Osmia ferruginea, Latreille, 1811

Bogusch, Petr, Hlavackova, Lucie, Petr, Libor & Bosch, Jordi, 2020, Nest structure, pollen utilization and parasites associated with two west-Mediterranean bees (Hymenoptera, Apiformes, Megachilidae) nesting in empty snail shells, Journal of Hymenoptera Research 76, pp. 113-125 : 113

Osmia ferruginea

Nest structure.

We collected 58 shells with nests of O. ferruginea in nine of the 13 localities surveyed. Most nests (48) were collected in the localities of a dry hilly area. The remaining 10 nests were collected in the river floodplains. All nests were found exposed (not hidden) at ground level. The surface of the shells had no traces of masticated leaf matter. The closing plug was made of green masticated leaf matter (Fig. 1B ). In most nests (38) it was placed at the shell aperture, but in some it was placed inside the shell. All nests had a vestibular (empty) cell below the plug. Brood cells were separated by narrow single partitions of masticated plant matter and the side walls of the brood cells were not lined (Fig. 1C ). At the time nests were dissected (March 2019), each cell contained a yellow to light yellow spherical pollen provision with an egg or a young larva (Fig. 1C ). The brood cells were always placed longitudinally along the spire of the shell. Brood cell partitions were around 1 mm thick and the closing plug 1.5-3 mm thick (mean 2.1 mm) (Fig. 1E ).

Shell choice.

Most nests (28, 48.3%) were built in Sphincterochila candidissima shells. The remaining nests were placed in shells of Eobania vermiculata (13, 22.4%), Cernuella sp. (11, 18.9%), Theba pisana (4, 6.9%), Iberellus sp. (1, 1.7%) and Otala lactea (1, 1.7%). The 58 nests collected contained 268 brood cells (mean ± SD: 4.6 ± 2.09; range: 1-9 brood cells per nest). The nests in S. candidissima shells contained 2-9 brood cells (mean 5.6, median 5), and those in E. vermiculata shells were similar 1-9 brood cells (mean 5.5, median 6). Nests in the smaller shells of Cernuella sp. and T. pisana contained fewer cells (range 1-5, mean 2.1, median 2 and range 2-3, mean 2.5, median 2-3, respectively).

Nest associates.

Altogether 56 (20.9%) of the brood cells contained dead, dry or mouldy contents. Most of the remaining brood cells (203) contained pupae or adults of O. ferruginea , while 19 contained parasitoids (9% of brood cells containing alive insects). The main parasitoid species was Sapyga quinquepunctata ( Sapygidae ; 18 cells from 11 nests, all from locality S7; 19% parasitism). All the individuals of this cleptoparasitic species reached adulthood by late summer or beginning of autumn (September). Brood cells parasitized by S. quinquepunctata were recognizable by the dark brown oval-shaped cocoon, distinct from the cubic cocoons of O. ferruginea . The bombyliid Anthrax aethiops was recorded in a single cell of one nest. The structure of all nests is illustrated on Fig. 2 .

Pollen contents.

We analysed six pollen samples from nests collected at three different localities. Most pollen grains were of Cistaceae , Fabaceae ( Cytisus type), and Lamiaceae (Table 1 ; Fig. 3B ).

Figures

Figure 1. Structure of Hoplitis fertoni (A, D) and Osmia ferruginea (B, C, E) nests A shell of Sphincterochila candidissima with nest of H. fertoni B shell of S. candidissima with nest of O. ferruginea C larva of O. ferruginea on pollen-nectar provision D nest structure of H. fertoni E nest structure of O. ferruginea. Photos and drawings by P. Bogusch.

Figure 2. Diagrams of nest structures of nests of Hoplitis fertoni (right) and Osmia ferruginea (left). The nests are identified by locality snail codes (Cern - Cernuella sp., Ever - Eobania vermiculata, Iber - Iberellus sp., Olac - Otala lactea, Scan - Sphincterochila candidissima, Tpis - Theba pisana. Each box represents one brood cell, starting with the innermost cell on the left. Colours represent the various species recorded. White boxes represent intercalary cells.

Figure 3. A Macrophotography of pollen of Lithodora fruticosa from a Hoplitis fertoni nest (locality S 35). Photo by L. Petr. B macrophotography of pollen from an Osmia ferruginea nest (locality S 7). Larger pollen grains are Thymus vulgaris; smaller grains are Cistus albidus. Photo by L. Petr.