Dixella lobata Chaverri and Borkent, 2007

Chaverri, Luis Guillermo & Borkent, Art, 2007, The Meniscus midges of Costa Rica (Diptera: Dixidae), Zootaxa 1575 (1), pp. 1-34 : 24-28

Dixella lobata Chaverri and Borkent n. sp.

( Figures 1I , 3C , 5C , 6I , 9B , 14A , 16B , 19A )

Diagnosis. Male: only species of Dixidae in Central America with the apical lobe of the gonocoxite slender and extending nearly to the apex of the gonostylus ( Fig. 14A ). Female: only species of Dixidae in Central America with a distinct pit on the lateral margin of abdominal segment 10 ( Fig. 16B ).

Description. Male. Head ( Fig. 1I ): brown, densely spiculate. Clypeus light brown, as wide as long. Antennal scape, pedicel brown, flagellomeres yellowish. Thorax ( Fig. 3C , 5C ): scutum with wide dark brown medial vitta extending from anterior margin to prescutellar area of scutum, narrowly continuing laterally to supraalar area; lateral dark brown vitta broadly joined to medial vitta anteriorly, extending to supraalar area, lateral margin notched above spiracular area. Scutellum, mediotergite dark brown. Pleura dark brown, somewhat patterned, except as follows: pronotum yellowish, yellowish below, posterior margin of katepisternum with yellow area. Wing ( Fig. 6I ; Table 1): with slight darkening over r-m; R2+3 originating at r-m; stem of R2+3 elongate, 0.65 length of R3. Halter: pale, 0.30 length of fore femur. Legs: coxae, trochanters brown; femora yellowish with brown apices; tibiae, tarsi uniformly pale brown; claws as figured ( Fig. 9B ). Genitalia ( Fig. 14A ): tergite 9 with anterior margin straight, posterior margin concave, with numerous scattered setae. Sternite 9 with posterior margin with broad excavation, with 6–8 elongate lateral setae. Gonocoxite wider than long; basal lobe absent; apical lobe longer than gonostylus, swollen at midlength, three elongate setae beyond midlength, two small subapical setae. Gonostylus densely spiculate, with elongate setae, apex tapering. Parameres directed anteromedially, tips heart-like. Aedeagus as figured. Tergite 10 tapering posteriorly, with posterolateral margin well-developed, protruding, medially with broad distal membrane with pale, difficult to discern, margin.

Female. As for male, with following differences: Wing ( Table 2). Genitalia ( Fig. 16B ): sternite 8 with posterior margin straight, with dense patch of medial setae; tergite 9 dark brown, lateral margin with posteriorly directed projection; tergite 9 with elongate, setose, posterolateral protuberance; sternite 9 narrow, anterior margin irregular, basal projection oriented anteromedially; segment 10 with apex truncate, 3–4 elongate subapical setae, 5 marginal setae shorter; cercus wide at base.

Immatures. not described.

Distribution and bionomics. This species is known from two localities in Costa Rica at elevations of 1540–2405 m ( Fig. 19A ) and is present during the wet season (July) and in virtually continuously wet habitats (March). Pupae and possibly larvae were found in ground pools, margins of a slowly moving stream (without fish) and in a seepage pool with a muddy substrate in a pasture. The specimens collected from 11 km N of San Isidro, Costa Rica, were collected as larvae from a ground pool. The habitats correspond to Premontane Moist Forest and Premontane Very Wet Forest transitional to Pluvial.

Taxonomic discussion. Adult C. lobata have the same pigmentation and wing characters as those of D. suzukii , but males of the two species are easily distinguished by their genitalia (see key; Figs. 14A, B ).

The male genitalia of this species exhibited significant variation in the shape of the gonostylus (tapering to rounded apically), the shape of the apical lobe of the gonocoxite (some more slender and sinuous), and the shape of the basal lobe of the gonocoxite. Further interpretation of such variation must await additional specimens.

Heinemann and Belkin (1977) recorded this species as Dixella sp. 2 , with the following specimens in the USNM labeled as such: CR 303-10, 101 and 303-100. The USNM has one male (lacking its genitalia and probably slide mounted earlier but apparently missing), with associated larval and pupal exuviae, one additional associated larval and pupal exuviae and one single larval exuviae all of which may be conspecific with D. lobata (CR303-11-13). Two specimens of D. lobata from 11 km N of San Isidro were identified as Dixella species 1 (?) by Heinemann and Belkin (1977).

Types. Holotype, male adult on microscope slide, labeled “ HOLOTYPE Dixella lobata Chaverri and Borkent ”, “ Costa Rica, Limón, Talamanca, Bratsi, Parque Internacional La Amistad , Valle del Silencio , 2405 m, 21-III-2003, G. Chaverri, En charco, LS 341222 577399, LGCh 582.01” ( INBC) . Allotype, female adult on microscope slide labeled as holotype with code LGCh 582.03 ( INBC) . Paratypes: 2♂, 1 ♀, on microscope slide labeled as holotype but with codes LGCh 582.02, 582.05 respectively (1♂, INBC; 1♂, 1 ♀, CNCI) ; 3♂, on microscope slides, one with associated larval and pupal exuviae, two with pupal exuviae, exuviae of all three on separate slides: Costa Rica, San Jose, San Isidro de Coronado, 5 km E of Rt. 216 junction on Natl. Rt. 6 and 0.2 km N on road to bridge over Rio Durazno , about 0.3 km W of bridge, 1540 m, 30-VII-1971, S.J. Heinemann ( USNM) ; 2♂ on microscope slide: Costa Rica, San José, La Ese , 11 km N of San Isidro on Natl. Rt. 2, 1300m, 20-XI-1962, R. Casebeer, C. Hogue & W. Powder, with codes 32 (without genitalia) and 32- 202 ( USNM) .

Derivation of specific epithet. The name lobata (lobe) refers to the short, setose, protuberance arising from the posterolateral margin of segment 9 of the female adult, a unique feature at least in Central America.

Figures

FIGURE 1. Head capsules of male Dixella, anterior view. (A) D. maculata; (B) D. hernandezi; (C) D. shannoni; (D) D. hansoni; (E) D. fernandezae; (F) D. jironi; (G) D. venezuelensis; (H) D. woodi; (I) D. lobata; (J) D. suzukii.

FIGURE 3. Thoraces of male Dixella, dorsal view. (A) D. venezuelensis; (B) D. woodi; (C) D. lobata; (D) D. suzukii.

FIGURE 5. Thoraces of male Dixella, lateral view. (A) D. venezuelensis; (B) D. woodi; (C) D. lobata; (D) D. suzukii.

FIGURE 6. Wings of male Dixella. (A) D. maculata; (B) D. hernandezi; (C) D. shannoni; (D) D. hansoni; (E) D. fernandezae; (F) D. jironi; (G) D. venezuelensis; (H) D. woodi; (I) D. lobata; (J) D. suzukii.

FIGURE 9. Claws of male Dixella. (A) D. woodi; (B) D. lobata; (C) D. suzukii.

FIGURE 14. Genitalia of male Dixella, dorsal view. (A) D. lobata; (B) D. suzukii.

FIGURE 16. Genitalia of female Dixella, ventral view. (A) D. venezuelensis; (B) D. lobata.

FIGURE 19. Distributions of Dixella species in Costa Rica: (A) D. woodi—O, D. lobata—#; (B) D. venezuelensis—O, D. suzukii—#.