Corethrella borkenti, Amaral, André P. & Pinho, Luiz Carlos, 2015

Amaral, André P. & Pinho, Luiz Carlos, 2015, New species and records of frog-biting midges from southern Brazil (Diptera: Corethrellidae), Zootaxa 3946 (2), pp. 274-284 : 275-281

Corethrella borkenti sp. n.

( Figures 3–21 )

Type material. Holotype: female adult with larval and pupal exuviae: Brazil, Santa Catarina State, Florianópolis, Bairro Pantanal, 27°36’35” S 48°30’57” W, 115 m a.s.l., 12.ix.2012, in bromeliads, LC Pinho et al. leg. ( MZUSP). Paratypes: 1 female adult with pupal exuviae, as holotype except 30.iii.2014, LC Pinho & AP Amaral leg. ( MZUSP). 1 female adult with larval and pupal exuviae, as holotype except 27.vi.2014 ( MZUSP). 2 male adults with pupal exuviae, same data as previous ( MZUSP, INPA). 1 male adult with larval and pupal exuviae, same data as previous ( MZUSP).

Etymology. The specific epithet honors Dr. Art Borkent, for his great contribution to the systematics of Corethrellidae and other Diptera families.

Diagnostic characters. Adult female: Only extant species in the New World with well-defined midlength wing band and some scattered dark scales posterior to the basal anterior margin (mainly on C and Sc); femora lacking scales, hind tibia with discrete basal and apical banding; flagellomere IV with one sensillum coeloconicum and III, IX–XII each with two. Adult male: Only extant species in the New World with well-defined midlength wing band, third antennal flagellomere with one sensillum coeloconicum and two sensilla coeloconica on each of flagellomeres 10–12; prescutal suture short (not extending more than halfway to dorsocentral row of setae); femora lacking scales, hind tibia with discrete basal and apical banding and tarsomeres 2–4 of all legs with banding.

Descriptions. Female adult (n=3).

Head ( Fig. 3 ). Outline in anterior view laterally elongate, about 1.4–1.5 times wider than long. Two large setae on frons, between ventromedial area of the ommatidia. Coronal suture elongate, almost reaching ventral margin of area between ommatidia or past ommatidia. Antenna lightly pigmented; pedicel with three stout, more elongate setae on dorsal/dorsolateral region, flagellomeres as in figure 5, sensilla coeloconica distributed as in Table 1 . Flagellomere XIII with well-developed apical bifurcation. Clypeus ( Fig. 6 ) wide with three stout setae on anterior face; mandible with small pointed teeth; palpus as in figure 7, pale ( Fig. 3 ).

Thorax ( Fig. 4 ). Medium to dark brown, scutellum uniformly pigmented and of the same color as scutum. Posterior portion of dorsocentral row with about 5 clustered stout setae. Prescutal suture short, not extending more than halfway to dorsocentral row of setae. Anepimeron uniformly brown with group of 10–13 setae. Anterior anepisternum divided diagonally by sinuous suture; dorsal portion about equal to ventral portion. Posterior anepisternum with ventral portion triangular, uniformly brown without setae.

Wing ( Fig. 8 ). Apex of R2 basal to M1; wing length 1.39–1.42 mm; R1 0.63–0.68 times the length of wing. Anterior margin with differently, discretely pigmented scales (indicating anterior margin of midlength band). Midlength band well defined, with darkest scales on C, Sc and R1, lacking dark scales on R4+5, just a few on M1. Some scattered dark scales on basal and subbasal areas of anterior margin. Halter pale, contrasting with darker scutellum.

Legs. Fore- and midfemur uniformly medium to dark brown, hind femur medium to dark brown with apical 0.3 lighter; foretibia medium to dark brown with discrete or non-discrete apical banding at apex; midtibia uniformly brown; hind tibia brown with discrete basal and apical banding; tarsomeres 2–4 with band of darker setae; coxae medium to dark brown; legs with only slender setae, lacking scales; claws of each leg equal to those of others and equal on each leg (without inner teeth). Empodia slender.

Abdomen. Uniformly brown; cercus lighter than 9th segment.

