Dimecoenia spinosa (Loew)

Mathis, Wayne N. & Marinoni, Luciane, 2016, Revision of Ephydrini Zetterstedt (Diptera: Ephydridae) from the Americas south of the United States, Zootaxa 4116 (1), pp. 1-110 : 84-87

26. Dimecoenia spinosa (Loew)

Figs. 115–121 , Map 26

Coenia spinosa Loew 1864: 99 .

Caenia spinosa [unjustified emendation].— Osten Sacken 1878: 204 [Nearctic catalog].— Aldrich 1905: 631 [Nearctic catalog]. Dimecoenia spinosa .— Cresson 1916: 152.— Sturtevant and Wheeler 1954: 166 [review].— Wirth and Stone 1956: 472 [review].— Wirth 1965: 755 [Nearctic catalog].— Steyskal 1970: 465 [review, Figs. of ♂ and ♀ terminalia].— Mathis and Simpson 1981: 30 -42 [revision, Figs. of adult and immatures, natural history].— Mathis and Zatwarnicki 1995: 240 [world catalog].— Mathis 1997: 65 –66 [review, Belize].

Diagnosis. This species is very similar to D. fuscifemur (Steyskal) , both having a less well developed interfoveal hump, but may be distinguished by the following combination of characters: legs stramineous to yellow, at most with dorsum of femora grayish; fronto-orbital setae nearly parallel with each other, both oriented obliquely posterolaterad; posteroventral portion of basal flagellomere and palpus also pale, mostly concolorous with legs; crossvein dm-cu distinctly arched, concave basally; face between antennal bases with broad, bronzish band; conformation of male and female terminalia distinctive. Moderately large to large shore flies, body length 4.40– 6.10 mm; mostly dull, olivaceous brown to grayish brown, dorsum with some subshiny to shiny areas.

Head ( Figs. 115–116 ): Head ratio 0.56–0.58; frontal ratio 0.44–0.47; mesofrons with metallic blue to greenish blue luster; parafrons not distinctly contrasted with mesofrons, subshiny; ocellar triangle more or less concolorous with parafrons; ocelli in equilateral triangle; medial ocellus marking posterior margin of slight depression, not as well developed as in specimens of C. austrina ; antenna mostly dark but with pale, yellowish orange areas, particularly toward posteroventral surface of basal flagellomere; arista longer than combined length of 1st 3 antennal segments, subpectinate above toward base, apical 1/3 style-like. Facial ratio 0.82–0.87; dorsal slope of interfoveal hump little evident, gradually projected; dorsum and antennal groove subshiny to shiny, mostly unicolorous and concolorous with shiny mesofrons; lower portion of face gradually becoming paler, nearly silvery in color; facial setae except along margins uniformly sized and space, marginal setae slightly larger, those extended from interfoveal hump widely separated in middle, numbering only 3–4 on each side; genal seta large, prominent, much larger than any facial seta. Eye ratio 1.23–1.26; gena-to-eye ratio 0.19–0.23. Gena moderately short; mostly bare and concolorous with face anteriorly, becoming darker and setose posteriorly; palpus noticeably pale yellow, sometimes slightly microtomentose, grayish.

Thorax ( Fig. 117 ): Generally dull, microtomentose, mostly olivaceous brown to grayish brown; mesonotum at most subshiny and slightly darker than pleural areas, with vittate pattern of dark and pale vittae, although difference between dark and pale areas slight; posterior portion of mesonotum and scutellum darker, frequently subshiny, dark brown; acrostichal setae mostly unseriated; dorsocentral setae 5 pairs. Legs wholly tawny, legs of male and female similar ( Fig. 118 ) lacking enlarged hindfemur and explanate tarsomeres bearing tufts of long hairs. Wing length averaging 3.95–4.14 mm; wing length-to-width ratio 0.42–0.47; costal vein ratio 0.23–0.26; M vein ratio 0.75–0.81; costal margin spinose; sometimes with slight infuscation along crossveins and veins.

