Acerocnema incisa sp. nov.

(Figs 1–6)

[Japanese name: Kiashi-kuchiboso-funbae]

Type material examined. Holotype ♂, Japan: Inada, Obihiro City, Tokachi, Hokkaido, 18. v. 2014, leg. H. Torikura (OUAVM) . Paratypes: Hokkaido, 3 ♂, 4 ♀, same locality as holotype, 15-25. v. 2014, leg. H. Torikura (OUAVM); 1 ♂, Kawanishi, Obihiro City, Tokachi, 11. v. 2014, leg. H. Torikura (OUAVM) ; 6 ♂, 34 ♀, Otofuke Town, Tokachi, 18-21. v. 2017, leg. H. Torikura (OUAVM) . Kyushu, 2 ♀, south of Ito campus, Kyushu Univ. Fukuoka City, 4. iv. 2015, leg. D. Kato (OUAVM) .

Diagnosis. Acerocnema incisa sp. nov. can be recognized by thorax with grey microtrichose, dorsal setulae on apical portion of vein R 1 of wing, and male surstylus anterodistally dilated

Description. Male. Head (Figs 1, 2): eyes reddish-brown; frons reddish; ocellar triangle black; face, parafacial, and gena yellow; occiput black and shining; postpedicel black and enlarged, approximately 2.5 times long as wide; arista basally pubescent and apically short-haired, approximately same length as postpedicel; palpi yellow and clavate; proboscis slender and sclerotized with reduced labella; vibrissal angle with a strong yellow vibrissa. Chaetotaxy (black): 3-4 fr, 3 or (1 proclinate, 1 lateroclinate, 1 latero-reclinate), 1 oc, 1 poc, 1 vti (strong), 1 vte. Thorax: wholly black; prescutum and scutum thinly grey microtrichose, with two longitudinally shiny stripes on scutum and with inconspicuous hairs (Fig. 1); scutellum shining; all thoracic pleura grey microtrichose; proepisternum anteriorly with hairs; anepisternum posteriorly hairy; katepisternum sparsely with long hairs; anepimeron, meron, and katatergite bare; metanotum shining in lower part. Chaetotaxy (yellow): 2 pprn, 2 npl, 1+1 ial, 1 sa, 2 pa, 1+3 dc, 1 bsc, 1 apsc,1 prepst, 1 prepm, 6-7 anepst, 1 kepst. Wings: hyaline, slightly tinged with brown; veins brown; R 1 with dorsal setulae on apical portion; veins R 4+5 and M 1 almost parallel; vein A 1 +CuA 2 disappear well before wing margin; calypter yellow, with hairs marginally; halteres yellow. Legs: entirely yellow, covered with hair-like setulae; fore femur with several pd setae distally; mid and hind femora with preapical setae; fore tibiae with 1 ad at two-fifths; mid tibia 1 ad at near half and subapical setae; hind tibia with 2 ad at one-third and half, and subapical setae; all tarsi yellow; fifth tarsomere somewhat compressed. Abdomen: tergites black and shining, covered with short hairs; sternites II to IV longitudinally rectangular, sparsely covered with hair-like setulae; sternite V (Fig. 3) deeply bilobate posteriorly; epandrium (Fig. 4) developed and sparsely with hairs but without setae; surstyli (Figs 4, 5) long, slender, curved and dilated antero-apically; aedeagus (Fig. 4) slender, apically swollen and membranous; epiphallus flattened, curved and pointed apically; parameres rod-shaped; hypandrium large, thick, and V-shaped; cerci stout and membranous, covered with hairs.

Female. Basal and ventral portions of postpedicel, postpronotum and proepisternum paler than those of male; abdominal tergites II to VI centrally black and laterally yellow to light brown; sternites III to VI longitudinally elongate; segments (tergites and sternites) VII to VIII (Fig. 6) compressed and tergite VIII strongly sclerotized; cerci, epiproct, and hypoproct weakly pigmented. Other characteristics as those of male.

Length (♂ ♀). Body, 4.0–4.2 mm; wings, 4.0–4.3 mm.

Distribution. Japan (Hokkaido and Kyushu).

Etymology. This new species is named after the scientific name of the flower species which has a close relationship with this fly.

Remarks. This new species is similar to A. kishimotoae Iwasa in general appearance, but differs from it in having the following characteristics: frons reddish; scutum grey microtrichose with inconspicuous hairs; male surstyli anterodistally dilated; female postpedicel same length as that of male. In A. kishimotoae, frons black; scutum shining, sparsely covered with distinct hairs; male surstyli gradually dilated toward the tip, not anterodistally; female postpedicel smaller than that of male.

Bionomics. Adults were collected from a flower community of Corydalis incisa (Thumb.) Per. in early spring. The larvae probably penetrate into the seed capsules of this flower.