Corethrella (Corethrella) pauciseta Borkent

Borkent, Art & Grafe, Ulmar, 2012, The Frog-Biting Midges of Borneo — From Two to Eleven Species (Corethrellidae: Diptera), Zootaxa 3279, pp. 1-45 : 15-16

Corethrella (Corethrella) pauciseta Borkent

( Figs. 5 C, 7B, 8I, 10D, 12I, 13H, 17)

Corethrella pauciseta Borkent, 2008:191 . Type locality: Hospital Ck., Wau, NE New Guinea. Holotype female (BPBM).

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 clypeus with 2–5 setae, plain wing ( Fig. 12I ), veins (other than along the wing margin) with definite but slender scales, and uniformly medium to dark brown thorax ( Fig. 10D ). Only extant species in Borneo with the combination of a plain wing ( Fig. 12I ), uniformly dark brown thorax ( Fig. 10D ), and clypeus with 2–5 setae.

DESCRIPTION: Male adult. Unknown. Female adult. As described by Borkent (2008), with the following modifications based on Brunei material. Descriptive statistics: See Tables 1 –5. Head: (as in Fig. 7B ). Pedicel with distinctive elongate, stout setae. Antennal flagellomeres medium brown; flagellomeres as in Fig. 8 I; sensilla coeloconica on flagellomeres 1, 8–13, only flagellomere 1 with more than one; flagellomere 13 with welldeveloped apical bifurcation. Clypeus ( Fig. 7B ) wider than long. Palpus ( Fig. 7B ) medium brown; segment 3 somewhat thicker at midlength. Thorax ( Fig. 10D ): Posterior portion of dorsocentral row with 2 elongate setae situated somewhat lateral to one another. Wing ( Fig. 12I ). Legs ( Fig. 10D ): Medium brown, but slightly lighter in some on apex of hind femur, bases of fore-, mid-, hind tibiae. Abdomen ( Fig. 13H ): Uniformly medium to dark brown.

Immature stages. Unknown.

DISTRIBUTION AND BIONOMICS: Corethrella pauciseta is known from a single specimen (holotype) from Papua New Guinea at an altitude of 1250 m and from numerous specimens from Brunei and Sarawak, Malaysia ( Fig. 17 ) at altitudes of 30– 120 m. Habitats include lowland peat swamps (including standing water and very slow moving streams) and steep terrain in mature mixed dipterocarp forest ( Fig. 1 A). It is uncertain how the holotype female was collected. Female adult C. pauciseta are the most common species collected with frog-call traps in the area south of Liang, Brunei (= Labi Road of Grafe et al. 2008; as morphotype 1). Females have been found feeding on calling males of four species of frogs in Brunei and Sarawak (Table 7).

Sixteen female C. pauciseta were collected 12.5 km S. Liang, Brunei (04°34.935' N 114°30.300'E, 20 m) on 8- XI-2010 from vegetation hanging about 1–2 meters above a shallow pool (about 3X 6 meters in size) at mid afternoon. Females did not have mature eggs and larvae, pupae and pupal exuviae were absent from the pool, suggesting that these were not recently emerged adults. One possibility is that they were waiting to feed on calling frogs later that night but we have no evidence this was so.

TAXONOMIC DISCUSSION: Borkent (2008) indicated that a female from Brunei was similar to C. pauciseta (known only from the female holotype) but likely was an undescribed species. Here, in spite of significant size differences between the Papua New Guinea holotype (wing length = 1.63 mm) and the specimens from Brunei (wing length = 0.98–1.06 mm), we consider them conspecific. Now that more material is available from Brunei, we no longer consider the difference in number of clypeal setae to be significant (5 in the holotype, 2–3 in specimens from Brunei), especially considering the size differences. In addition, the holotype has one anepimeral seta compared to 2–5 setae in material from Brunei. Further material, especially from Papua New Guinea would be helpful in resolving these small meristic differences.

Borkent (2008) stated that C. pauciseta did not have distinctive elongate pedicel setae but fresh material from Brunei shows that they actually do. The habitus of the holotype from Papua New Guinea was poor.

Specimens from Ulu Temburong National Park in eastern Brunei appeared lighter in overall pigmentation compared to those from the Liang – Labi area in western Brunei. We presently consider this intraspecific variation.

The phylogenetic position of C. pauciseta is uncertain ( Borkent, 2008) and even though character 40 (from Borkent, 2008) is now known to be apomorphic for this species (it is a homoplastic feature), it does not shed further light on its position. There remains a conflict of character states, with C. pauciseta having the derived condition of characters 1–7, 21, 23, 25, 26, 40, 41, and 62 but the plesiomorphic state for characters 28, 35, 39, 42, 43, 46, and 47. The male and pupa of this species are needed for further interpretation.

MATERIAL EXAMINED: Holotype (as recorded in Borkent, 2008) ( CNCI); slide-mounted: 5 Ƥ, 12 km. S. Liang, Brunei, 30 m, various dates: 24-IV-2007, 4-V-2007, 15-V-2007, 28-V-2007 ( CNCI); 1 Ƥ, 15 km. S. Liang, Brunei, 40 m, 22-IV-2007 ( CNCI); 4 Ƥ, 17 km. S. Liang, Brunei, 40 m, 6-IV-2007 (3 CNCI; 1 UBD); 1 Ƥ, lower Sungai Apan, 0.6 km E. headquarters, Ulu Temburong National Park, Brunei, 110 m, 9-II-2010 ( UBD); 1 Ƥ, tributary of Sungai Belalong in the Temburong district, Brunei, 110 m, 115° 09'E, 4° 33'N, 50 m, 7-VIII-2006 ( CNCI). Pinned specimens: 1 Ƥ, lower Sungai Apan, Ulu Temburong NP, Brunei, 110 m, 9-II-2010 ( CNCI); 10 Ƥ, 12 km S. Liang, Brunei, 30 m, 4-III-2011 (8, CNCI; 2 UBD); 9 Ƥ, from previous locality but 4-XI-2010 ( CNCI); 1 Ƥ, Sungai Baki, Ulu Temburong NP, Brunei, 120 m, 18-VII-2008 ( CNCI); 8 Ƥ, Sungai Ingei, 8.2 km S. Melilas, Brunei, 50 m, VII-2010 ( CNCI); 7 Ƥ, from previous locality but 10-VII-2010 ( CNCI); 2 Ƥ, Lanjak Entimau, Sarawak, Malaysia, 80 m, 21-VI-2008 ( CNCI, SMKM); 4 Ƥ, Gunung Mulu NP, Sarawak, Malaysia, Headquarters, 30 m, 26-XI-2009 ( CNCI), 2 Ƥ, from previous locality but 14-XI-2009 ( CNCI); 1 Ƥ, from previous locality but 23- XI-2009 ( CNCI).

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 5. Habitus of adult female Corethrella, in lateral view, all in alcohol.

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 17. Distribution of Corethrella pauciseta.

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

FIGURE 10. A – D. Thoraces and legs of female Corethrella, lateral view; slide-mounted.

FIGURE 7. A – D. Head capsules of female Corethrella, anterior view. E – H. Antennal flagellomeres 1 – 4 of female.

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