Palaearctic Osmiine Bees

Female of Hoplitis (Hoplitis) lepeletieri (Pérez, 1879) on her exposed nest built on the surface of a rock. Foto A. Krebs.

Biogeography and diversity

The genus Hoplitis Klug is distributed in the Palaearctic, the Nearctic and the Afrotropical region, a few species also occur in the Oriental region (Michener, 2007).

Hoplitis is the most diverse osmiine genus in terms of number of species: 352 species have been described so far, 284 of which occur in the Palaearctic. At least 1 extra-Palaearctic and about 83 Palaearctic species are still undescribed.

Phylogeny and classification

The genus Hoplitis, whose monophyly is well supported, is sister to the clade Wainia+Atoposmia+Ashmeadiella+Osmia (Praz et al., 2008b). It was subdivided into 27 subgenera by Michener (2007). In contrast to Micheners’ classification, Stenosmia is treated here as a subgenus of Hoplitis rather than as a genus of its own, Micreriades is recognized as a subgenus of Hoplitis rather than as a synonym of Alcidamea, and the subgenus Nasutosmia is transferred from Hoplitis to Osmia (Praz et al., 2008b). In addition, the separation of the subgenus Exanthocopa from the subgenus Anthocopa appears to be unwarranted due to the close morphological similarity of the recently discovered females of H. oxypyga, the only representative of Exanthocopa, with the females of H. (Anthocopa) bisulca.

The Palaearctic Hoplitis species belong to the following 20 subgenera:

Alcidamea with 50 described and 4 undescribed species

Annosmia with 30 described and about 8 undescribed species

Anthocopa with 62 described and 8 undescribed species

Bytinskia with 3 described and 1 undescribed species

Chlidoplitis with 7 described and 2 undescribed species

Coloplitis with 2 described species

Eurypariella with 2 described and 1-2 presumably undescribed species

Formicapis with 3 described and 1 undescribed species

Hoplitis s. str. with 50 described and 45 undescribed species

Jaxartinula with 2 described species

Kumobia with 4 described species

Megahoplitis with 1 described species

Megalosmia with 7 described species

Micreriades with 9 described species

Monumetha with 1 described species

Pentadentosmia with 22 described and 6 undescribed species

Platosmia with 9 described and 1 undescribed species

Prionohoplitis with 7 described species

Stenosmia with 10 described and 5 undescribed species

Tkalcua with 2 described and 1 undescribed species

Subgenus uncertain with 1 described species

A recent molecular phylogeny of the osmiine bees (Praz et al., 2008b) as well as preliminary results of an ongoing phylogenetic study of the genus Hoplitis (C. Sedivy, A. Müller, A. Widmer and S. Dorn, unpublished) indicate that neither the subgenus Alcidamea nor the subgenus Prionohoplitis appears to be monophyletic and that the following subgenera most probably form monophyletic clades:

Annosmia+Coloplitis+Bytinskia+Hoplitis

Micreriades+Tkalcua+Platosmia+Formicapis (including the Nearctic Proteriades, Penteriades and Hoplitina)

Alcidamea+Prionohoplitis+Monumetha+Megalosmia (including the Nearctic Cyrtosmia and Dasyosmia)

Nesting biology

Information on the nesting biology is available for 110 Hoplitis species belonging to 20 subgenera from the Palaearctic, Nearctic, Afrotropical and Oriental region (A. Müller, C. Praz, J. Neff, G. Le Goff and C. Sedivy, unpublished).

The diversity of nesting sites in the genus Hoplitis is very high and encompasses the whole diversity observed in the osmiine bees. There are species that

nest in excavated burrows in the soil (e.g. Annosmia, many Anthocopa, Pentadentosmia) or in pithy stems (e.g. many Alcidamea);

nest in preexisting cavities as insect burrows in dead wood (e.g. Formicapis), in pithy stems (e.g. many Alcidamea), in galls or in the soil; abandoned cells in exposed nests of other aculeates; in empty snail shells (e.g. H. (Hoplitis) fertoni); in fissures, cracks or holes in rocks (e.g. many Hoplitis s. str.); between vegetative parts (e.g. H. (Alcidamea) mitis);

build exposed nests (e.g. some Hoplitis s. str.);

have a cleptoparasitic behaviour (Bytinskia).

Similarly diverse is the nesting material used for the construction of cell partitions and nest plug or for building entire cells. Depending on the subgenus or species, mud and pebbles, leaf pulp, whole leaves, whole petals or pith are used alone or in diverse combinations. In contrast to the species of the Heriades group, for which the use of resin is widespread, the only Hoplitis species known to collect resin for cell construction is the Nearctic Hoplitis (Dasyosmia) biscutellae (Rust, 1980).

Many Hoplitis species nesting in narrow cavities use the nesting material only to delimit the linearly arranged cells by walls and to plug the nest. Some of these species, especially when nesting in larger cavities, have the flexibility to arrange cells more irregularly by partially or wholly constructing also the walls of the cells. Other species invariably build their entire cells with foreign material (e.g. many Anthocopa species with whole petals, many Hoplitis s. str. species with mud and pebbles, some Alcidamea and Prionohoplitis species with whole leaves or leaf fragments, Hoplitis (Megalosmia) fulva with leaf pulp).

Flower preferences

The knowledge about the pollen preferences of the Palaearctic Hoplitis species is still in a poor state. To our current knowledge, all categories of bee host ranges as proposed by Müller and Kuhlmann (2008) can be found in the Palaearctic Hoplitis fauna, except true monolecty and eclectic oligolecty:

narrow oligoleges, which restrict pollen collection to one single plant genus only, e.g. to Allium (Alliaceae), Echium (Boraginaceae), Linum (Linaceae), Muscari (Hyacinthaceae), Reseda (Resedaceae) and possibly to Haplophyllum (Rutaceae), Heliotropium (Boraginaceae), Onosma (Boraginaceae), Tamarix (Tamaricaceae) and Trichodesma (Boraginaceae);

broad oligoleges, which restrict pollen collection to one plant family or tribe, e.g. to Asteraceae, Campanulaceae, Chenopodiaceae, Convolvulaceae, Dipsacaceae, Fabaceae, Malvaceae, Scrophulariaceae and Zygophyllaceae;

probable mesoleges, which collect pollen on only two to three plant families, e.g. on Boraginaceae and Fabaceae or on Asteraceae and Fabaceae;

polyleges with a strong preference, e.g. for Asteraceae, Resedaceae, Fabaceae;

polyleges, which collect pollen on at least four plant families.

Several Hoplitis species are equipped with specialized bristles on the forelegs (e.g. H. (Hoplitis) flabellifera) or on the proboscis (e.g. H. (Coloplitis) persica, H. (Hoplitis) pici) to remove pollen from anthers hidden in the narrow flower tubes of Anchusa (Boraginaceae), Heliotropium (Boraginaceae) and Muscari (Hyacinthaceae), respectively. Similarly, several Hoplitis species of the subgenus Micreriades possess a specialized pilosity on clypeus and frons composed of apically twisted bristles, which most probably serve to remove pollen from the nototribic anthers of Lamiaceae.