Corethrella (Corethrella) davisi Shannon and Del Ponte, 1928

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 : 47-50

Corethrella (Corethrella) davisi Shannon and Del Ponte, 1928

Fig. 21 ; Appendix 1

Material examined

BRAZIL – Bahia State • 1 ♀, adult; Ilhéus, road to Lagoa Encantada ; 14°38ʹ52ʺ S, 39°05ʹ16ʺ W; 2 m a.s.l.; 18 Nov. 2019; A.P. Amaral leg.; F. call trap ( H. gratiosa , B. faber , P. cuvieri ); CE-MHS • 1 ♂, adult, with larval and pupal exuviae; Ilhéus, Cabruca da UESC ; 14°47ʹ33ʺ S, 39°10ʹ23ʺ W; 38 m a.s.l.; 20 Sep. 2019; A.P. Amaral leg.; stream; CE-MHS • 1 ♂, adult; same collection data as for preceding, except 4 Sep. 2019; CE-MHS • 1 ♀, adult; same collection data as for preceding, except 20 Sep. 2019; CE-MHS • 1 ♂, adult; same collection data as for preceding, except 14°47ʹ44ʺ S, 39°10ʹ21ʺ W; 35 m a.s.l.; 30 Sep. 2019; puddle; CE-MHS • 1 ♂, adult; Maraú, Lagoa Azul ; 13°58ʹ03ʺ S, 38°56ʹ22ʺ W; 4 m a.s.l.; 28 Sep. 2019; A.P. Amaral leg.; bromeliad; CE-MHS. – Santa Catarina State • 1 ♂, adult; São Francisco do Sul, CEPA Vila da Glória, “Açude do Alojamento” [pond by the lodge]; 26°13ʹ41ʺ S, 48°40ʹ55ʺ W; 13 m a.s.l.; 21 Apr. 2018; A.P. Amaral and L.C. Pinho leg.; hand net; CE-MHS.

Diagnosis

Larva

Only extant species with the following combination of characters: darkly pigmented tergal plates ( Fig. 21D ); a darkly colored mandibular lobe ( Fig. 21D ); head, siphon, and segment X medium brown ( Fig. 21D ), postmentum dark brown ( Fig. 21D ); basal width of postmentum 2.0–2.7 times its length ( Fig. 21E ).

Pupa

Only extant species with the following combination of characters: a flattened, wide, trilobed respiratory organ ( Fig. 21G ); a strongly tapered and short abdomen, with paddles short and narrow ( Fig. 21H ); abdominal margins not expanded laterally, with lateral setae weakly developed, shorter than each segment ( Fig. 21H ).

Description

Male and female adults (4 ♂♂, 1 ♀)

HEAD. Sensilla ( Fig. 21A ): Ocular row with 2 thick offset setae at ventral part, 9–10 setae more dorsally, shortly extending posteriorly. With subocular row of about 12 slender setae. Postgenal row with 7–9 slender setae, restricted to posteroventral region. With 1 ventromedial thick seta.

THORAX. Sensilla ( Fig. 21B ): Antepronotum with 1–3 intermediate anteromedial setae. Postpronotum with 1 thick dorsal and 2–3 slender setae. Scutum, prescutal area with 2–4 thick ventral setae and 2–3 posterodorsal setae near dorsocentral row. Antealar area with cluster of 5–9 thick/intermediate and 2–4 slender setae on posteroventral portion. Supraalar area with 3 thick and 3 slender setae on ventral portion. Dorsocentral row, posterior part with 4–5 thick offset setae, longitudinally aligned; 16–18 thick/ intermediate and 6–8 slender setae filling row. Scutellum with 10 thick setae. Posterior anepisternum with 1–2 slender dorsal setae. Anepimeron with 2–3 slender setae.

WING. Male R 3 /R 1: 0.64 (0.53–0.70); R 2+3 /R 2: 0.50 (0.37–0.66). Female R 3 /R 1: 0.67; R 2+3 /R 2: 0.39.

LEGS. Empodium ( Fig. 21C ) short, slender, with 2 branches. Male Ta1/Ta2: 2.43 (2.07–2.77); Ta3/Ta4: 1.35 (1.29–1.50). Female Ta1/Ta2: 2.30; Ta3/Ta4: 1.17.

Larva (n = 5)

EXUVIA ( Fig. 21D ). Head, siphon, and segment X medium brown, postmentum dark brown. Darkly pigmented tergal plates on I–VII.

