Chrysotus interfrons sp. nov.

Runyon, Justin B., 2020, The Dolichopodidae (Diptera) of Montserrat, West Indies, ZooKeys 966, pp. 57-151 : 57

Chrysotus interfrons sp. nov. Figs 24 , 25 , 26

Type material.

Holotype, ♂ labelled: "MONTSERRAT:/ Cedar Ghaut/ 04AUG2005, V. G./ Martinson, D. Hughley/ Yellow Pan Trap"; "HOLOTYPE/ ♂ Chrysotus / interfrons / Runyon [red label]" (USNM, type number USNMENT01350615). Paratypes: Montserrat: 1 ♂, Woodlands, Riverside House, 5-7 January 2002, Malaise trap, Ivie, Marske & Puliafico; 2 ♂, 1 ♀, Hope Ghaut, 8-10 January 2002, yellow pan trap, K.A. Marske; 1 ♂, Cassava Ghaut, 877 ft, 16°45.75'N, 62°12.47'W, fogging at dawn, K. Marske & J. Boatswain; 1 ♂, Beattie House, 21-30 June 2002, uv light, M.A. Ivie; 2 ♂, Fogarty Ghaut (Soldiers), 16°46.41'N, 62°12.44'W, 21 June 2017, J.B. Runyon; 1 ♂, Runaway Ghaut, 175 m, 16°45.43'N, 62°12.89'W, 23 June 2017, J.B. Runyon; 1 ♂, Fairy Walk River, 260 m, 16°45.162'N, 62°10.854'W, 26 June 2017, J.B. Runyon (MTEC, USNM).

Description.

Male (Fig. 24 ). Body length 2.7-2.8 mm, wing length 2.2-2.3 × width 0.9-1.1 mm. Head: Face recessed, ca. 1.5 × as high as wide, nearly rectangular but very slightly narrowed below middle, ca. 3 × as wide as frons, metallic green cuticle almost completely obscured by yellowish white pruinosity. Frons (Fig. 25B ) narrowed above with narrowest width subequal to width of anterior ocellus, dark metallic green mostly obscured by white to yellowish white pruinosity. Palpus narrowly oval, pale yellow with a few small black setae. Proboscis dark yellow, with very fine brown hairs along margin. Antenna brown-yellow; first flagellomere small, truncated-triangular, two-thirds as long as high; arista-like stylus arising from median-apical sinus. Postocular setae pale yellow, uppermost four or five becoming brown; ventral postcranium with ca. four pale yellow setae per side that are longer than postocular setae. Thorax: Scutum and scutellum dark metallic green with weak copper and blue reflections and sparse light brown pruinosity that is denser on anterior and lateral slopes; setae on scutum light brown to black; seven pairs of biseriate acrostichal setae; six pairs of dorsocentral setae, anterior-most pair small; scutellum with one pair of large marginal setae and one pair of very small setae just lateral to larger setae. Pleuron dark brown with metallic blue reflections and moderately dense gray pruinosity; 1-3 yellow setae on lower proepisternum; upper proepisternum bare. Legs: Yellow, except most of coxa II, basal half or more of coxa III and 5th segment of tarsi brown. Anterior surface of coxa I with scattered, rather long yellow to brown setae; coxa II with scattered yellow to brown setae on anterior surface and large ad yellowish seta near 1/2; coxa III with large yellowish lateral seta near base. Femora I and II with pv row of brown setae (length <width of femur), those distally longest; femur III anteriorly and posteriorly with one or two erect yellow setae near base. Tibia I without distinctive setae but setae along ventral surface slightly longer (length subequal to width of tibia), finer, and usually paler than those on dorsal surface; tibia II with very small brown to black ad seta near 1/5 (length <width of tibia), sometimes a trace of a pd seta near 1/2, and 2 larger brown ventral setae at apex; tibia III with small ad seta near 1/5, usually larger pd seta near 2/5, 3/5, near tip, and very small pd seta near 1/6. Tarsi with pulvilli enlarged, on tarsus I slightly larger than tarsomere 5, less enlarged on tarsi II and III; tarsal claws absent on all legs. Ratios of tibia:tarsomeres: leg I: 36-22-10-5-4-4; leg II: 42-24-11-7-3-4; leg III: 50-16-13-8-5-4. Wing: Hyaline, broadly elliptical with well-developed anal lobe, veins brown. R2+3 straight, slightly and evenly diverging from R4+5. R4+5 and M1 nearly parallel beyond crossvein dm-cu. Crossvein dm-cu slightly less than half as long as last part of CuA1. Calypter yellow with yellow to light brown setae. Halter knob and stem light yellow. Abdomen: Cylindrical, metallic green with bronze reflections, sides of tergite II and basal sternites yellow. Setae of tergites brown to black, sternites with longer usually yellow setae. Tergite VI bare except one distolateral seta at lower margin. Sternite VIII with ca. eight brownish setae of various sizes, the largest two or three only slightly larger than setae along margins of tergites. Hypopygium (Fig. 26 ) small, brown, positioned in ventral notch at tip of abdomen. Hypopygial foramen lateral but positioned relatively far posteriorly and near dorsal edge. Epandrium brown, ventrally with small spine-like projection where phallus emerges; with broad ventroapical lobe that is subquadrate apically with ca. three small setae. Surstylus elongate, rounded ventrally, shining brown, with strong apical cylindrical seta with rounded tip that is subtended by a smaller seta. Cercus digitiform with slightly pointed apex, brownish yellow, with numerous stiff yellow to brown setae especially along basal half of dorsal margin. Phallus narrow with apex round; sheath of phallus membranous, slightly expanded subapically with a small tooth in membrane. Postgonites rounded apically with some microtrichia. Hypandrial apodemes rather long and narrow.

