Corethrella (Corethrella) bipigmenta Borkent & Grafe

Borkent, Art & Grafe, Ulmar, 2012, The Frog-Biting Midges of Borneo — From Two to Eleven Species (Corethrellidae: Diptera), Zootaxa 3279, pp. 1-45 : 10-11

Corethrella (Corethrella) bipigmenta Borkent & Grafe , new species

( Figs. 2 C, 4D, 6D, 8D, 9D, 12D, 13D, 15B)

DIAGNOSIS: Male adult. Unknown. Female adult. Only extant species of Corethrella in the Palaearctic, Oriental, Oceanian and northern Australasian Regions with the combination of no pigmentation distal to the single distinct midlength wing band (no subapical band) ( Fig. 12D ), flagellomeres 1–4 elongate, each similar in length to flagellomere 5 ( Fig. 8 D), with non-discrete darker pigmentation on the basal 0.5 of the midfemur and basal 0.3–0.4 of the hind femur, uniformly yellow or light brown hind tibia ( Fig. 9D ), and abdominal tergites each with anterolateral darker pigmentation ( Fig. 13D ). Only extant species in Borneo with the combination of flagellomeres 1–4 elongate, each similar in length to flagellomere 5 ( Fig. 8 D) and palpal segments 1 and 2 dark brown and contrasting with pale segments 3 and 4 (5 grading from pale to medium brown) ( Fig. 6 D).

DESCRIPTION: Male adult. Unknown. Female adult. Descriptive statistics: See Tables 1 –5. Head: Outline in anterior view somewhat circular ( Fig. 6 D). Coronal suture elongate, extending ventrally past ommatidia. Two large setae on frons between ventromedial area of ommatidia (as in Fig. 16B ). Antenna uniformly medium brown; pedicel with distinctive elongate, stout setae. Antennal flagellomeres as in Fig. 8 D; sensilla coeloconica on flagellomeres 1–2, 9–13, only flagellomere 1 with more than one; flagellomere 13 with well-developed apical bifurcation. Clypeus somewhat square. Mandible with moderately small, pointed teeth. Palpus ( Fig. 6 D) with segments 1–2 dark brown, segments 3–5 light brown, segment 5 darker apically; segment 3 swollen apically. Thorax ( Fig. 9D ): Scutum, scutellum mostly light to medium brown, contrasting with darker brown pleura; pale sclerites around base of wing. Posterior portion of dorsocentral row with 2 elongate setae situated somewhat lateral to one another. Prescutal suture elongate, thick, uninterrupted, extending to near dorsocentral row of setae.

Anterior anepisternum divided diagonally by sinuous suture, dorsal portion about equal to ventral portion. Ventral portion of posterior anepisternum triangular, uniformly brown, with anterodorsal margin not thick. Wing ( Fig. 12D ): Apex of R2 slightly distal to apex of M1. Anterior margin with differently, discretely pigmented scales (indicating anterior margin of midlength band), with midlength band, with darker more basal scales restricted to vein C, Sc, slightly in more posterior veins, with basal scales on posterior margin of wing dark; veins (other than costa and wing margin) with well-developed scales. Halter medium brown, equal to or slightly lighter than scutellum. Legs ( Fig. 9D ): Light brown, with about basal 0.5 of forefemur slightly darker, about basal 0.5 of midfemur darker, about basal 0.3–0.4 of hind femur darker; with darker pigmentation not discrete. With only slender setae, lacking scales. Midleg with thick, subapical setae on each of at least tarsomeres 1–3. Claws of each leg equal to those of others; equal on each leg, simple (without inner teeth). Empodia thick. Abdomen ( Fig. 13D ): Tergites 2–7 pale or light brown with anterolateral corners more darkly pigmented, tergite 8 pale or light brown, sternites light brown with sternites 2–6 with anterior portions medium brown, posterior margins pale, sternites 7–8 medium brown. Cercus medium light brown.

Immature stages. Unknown.

DISTRIBUTION AND BIONOMICS: Corethrella bipigmenta is known only from steep terrain in the mature mixed dipterocarp forest ( Figs. 1 E, F) of Ulu Temburong National Park, Brunei, at elevations of 50–120 meters ( Fig. 15B ). Three females in the type series were collected on 22-VII-2006 from a calling male Megophrys nasuta (Schlegel) at 8:30 PM ( Fig. 2 C). A photograph by the second author ( Fig. 2 C) shows numerous identical looking female Corethrella on and surrounding the frog: seven were on the legs, two were on the back, and at least 10 were on nearby substrate. Further specimens were collected from other M. nasuta and one other frog species (Table 7). This species has not yet been collected with a frog-call trap.