Male adult: (n=3) as female, except:

Head ( Fig. 9 ). about 1.6–1.7 times wider than long. Flagellomeres as in figure 11, sensilla coeloconica distributed as in Table 1 . Clypeus elongate with 1 stout seta on anterior face.

Thorax ( Fig. 10 ). Anepimeron with group of 8–18 setae.

Wing ( Fig. 12 ). length 1.44–1.46 mm; R1 0.7 times the length of wing; anterior margin with differently, discretely pigmented scales (indicating anterior margin of midlength band); midlength band well defined, with darkest scales on C, Sc and R1, lacking dark scales on R4+5 and just a few on M1; patches of dark scales on M, basal to the midlength band.

Legs. Midleg with thick, subapical setae on each of at least tarsomeres 1–3. Claw of foreleg longer than those of mid-, hind leg; each claw without inner tooth; anterior claws of each leg without a basal prong; foreleg claws unequal; midleg claws equal.

Abdomen ( Fig. 13 ). Uniformly brown with 9th segment darker.

Genitalia ( Figs. 13–15 ). Gonocoxite ( Fig.14 ) medium brown, about 3.4–3.8 longer than wide (at midlength), gently tapering from base to apex, with base about 2 times wider, about 1.25 times longer than gonostyle; gonocoxite with well-defined dorsal row of 5 slender setae plus a more ventral thick one, located near the two basal ones. Gonostylus slender, straight for most of its extension, but curved apically; subbasal area thicker with a long whip-like seta displaced anteriorly; apex pointed with somewhat elongate apical seta, with one or two tiny setae close to apex. Aedeagus ( Fig. 15 ) slender, elongate, tapering from base, slightly rounded apically, with lateral margins fusing subapically.

Pupa (n=6). Total length 2.49–3.10 mm. Third abdominal segment 0.64–0.84 mm wide. Exuviae ( Fig. 16 ) medium brown with abdominal segments II–VII darker on medial portion.

Cephalothorax. Scutum, metathorax with spherical sensory pits. Respiratory organ ( Fig. 17 ) elongate, 13–18 times its basal width, slender, somewhat cylindrical, with 319–384 µm, maximum width about 29–49 µm.

Abdomen ( Fig. 18 ). Chaetotaxy as in figure 18. D2 and L4 very long on segments III–VII, with D2 progressively shorter on posterior segments; on segment II, D2 very short, L4 elongate but shorter than on III and more posteriorly; sclerite III with L4 1.9–2.1 times its medial length; segment VIII without sensilla. Segments expanded laterally with rounded, serrate margins. Terminal process 0.34–0.40 mm long, serrate on margins, with spined apex bearing long hook-like seta, mesial seta on external margin.

Larva (n=3). Coloration greyish.

Head ( Fig. 19 ). Length 0.59–0.62 mm, width 0.74–0.76 mm. Antennae 0.4 times length of head, bearing three stout apical spines, one longer than others, about 0.4–0.5 times as long as shaft. Mandible ( Fig. 20 ) with two dorsal teeth, one large apical tooth, five short inner teeth. Mandibular lobe large, pale. Outer margin with irregular contour; ventrally, two thick setae next to apex, a slightly shorter one at center, beside long one; basally a brush with eight stout, serrate spiniform setae. Mentum ( Fig. 21 ) with 12–14 bold teeth, increasing in size from lateral to center, except for teeth on each side of central one, which have approximately half of its size. Posterolateral row with 13–17 spines, of which 5–8 located dorsally, 8–9 ventrally.

Body. Damaged, chaetotaxy not described. Integument light greyish. Anal segment cylindrical, about 1.8 times longer than wide; siphon cylindrical 289–294 µm long, 88 µm wide.

Distribution and bionomics. This species is so far known only from the 115m a.s.l. type locality in Florianópolis, Santa Catarina state, Brazil. The specimens were sorted from mixed samples of Nidularium innocentii Lem. and Edmundoa lindenii (Regel) Leme.