Abdomen: Generally subshiny; anterior portion of each tergite darker, browner, posterior portion paler, grayish green; male tergite 5 as long as wide, longer than tergite 4; structures of male terminalia as follows ( Figs. 119– 120 ): epandrium more or less oval in posterior view, anteroventral margin evenly rounded; surstyli with large medial flange and posterolateral, slender process; gonite much longer than wide, 4 times, anteroventral margin broadly and shallowly U-shaped; phallapodeme with posteromedial, broad flange; aedeagus a simple tube, mostly parallel sided; female ventral receptacle ( Fig. 121 ) with operculum much smaller than extended process, trapezoidal in conformation, extended process broadly C-shaped.

Type material. Lectotype female of Coenia spinosa (designated by Mathis and Simpson 1981) is labeled “Mass[achusetts]./123/Loew Coll./ spinosa , m./ Type 11182 [red].” The lectotype and one female paralectotype are mounted on the same pin; the bottom specimen is the lectotype. Both specimens are deposited in the MCZ (11182).

Type locality. United States. Massachusetts. (42°'N, 70°W).

MAP 26. Distribution map for Dimecoenia spinosa Loew.

Additional specimens examined. BELIZE. Stann Creek District: Twin Cays (West Pond; 16°49'S, 88°06'W), Nov 1987, Mar 1988, W. N. and D. Mathis (4♂; USNM).

MEXICO. Baja California: San Quintin (30°29'S, 115°57'W), 18 Jul 1922, G. D. Hanna (1♂; USNM). Quintana Roo: Espiritu Santo Bay, Cozumel (20°25'S, 86°55'W), 5 Apr 1960, J. F. G. Clarke (1♀; USNM).

WEST INDIES. CAYMAN ISLANDS. Grand Cayman, North Sound, Booby Cay (19°20'S, 81°18'W; light trap), 6 May 1938, C. B. Lewis, G. H. Thompson (1♂, 2♀; BMNH).

JAMAICA. Clarendon: Portland Cottage (1 km S; 17°45.8'N, 77°12.6'W), 13 May 1996, D. and W. N. Mathis, H. Williams (1♀; USNM). St. Elizabeth: Salt Pond, Parottee Beach (1758.1'N, 77°50.2'W), 19 Apr 2000, W. N. Mathis (3♀; USNM).

Distribution (Map 26): Nearctic: Canada (New Brunswick, Nova Scotia), United States (California, Connecticut, Delaware, Florida, Georgia, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Rhode Island, Texas, Virginia). Neotropical: Belize, Mexico (Baja California, Quintana Roo), West Indies (Grand Cayman, Jamaica).

Natural history. Adults are encountered commonly in salt marshes where they sometimes “skate” on the water's surface. Mathis and Simpson (1981) described the immature stages that were collected and reared from submerged detritus and mud. They discovered that larvae of D. spinosa are unlike most of the tribe Ephydrini , lacking well-developed, paired prolegs except for a large, subcylindrical proleg on segment 12. They also suggested that the third-instar larva, which has sharply pointed posterior spiracles, may tap air stored in the stems and roots of aquatic plants for respiratory purposes when they are in submerged mud at some distance from the air/ water interface. See Mathis and Simpson (1981) for further details concerning the natural history and description of immature stages.

Figures

FIGURES 115 – 118. Dimecoenia spinosa (Loew). (115) head, lateral view; (116) same, anterior view; (117) mesonotum, dorsal view; (118) hindleg of male, lateral view (from Mathis and Simpson 1981).

FIGURES 119 – 121. Structures of male and female terminalia of Dimecoenia spinosa (Loew). (119) male terminalia, lateral view; (120) ventral margin of epandrium and surstyli, posterior view; (121) female ventral receptacle, lateral view (from Mathis and Simpson 1981).