F1 (Figure 86); scape 0.8 × as long as combined length of pedicel, anellus, F1 and F2; Pedicel elongate, 1.3 × longer than F1; anellus subquadrate; F1 1.8 × as long as wide, shorter than the other segments, 0.8 × shorter than F2; F2 1.9 × as long as wide; following funicular segments same as F2, except F7 and F8 tending to subquadrate, with F7 1.4 × as long as wide. Pronotum with 8 very strong transverse carinae (Figure 84), mid- lobe of mesoscutum with 7 coarse transverse carinae extending onto lateral lobes; axillae with 3 weaker, longitudinal, carinae. Mid-lobe of mesoscutum 1.2 × as long as scutellum length. Scutellum 1.2 × as long as wide, with transverse, irregular striae anteriorly; frenum smooth, 0.3 × as long as scutellum length. Stigma oval, about 1.2 × as long as wide (Figure 87); upper part of stigmal vein very short, 0.3 × as long as stigma length; uncus comparatively elongate, 1.2 × longer than upper part of stigmal vein; marginal vein 0.8 × as long as postmarginal vein. Propodeum reticulate with 2 oblique carinae diverging from the center of the anterior suture (Figure 84).

Male. Body length 4.2 mm; Body colour, pilosity and black patterns similar to female (Figures 88-91) except gaster with 6 rows of brown spots laterally on dorsum; those on the first two segments elongate with the second longer, the 3 following more rounded, comma-like, and the last a simple spot (Figure 88). Forewing stigma brown without infuscation; basal cell closed, with 21 setae on disc; basal setal line with 7 setae; costal setal line with 21 setae; costal cell with 20 setae arranged in 3 rows (Figure 94). Thorax pilosity as in female.

Head subquadrate, width: height ratio: 1.1 × (Figure 91); POL: OOL 1.3; torulus ca. 1.2 × as long as wide; inter-antennal area short, 0.6 × as broad as torulus width; scrobe elongate, ca. 3.9 × as long as wide; eyes protruding. Scape as long as combined length of pedicel, anellus and F1 (Figure 92); scape 0.7 × as long as combined length of pedicel, anellus, F1 and F2; pedicel 1.2 × longer than F1; anellus subquadrate; F1 2.1 × as long as wide; F2 1.9 × as long as wide; following funicular segments similar to F2, only F7 tending to suquadrate (1.2 × as long as wide). Pronotum with coarse transverse carinae as in female but irregular; some carinae interrupted in their middle on mid-lobe of mesoscutum (Figure 93); axilla with curved longitudinal striae; mid-lobe of mesoscutum 1.1 × as long as scutellum length. Scutellum 1.2 × as long as wide, with transverse striae in the anterior part only, then smooth; frenum entirely smooth, 0.2 × as long as scutellum length (Figure 93). Forewing stigma subquadrate, 1.1 × as long as wide (Figure 94); upper part of stigmal vein short, 0.3 × as long as stigma length; uncus as long as upper part of stigmal vein; marginal vein 0.8 × as long as postmarginal vein. Propodeum with several oblique, irregular carinae (Figure 93). Genitalia with aedeagus relatively elongate, its part above digitus about 1.6 × as long as digitus length; digitus enlarged at its extremity, only twice as long than its maximum width, with 3 teeth (Figure 95).

Variation. Females range in length from 3.5 to 4.0mm. The number of lateral spots on gaster varies from 6 (with two on T3) to 2 (only the large ones remaining), the 3 last lateral spots sometimes fused into a line. Pilosity on thorax paler in one female paratype. Males range in length from 4.1 to 4.5 mm. The spots on gaster sometimes larger, the pairs of lateral hairs on scutellum ranging up to 6 in both sexes.

Host plants.

Grewia stuhlmannii , Grewia tephrodermis ( Malvaceae ). Probably a seed feeder, based on its place in the molecular phylogeny of Megastigmus spp. (Figure 14). Sequencing of four specimens from Arabuko-Sokoke forest showed they differed by less than 0.3% in COI, confirming the validity of the single specimen that we used in the analyses, even if the position remains unresolved. A large number of species of Grewia coexist in East Africa (Brink and Achigan-Dako 2012) and it would be interesting to find if other Megastigmus species or sub-species are able to attack their seeds.

Distribution.

Known from dry Acacia / Commiphora savanna, moderately wet mid-altitude mountain forest, and bush associated with costal forest. Adults emerged from 2.7% of Grewia stuhlmannii fruits and 13% of Grewia tephrodermis fruits (Table 3).

Etymology.

Named after the genus of its host plant.

Diagnosis.

Females are easily separated from those of Megastigmus copelandi , the other species reared from Grewia fruits, by their significantly larger size (4.1 mm vs. 2.6-2.7) and the relatively longer ovipositor (ca. 1.8 × longer than gaster length vs. 0.9 × in Megastigmus copelandi ). Females and males are also easily distinguished from the other species of Afrotropical Megastigmus by the unique pattern of a longitudinal black stripe extending 7/8 of the length of the side of the pronotum (Figures 82-83, 89-90).