2. Colocasiomyia oligochaeta species subgroup, new

Diagnosis. Antennal arista apically truncate, stick-shaped (ch.4-1; Fig. 3D, E). Proclinate, orbital setae absent (ch.8- 1; Fig. 2D, E). Anterior, dorsocentral setae absent (ch.26-2; Fig. 6D, E). Patch of supracervical setae present over basal portion of dorsolateral, tentorial apodeme (ch.13-1; Fig. 4D, E). Dorsolateral, tentorial apodemes distally strongly curved outward (ch.14-1; Fig. 4D, E). Palpus without prominent seta (ch.17-2; Fig. 5D 1, E 1). 5x index> 4.0 (ch.32-2; Fig. 8D 2, E 2). Hind tibia apicoventrally with two stout setae (ch.40-1; Fig. 9D 3, E 3). Epandrium with neither pubescence nor setae (ch.53-1, ch.54-1; Fig. 11-2D, E).

Shared characters. Antennal pedicel grayish brown (Fig. 14D, E). Eye with fine, sparse, interfacetal setulae (ch.7-0; Fig. 2D 1, E 1). Outer, vertical setae absent (ch.9-1; Fig. 4D, E). Inner (convergent) vertical setae dislocated outside line of ipsilateral orbitals; posterior reclinate orbitals longest on head (Fig. 2D 2, E 2). Upper, postocular setae upright or up-curved (ch.10-1; Fig. 4D, E). Dorsomedial, tentorial apodeme reaching 1/5 to vertex (Fig. 4D, E). Facial carina wider than 1st flagellomere, as long as pedicel + 1st flagellomere (Fig. 2D 2, E 2). Clypeus thicker than 1/2 length of cibarium (Fig. 5D 1, E 1). Cibarial, medial sensilla 2 per side; posterior sensilla absent (ch.21-3; Fig. 5D 2, E 2). Labellum with 7 pseudotracheae (ch.24-0; Fig. 5D 1, E 1). Postpronotal lobe with 1 prominent seta (ch.25- 2; Fig. 6D, E). Prescutellar, acrostichal setae absent (ch.27-1; Fig. 6D, E). Only one prominent katepisternal seta longer than acrostichal setulae (ch.29-2; Fig. 7D, E). Costal setae in middle row from 2nd costal section to proximal portion of 3rd section all weak, trichoid; sparse setae in upper row stout, longer, trichoid (ch.30-2, ch.31-1; Fig. 8D 1, E 1). Patch covered with only minute pubescence present on anterodorsal portion of fore tarsomere I (ch.33-1; Fig. 9D 1, E 1). Fore tarsomere II with 1 large and 1 small pegs; latter 1/3 as long as former (ch.37-1; Fig. 9D 1, E 1). Mid tarsomere I as long as tarsomeres II, III and IV combined; hind I slightly longer than II+III+IV (Fig. 9D 2,3, E 2,3). Claws as long as tarsomere V (ch.43-1; Fig. 9D, E). Abdominal tergites blackish brown (Fig. 14D, E). All sternites longer than wide and I fused to II in both sexes (ch.45-2; Fig. 10D, E); male V not fused to VI, and VI completely bilobed (ch.46-0, ch.47-1; Fig. 10D 1, E 1); female sternite VII more or less convex on distal margin (ch.51-2; Fig. 10D 2, E 2). Female tergite VII mid-dorsally separated into 2 triangular, lateral plates (ch.52-0). Epandrial, ventral lobe differentiated (ch.56-1; Fig. 11-2D, E). Surstylus absent (ch.59-4; Fig. 11-2D, E). Hypandrial phragma anterior, strongly sclerotized rod-like portion (ch.68-2; Fig. 11-2D, E). Membranous aedeagus long, tube-like (ch.70-1; Fig. 11-2D, E). Phallal sheath not pubescent (ch.74-0; Fig. 11-2D, E). Phallapodeme articulated to and not shorter than phallal sheath (ch.75-0, ch.76-0; Fig. 11-2D, E). Hypoproct partly pubescent (ch.80-1; Fig. 12D 1, E 1). Epigynium dorsally separated into 2 lateral lobes (ch.81-1; Fig. 12D 1, E 1). Perineal membrane with patch of dense, distinct warts (ch.84-1; Fig. 12E). Hypogynial valve with trichoid sensilla on only distal portion; distal, narrow portion as long as basal, broad portion (Fig. 12D, E).

Remarks. This species subgroup is well demarcated by a number of non-homoplastic synapomorphies (Fig. 13) defined as the diagnostic characters, especially the peculiar chaetotaxy that the proclinate orbital, outer vertical, and anterior dorsocentral setae are lacking. Such an anomaly from the basic chaetotaxy is rare in the Drosophilidae, but is seen in a few species of Colocasiomyia: C. crassipes (de Meijere) and C. micheliae of the crassipes group lack the outer vertical and dorsocentral setae (Grimaldi 1991; Yafuso et al. 2000); and C. ecornuta Toda & Takano of the cristata group lacks the outer vertical setae (Takano et al. 2021).

Included taxa. Colocasiomyia oligochaeta sp. nov., and C. grimaldii sp. nov.