Key to the Palaearctic species of Trichactia Stein

The examination of the holotype of T. nubilinervis and of numerous specimens of T. meridiana sp. nov. and T. pictiventris showed that certain characters used by Mesnil (1973) tend to vary among individuals, and are misleading and not reliable for an accurate identification at the species level. The following characters in Mesnil’s (1973) key cannot effectively be used to separate specimens of T. pictiventris from T. nubilinervis: postpedicel to pedicel length ratio; postpedicel colouration; parafacial setulosity; wing vein R 1 setulosity and cu 1 to dm–cu length ratio. Therefore, these characters are excluded from our new key.

1. Head with 7–9 frontal setae and with 1 lateroreclinate upper orbital seta, 1 lateroclinate middle orbital seta and 1 proclinate lower orbital seta; lower facial margin slightly protruding (Fig. 5); wing vein R 4+5 with 6–10 basal setulae dorsally, nearly reaching crossvein r–m; bend of vein M right-angled, apical part curved (Fig. 8); parafacial and calypters yellowish. Distributed in central-southern European mountainous regions and central-northern European lowlands.... pictiventris (Zetterstedt)

- Head with 5–6 frontal setae and with 1 lateroreclinate upper orbital seta and 2 proclinate middle and lower orbital setae; lower facial margin strongly protruding (Figs 6–7); extension of dorsal setulae on vein R 4+5 variable; shape of vein M variable; parafacial and calypters whitish-grey. Distributed in the Canary Islands, East Mediterranean and West Asia.................. 2

2. Scutum with 3+4 dorsocentral setae; katepisternum with 2 setae; wing vein R 4+5 with 7–9 basal setulae dorsally, nearly reaching crossvein r–m; bend of vein M right-angled, apical part curved; abdomen dorsally and laterally black in both sexes. Endemic to the Canary Islands ..................................................................... nubilinervis (Becker)

- Scutum with 3+3 dorsocentral setae; katepisternum usually with 3 setae; wing vein R 4+5 with 2–6 basal setulae dorsally, reaching at most halfway to crossvein r–m; bend of vein M obtuse-angled, apical part nearly straight (Fig. 9); abdomen of male orange laterally at least on tergites 2–4. Distributed in the East Mediterranean and West Asia............ meridiana sp. nov.