Female. Body length 2.8 mm, wing length 2.0 × width 0.9 mm. Similar to male, but face and frons with blue-violet reflections and yellow-brown pruinosity that is denser along eyes; frons as wide as face; clypeus distinct and forming lower one-third of face; palpus broader with a few more setae; antenna slightly shorter and more rounded distally; femora I and II with pv row of setae smaller and indistinct basally; femur III without erect setae near base; pulvilli not enlarged; wing tinged with brown; tarsal claws present on all legs.

Etymology.

This species is named for the relative width of the frons in males which is intermediate to males of the closely related species Chrysotus flavipes (Aldrich) and Chrysotus parvulus (Aldrich) (Fig. 25 ).

Distribution.

Montserrat.

Remarks.

Chrysotus interfrons forms a closely related group with two other West Indian species that have to date been treated in the genus Diaphorus . However, these species do not fit in the current definition of Diaphorus proposed by Robinson and Vockeroth (1981) since they lack setae on the upper proepisternum, black calypteral setae, a completely bare tergite VI, and four to eight long strong setae on sternite VIII (see discussion in Capellari and Amorim 2010). Diaphorus parvulus Aldrich was transferred to Chrysotus by Becker (1922, page 170), an act that has been largely overlooked. Diaphorus flavipes Aldrich is herein moved to Chrysotus : Chrysotus flavipes (Aldrich) comb. nov. Chrysotus mundus (Loew) is very similar to Chrysotus flavipes and the two are possibly conspecific.

Chrysotus interfrons is most easily separated from West Indian members of this group by the narrow frons (Fig. 25 ); additional characters distinguishing these related species are given in Table 3 . Chrysotus flavipes and C. parvulus are widespread in the Lesser Antilles, and both occur on Dominica ( Robinson 1975), Grenada ( Aldrich 1902), and St. Vincent ( Aldrich 1896) but C. flavipes is absent on Monserrat.

Figures

Figure 24. Chrysotus interfrons sp. nov. habitus of holotype male, left lateral. Scale bar: 1.0 mm.

Figure 25. Heads of males, anterodorsal views A Chrysotus flavipes (Aldrich) (Dominica) B Chrysotus interfrons sp. nov. (Montserrat) C Chrysotus parvulus (Aldrich) (Montserrat). Note differences in width of frons and enlargement of ommatidia. Scale bar: 0.5 mm.

Figure 26. Chrysotus interfrons sp. nov. male terminalia, left lateral. Abbreviations: epand-epandrium; ep lobe-epandrial lobe; hypand ap-hypandrial apodeme. Scale bar: 0.25 mm.