Mesorhaga isthmia
Creators: name: Bickel, Daniel J.
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Dolichopodidae
Mesorhaga
Mesorhaga isthmia

description: The isthmia group
The isthmia group is characterized by:
1. Male lateral frons and ocellar tubercle with white supernumerary setae.
2. Lower calypter with long white setae in males, black in females.
3. Cercus straight but massive, distally rounded and clavate (e.g. Fig.3 a).
4. Male tarsus I sometimes modified (Fig. 3 c): It2 with 6–7 black ventral spine-like setae; It3 very short, much shorter than adjacent tarsomere, It4 with 4 short ventral setae (all MSSC).
5. Male IIIt4–5 sometimes flattened and ventrally pad-like.
This group comprises three species, from both the Neotropical and Nearctic regions: Mesorhaga isthmia,
n. sp., is widespread in Central America and has all the characters listed above. M. ornatipes Van Duzee from
Cuba has all the above characters except the male IIIt4–5 is not flattened. M. clavicauda Van Duzee from east-
ern North America has all the above characters except male tarsus I is unmodified.
Mesorhaga isthmia n. sp. (Figs 3 a-d)
Type material. El Salvador: Holotype ɗ, Sonzacate, 25.vi.1958, L.J. Bottimer (USNM). Paratypes, ɗ, 2 Ψ, Quezaltepeque, 500 m, 5.vii.1963, 19.vi.1963, D.Q. Cavagnaro & M. E. Irwin (CAS).
Additional material. ɗ, Costa Rica: GUANACASTE, 14 km S of Cañas, 28.vii.1991, F. D. Parker (EMUS). ɗ, Mexico: VERACRUZ: Puente Nacional, 30.ix.1975, flight trap, J.A. Chemsak (CAS). 4 ɗ, 10 Ψ, Nicaragua: Managua, km 12 Carretera Norte, 6 & 20.viii.1975, R. Mairena & M.J. Somneijer (INHS); ɗ, Panama: Bayano, Tucumen, 19.xi.1977, M.E. Irwin (INHS).
Description. Male: body length: 3.8 – 4.0 mm; wing: 3.4 x 1.3 mm.
Head: frons, face, and clypeus dark metallic blue-green, face/ clypeus with orientated silvery pruinosity; ocellar tubercle with pair strong diverging ocellars, with 14–16 pale, white, short hairlike setae posteriad (MSSC); with 3 strong postvertical setae present, in line with postoculars; with 3 setae present on lateral slope of posterior frons (MSSC); strong proclinate vertical present on lateral frons; palp brownish with black apical seta; proboscis yellowish; antenna black; pedicel with white setae, long ventrally, shorter dorsally; first flagellomere subrectangular; arista dorsal; ventral postcranium with white setae.
Thorax: metallic blue-green with bronze reflections; setae black; pleura with some grey pruinosity; 6–7 irregularly paired ac; lateral scutellar setae about one-third length of medians.
Legs: all coxae metallic green; trochanters I and II yellow, trochanter III dark brown; basal three- quarters of FI and FII, and almost all FIII dark brown with metallic green reflections; distal quarter of FI and FII, knee of FIII, all tibiae and tarsi I and II, and basitarsis III yellow; distal tarsomeres III brown; CI and CII with white, anterolateral setae; CIII with strong, white, lateral seta and some white shorter setae. I: 4.2; 4.2; 2.5/ 1.3/ 0.4/ 0.7/ 0.5; FI with av and pv pale setae in basal three-quarters; TI bare of major setae; It2–4 modified (Fig. 3 c): It2 with 6–7 black ventral spine-like setae; It3 very short, much shorter than adjacent tarsomere, It4 with 4 short ventral setae (MSSC). II: 5.0; 5.1; 3.0/ 1.2/ 0.8/ 0.7/ 0.4; FII with rows of white av and pv setae in basal third, av row with longer white setae to 1/2, with longest white seta at 1/2 (=almost one-third length of FII), followed distad by row of 6–8 long black setae decreasing in length from 1/2 to apex (MSSC), with only short white setae in pv row; TII with dorsal seta at ¼. III: 5.5; 6.4; 2.4/ 2.0/ 1.2/ 0.8/ 0.5; FIII with short white av and pv setae full length; TIII without major setae; IIIt4–5 flattened and ventrally pad-like (MSSC).
Wing: (Fig. 3 d) hyaline; vein M with gentle, right-angle curve; CuAx ratio: 0.8; lower calypter yellow, with black rim and fan of long, pale yellow setae (MSSC); halter yellow.
Abdomen: tergum 1 covered with short pair hairs, with black marginal setae; terga 2–5 metallic blue-green, with bronze reflections and matt brown areas with metallic reflections at tergal overlap between segments 2–6; segments 6 and 7 and hypopygium, dark brown; hypopygium (Fig.3 a); base of epandrium (normally covered by sternum 8) with whitish, almost translucent cuticle, with dark rim showing track of phallus around epandrium; phallus and hypandrium elongate and narrow, phallus when fully extended arching as shown; epandrial lobe ovate, with setae at 2/5 and 3/4; surstylus with 3 short arms and setae as figured; cercus massive and straight, heavily scletotised and distally clavate, with strong spinelike setae as figured.
Female: similar to male except: wing: 3.5 x 1.3; ocellar tubercle without pale hairs; 2 pairs shorter black setae posteriad; lateral frons with only vertical seta; femora with only short pale ventral setae; tarsi I and III unmodified; lower calypter with black setae.
Remarks. Mesorhaga isthmia is known mostly from lowland localities from Veracruz, Mexico, to Panama. The specific epithet is from the Greek isthmus, and refers to its occurrence on the narrow Mesoamerican isthmus connecting North and South America.
This species is distinctive in having obvious MSSC: white hairs on the ocellar tubercle, long white setae on the lower calypter, ventral spine-like setae on It2–4 (Fig. 3 c), and flattened pad-like tarsomeres IIIt4–5.
description: Published as part of Bickel, Daniel J., 2007, The Mesoamerican Mesorhaga (Diptera: Dolichopodidae), with a taxonomic conspectus of the New World fauna, pp. 47-67 in Zootaxa 1411 on pages 58-59, DOI: 10.5281/zenodo.175599