Isomerocera heteraspis James, 1949

Mason, F. & Rozkošný, R., 2015, Morphology, taxonomy, distribution and relationships of the Afrotropical genus Isomerocera (Diptera: Stratiomyidae), African Invertebrates 56 (1), pp. 75-75 : 81-85

Isomerocera heteraspis James, 1949

Figs 13, 14 , 17 , 23, 24 , 29–41

Isomerocera heteraspis James, 1949 b: 106 .

Diagnosis: Both sexes of this species can be easily recognised by the scutellar spines located on the posterior margin of the scutellum in two markedly different planes ( Figs 13, 14 ). The male has paired projections on flagellomeres 3–5 ( Fig. 31 ) and the female only on flagellomeres 3 and 4 ( Fig. 38 ).

Male (holotype) ( Figs 29–35 ).

Description:

Length (mm): Body 8.0, wing 7.4.

Head: Semi-globular in lateral view, 1.7× higher than long ( Fig. 30 ), transverse in dorsal view, almost 1.9× as broad as long ( Fig. 29 ). Large eyes covering greater part of head, touching on frons, gena and postocular area not visible in lateral view. Ocellar triangle prominent in lateral view, no preocellar tubercle developed. Facets in lower third contrastingly smaller. Upper frons triangular, barely as long as ocellar triangle, lower frons almost equilateral, both covered with white tomentum but part of lower frons above antennae and its tip almost bare. Face brown, swollen below antenna, distinctly prominent as a rounded tubercle in lateral view. Antenna ( Fig. 31 ): scape 3× as long as pedicel, brownish, darker than reddish pedicel. Flagellomeres 1 and 2 with sensory pits, the third only with some scattered pits hidden among short hairs.All flagellomeres dark brown, only last flagellomere snow white. Flagellomeres 3–5 asymmetrical, with paired projections, flagellomere 6 subconical and 7 subcylindrical.Apical flagellomere slender and elongate, twice as long as preceding flagellomere, completely snow white. Thorax: Black, finely punctate, with greyish scales on anterolateral part of scutum. Proepisternum with long silvery hairs, anterior part of anepisternum bare, posterior part covered with greyish shining scales. Katepisternum, meron and the area near the posterior spiracle with long silvery hairs. Proximal half of wing membrane infuscated, darker on distal part of br cell. Legs chiefly brown but coxae black, anteriorly with long silvery hairs. Distal third of mid and hind femur as well as all tibiae black, tarsi pale.

Abdomen: Black, finely punctate, with appressed silvery hair patches only on tergites 4 and 5 ( Fig. 29 ), venter covered with fine appressed silvery hairs being longer on sternite 1. Male terminalia as in Figs 33a–c . Genital capsule ( Fig. 32 ) with posterior medial process relatively deeply emarginate at middle, tripartite aedeagal complex ( Figs 33a–c ) slightly longer than the massive lateral aedeagal projections, parameral sheath bipartite as in I. quadrilineata but aedeagal apodeme distinctly dilated proximally.

Female ( Figs 13, 14 , 17 , 23, 24 , 36–41 ).

Description:

Length (mm): Body 6.2–6.9 (n =2); wing: 7.2–7.4 (n =2).

Head ( Fig. 37 ): About 1.7× as high as long in profile and slightly more than twice as broad as long in dorsal view. Frontal index 1.5–1.8 (x =1.65, n =2). Ocellar triangle prominent in lateral view and in front of anterior ocellus a distinct preocellar tubercle (pot) is present ( Fig. 12a, b ), as in female of I. quadrilineata . Pilose area behind and around ocellar triangle is mostly brown anteriorly but more silvery in posterior part. Upper postocular area covered with three to five rows of silvery, appressed scales ( Fig. 17 ). White tomentose patches on frontal band developed as two semicircular pilose spots on upper part of frons continuing with the brown short hairs around the ocellar triangle and as a pair of medially divided spots in middle of frons ( Fig. 37 ). Antenna ( Fig. 38 ) predominantly dark. Scape dark brown, pedicel and flagellomeres 1–2 pale brown, flagellomeres 3–7 dark brown, apical half of last flagellomere snow white. Sensory pits present on both sides of flagellomeres 1–5. Projections on flagellomeres 3–4 asymmetrical, shorter than in male. Face brown with low and rounded nose-like projection, bare on top, covered with silvery hairs along eye margin.

