Corethrella (Corethrella) stenostyla, Amaral & Bello-González & Pinho, 2021

Amaral, André P., Bello-González, Orestes C. & Pinho, Luiz Carlos, 2021, Corethrella stenostyla sp. n., a new frog-biting midge (Diptera: Corethrellidae) from Cuba, Zootaxa 5060 (4), pp. 595-598 : 595-598

Corethrella (Corethrella) stenostyla sp. n.

( Figs. 1 & 2 )

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Type material. Holotype: male adult, slide mounted: “HOLOTYPE Corethrella stenostyla Amaral, Bello-González & Pinho ♂, CUBA, Granma Province, Guisa, La Bayamesa National Park, 1km of ‘ Pico La Bayamesa’ , xii.2015, Malaise trap, Orestes C. Bello-González leg.” ( CEMHS).

Etymology. The specific epithet refers to the slender shape of the gonostylus, also present in other species.

Diagnostic characters. Male adults: only extant species in the New World with a plain wing; ventral portion of posterior anepisternum triangular, without a thickened anterodorsal margin; thorax brown, ventral portion of anepimeron, trochanters and bases of hind and midfemora pale; foreleg third tarsomere shorter than fourth.

Description. Male adult (n=1).

Head ( Fig. 2A ). Medium to dark brown. Outline in anterior view moderately laterally elongate, 1.43 times wider than long. Coronal suture complete, reaching ventral margin of interocular space. Clypeus ( Fig. 2B ) square, 1.08x wider than long, with 3 setae. Palpus ( Figs. 2A, C ) slightly less pigmented than head, third segment with constant width, length of fifth 0.83. Antenna ( Fig. 2D ): pedicel dark brown, flagellum medium to dark brown with very base of flagellomeres II–XIII pale; flagellomeres ( Fig. 2E ) I, III elongate, II somewhat short; flagellomere XIII apically bifurcated. Sensilla coeloconica distribution: 1(IX–XIII), 4(I). Sensilla ( Fig. 2B ): Ocular row with 1 thick offset seta at ventral part, 12 more dorsally, extending a little beyond vertex. With subocular row not well-defined, many slender setae on vertex and interocular space. Postgenal row with 10 intermediate setae, contiguous to ocular row, extending to ventral margin. With 1 ventromedial seta.

Thorax ( Figs. 2F, G ). Medium to dark brown; ventral portion of anepimeron and hind coxa pale, sclerites around wing light brown. Prescutal suture moderately elongate, fading dorsally. Anterior anepisternum divided longitudinally by sinuous suture. Posterior anepisternum triangular, with anterodorsal margin not thick. Sensilla ( Fig. 1H ): Antepronotum, 13 intermediate setae on anterior and lateral portions. Postpronotum with 1 thick, dorsal seta and 3 intermediate, more posterior setae. Scutum, prescutal area with 8 intermediate and slender setae located anteriorly, 2 thick and 1 intermediate near prescutal suture. Antealar area with 3 thick setae and 1 slender seta near prescutal suture, 13 thick and intermediate setae spread posteriorly on ventral portion. Supraalar area with 2 thick setae on posterior portion, 6 slender and 4 intermediate ones more anteriorly. Dorsocentral row, posterior part with 4 thick offset setae, about 26 thick and intermediate, 13 slender setae filling the row. Scutellum with 12 thick setae. Posterior anepisternum bare. Anepimeron with 3 slender posterodorsal setae.

Wing ( Figs. 2J, K ). Medium brown, somewhat greyish. non-marginal veins with narrow scales. Without pattern of pigmentation. Apex of R 2 slightly basal to apex of M 1. Ratio of lengths of R 3 /R 1: 0.64; R 2+3 /R 2: 0.37. Pigment of haltere same as that of scutellum.

Legs ( Fig. 2F ). Medium brown, with trochanters and bases of hind and midfemora pale. Tibiae and femora without scales. Midleg tarsus apparently lacking distinctively thick subapical setae. Ratio of lengths of Ta1/Ta2: 3.00; Ta3/Ta4: 0.52. Tarsal claws of foreleg unequal and longer than hind and midleg claws. Empodium ( Fig. 2I ) of intermediate thickness and length, with 4 branches.

Abdomen ( Fig. 2L ). Medium brown, with segments 7–9 and gonocoxite darker. Segment 8 pale posteriorly.

Genitalia ( Figs. 2M, N ). Gonocoxite slender, without distinctively elongate spicules on anteromedial area; dorsal row well-defined with 6 stout elongate setae restricted to dorsal region; 1 dorsomedial stout seta, tapering from base, located at 0.17 from base of gonocoxite. Gonostylus slender, with nearly constant width; sub-basal seta simple and elongate, situated anteriorly, at 0.28 from base; gonostylus with blunt, peg-like bristle inserted at apex and 5 small subapical setae. Aedeagus strongly tapering from midlength, margins fused subapically.

Female and immatures. Unknown.

Distribution and biology. This species is known solely from the male holotype, collected in a Malaise trap set in La Bayamesa National Park, Cuba, in an area of montane rainforest, at approximately 1400m a.s.l. ( Figure 1 ).

Taxonomic discussion. Corethrella stenostyla sp. n. is morphologically peculiar. According to the phylogeny proposed by Borkent (2008), it presents the derived conditions of characters 1–3, 5–10, 13–18, 21, 25–26, 28–30, 33, 41, 43, 63–65, 68–69, 82, but is plesiomorphic to 42–44, 70–81, 84–89. Among the derived traits are: a short third anterior tarsomere, the presence of a slender, anteriorly positioned sub-basal seta on the gonostylus and the gonocoxite with the dorsomedial seta more basally located. Conflicting plesiomorphic characters are the posterior anepisternum without a thick, discrete anterodorsal margin and apex of gonostylus with an apical peg-like bristle instead of a slender seta. Three species, Corethrella evenhuisi , C. canningsi and C. pauciseta , belonging to Oceanian region (the latter also present in Orienatal region), present a similar combination of apomorphic and plesiomorphic character states ( Borkent, 2008). Unfortunately, those species are only known as females, thereby hampering further comparisons, given that many of the relevant characters in C. stenostyla are related to male genitalia. Still, Corethrella stenostyla differs from those three species by its plain wings with narrow veins and mid and hind femora pale at base. It is nevertheless remarkable that the species with greatest similarity in morphology are found in such distant biogeographical regions, though only a new phylogenetic analysis of the family, including adults and immatures, molecular and other sources of character data will satisfactorily resolve their affinities.

The other species recorded for Cuba, C. maculata ( Lane, 1939) , can be promptly differentiated from C. stenostyla sp. n. by its banded wings, pale halteres, tergites with whitish apical bands and gonocoxite with a dorsal row of five stout setae.

Figures

FIGURE 1. Collection site in La Bayamesa National Park, Cuba.

FIGURE 2. Corethrella stenostyla sp. n., adult male. A, head in dorsal view. B, cranial setae, anterior and posterior views. C, palpus. D, antenna. E, flagellomeres. F, thorax and legs, lateral view. G, detail of thorax, lateral view. H, thoracic setae. I, empodium. J, wing. K, wing venation. L, abdomen. M, abdominal segments 8–9 and genitalia, dorsal view. N, genitalia.