Taxonomic discussion. The identification key provided by Borkent (2008) led the female adult specimens to couplet 96, which ends in Corethrella wirthi Stone, 1968 and C. ananacola Dyar, 1926 . After comparing the descriptions of those species with female adults of C. borkenti sp. n., some significant differences were found and support the recognition of a new species. These are the distribution of sensilla coeloconica (female of C. borkenti sp. n. with at least one sensillum on flagellomeres 1–4, 9–13, C. wirthi 1–3, (7–8) 9–13, C. ananacola 1–2, (3), 8– 13) coronal suture elongate instead of short on both C. wirthi and C. ananacola , clypeus wide with three stout setae (squarish with three setae on C. ananacola and squarish and with several setae on C. wirthi ), prescutal suture short (elongate in C. ananacola ), three stout setae on pedicel (Borkent does not specify how many, just describes the condition as at least one on both species). In addition, C. wirthi is known only from the Nearctic Region.

The key by Borkent (2008) can be modified to incorporate the new species as follows:

For male:

77 (75). Flagellomeres 10–12 each with two sensilla coeloconica..................................................... 78 - Flagellomeres 10–12 each with one sensillum coeloconicum.................................................. 79 78 (77). Palpus medium brown, with apex of segment 3 pale, segment 4 somewhat lighter. Antenna medium brown.......... wirthi - Palpus pale. Antenna light brown................................................................... borkenti

For female:

96 (95). Coronal suture elongate. Flagellomere IV with at least one sensillum coeloconicum.......................... borkenti - Coronal suture short. Flagellomere IV without sensilla coeloconica............................................ 97 97 (96). At least mid-, hind leg tarsomeres 2–4 with banding.......................................... ananacola (in part) - Mid-, hind leg tarsomeres uniformly pigmented.......................................................... wirthi

Borkent (2008) provided a cladistic analysis for the species of Corethrella . Based on available evidence, i.e., the presence of a sensillum coeloconicum on the third flagellomere, C. borkenti belongs to the wirthi species group. However, the character state is susceptible to homoplasy and, as acknowledged by Borkent (2008) the group is poorly supported.

Immatures stages also provide important taxonomic information. Borkent (2008) synonymized two species, C. downsi and C. bromelicola (described by Lane 1943; 1939b, respectively) with C. ananacola , stating that he could not find “distinguishing features separating the types ” (even though he could not locate the immatures of C. downsi ). Relying on the original descriptions of C. ananacola and its junior synonyms, it is possible to distinguish the pupae of C. borkenti sp. n. The length and shape of the respiratory organ (length six times basal width in C. downsi , according to Lane 1943; short in C. bromelicola , apparently nine times basal width in C. ananacola , based on Lane 1953 ’s drawing; 13–18 times basal width in C. borkenti sp. n.), and the size of abdominal setae D- 2-IV and L- 4-IV (short to medium sized on the three synonyms, but none with setae as long and arranged as in C. borkenti sp. n.) are also distinctive in the new species.

Figures

FIGURES 3 – 8. Corethrella borkenti sp. n., female adult. 3. Head, anterior view. 4. Thorax and legs, lateral view. 5. Antenna. 6. Clypeus. 7. Right palpus. 8. Wing.

FIGURES 9 – 15. Corethrella borkenti sp. n., male adult. 9. Head, anterior view. 10. Thorax and legs, lateral view. 11. Antenna. 12. Wing. 13. Abdomen, dorsal view. 14. Left gonocoxite and gonostylus, dorsal view. 15. Aedeagus.

FIGURES 16 – 21. Corethrella borkenti sp. n., pupa (16 – 18) and larva (19 – 21). 16. Pupal exuviae, dorsal view. 17. Right respiratory organ. 18. Metathorax and abdomen, tergites to the left, sternites to the right. 19. Larval head capsule, ventral view. 20. Right mandible, dorsal view. 21. Mentum.

Tables

TABLE 1. Numbers of sensilla coeloconica on adults of Corethrella borkenti sp. n.

Flagellomeres	I	II	III	IV	V	VI	VII	VIII	IX	X	XI	XII	XIII
Females	3	2	2	1	0	0	0	1	2	2	2	2	1
Males	2	1	1	0	0	0	0	0	1	2	2	2	1