(Figs. 40–45, 138)
Diagnosis. Male: the only species of Neotropical Forcipomyia (Metaforcipomyia) with a hind tarsal ratio of 0.76–0.80, hind femur with midportion slightly darker, parameres absent and aedeagus without a distal prong. Female: unknown.
Description. Male. Head. Brown. Eyes abutting medially for length of four ommatidia. Antenna (Fig. 40) pale brown with plume setae well developed, flagellomeres 2–4 spherical, flagellomere 10 1.39–1.43 (1.41, n = 2) X longer than flagellomere 11, flagellomeres 10–13 elongate; flagellomere 13 with apical nipple, not constricted basally; AR 1.02–1.04 (1.03, n = 2). Palpus (Fig. 41) pale brown; segment 3 slightly swollen proximally, with irregular sensory pit at midlength; PR 2.67–3.12 (2.92, n = 4). Labrum tapering apically.
Thorax. Pale brown except scutellum and postscutellum brown; scutellum with 6 strong setae. Legs (Fig. 42) uniformly light brown except hind femur with midportion slightly darker; apex of hind tibia with 4 spines, the third farther from the spur longer; tarsomeres with pectinate scales; tarsomere 1 of foreleg with row of 7, 8 spine-like setae, tarsomere 1 of hind leg with two rows of setae on basal half; foreleg TR 1.44 (n = 3), midleg TR 0.59–0.67 (0.63, n = 3), hind leg TR 0.76–0.80 (0.80, n = 3); claws curved, moderately stout. Wing (Fig. 43) plain, without pattern of pigmented membrane; M 2 only visible at wing margin; first radial cell obliterated; second radial cell well developed, triangular; fork of cubitus situated slightly distad to level of apex of costa; wing length 0.61–0.64 (0.63, n = 4) mm; breadth 0.20–0.24 (0.22, n = 4) mm; CR 0.38–0.40 (0.39, n = 4). Halter whitish.
Abdomen. Tergites pale brown with brownish lateral spots. Genitalia (Fig. 44): Brown. Tergite 9 short, only extending to 1 / 4 length of gonocoxite; posterior margin broadly rounded; cercus lobe-like, produced beyond 1 / 2 length of gonocoxite; sternite 9 broad, with posterior margin nearly straight. Gonocoxite slender, 2.10 X longer than greatest breadth; gonostylus 0.85 length of gonocoxite, almost straight, tip pointed. Parameres absent, gonocoxal apodemes nearly straight. Aedeagus (Fig. 45) stout, triangular, posterior margin difficult to see, without distal prong; basal arch sclerotized extending to 1 / 8 of total length; lateral arms nearly straight directed laterally.
Female. Unknown.
Distribution. This species is known only from the lowlands of the Osa Peninsula in Costa Rica at 250–300 meters (Fig. 138).
Taxonomic discussion. This species is very similar to F. pluvialis, but in F. pluvialis the basal third of the hind femur is darkly pigmented, its apical portion is pale and the pigmentation of the scutum is variable (pale, with patch of darker pigmentation anteriorly, more extensively partially pigmented or entirely darkly pigmented) contrasting with the unicolourous pale brown scutum of F. osaensis.
Type material. Holotype male on microscope slide, labeled “ HOLOTYPE Forcipomyia (Metaforcipomyia) osaensis Spinelli, Marino and Borkent, Costa Rica, Puntarenas prov., Península de Osa, Río Agujas, Est. Agujas, Send. Purruja, 300 m, 10 / 20 -VIII- 1996, A. Azofeifa, Malaise tp. LS 276750 526550 # 32629, CD 5079 ” (INBC). Paratypes, 3 males as follows: same data as holotype, 1 male (CNCI). Costa Rica, Puntarenas prov., Pto. Osa, Est. Agujas, 300 m, 15 -VII / 15 -VIII- 1999, J. A. Azofeifa, CD 5089, 1 male (INBC). Costa Rica, Puntarenas prov., Golfito, Est. Agujas, 250-300 m, 3 / 24 -VII- 1999, J. Azofeifa, red de golpe, CD 5162, 1 male (MLPA).
Derivation of specific epithet. The name osaensis refers to the type-locality at the Osa Peninsula.