TAXONOMIC DISCUSSION: The three type specimens of C. bipigmenta were noted by Borkent (2008) in the taxonomic discussion of C. nippon (but mistakenly stated as coming from Sungai Belalong). This species is very similar to C. nanoantennalis but differs in the relative lengths of flagellomeres 1–4.

Corethrella bipigmenta is placed in the drakensbergensis species group for the same reason that C. nanoantennalis was placed there, along with the same caveats ( Fig. 19 ). However, it appears that this species has synapomorphy 40 (pedicel with strong setae), which would place it elsewhere in the phylogeny of the Corethrellidae . We are inclined however, to question the validity of this synapomorphy – it is often difficult to interpret consistently in specimens and its distribution may have been misrepresented by Borkent (2008).

TYPES: Holotype, female adult on microscope slide, labeled " HOLOTYPE Corethrella bipigmenta Borkent and Grafe ", "Tributary of Sungai Temburong in Temburong district of Brunei Darussalam, 115° 09'E, 4° 33'N, 22-VIII-2006, U. Grafe, CD2069" (CNCI). Paratypes on microscope slides: 2 Ƥ, labeled as for holotype (1, CNCI; 1 UBD). Paratypes on pins: 2 Ƥ, from Kuala Belalong, Ulu Temburong NP, Brunei, 50 m, 23-VII-2007 (CNCI); 4 Ƥ, from Sungai Esu, Ulu Temburong NP, Brunei, 60 m, 11-VII-2008 (CNCI); 2 Ƥ, from Sungai Baki, Ulu Temburong NP, Brunei, 120 m, 18-VII-2008 (1 CNCI; 1 UBD); 1 Ƥ, Sungai Mata Ikan, Ulu Temburong NP, Brunei, 110 m, 10-VII-2008, (UBD).

DERIVATION OF SPECIFIC EPITHET: The name bipigmenta (two, pigment) refers to differently pigmented palpal segments 1–2 (dark) and segments 3–5 (lightly pigmented) of females of this species.

Figures

FIGURE 1. Habitats from which Corethrella adults were collected with a frog-call trap in Brunei (species collected given in parentheses). A. 12 km S. Liang, Brunei (C. tigrina, C. lutea, C. calathicola, C. pauciseta, C. gilva) (authors, for scale). B. Nepenthes ampullaria, 12 km S. Liang, Brunei (C. calathicola). C. 12.5 km S. Liang, Brunei (same species as for A) (first author, for scale). D. 20 km N. Labi, Luagan Lalak Forestry Rec. Site, Brunei (C. lutea). E. Belalong River, Kuala Belalong Field Studies Centre, Brunei (C. lutea, C. bipigmenta, C. mitra). F. Sungai Esu, Ulu Temburong NP, Brunei (C. tigrina, C. bipigmenta, C. mitra) (first author's wife Annette, for scale). G. Pa Umor, 5 km E. Bario (C. bicincta, C. unizona).

FIGURE 2. Female adult Corethrella feeding on calling male frogs in Borneo. A. C. tigrina on Metaphrynella sundana (Peters) (Ashton Trail in the Ulu Temburong National Park, Brunei Darussalam). B. C. lutea resting on somewhat drooping leaf after feeding on Rhacophorus appendiculatus (Günther) (Sungai Ingei Conservation Forest, 8.2 km S. Melilas, Brunei Darussalam). C. C. bipigmenta on Megophrys nasuta (Ulu Temburong National Park, Brunei). All photographs by second author.

FIGURE 6. Head capsules of female Corethrella, anterior view.

FIGURE 8. Antennae and male genitalia of Corethrella. A – K. Antennae of female Corethrella. L. Antenna of male C. tigrina. M. Male genitalia of C. tigrina, dorsal view; parts drawn in proportion to each other.

FIGURE 19. Phylogenetic relationships of Corethrella from Borneo to other species and showing their distributions. Numbers refer to character states given in Borkent (2008). Evidence for cladistic relationships given in Borkent (2008).

FIGURE 12. A – K. Wings of female Corethrella.

FIGURE 9. A – D. Thoraces and legs of female Corethrella, lateral view; slide-mounted.

FIGURE 13. A – J. Abdomens of female Corethrella, ventral view.

FIGURE 16. A – B. Distributions of species of Corethrella from Borneo.

FIGURE 15. A – B. Distributions of species of Corethrella from Borneo.