Chrysotus soya Runyon, 2022

Runyon, Justin B., Beckendorf, Eric & Hesler, Louis S., 2022, A new species of Chrysotus Meigen (Diptera, Dolichopodidae) from soybean fields in South Dakota, USA, ZooKeys 1135, pp. 171-180 : 171

Chrysotus soya Runyon sp. nov.

Figs 1-3 , 4 , 5, 6 , 7-8

Type material.

Holotype, ♂ labelled: "South Dakota: Brookings Co/ North Central Ag[ricultural] Res.[earch] Lab/ soybean, 44.3388°, -96.7924° / 11 Aug 2021, red pan traps/ L. Hesler & E. Beckendorf"; "HOLOTYPE/ ♂ Chrysotus / Chrysotus soya / Runyon [red label]" (USNM, type number USNMENT01828501). Paratypes: South Dakota: 4 ♂, 57 ♀, same data as holotype (USNM, MTEC, NCARL). Montana: 1 ♂, Dawson Co., 1.5 km southwest of Glendive, 47.093354°N, 104.72388°W, 625 m, 10 July 2019, bee bowls, J. Brower (MTEC); 1 ♀, Sheridan Co., N Westby Road, 48.88642°N, 104.06082°W, 644 m, 29-30 August 2020, bee bowls, Z. Pritchard & J. Botti (MTEC).

Diagnosis.

Males of Chrysotus soya sp. nov. can be distinguished from other known New World species of Chrysotus by the following combination of characters: eyes contiguous below antenna; antenna entirely black (Fig. 2 ); palpus yellow, small, oval; calypteral setae and halteres white; legs lacking male secondary sexual characteristics; and the distinct coloration of the femora (dark brown, except base and apex of fore and mid femora and nearly basal half of hind femora yellow; Figs 1 , 3 ) with tibiae entirely yellow. In Van Duzee (1924), C. soya sp. nov. fits in the C. choricus species group and keys to C. parvicornis Van Duzee (= C. exiguus Van Duzee), but the latter species has dark femora with only the extreme tips yellow. In Robinson (1964), C. soya sp. nov. keys to C. flavicauda Van Duzee, but this species differs in having black calypteral setae and a yellowish hypopygium.

Description.

Male (Figs 1-3 , 5 ): body length 1.9-2.0 mm; wing length 1.7-1.8 mm. Head: eyes contiguous below, with anterior ommatidia slightly enlarged; upper face narrowly triangular, metallic green with dense light brown pruinosity along eye margins. Frons metallic green with bronze reflections and sparse light brown pruinosity. Postcranium metallic green with stronger bronze reflections and brown pruinosity. Palpus small, oval, light yellow, with 2-3 yellow to light brown setae. Proboscis small, brown with fine brown hairs along margin. Antenna (Fig. 2 ) entirely black; scape short, funnel-shaped; pedicel subequal in length to scape, spheroidal with subapical circlet of setulae; postpedicel reniform, 1.5 × wider than long, with a small point below insertion of arista-like stylus; arista-like stylus inserted just lateral to apex, length about 2 × combined length of scape, pedicel and postpedicel. Postocular setae white with uppermost setae grading to dark brown. Thorax: scutum and scutellum metallic green-blue with strong bronze reflections and sparse light brown pruinosity; about 6 pairs of biseriate acrostichal setae in offset rows; 6 pairs of dorsocentral setae, anterior-most pair small; scutellum with 1 pair of large marginal setae and 1 pair of small lateral setae. Pleuron metallic bluish green with dense gray pruinosity; 2-3 pale setae on lower proepisternum. Legs (Figs 1 , 3 ): coxae concolorous with pleuron but often slightly browner, with yellow apices; fore coxa with white to yellow-white setae; setae of mid coxa usually white but light brown in one specimen; hind coxa bare except for white to light brown anterodorsal seta. Trochanters yellow. Fore and mid femora yellow at base and apex, with broad dark brown band with green-blue reflections around middle; hind femur yellow with approximately apical half dark brown with green-blue reflections, dark coloration extending further towards base dorsally and ventrally; hind femur with 2-3 distinct anteroventral setae near tip. Tibiae entirely yellow; fore tibia with small anterodorsal seta near 1/4; mid tibia with large anterodorsal seta near 1/4 and 1/2, 2-3 indistinct posterodorsal setae on basal half, and apical ring of 4 setae with ventral seta strongest; hind tibia with anterodorsal seta near 1/4 and 1/2, 4-5 smaller posterodorsal setae, and apical ring of 4 setae. Tarsi unmodified, yellow with distal tarsomeres becoming brown, all legs with small claws and very small pulvilli. Ratios of tibia:tarsomeres for foreleg: 20-10-5-4-3-4; for midleg: 26-14-6-5-4-4; for hindleg: 24-8-6-4-3-2. Wing (Fig. 1 ): hyaline, narrowly elliptical, without anal lobe. Vein R2+3 nearly straight and slightly but evenly diverging from R4+5. Veins R4+5 and M1 slightly diverging before to just beyond crossvein dm-cu, then nearly parallel in apical fourth of wing. Vein M1 ending before wing apex. Crossvein dm-cu placed near 2/5 of wing length, about one-fifth as long as last part of CuA1. Calypter white with white setae. Halter stem yellow, knob white. Abdomen: cylindrical, only slightly tapering to apex. Tergites dark metallic green-blue with bronze reflections and sparse gray pruinosity, with dark brown to black setae; tergite 6 with numerous setae. Sternites concolorous with tergites; basal sternites with whitish setae, distal sternites with brown to black setae; sternite 8 covering hypopygial foramen, with small setae. Hypopygium (Fig. 5 ) partially embedded in tip of abdomen. Hypopygial foramen left lateral. Epandrium dark brown, ventral two-thirds shiny, dorsal one-third covered with minute pale setulae; ventroapical epandrial lobe rather flattened, with 3 broad lobes each bearing a pale seta. Surstylus shining brown, broadened ventrally near base; in lateral view, narrowed apically with slightly broadened and shallowly bilobed apex; in ventral view, spatulate; with apical small pale seta and 2-3 smaller subapical setulae. Cercus pale brown with numerous pale hairs and setae. Phallus narrow with sharply pointed apex; encircled by external membranous sheath that is expanded dorsally, this expanded area contains numerous narrowly-triangular spicules. Postgonites rather large, broadly rounded and covered with sparse microtrichia apically.

