Abstract
Platosmia, a subgenus of the osmiine bee genus Hoplitis (Megachilidae), contains ten species, which are confined to desertic and semidesertic areas of the Palaearctic region. Analysis of female pollen loads and field observations indicate that several H. (Platosmia) species are strictly oligolectic on Reseda (Resedaceae) and possibly Hedysareae (Fabaceae), while others are mesolectic on both Reseda and Fabaceae. The few data available so far suggest that preexisting cavities in stones and rocks serve as nesting sites of H. (Platosmia). The taxonomic revision of H. (Platosmia) revealed the existence of an undescribed species from the Arabian peninsula, H. arabiae spec. nov.. Hoplitis incognita Zanden, 1996 and H. quarzazati (Zanden, 1998) are newly synonymized with H. maghrebensis (Zanden, 1992) and H. platalea (Warncke, 1990), respectively. Identification keys for all H. (Platosmia) species are given including the hitherto unknown male or female sex of three species.