Corethrella (Corethrella) calathicola Edwards

Published, First, 2008, The Frog-Biting Midges of the World (Corethrellidae: Diptera), Zootaxa 1804, pp. 1-456 : 145-147

Corethrella (Corethrella) calathicola Edwards

Corethrella calathicola Edwards 1930:529 . Type locality: Singapore, Malaysia. Lectotype male, here designated (BMNH). Mogi and Yong 1992:180.

DIAGNOSIS: Male and female adults: only extant species of Corethrella in the Oriental, Australasian, and Oceanic Regions with a pale or light brown palpus (contrasting with dark brown clypeus) ( Fig. 12C), patterned wing (with a midlength band, darker where R 1 joins the costa) (Figs. 64D, 70J), uniformly dark brown midfemur, hind tibia with dark pigmentation at base and apex ( Fig. 53B), and with abdominal tergites 1–8 uniformly dark brown (Fig. 79I).

DESCRIPTION: Male adult. Descriptive statistics: see Tables 2–5. Head: Outline in anterior view somewhat laterally elongate (as in Fig. 12C). Two large setae on frons between ventromedial area of ommatida (as in Fig. 16B). Antenna light brown; pedicel with at least one distinctive, more elongate, stout, dorsal or dorsolateral seta; flagellomeres as in Fig. 23D, sensilla coeloconica distributed as in Table 1; flagellomere 13 with well-developed apical bifurcation. Palpus pale; segment 3 of nearly constant width, somewhat ovoid at or near midlength. Thorax (as in Fig. 53B): Dark brown, pale sclerites around base of wing. Posterior portion of dorsocentral row with group of about 4 elongate setae. Prescutal suture short, not extending more than half way to dorsocentral row of setae. Anterior anepisternum divided diagonally by sinuous suture, dorsal portion about equal to ventral portion. Ventral portion of posterior anepisternum triangular, uniformly brown, with anterodorsal margin thick. Wing (Fig. 64D): Apex of R 2 basal to apex of M 1. Anterior margin with differently, discretely pigmented scales (indicating anterior margin of midlength band), slightly darkened scales on basal half of wing on C to M, with midlength band; veins (other than costa and wing margin) with well-developed scales. Halter as dark as scutellum. Legs (as in Fig. 53B): Medium to dark brown with apex of foretibia, base and apex of midtibia darker, apical 0.3–0.4 of hind femur pale, hind tibia with discrete basal and apical dark brown pigmentation, at least hind leg tarsomeres 2–4 with banding. Femora, tibiae with slender scales (also 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. Apices of fore-, midleg fifth tarsomeres undivided, with claws slightly subapical to apical (as in Fig. 75F). 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. Foreleg third tarsomere shorter than fourth tarsomere. Empodia slender. Abdomen (Fig. 79I): Segments 1–7, 9 light to medium brown, segment 8 pale. Genitalia (Fig. 94A): Gonocoxite uniformly medium brown, gently tapering; with well-defined dorsal row of setae; anteromedial area with spicules similar in length to those elsewhere on gonocoxite; with seta 2 slightly thicker than others, with row restricted to dorsal portion of gonocoxite. With one dorsomedial stout seta, more or less of even thickness for most of length, tapering near apex. Gonostylus (partially extended) mostly straight, curved subapically, slender, narrowed slightly at midlength, rounded apically; one elongate, slender subbasal seta, situated anteriorly or anteroventrally; apical seta slender, elongate, simple or bifurcating. Aedeagus slender, elongate, tapering gradually to apex, pointed apically, with lateral margins fused at apex.

Female adult. Descriptive statistics: see Tables 6–11. As for male, with following differences. Head: Coronal suture elongate, extending ventrally past ommatida (as in Fig. 16B. Antenna medium brown; with flagellomeres as in Fig. 30H, sensilla coeloconica distributed as in Table 1. Clypeus ( Fig. 18S) wide. Mandible with small, pointed teeth. Palpus as in Fig. 34 AE. Wing (Fig. 70J): as for male but with basal half of wing nearly entirely with dark scales (equal to those of midlength scale), some darkening of scales on apical portion of wing in some. Legs: Claws of each leg equal to those of others; equal on each leg, simple (without inner teeth). Abdomen: Medium to dark brown. Cercus medium to dark brown.

