Corethrella (Corethrella) lutea 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 : 8-9

Corethrella (Corethrella) lutea Borkent & Grafe , new species

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

DIAGNOSIS: Male adult. Unknown. Female adult. Only extant species of Corethrella in the Palaearctic, Oriental, Oceanian and northern Australasian Regions with the combination of a plain wing ( Fig. 12B ), flagellomeres 1–4 relatively short ( Fig. 8 B), scutum a lighter brown, contrasting with darker, mottled, pleura ( Fig. 9B ) and midfemur relatively thick ( Fig. 9B ) (compared to that of C. nippon Miyagi). Only extant species in Borneo with the combination of a plain wing ( Fig. 12B ) and a thorax with patterned pigmentation (especially the pleura) ( Fig. 9B ).

DESCRIPTION: Male adult. Unknown. Female adult. Descriptive statistics: See Tables 1 –5. Head: Outline in anterior view somewhat circular ( Fig. 6 B). Coronal suture elongate, extending ventrally past ommatidia. Two large setae on frons between ventromedial area of ommatidia. Antenna uniformly medium brown; pedicel without distinctive elongate, stout setae. Antennal flagellomeres as in Fig. 8 B; sensilla coeloconica on flagellomeres 1–2, 9–13, flagellomeres 1 with several, (10), 11–12 with 2 sensilla; flagellomere 13 with well-developed apical bifurcation. Clypeus ( Fig. 6 B) somewhat square. Mandible with moderately sized, pointed teeth. Palpus ( Fig. 6 B) brown; segment 3 swollen apically. Thorax ( Fig. 9B ): Scutum mostly light to medium brown, contrasting with darker brown pleura; scutellum, mediotergite, most of pleura dark brown, katepisternum with pale area at midheight, posterior portion of anepimeron paler, 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. 12B ): Apex of R2 slightly distal to apex of M1. Plain, without pattern of pigmented veins and/or scales; veins (other than costa and wing margin) with slender scales. Halter light to medium brown, equal to or somewhat lighter than scutellum. Legs ( Fig. 9B ): Light brown, forecoxa lighter than mid-, hind coxae, with about basal 0.4 of hind femur dark brown. 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. 13B ): Pale or light yellow, tergites 2–6 with anterolateral light brown pigmentation, sternites medium brown, 3–5 somewhat darker anteriorly, segment 7 light to dark brown, segments 8–9 dark brown. Cercus light brown or pale.

Immature stages. Unknown (but see below).

DISTRIBUTION AND BIONOMICS: Corethrella lutea is known from Brunei and Sarawak, Malaysia from 30–200 m ( Fig. 15A ). Habitats include lowland peat swamps (including standing water and very slow moving streams) and steep terrain in mature mixed dipterocarp forest ( Figs. 1 A, D, E). They are relatively common in frog-call traps in Brunei ( Grafe et al. 2008, as morphotype 2) and have been collected feeding on calling males of three species of frogs (Table 7).

TAXONOMIC DISCUSSION: The seven females noted by Borkent (2008) in the taxonomic discussion of C. nippon , collected from a tributary of Sungai Belalong, Temburong district, Brunei, are paratypes of C. lutea here.

Six females collected from the headquarters of Gunung Mulu National Park, Sarawak, Malaysia (113° 55'E, 4° 23'N) on 14-XI-2009 with a frog-call trap differed from other C. lutea in having only a single sensilla coeloconicum on each of flagellomeres 10–12 and relatively shorter flagellomeres 2–3 (only one slide-mounted). For the present we consider these as variants of C. lutea .

The females of C. lutea are very similar to those of C. nippon but the latter have relatively thicker midfemora. Although the male of C. lutea is unknown, and therefore we do not know if this species shares the only synapomorphy for the group (unequal male midclaws), we consider it a member of the drakensbergensis species group ( Fig. 19 ). It has synapomorphy 25 but lacks 26 and 27 (hence, an unresolved lineage along with C. nippon and C. harrisoni Freeman (Borkent, 2008)) .

TYPES: Holotype, female adult on microscope slide, labeled " HOLOTYPE Corethrella lutea Borkent and Grafe ", " 12 km S. Liang, Brunei, 30 m, 10-V-2007; on Hylarana glandulosa ; U. Grafe; 18-2/3", "18-2/3 261107 " (CNCI). Paratypes on microscope slides: 1 Ƥ labeled as for holotype but 18-2/2, 231007 (CNCI); 3 Ƥ from type locality but 21-IV-2007, 30-IV-2007, 15-V-2007 (CNCI); 1 Ƥ, 15 km S. Liang, Brunei, 40 m, 9-V-2007 (CNCI); 1 Ƥ, 17 km N. Labi, Brunei, 40 m, 6-IV-2009 (UBD); 1 Ƥ, from previous locality but 8-IV-2009 (CNCI); 7 Ƥ, tributary of Sungai Belalong, Temburong district, Brunei, 110 m, 115° 09'E, 4° 33'N, 50 m, 7-VIII-2006 (6 CNCI; 1 UBD); 1 Ƥ, Gunung Mulu NP, Sarawak, Malaysia, 30 m, 14-XI-2008 (CNCI); 5 Ƥ, Matang, Sarawak, Malaysia, 200 m, 4-IX-2008 (CNCI). Paratypes on pins: 1 Ƥ, Kuala Belalong Field Studies Centre, Brunei, 50 m, 17-XI-2010 (CNCI); 1 Ƥ, Belalong Münd (estuary), Ulu Temburong NP, Brunei, 4-VII-2008 (CNCI); 1 Ƥ, lower Sungai Apan, Ulu Temburong NP, Brunei, 110 m, 8-VII-2008 (CNCI); 1 Ƥ, from previous locality but 13-VII-2008 (CNCI); 8 Ƥ, 12.5 km S. Liang, Brunei, 33 m, 28-I-2011 (6, CNCI; 2 UBD); 12 Ƥ, from previous locality but 2-IV-2009 (CNCI); 6 Ƥ, 20 km N. Labi, Luagan Lalak Forestry Rec. Site, Brunei, 6-XI-2010 (CNCI); 2 Ƥ, Sungai Ingei, 8.2 km S. Melilas, Brunei, 50 m, 9-VII-2010 (CNCI); 11 Ƥ, from previous locality but 12-VII-2010 (CNCI); 4 Ƥ, from previous locality but VII-2010 (CNCI); 2 Ƥ, from previous locality but 10-VII-2010 (CNCI); 5 Ƥ, Gunung Mulu NP, Sarawak, Malaysia, 30 m, 14-XI-2008 (CNCI); 3 Ƥ, from previous locality but 26-XI-2009 (CNCI).

DERIVATION OF SPECIFIC EPITHET: The name lutea (yellow) refers to the overall yellowish appearance of the 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 15. A – B. Distributions of species of Corethrella from Borneo.