Corethrella (Corethrella) edwardsi Lane, 1942

Amaral, André P., Mariano, Rodolfo & Pinho, Luiz Carlos, 2023, Description of five new species of frog-biting midges (Diptera, Corethrellidae) from Brazil and examination of new morphological characters with utility for taxonomic and phylogenetic studies, European Journal of Taxonomy 874 (1), pp. 1-120 : 72-75

Corethrella (Corethrella) edwardsi Lane, 1942

Fig. 34 ; Appendix 1

Diagnosis

Larva Only species with the following combination of characters: exuvia uniformly light brown ( Fig. 34D ); prementum and mandibular teeth lightly pigmented ( Fig. 34D ); siphon with seta 2-S very thick and located at midlength ( Fig. 34F ).

Pupa

Only species with the following combination of characters: respiratory organ tubular ( Fig. 34H ), elongate, and expanded subapically, without an apical opening, reticulate on distal half; lacking campaniform sensilla supraalar 2 and metathoracic 2 ( Fig. 34I ).

Material examined

BRAZIL – Bahia State • 2 ♂♂, adults, with larval and pupal exuviae; Maracás, Sítio do Pidi , pool; 13°17ʹ30ʺ S, 40°35ʹ23ʺ W; 425 m a.s.l; 8 Jun. 2019; A.P. Amaral leg.; CE-MHS • 1 ♀, adult, with pupal exuvia; same collection data as for preceding; CE-MHS • 1 ♀, adult; Porto Seguro, RPPN Veracel , muçununga; 16°21ʹ33ʺ S, 39°08ʹ15ʺ W; 72 m a.s.l.; 30 Aug. 2019; A.P. Amaral leg.; frog-call trap (chorus); CE-MHS .

Description

Male and female adults (1 ♂, 3 ♀♀)

HEAD. Sensilla ( Fig. 34A ): Ocular row with 2 thick offset setae at ventral part, more dorsally 10–12 setae shortly extending posteriorly. Subocular row well-defined, with about 12–14 setae from anterodorsal to posterodorsal portions. Vertex with several slender setae. Postgenal row with 12–15 intermediate setae, ranging from mid-posterior part of head to ventromedially. With 1 ventromedial thick seta.

THORAX. Sensilla ( Fig. 34B ): Proepisternum with 4–12 intermediate setae. Antepronotum with 1 thick anteroventral, 3–4 slender anterodorsal, and 4–6 slender lateral setae. Postpronotum with 1 thick and 2–6 slender dorsal setae.Scutum, prescutal area with 4–5 thick/intermediate anterior setae, 3 thick setae more posteriorly, and 6–7 slender setae in between. Antealar area with about 10–12 thick/intermediate setae anteriorly grouped and 9–10 slender setae scattered from ventral to dorsal portions. Supraalar area with 2–3 thick seta, with 5–7 slender setae surrounding; 4 intermediate setae anteriorly. Dorsocentral row, posterior part with 3 thick and 2 slender offset setae; 23–27 thick/intermediate and 20–31 slender setae filling row. Scutellum with 10 thick setae. Posterior anepisternum bare. Anepimeron with 5–9 slender setae.

WING. Male R 3 /R 1: 0.48; R 2+3 /R 2: 0.74. Female R 3 /R 1: 0.55 (0.54–0.57); R 2+3 /R 2: 0.53 (0.50–0.56).

LEGS. Empodium ( Fig. 34C ) of intermediate length and intermediate thickness, with 4 branches. Male Ta1/Ta2: 2.81; Ta3/Ta4: 0.55. Female Ta1/Ta2: 2.52 (2.42–2.65); Ta3/Ta4: 1.13 (1.08–1.20).

Larva (n = 2)

EXUVIA ( Fig. 34D ). Uniformly light brown; without tergal plates.

HEAD ( Fig. 34E ). Roughly triangular in dorsoventral view, 1.18–1.24 times as wide as long. Antenna 0.59–0.64 times length of head; antennal groove 1.27–1.32 times length of antenna. Ventral margin of antennal groove with about 5 well-developed denticles. Postmentum wide, tapering from base, 1.45–1.63 as wide as long; length 0.36–0.39 of head. Prementum straight, with 12–13 triangular teeth, lightly pigmented, central one largest, second small, third large, fourth smaller, fifth and sixth large. Anteromedial margin of gena not projected anteriorly, surface smooth. Postcoila indistinct, present as a faint line reaching lateral portion of head. Subgenal carina with multiple small spinules. Crown with 15–17 spines, regularly distributed, sizes growing posteriorly, ventral teeth shortest; largest spine 0.11–0.13 mm long. Seta 16-C mesial to crown. Mandible with lightly pigmented teeth; apical tooth length 1.20–1.30 of first dorsal tooth; seta 3-Mn 0.34–0.47 times length of 4-Mn; lacinia mobilis with 5 blades; mandibular lobe well-developed, pale, apart from teeth. Sensilla: 9-C elongate, bifurcated; 10-C elongate, simple; 11-C elongate, fan-like; 12-C elongate, simple; 13-C short, fan-like; 14-C elongate, simple; 15-C moderately elongate, forked; 16-C elongate, fan-like. 0a-Mn short, fan-like; 0b-Mn elongate, simple. 6-Mx elongate, fan-like; 4-Mx moderately elongate, fan-like; 5-Mx short, fan-like.

