Isomerocera Enderlein, 1914

Mason, F. & Rozkošný, R., 2015, Morphology, taxonomy, distribution and relationships of the Afrotropical genus Isomerocera (Diptera: Stratiomyidae), African Invertebrates 56 (1), pp. 75-75 : 77-81

Genus Isomerocera Enderlein, 1914

Isomerocera Enderlein, 1914: 302 .

Type species: Diphysa maculiventris Macquart, 1850 (= Stratiomys quadrilineata Fabricius, 1787 ), by original designation.

The external morphology of Isomerocera spp. corresponds with the groundplan of the diverse and extensive subfamily Pachygastrinae , which is characterised by the loss of vein M 3 in particular. Nevertheless, Woodley (2001) stated the instability of this character and concluded that the monophyly of the Pachygastrinae is only weakly supported on a world level. Isomerocera ( Fig. 1 ) belongs to the group of pachygastrine genera distinguished by the following features: (1) some medial flagellomeres of the antenna have finger-like projections ( Figs 31, 38 , 45, 46, 64, 65 ), (2) the scutellum is armed with four strong spines ( Figs 13–16 ), (3) vein R 2+3 arises beyond crossvein r-m, (4) vein R 4 is present ( Fig. 4 ), (5) the abdomen is short and rounded, markedly convex dorsally ( Figs 1–3 ) and (6) the male terminalia ( Figs 6–8 ) show a unique parameral sheath. From these characters only characters (1) and (6) are apparently apomorphic though partly shared with Ptilocera (see Mason & Rozkošný 2011).

Head of Isomerocera ( Figs 2 , 30, 37 , 44 ) holoptic in males and dichoptic in females, transverse in dorsal view and almost hemispherical, higher than long in lateral view, eyes bare in both sexes. Facets in upper part of male eye distinctly larger than in lower third, male ocellar triangle prominent in lateral view and frons divided by contiguous eyes into upper short part and lower, broader, subtriangular part, both covered with pale appressed hairs. Postocular area not visible in male but well developed in female. Female ocellar triangle is distinctly elevated above the level of eyes and this elevation visible also in front of the anterior ocellus as a preocellar tubercle ( Figs 12 a, b ). Female frons nearly parallel-sided, slightly narrower than scape is long. Antenna relatively long and slender, about 2–3× as long as head. Scape 3–4× longer than pedicel and pedicel cup-like, distinctly shorter than first flagellomere. Male flagellomeres 3–5 provided with paired finger-like projections, longer ventral and shorter dorsal ones. In females an additional, short ventral projection on flagellomere 2 distinct. Face slightly arched at middle below antennae. Proboscis ( Fig. 25 ) unmodified and palpus two-segmented ( Fig. 26 ).

Thorax without any apomorphic characters at generic level. Prealar prominence ( Figs 21–23 ) present in front of wing base. Four strong marginal spines on scutellum of Isomerocera quadrilineata ( Figs 15, 16 ) arranged in one plane but in two different planes in I. heteraspis ( Figs 13, 14 ) (see James 1949 b). Wing venation ( Figs 1 , 4 ) characterised by vein R 2+3 arising beyond crossvein r-m and presence of R 4. Stronger veins in basal half of wing contrastingly pigmented and virtually all veins reach wing margin. Darkening on wing in front of crossvein r-m characteristic for both species. Wing membrane covered with dense microtrichia reduced in upper half of cup cell. Legs without any special structures, pretarsus corresponding with state found in all families of Homeodactyla ( Fig. 27 ). In Isomerocera quadrilineata , extensive variation in leg colour pattern exists (see Figs 75–88 ).

Abdomen rounded and dorsally convex ( Fig. 3 ). Silverish white hair patches on terga with extensively variable pattern (see Figs 42, 43, 59–61 ). Shape of male terminalia unique. Parameral sheath apparently bipartite (though connected by hyaline membrane) in both examined species of Isomerocera . Lateral projections of aedeagal complex unique within Pachygastrinae , represented by apically pointed appendages.

Figures

Fig.1. Isomerocera quadrilineata (Fabricius), female (South Africa, KwaZulu-Natal,South Coast Uvongo, orig. F. Mason). Scale bar=1.0 mm.

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.