HEAD ( Fig. 21E ). Roughly triangular shape in dorsoventral view, 1.22 (1.14–1.28) times as wide as long. Antenna 0.59 (0.53–0.65) times length of head; antennal groove 1.32 (1.18–1.48) times length of antenna. Ventral margin of antennal groove with 5–8 large denticles. Postmentum with base wide, strongly tapering, 2.42 (2.05–2.69) times as wide as long; length 0.28 (0.24–0.36) of head. Prementum straight, with 11–13 triangular teeth, darkly pigmented, central one largest, remaining ones somewhat smaller and equal. Anteroventral projection of gena somewhat projected anteriorly, slightly angular laterally, surface irregular. Postcoila short, not extending to lateral margin of gena. Subgenal carina with smooth surface. Crown with 9–10 spines, more sparse ventrally, sizes growing towards lateral; largest spine 0.03–0.04 mm long. Seta 16-C situated mesially from crown. Mandible with darkly pigmented teeth. Apical tooth length 1.73 (1.38–2.16) of first dorsal tooth. Seta 3-Mn 0.26 (0.21–0.33) times length of 4-Mn. Lacinia mobilis with 7 blades. Mandibular lobe well-developed, darkly pigmented apart from teeth. Sensilla: 9-C short, fan-like; 10-C elongate, simple; 11-C short, fan-like; 12-C elongate, simple; 13-C short, simple; 14-C short, simple; 15-C short, fan-like; 16-C elongate, simple. 0a-Mn short, simple or fan-like; 0b-Mn elongate, simple or fan-like. 6-Mx short, bifurcated; 4-Mx short, fan-like; 5-Mx short, fan-like.

SIPHON. 0.21 mm (0.20–0.22) long. Seta 1 bifurcated, at 0.30 (0.28–0.33) of length from base; 6-S and 9-S lightly colored; length of 6-S/9-S: 0.86 (0.80–0.95).

Pupa (n = 6)

EXUVIA ( Fig. 21F ). Medium to dark brown, with medial portion of abdominal segments III–VII somewhat darker; all setae lightly pigmented.

CEPHALOTHORAX. Length 0.91 mm (0.85–1.02). Respiratory organ ( Fig. 21G ) flattened, wide, trilobed, 0.48 mm (0.37–0.57) long longitudinally. Dorsal seta 1 short, thick, about two lengths apart from dorsal 2; dorsal 2 approximately twice as long, slender. Both setae arising from undifferentiated cuticle. Metathoracic and supraalar sensilla absent.

ABDOMEN ( Fig. 21H ). Short, strongly tapered posteriorly, surface smooth; length of segments I–VIII: 0.60 mm (0.51–0.73), width/length: 1.07 (0.94–1.21). Margins smooth, not expanded laterally. Setae D-2 shorter than half length of respective segments, equal from II–VII. Lateral setae L-4 short, about half length of respective segments. Largest seta V-5-III, 0.55 (0.40–0.66) times length of segment. Terminal process short, basal width 0.71 (0.65–0.80) of length, with narrow paddles, small indentation on mesial margin; D-1-IX somewhat short, located at about 0.5 from base; apical spine not articulated; lacking ventroapical seta V-1-IX; female genital lobe tapering, occupying most of basal portion; genital lobe ovate in male, slightly extending beyond base. Chaetotaxy as as illustrated.

Distribution and biology

The examined specimens were collected as immatures in puddles, margins of small brooks, and a pond, except one which was captured in the tank of a giant ground bromeliad, Aechmea multiflora L.B.Sm. , in Bahia. It is not clear whether this is a typical immature habitat for the species or it was an exceptional case. Corethrella pallida of the peruviana group has also been found in bromeliads, as well as in treeholes ( Borkent 2008). Individuals were found at altitudes ranging from 4 to 38 m a.s.l. in Atlantic forest fragments with different degrees of disturbance in Bahia and Santa Catarina states.

This species is also known throughout Central America, northern South America, and the Brazilian states of BA, MG, MS, PA, RJ, SC, and SP, at altitudes ranging from 0 to 637 m a.s.l. ( Borkent 2008; Amaral et al. 2019). It is possible that at least some of these records actually refer to C. bifida sp. nov.

Remarks

The specimens examined here present some slight variation in relation to previous descriptions of Corethrella davisi , which is expected as intraspecific variation of a broadly distributed species. Those variable features are the adult scutellum with 10 thick setae (12 in Lane 1953), pupa medium/dark brown (yellowish in Lane 1953), larval prementum with 13 teeth (10 in Lane 1953) and larval antenna 0.53–0.65 times the length of the head. With respect to the latter character, Lane describes the length of the antenna as the same as that of the head, what has not been observed in any species examined in the present study. The largest relative length of the antenna observed is in C. davisi , but this is only 0.65 of head length. We suspect that the character was possibly misinterpreted by Lane. In adults, the elongated setae on the posterior part of the dorsocentral row are here differently interpreted than in Borkent (2008) (see Morphology remarks).

Figures

Fig. 21. Corethrella davisi Shannon & Del Ponte, 1928. 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. Exuvia of larval head, ventral view, except mandible in dorsal view. F. Pupal exuvia, dorsal view. G. Pupal respiratory organ, dorsal view. H. Pupal methatorax and abdomen, dorsal and ventral views. Scale bars: 0.2 mm.