Female (Figs 4 , 6 ): body length 2.2-2.8 mm, wing length 2.0-2.5 mm. Similar to male except as follows: Head: face wide (width subequal to width of postpedicel), nearly parallel-sided, covered with dense light gray pruinosity which becomes yellowish along eyes. Palpi larger, yellow with base brownish, covered with yellow microtrichia and about five yellow to light brown setae. Postpedicel slightly shorter and wider (2.0 × wider than long). Legs: fore and mid femora with dark brown banding often reduced to nearly absent (in a few specimens, the fore and mid femora are entirely yellow). Abdomen: broader, more abruptly tapering to apex. Terminalia (Fig. 6 ) typical for Chrysotus species ( Capellari 2018). Acanthophorites (syntergites 9+10) each with four spines. Eggs (Figs 7 , 8 ): one dissected female contained seven eggs within the abdomen. These eggs were light yellow in color, elongate oval in shape, and of uniform size: approximate length 650 µm, width 170 µm. Chorion smooth and shiny. Yolk homogenous and evenly distributed throughout the cytoplasm. Micropyle located at the anterior tip. No other structures (e.g., aeropyles, nucleus) could be detected using light microscopy.

Etymology.

The specific epithet soya is derived from soya bean, a common name of soybean, Glycine max , and should be regarded as a noun in apposition.

Distribution.

Montana, South Dakota.

Remarks.

A heavily female-biased sex ratio of approximately 10:1 (females:males) was found in specimens of Chrysotus soya sp. nov. collected in South Dakota soybean fields. This skewed sex ratio occurred in both sets of specimens used in this study, those collected in red pan traps in 2021 (57 females, 5 males), and those collected on red sticky traps in 2016-2017 (1978 females, 218 males). Whether this reflects the true sex ratio is unclear, as females could be more attracted to red color than males.

Figures

Figure 4. Female habitus of Chrysotus soya sp. nov. In some specimens the dark coloration on the fore and mid femora is reduced, and in a few specimens, the fore and mid femora are entirely yellow.

Figures 1 - 3. Habitus, antenna, and fore and mid femora of the male holotype of Chrysotus soya sp. nov. 1 habitus, left lateral view 2 antenna, medial view 3 fore (top) and mid (bottom) femora, posterior view.

Figures 5, 6. Male and female terminalia of Chrysotus soya sp. nov., left lateral view 5 hypopygium of male 6 ovipositor of female. Abbreviations: ac - acanthophorite; epand - epandrium; ep lobe - epandrial lobe; ms - membranous swelling; pgon - postgonite; ph sheath - sheath of phallus; s - sternite; t - tergite.

Figures 7, 8. Egg extracted from abdomen of female Chrysotus soya sp. nov. 7 egg, lateral view 8 anterior tip of egg. Arrows indicate the micropyle.