SIPHON ( Fig. 34F ). 0.39 mm (0.38–0.40) long. Seta 1 stout and forked, situated at 0.30 (0.28–0.32) of length from base; a thick and spine-like seta located at midlength; 6-S pale, 9-S lightly pigmented; 6-S/9-S: 0.70 (0.69–0.72).

Pupa (n = 3)

EXUVIA ( Fig. 34G ). Uniformly medium brown; setae on metathorax and abdominal segments I–II darkly pigmented and directed anteriorly; cephalothorax dorsal setae and abdominal setae III–VIII lightly pigmented.

CEPHALOTHORAX.Length 1.26 mm (1.22–1.32). Respiratory organ ( Fig. 34H ) tubular, elongate, expanded subapically, without apical opening, reticulate on apical half; 0.47 mm (0.42–0.49) long. Dorsal seta 1 moderately short, thick; about one length apart from dorsal 2; dorsal 2 of same length and thickness; both setae arising from elevated tubercule. Metathoracic 2 and supraalar 2 sensilla absent. Metathoracic seta 1 elongate, simple, moderately thick.

ABDOMEN ( Fig. 34I ). Elongate, gently tapering from II–VII, surface of tergites somewhat corrugated; length of segments I–VIII: 1.32 mm (1.24–1.37), width/length: 0.55 (0.53–0.57). Margins smooth, not expanded laterally. Setae D-2 moderately elongate, subequal from II–VII. Lateral setae short. Largest seta D-2-I, length 0.19–0.20 mm. Terminal process distinctly elongate, basal width 0.35 (0.34–0.36) of length, with paddles broad and spine-like process on mesial margin; D-1-IX thick, elongate, at about 0.70 from base; apical spine articulated; ventroapical seta V-1-IX about 1.3 times as long as apical spine; female genital lobe tapering, shorter than basal portion of terminal process; genital lobe in male elongate, tapering, extending shortly past basal portion. Chaetotaxy as illustrated.

Distribution and biology

This species is newly recorded both from the state of Bahia and from the Brazilian Northeast region. Immatures were collected from small ground pools in Maracás, an area of xeric shurbland (caatinga). Two individuals were captured with frog-call pan traps in the Atlantic forest of Porto Seguro. Altitudes range from 72 to 425 m a.s.l.

Corethrella edwardsi is also known from Costa Rica to Colombia, Guyana, and the Brazilian states of ES, MG, and MS, Central-West and Southeast regions, at altitudes ranging from 5 to 180 m a.s.l. ( Borkent 2008).

Remarks

The immatures of Corethrella edwardsi have not previously been formally described. Borkent (2008) briefly described the pupa, adding photographs of the abdomen and respiratory organ which match the specimens studied here. The pupal respiratory organ is unique among the species studied, without an apical opening and with pores distributed on the outer surface. The terminal process is also peculiar, distinctively elongate (the lowest average value of width/length), seta D-1-IX relatively long and thick, and apical spine also elongate. The pupa, similarly to the others of the peruviana group, lacks campaniform sensilla supraalar 2 and metathoracic 2, although, differing from that group of species, it has a metathoracic 1 seta, a trait shared with C. quadrivittata Shannon & Del Ponte, 1928 and C. whartoni Vargas, 1952 ( Borkent 2008). Curiously, the pupae examined here and the photograph in Borkent (2008) show the metathoracic and abdominal I–II setae directed anteriorly, with the rest of the setae directed laterally and posteriorly. Since this has not been observed in other species, we conclude it is peculiar of C. edwardsi .

On the larval siphon, the thick, spine-like seta at midlength was also not seen in any other examined species but is possibly present in C. quadrivittata (and perhaps other species in the quadrivittata group), as suggested by the illustration in Balseiro & Spinelli (1984).

Additionally, adults of Corethrella edwardsi and C. quadrivittata are the only species in the study with proespisternal setae. The quadrivittata species group is restricted to the Neotropical Region and has several unique synapomorphies, some revealed in the present study. When immature stages of other members of the group are discovered, it should be possible to better interpret their biogeographic history and the evolution of those characters, and further establish the position of the group within the family.

Figures

Fig. 34. Corethrella edwardsi Lane, 1942. A. Adult cranial setae, anterior and posterior views, and female clypeus in anterior view. B. Adult thoracic setae, lateral view. C. Hind leg claw and empodium, lateral view. D. Larval exuvia, ventral view. E. Larval head, ventral view, except mandible in dorsal view. F. Larval siphon, dorsal view. G. Pupal exuvia, dorsal view. H. Pupal respiratory organ, dorsal view. I. Pupal metathorax and abdomen, dorsal and ventral views. Scale bars: 0.2 mm. Abbreviations: 1, 6, 9-S = siphon setae.