Pupa. Described by Edwards (1930). Thorax: Scutum, metathorax each with spherical sensory pit (as in Fig. 100A). Respiratory organ (Fig. 102J): Tubular. Abdomen (Fig. 108C): Segments 3–7 somewhat expanded laterally. Paddle only moderately elongate; apicodorsal thick spine articulating; apicoventral seta longer than thick spine.

Larva. Described by Edwards (1930).

Egg. Unknown.

DISTRIBUTION AND BIONOMICS: Corethrella calathicola is known from Singapore, Malaysia and Indonesia (Fig. 115A) at altitudes ranging from 0– 7 m. Although the exact locality of the specimens from Sarawak is somewhat uncertain (they were labeled with “Kuching?”), I have considered them from Kuching and placed this locale on the map. Borkent (2004) gave a synopsis of the family and pointed out that C. calathicola was the only species of Corethrella known from southeast Asia.

Edwards (1930) noted the presence of the immature stages of this species in “pitcher plants” and Barr and Chellapah (1963), Beaver (1979, 1983), Mogi and Chan (1996) and Mogi and Yong (1992) specifically described C. calathicola from the aerial pitchers of Nepenthes ampullaria , a beautiful epiphytic pitcher plant in Malaysia. Larvae of C. calathicola preyed on first to third instar larvae of Dasyhelea sp. and Tripteroides tenax , at least under laboratory conditions ( Mogi and Chan 1996). More than 65% pupated within 20 days, if prey were made readily available. Without prey, larvae were cannibalistic, with less than a 2% pupation rate. Beaver (1979), however, found cannibalism to be rare in nature, even though the distribution of larvae among Nepenthes pitchers was clumped. Mogi and Yong (1992) described the inter-pitcher distribution and number of larvae of C. calathicola and other organisms found in N. ampullaria . The maximum number of larvae found in one pitcher was five. Kitching (2000) referred to a Corethrella in the aerial pitchers of species of Nepenthes bicalcarata that may be those of C. calathicola and described in some detail the important role of Corethrella larvae in the aquatic community of Nepenthes ampullaria and N. bicalcarata . Nearly all adults studied here were reared or were collected in an unknown manner (specimens from Tarakan).

TAXONOMIC DISCUSSION: Males and females were associated through their shared pigmentation pattern and were reared from the same habitat. All the adult type material was previously on pins and is now slide-mounted. One male paralectotype from Sarawak was in poor condition, missing most of the thorax and abdomen (including the genitalia).

Edwards (1930) described the larva and pupa of C. calathicola and drew attention to similarities and differences with those of other species. He did not include these in his list of types but they clearly formed a basis for his recognition of the species. I have considered these as paralectotypes and have added labels to indicate this.

MATERIAL EXAMINED: Lectotype, here designated, adult male on microscope slide, labeled “ Corethrella calathicola Edwards , Lectotype, desig. A. Borkent”, “ Syntype Corethrella calathicola Edwards det. J.E. Chainey, 1995”, “ Type ”, “ Syntype ”, “ Corethrella calathicola Edw., F.W. Edwards. det. 1930”, “ Singapore. D.H.C. Given. B.M. 1925-518”, “bred from pitcher plants” ( BMNH) . Paralectotypes: 2 ♂, 3 ♀, 9 larvae (on 3 slides), labeled as for holotype; 2 ♂, Sarawak, Kuching? ( BMNH) . Other material: 2 ♂, Tarakan, Borneo, Indonesia, 20-VI-1945 ( USNM) ; 1 ♂, with larval and pupal exuviae, Pekan Rd. , Swamp Forest, Pahang Kuantan, Malaysia, 28-I-1959 ( ANIC) ; 1 ♀, with pupal exuviae, as for previous locality but II-1959 ( ANIC) .

DERIVATION OF SPECIFIC EPITHET: The name calathicola (basket in shape of a bowl, dweller) almost certainly refers to the pitcher plant habitat of the larvae, as noted by Edwards (1930).