Figs 42–74. Isomerocera quadrilineata (Fabricius), (42–58) male and (59–74) female: (42) male body in dorsal view, (43) abdomen variation: South Africa, Port St. Johns; (44) head in frontal view; (45) antenna,(46) variation:SouthAfrica,Umgeni River,Nagle Dam; (47)genital capsule,(48) variation: South Africa, Mfongosi; aedeagal complex in (49) ventral and (50) lateral view; (51) tergites 6–8; (52) proctiger, cerci and epandrium; colour pattern of legs: (53) fore, (54) middle and (55) hind leg, variation:South Africa, Durban, (56) fore, (57) middle and (58) hind leg; (59) female body in dorsal view, abdomen variation: (60) South Africa, Eshowe, Dlinza Forest and (61) Democratic Republic Congo, Eala; (62) head in frontal view, Democratic Republic Congo, Bambesa, (63) variation: Cameroon, Sangmelima; (64) antenna, Zimbabwe, Vumba, (65) variation: South Africa, Eshowe, Dlinza Forest; (66) genital furca, (67) variation: South Africa, Eshowe, Dlinza Forest; subgenital plate (68); colour pattern of legs Democratic Republic Congo, Eala: (69) fore, (70) middle and (71) hind leg, variation: South Africa, Ngoye Forest, between Eshowe and Empangeni: (72) fore, (73) middle and (74) hind leg.

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.

Fig. 4. Isomerocera quadrilineata (Fabricius), female wing, veins and cells. Abbreviations: A1 – anal vein, alu– alula,anl – anal lobe, bm– basal medial cell,br – basal radial cell, C – costal vein,c – costal cell, CuA1and CuA2– branches of anterior cubital vein, cua1 – anterior cubital cell, cup – posterior cubital cell, dm– discal cell, h – humeral crossvein,M1–2 – medial veins,m1–2 – medial cells,R1-5– radial veins, r1–5 – radial cells, r-m – crossvein between R and M veins, Sc – subcostal vein, sc – subcostal cell.

Fig.2.Isomerocera quadrilineata (Fabricius),female in dorsal view withmorphological terms.Abbreviations: ey – eye, fr – frontal vitta, occ – occiput, oct – ocellar triangle, pa – prescutellar area, pac – prealar callus, pnt– pronotum, po – postsutural area of scutum,poa – postocular area,pot – preocellartubercle, ppc – postpronotal callus,pr – presutural area of scutum,prp – prealar prominence,sc – scutum, scs– scutellar spine, sct – scutellum, tg1–5– tergite 1–5, ts – transverse suture, vtx – vertex, wb – wing base.

Fig.3. Isomerocera quadrilineata(Fabricius), femalethorax and abdomen in lateral view withmorphological terms. Abbreviations: aep – anepimeron, aes – anepisternum, as – anterior spiracle, atg – anatergite, cx1–3 – coxa1–3, ha – halter,kep – katepimeron,kes – katepisternum,ktg – katatergite,ltg – laterotergite, mr – meron, mtg – mediotergite, pac – postalar callus, pem – proepimeron, pes – proepisternum, po– postsutural area of scutum,ppc – postpronotal callus,pr – presutural area ofscutum, prp – prealar prominence, ps – posterior spiracle,sc – scutum,scs – scutellar spines, sct – scutellum,st1–5 – sternites 1–5, tg1–5 – tergites 1–5, ts – transverse suture.

Figs 5–10. Isomerocera quadrilineata (Fabricius), male and female terminalia: Male: (5) dorsal part; (6) ventral part; aedeagal complex in (7) dorsal and (8) lateral view. Female: (9) terminalia in dorsal view and (10) genital furca.Abbreviations: aa – aedeagal apodeme,alp – aedeagal lateral projection, ast – attachment structure, c – cercus, ep – epandrium, ga – gonocoxal apodeme, gf – genital furca, gs – gonostylus, ma – medial aperture, mp – median process of synsternum, pb – posterior bridge, pha – phallic organ, pl – posterolateral projection, pr – proctiger, psh – parameral sheath, tg – tergite.

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 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 75–88. Isomerocera quadrilineata (Fabricius), variation of legs colour pattern, males (75–82) and females (83–88): Males: (75–78) Mozambique, Gorongosa; (79) Zimbabwe, Chirinda Forest; (80) Democratic Republic Congo, Yangambi; (81) Mozambique, Gorongosa; (82) Malawi, Nkwadzi. Females: (83) South Africa, Eshowe, Dlinza Forest; (84) South Africa, St. Helier, Hillcrest; (85) Malawi, Zomba; (86) Democratic Republic Congo, Bambesa; (87) Uganda, Jinja; (88) Democratic Republic Congo, Stanleyville [= Kisangani]. Abbreviations: l1, l2, l3 – fore, middle and hind leg.