Corethrella

Borkent, Art & Grafe, Ulmar, 2012, The Frog-Biting Midges of Borneo — From Two to Eleven Species (Corethrellidae: Diptera), Zootaxa 3279, pp. 1-45 : 3-4

Key to the species of Corethrella of Borneo

This key will successfully identify material in either alcohol or slide-mounted specimens. Material in good condition, retaining their setae and scales, are significantly easier to identify than rubbed specimens. Nevertheless, pigmentation patterns, although not as clear, are yet present in the underlying cuticle of damaged material. Identification of the antennal sensilla coeloconica requires slide mounting but we have added other features to the key so they are not vital to identification. Readers should be aware that most of our material came from Brunei or nearby localities in Sarawak. It is very likely that undescribed species are yet to be found in Borneo, especially from elsewhere on the island. As such, slide mounting of at least representative material will increase the likelihood of accurate identification of the species.

The key below is based primarily on females because the males of only two of the 11 species are known, namely those of C. tigrina and C. calathicola . However, our use of colour patterns, likely shared by males and females, suggests that the key will work with both sexes. The pigmentation of the abdomen is described below based on cleared, slide-mounted specimens. At times, material in alcohol can be confusing because of underlying pigmentation of body tissues; in such instances, special care should be taken to study only the tergites and/or sternites.

Rubbed, pinned specimens of C. gilva , which otherwise have a midlength wing band ( Fig. 12K ), may appear to have no wing pigmentation. Such specimens would run to couple 2, but the combination of a scutum lighter than the dark pleura and pale abdominal tergites 2–6 ( Fig. 5 E) will correctly identify these.

1. Wing plain, without discrete pattern of pigmented scales ( Figs. 12B, E, F, I )....................................... 2

- Wing with at least some pattern of pigmented scales (anterior margin always with at least one distinct and discrete band of dark scales) ( Figs. 12A, C, D, G, H, J, K )....................................................................... 5

2 (1). Wing yellow ( Fig. 4 B); scutum yellow ( Fig. 4 B); katepisternum with at least some pale cuticle, contrasting with dark posterior anepisternum ( Fig. 9B ); base of hind femur dark brown, strongly contrasting with yellow base of midfemur ( Fig. 9B )... lutea ( Brunei, Malaysia ( Sarawak))

- Wing brown ( Figs. 4 E, F, 5C); scutum brown; pleura (including katepisternum and posterior anepisternum) uniformly dark brown (scutum and pleura not equal in some) ( Figs. 4 E, 10A, D); bases of mid- and hind femora equally pigmented, medium to dark brown ( Figs. 4 E, 10A, D)........................................................................... 3

3 (2). Scutum more lightly pigmented than pleura ( Fig. 10A ); abdominal tergites and sternites uniformly pigmented or at least each of abdominal tergites 2–5 more lightly pigmented posteriorly ( Fig. 13E )....................................... mitra ( Brunei, Malaysia ( Sarawak, Sabah))

- Scutum as dark brown as pleura ( Figs. 4 E, 5C, 10D); abdominal tergites uniformly brown ( Figs. 4 E, 13H)............... 4

4 (3). Clypeus with about 23 setae; wing length 1.30 mm (known from one specimen).............................. brunnea ( Malaysia ( Sarawak))

- Clypeus with 2–5 setae; wing length of Bornean specimens less than 1.07 mm .............................. pauciseta ( Brunei, Malaysia ( Sarawak), Papua New Guinea)

5 (1). Wing with a distinct subapical band ( Figs. 12A, J )............................................................ 6

- Wing with single midlength band represented by at least dark pigmentation on anterior margin of wing ( Fig. 12C, D, G, H, K ); with, at most, slightly darker pigmentation at very apex of veins R2, R3, and R4+5 ( Figs. 12H ).......................... 7

