Key to Japanese species of Orius

1. Pronotum with four (anterior + posterior) corner setae (Fig. 5G)................................................ 2

- Pronotum with either anterior or posterior corner setae, or lacking any........................................... 4

2. Hemelytron uniformly shiny fuscous; flagellum bifurcate................................... O. (Trichorius) atratus

- Hemelytron almost entirely pale brown, with cuneus sometimes narrowly darkened; flagellum simple, not branched....... 3

3. Pronotum wide, not much polished, densely setose, with wide collar area, narrow callus and angulate anterolateral corner; inhabiting a deciduous oak, Quercus accutissima in Honshu and Kyushu. ..................... O. (Xylorius) miyamotoi

- Pronotum trapezoidal, highly polished, almost impunctate and sparsely setose, with narrower collar area, wide callus and rather rounded anterior corner; inhabiting a fabaceous vine, Pueraria montana on Okinawa Island of Ryukyus...... O. (O.) takaii

4. Dorsal vestiture very short; pronotal callus flat, distinctly and deeply punctate; hemelytron uniformly pale yellow, semitransparent.......................................................................... O. (Dimorphella) tantillus

- Dorsum with noticeable setae; callus more or less inflated, with sparse and fine punctures; hemelytron pale brown; cuneus usually with darkened (at least) apical part (often uniformly dark brown in O. hibiscus and O. strigicollis)............................................................................................. 5, species of subgen. Heterorius

5. Body obviously tiny, with total length <1.6 mm (♂) / <1.8 mm (♀); legs generally short, with metatibia shorter than 0.5 mm ........................................................................... O. (Heterorius) hibiscus sp. n.

- Body moderate in size, longer than 1.7 mm (♂) / 1.9 mm (♀); legs long, with metatibia longer than 0.5 mm (usually 0.6–0.7 mm)................................................................................................ 6

6. Head bicolorous, fuscous with yellow or yellow-brown clypeus; pronotum oily shiny, with noticeable anterior corner seta (Fig. 5A), and very sparsely distributed punctures and setae; pronotal callus widened and flattened; all legs uniformly yellow............................................................................................. O. (H.) nagaii

- Head uniformly fuscous; pronotum weakly shining, with distinct punctures and semierect setae but lacking corner seta (Fig. 5D); pronotal callus narrow, more or less inflated; femora and/or tibiae usually partly or widely darkened............... 7

7. Metafemur entirely pale, or if metafemur darkened, then its apex and entire metatibia also fuscous; paramere with slender, stout conus and short flagellum (Fig. 5F); copulatory tube short, tiny (<0.05 mm), without apical segment........ O. (H.) sauteri

- Metafemur usually dark, always with pale apex; metatibia sometimes darkened except for base and apex; paramere with wide and disk-like conus and long flagellum (Figs. 4D, O); copulatory tube ≥ 0.1 mm, with both apical and basal segments elongate as in Fig. 2H........................................................................................ 8

8. Cuneus (usually at least its apical half) infuscate, well contrasting to yellowish corium (cf. Fig. 1F); paramere with small denticule removed from base of flagellum (Fig. 4E); basal segment of copulatory tube expanded at apex.... O. (H.) strigicollis

- Cuneus entirely pale, or darkened at apex; paramere with large denticule contiguous to base of flagellum (Fig. 4O); basal segment of copulatory tube slender and linear..................................................... O. (H.) minutus