Corethrella (Corethrella) solomonis Belkin, 1962

Published, First, 2008, The Frog-Biting Midges of the World (Corethrellidae: Diptera), Zootaxa 1804, pp. 1-456 : 50-51

Corethrella (Corethrella) solomonis Belkin

Corethrella solomonis Belkin 1962:540 . Type locality: Tenaru area , Guadalcanal, Solomon Islands. Holotype ♀ with associated pupal and larval exuviae (USNM).

Corethrella sp. Laird 1956:32 .

DIAGNOSIS: Male adult: unknown. Female adult: only extant species of Old World Corethrella with wing pigmentation restricted to a well-defined midlength band and with a few dark scales at the apex of R 4+5 (Fig. 66F), and with the fore- and midtibia each with discrete, narrow basal and apical dark pigmentation ( Fig. 38B).

DESCRIPTION: Male adult. Unknown. Female adult: Descriptive statistics: see Tables 6–11. Head: Outline in anterior view somewhat circular ( Fig.6E). Coronal suture elongate, extending ventrally past ommatida (as in Fig. 16B). Two or 4–6 large setae on frons between ventromedial area of ommatida (as in Figs. 16B, D). Antenna light brown, with basal half of flagellomere 1, apical portion of flagellomeres 6–8, all of flagellomeres 9–13 medium brown; pedicel without distinctive, more elongate, stout, dorsal or dorsolateral setae; flagellomeres as in Fig. 25L, sensilla coeloconica distributed as in Table 1; flagellomere 13 with welldeveloped apical bifurcation. Clypeus ( Fig. 17F) squarish or somewhat wider than long. Mandible with small, pointed teeth. Palpus ( Fig. 33F) dark brown; segment 3 of nearly constant width. Thorax ( Fig. 38B): Light brown with following medium to dark brown: paratergite and margin of scutum posterior to paratergite, posteromedial portion of scutum, scutellum, dorsal portion of mediotergite, anterior anepisternum, dorsal and ventral portion of anepimeron (pale at midheight), dorsal portion of katepisternum, metanepisternum. Posterior portion of dorsocentral row with 2 elongate setae situated somewhat lateral to one another. Prescutal suture elongate, thick, uninterrupted, extending to near dorsocentral row of setae. Anterior anepisternum divided diagonally by sinuous suture, dorsal portion about equal to ventral portion. Ventral portion of posterior anepisternum triangular, anterior margin with dark spot, posterior area pale, with anterodorsal margin not thick. Wing (Fig. 66F): Apex of R 2 equal to apex of M 1. Anterior margin with differently, discretely pigmented scales (indicating anterior margin of midlength band), with midlength band, R 4+5 with dark scales at apex; veins (other than costa and wing margin) with well-developed scales. Halter pale. Legs ( Fig. 38B): Light brown with forefemur with apical darker pigmentation, each of following with discrete basal and apical dark pigmentation: foretibia, midtibia, hind femur, hind tibia, midfemur with apical pigmentation but with or without basal pigmentation, at least mid-, hind leg tarsomeres 2–4 with banding. With only slender setae, lacking scales (except for some in patch of whip-like setae on posterior portion of hind tibia). Midleg with thick, subapical setae on each of at least tarsomeres 1–3. Claws of each leg equal to those of others; equal on each leg, simple (without inner teeth). Empodia slender. Abdomen: Light brown with anterior margins of each of tergites 2–7 and posterolateral areas of sternites 2–7 medium brown, segments 8–9 medium brown. Cercus medium brown.

Pupa. Described by Belkin (1962). Thorax: Scutum, metathorax each with spherical sensory pit (as in Fig. 100A). Respiratory organ (Fig. 101A): Tubular. Abdomen (Fig. 104A): Segments 3–7 somewhat expanded laterally. Paddle only moderately elongate; apicodorsal thick spine articulating; apicoventral seta longer than thick spine.

Larva (Fig. 81F–I). Described by Belkin (1962).

DISTRIBUTION AND BIONOMICS: Corethrella solomonis is known from the Solomon Islands (Fig. 115B) at at least 51 meters elevation. It is uncertain where the exact type locality is on Guadalcanal Island (which rises to 2331 meters). The holotype was reared from a larva collected from the leaf axil of a pandanaceous plant (likely Sararanga sp. ).

Larvae were collected from the base of fronds of two species of palms. Belkin (1962) further recorded this species, based on unreared larvae collected from an “arum-like plant” (also possibly Sararanga sp. ), on Bougainville Island but, although close to the Solomon Islands, these are actually from Papua New Guinea. The identity of these larvae, at least some of which are paratypes, is uncertain (see below).

TAXONOMIC DISCUSSION: The holotype female was originally on a pin and was slide-mounted for this study. Belkin (1962) recorded some larvae from other localities in the Solomon Islands but there are now two species known from these islands (see C. canningsi ) and the identification of these unreared larvae is therefore uncertain. Belkin (1962) recognized that the larval material he examined was strikingly variable and he excluded some, but not all of these, from the type series of C. solomonis . The discovery of a second species on the Solomon Islands suggested that at least some of these excluded larvae may those of C. canningsi .

Belkin (1962) listed the reared holotype female (with larval and pupal exuviae), one pupa, 33 larvae and “1 individual larval rearing” (possibly referring to the holotype) but noted that some of the larvae were excluded from the type series, without indicating the exact number. Aside from the holotype (with larval and pupal exuviae), I examined 10 larvae. Of these larvae, seven were labeled as paratypes. These seven larval paratypes were all from Belkin’s “Lot 834", which Belkin (1962: 542) indicated were collected in a different locality than the reared holotype. It is uncertain whether there are other paratypes and, if so, where they are located.

The two females studied here differ in the number of strong setae on the frons (2 or 6 ventromedially between the dorsal ommatidia), the shape of the first few flagellomeres (one specimen had only flagellomeres 1–4 present but 1–3 were significantly shorter) and degree of pigmentation of the antenna and the abdomen, suggesting the likelihood of two species being represented under this name. I have conservatively placed them in the same species.

Belkin (1962) mentioned that C. solomonis was unique in the genus in lacking mesepimeral setae (here = anepimeral) but there are a number of species without these setae ( Table 11).

MATERIAL EXAMINED: Holotype, adult female on microscope slide, larval and pupal exuviae on separate slide, labeled “ Holotype Corethrella solomonis Belkin ”, “ Holotype USNM 64799”, “ Guadalcanal Is., Br. Solomon Is. Oct’ 43-May’ 45, J.N. Belkin & al”, “Lot 920 Sub 301” ( USNM) . Paratypes: 7 larvae from type locality but labeled “Lot 823 sub 1" ( USNM) . Other material: 1 ♀, Tatamba , Santa Isabel Is., Solomon Islands ( BPBM) ; 3 larvae, Bougainville, Papua New Guinea, VI-1944 ( USNM) .

DERIVATION OF SPECIFIC EPITHET: The name solomonis certainly refers to the islands where the types originated.