6 (5). Thorax uniformly brown (alcohol specimens with scutum with three narrow longitudinal vittae) ( Fig. 11A ); basal 0.7 of forefemur, all of midfemur and about basal half of hind femur similarly and uniformly brown (pigmentation not discrete) ( Fig. 11A );

abdomen uniformly brown ( Fig. 13I )................................................................ bicincta ( Brunei, Malaysia ( Sarawak)) Thorax with patterned pigmentation ( Fig. 9A ); forefemur with basal, midlength and apical darker pigmentation, mid- and hind femur with narrow basal and apical bands of dark pigmentation (pigmentation discrete) ( Fig. 9A ); at least each of abdominal tergites 2–6 more lightly pigmented posteriorly ( Fig. 13A )................................................ tigrina ( Brunei, Malaysia ( Sarawak)) 7 (5). Hind tibia with distinct basal and apical bands of dark pigmentation ( Fig. 10C ); palpus pale, contrasting with dark brown clypeus ( Fig. 7A ); midfemur with well-developed scales ( Fig. 11 C); wing with midlength band somewhat scattered, with scales on R4+5 pale (so that the dark scales on C, R1 and R 2+3 appear as a separate anterior darker spot), and with posterior portion of band situated separately at apex of CuA2 ( Fig. 12H )............................................. calathicola ( Singapore, Malaysia (Pahang, Sarawak), Indonesia (East Kalimantan), Brunei)

- Hind tibia with, at most, some darker pigmentation at very base and at apex ( Fig. 10B ); palpus entirely medium brown or with segments 1 and 2 brown and contrasting with pale segments 3–5 (base of segment 3 may be brown in some) ( Figs. 6 C, D, F, 7D); midfemur without scales; wing with midlength band forming a single anterior to posterior band of uniform pigmentation ( Figs. 12C, D, G, K ).................................................................................... 8

8 (7). Palpus with segments 1 and 2 (in some the very base of 3) dark brown, contrasting with light brown or pale segments 3 and 4 (5 grading apically to medium brown) ( Figs. 6 C, D); at least each of abdominal tergites 2–6 with darker pigmentation restricted to lateral margins, sternites 2–6 more lightly pigmented posteriorly ( Figs 13C, D ).......................... 9

- Palpus with all segments uniformly medium brown ( Figs. 6 F, 7D); abdominal tergites 2–6 uniformly pigmented, sternites 2–6 uniformly pigmented (in some with tergites lighter than sternites) ( Figs. 13F, J )................................... 10

9 (8). Flagellomeres 1–4 short, each notably shorter than flagellomere 5 ( Fig. 8 C)............................ nanoantennalis ( Brunei, Malaysia ( Sarawak))

- Flagellomeres 1–4 elongate, similar in length to flagellomere 5 ( Fig. 8 D)................................. bipigmenta ( Brunei)

10 (8). Hind tibia with dark pigment apically ( Fig. 10B ); 0–1 clypeal setae; flagellomeres 1, (sometimes 8), 9–13 with sensilla coeloconica and 9–12 (sometimes 13) with 2 sensilla coeloconica (1 with a few sensilla coeloconica).................. unizona ( Brunei, Malaysia ( Sarawak))

- Hind tibia with, at most, lightly pigmented apex ( Fig. 11B ); with 13–25 clypeal setae; flagellomeres 1, 9–13 with sensilla coeloconica and only flagellomere 1 with more than one sensilla coeloconicum.................................... gilva ( Brunei)

Figures

FIGURE 4. Habitus of adult female Corethrella, in lateral view, A – D, F in alcohol, E on microscope slide. C, F, with blood meal apparent in abdomen.

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

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 12. A – K. Wings of female Corethrella.

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

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

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

FIGURE 11. A – B. Thoraces and legs of female Corethrella, lateral view; slide-mounted. C. Portion of midfemur of female C. calathicola, at about distal third of femur, showing scales, dorsal view (with leg extended laterally from body).

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