Dixella shannoni Lane

Chaverri, Luis Guillermo & Borkent, Art, 2007, The Meniscus midges of Costa Rica (Diptera: Dixidae), Zootaxa 1575 (1), pp. 1-34: 11-12

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http://doi.org/ 10.11646/zootaxa.1575.1.1

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Dixella shannoni Lane


Dixella shannoni Lane  

( Figures 1C View FIGURE 1 , 2C View FIGURE 2 , 4C View FIGURE 4 , 6C View FIGURE 6 , 7C View FIGURE 7 , 11A View FIGURE 11 , 15B View FIGURE 15 , 18A View FIGURE 18 )

Dixella shannoni Lane, 1942: 88   ; 1953:51. Type-locality: San Mateo, Higuito, Costa Rica. Holotype male (USNM).

Diagnosis. Male: only species of Dixidae   in Central America with a wide pale medial band on the pleura extending from the anterior margin of the katepisternum to the posterior margin of the anepimeron ( Fig. 4C View FIGURE 4 ), with the gonostylus rounded apically, and with the aedeagus triangular anteriorly (not bilobed) ( Fig. 11A View FIGURE 11 ). Female: only species of Dixidae   in Central America with a wide pale medial band on the pleura extending from the anterior margin of the katepisternum to the posterior margin of the anepimeron and R2+3 originating distal to r-m (females of D. jironi   n. sp. and D. hansoni   n. sp. are unknown but likely are the same as D. shannoni   in this regard).

Description. Male. Head ( Fig. 1C View FIGURE 1 ): brown, densely spiculate. Clypeus brown, as wide as long. Antennal scape, pedicel brown, flagellomeres brown. Thorax ( Fig. 2C View FIGURE 2 , 4C View FIGURE 4 ): scutum yellowish, with narrow lateral light brown band extending from anterior margin, widening near prescutal suture, continuing laterally to supraalar area, anterior to middle of scutum lateral band continues medially as faint yellow line; with row of setae to prescutellar area; acrostical, anterior dorsocentral, supraalar setae short, scattered; with 2–3 setae on posteroventral margin of posterior anepisternum. Scutellum brown, mediotergite yellowish. Pleura light brown, with wide pale medial band extending from anterior margin of katepisternum to posterior margin of anepimeron. Wing ( Fig. 6C View FIGURE 6 ; Table 1): without dark spot over r-m; R2+3 originating slightly distal to distal to rm; stem of R2+3 0.45-0.50 length of R3. Halter: pale, 0.30 length of fore femur. Legs: uniformly yellowish or brown; claws as figured ( Fig. 7C View FIGURE 7 ). Genitalia ( Fig. 11A View FIGURE 11 ): Tergite 9 with anterior, posterior margins curved, with mostly scattered setae, larger group of medial setae. Sternite 9 with posterior margin with narrow, slightly bilobed excavation, with submedial elongate seta, three lateral setae in row. Gonocoxite as long as wide; basal lobe short, spiculose with medial margin truncate; apical lobe cylindrical, tusk-like, slightly curved dorsally, tip slightly rounded, 0.5 length of gonostylus, with elongate basal seta, elongate midlength seta, two subapical setae. Gonostylus swollen at base and apex, with subapical spine as long as width of apex of gonostylus. Parameres dark brown, mostly directed dorsally but with apices directed posteriorly. Aedeagus as figured. Tergite 10 light brown, posterolateral portion with group of short sensilla.

Female. As for male, with following differences: Wing ( Table 2). Genitalia ( Fig. 15B View FIGURE 15 ): sternite 8 nearly as long as width of posterior margin, posterior margin concave medially, with numerous setae; tergite 9 with posterolateral margin rounded, projecting posteriorly; sternite 9 elongate, narrow, laterally with anteromedially directed projection, apically curved laterally or posteriorly; segment 10 with setae evenly distributed, posteroventral margin rounded; cercus short, broad, with elongate setae.

Immatures. Unknown.

Distribution and bionomics. Dixella shannoni   is known only from Costa Rica from altitudes of 180– 700 m ( Fig. 18A View FIGURE 18 ). Adults have been collected during the dry season (January) and habitats include Tropical Moist Forest and Premontane Moist Forest. The adults from 4 km W. Ciudad Colon were swept with an aerial net along a stream in Zona Protectora El Rodeo. One male from Navarro was collected with a light trap.

Taxonomic discussion. The male and female of this species were associated by their similar pigmentation pattern and were collected together 4 km W. of Ciudad Colón, Costa Rica. The male of Dixella shannoni   is morphologically very similar to those of D. jironi   and D. hansoni   but each may be distinguished through differences in the genitalia (in the latter two females are unknown).

The holotype and a male paratype of D. shannoni   have the base of R2+3 arising from very near r-m, while in the remaining specimens it is more distal. The significance of this variation is unclear.

A female from Monteverde, 2 km E. Santa Elena, Costa Rica (26-VI-1993, A. Borkent; INBC) was originally thought to be a member of this species because it has the pale pleural stripe on the thorax. However, the specimen had an elongate clypeus and a short abdominal sternite 8 (elongate in D. shannoni   ) and it likely represents an unnamed species. We prefer to await the discovery of the male before formally describing this species.

Lane (1942) noted the presence of a male holotype, a female allotype, and three male paratypes. We examined the holotype, allotype and two male paratypes. One paratype appears to be missing and one of the two known paratypes is represented by only one leg.

Types. Holotype, male adult on microscope slide, labeled “Holotipo”, “ Dixella shannoni Lane   , 41", “Higuito, San Mateo, CR”, “Pablo Schild Coll” ( USNM)   . Allotype, on microscope slide, labeled as for holotype ( USNM)   . Paratypes: 2♂, labeled as for holotype (one on microscope slide, one on pin (a single leg); USNM)   . Other material: 15♂, 12 ♀, on microscope slides, Costa Rica, 4 km W. Ciudad Colon, 700 m, 7-I- 1994, A. Borkent, CD 1732, (6♂, 4 ♀, INBC; 9♂, 8 ♀, CNCI)   ; 1♂, on microscope slide, Costa Rica, Prov. Cartago, Navarro , VII-1962, F.S. Blanton, light trap ( USNM)   ..

Derivation of specific epithet. This species was named for R.C. Shannon by Lane (1942).


Smithsonian Institution, National Museum of Natural History


Instituto Nacional de Biodiversidad (INBio)


Canadian National Collection Insects














Dixella shannoni Lane

Chaverri, Luis Guillermo & Borkent, Art 2007

Dixella shannoni

Lane, J. 1953: 51
Lane, J. 1942: 88