Thorax: Black, finely punctate. Pile and scales on thorax as in male but generally with longer shining scales. Scutum with two metallic lines consisting of scales with purple reflections. Scutellum twice as wide as long with four spines ( Figs 13, 14 ), lateral ones smaller and medial ones larger, brownish yellow with darkened tips. Proximal half of wing membrane darkened, blackish on br cell, as in males. Legs ( Figs 39–41 ) orangeyellow and black. Coxae, mid femur except apex and almost entire tibiae darkened, all tarsi pale.

Abdomen: Black, finely punctate, with appressed silvery hair patches on margins of tergites 2–5 ( Fig. 36 ), venter with fine appressed short silvery hairs on sternites 2–5 and longer on sternite 1. Genital furca not examined.

Condition: Very good, but the costal vein broken on both wings and the body with some rusty incrustation. The male genitalia dissected and attached on the same pin.

Remarks: The unusual position of the scutellar spines (in two different planes) is also known in all three species of the Afrotropical pachygastrine genus Diplephippium Speiser, 1908 (see James 1949 a, Lindner 1966 a). However, Diplephippium differs from Isomerocera by the absence of finger-like projections on flagellomeres, its scutum is provided with a long and pointed spine in front of the wing base and the wing pattern in both genera is different.

Published record: James (1949 b): UGANDA: West Ruwenzori [00°23'N 29°52'E] (holotype) .

Other material examined: BURUNDI: 1♀ Bururi [03°57'S 29°37'E], 3.viii.1949, F.J. François ( IRSNB) ; 1 ♀ 23.x.1949 ( USNM) .

Type material remarks:The male holotype from Uganda is deposited in BMNH (Woodley 2001) and labelled “Holotype [red circular label]/Pres. by Com. Inst. Ent. B.M. 1950– 322/Van Someren. W. Ruwenzori, 8–9000 ft, July 1946 / Isomerocera heteraspis James , HOLOTYPE” [handwritten label by James] .

Figures

Figs 11–16.Isomerocera quadrilineata (Fabricius): (11) antenna; ocellar triangle in (12a) frontal and (12b) dorsal view (Abbreviations: aoc – anterior ocellus, loc – lateral ocellus, oct – ocellar triangle, pot – pre-ocellar tubercle).Isomerocera spp., scutellum:I.heteraspis James, female,in (13) posterolateral and (14) posterior view; I. quadrilineata (Fabricius), (15) male and (16) female in lateral view.

Figs 17–22. Isomerocera heteraspis James, female: (17) scales on postocular area. I. quadrilineata (Fabricius), female: (18) (a) hairs and (b) scales on presutural area of scutum; (19) male posterior stigma (ps – posterior spiracle); (20) postpronotal callus and anterior stigma (as – anterior spiracle, ppc – postpronotal callus); prealar prominence of (21) male and (22) female.

Figs 23–28. Isomerocera heteraspis James, female: (23) prealar prominence; (24) hair tuft (tft) between postalar callus andanatergite.I.quadrilinenata (Fabricius):(25) labellarlobes and palpi; (26) palpus; (27) hind tarsus (clw – claw, emp – empodium, pulv – pulvillus terminalia); (28) female terminalia (crc – cerci).

Figs 29–41. Isomerocera heteraspis James, (29–35) male holotype and (35–41) female: (29) male body in dorsal view; (30) head in lateral view; (31) antenna; (32) genital capsule; (33) aedeagal complex in (a) ventral, (b) dorsal and (c) lateral view; (34) tergites 6–8; (35) proctiger, cerci and epandrium; (36) female body in dorsal view; (37) head in frontal view; (38) antenna; colour pattern of legs: (39) fore, (40) middle and (41) hind leg.