Rhodanthidium sticticum (Fabricius)

Hostinska, Lucie, Kunes, Petr, Hadrava, Jiri, Bosch, Jordi, Scaramozzino, Pier Luigi & Bogusch, Petr, 2021, Comparative biology of four Rhodanthidium species (Hymenoptera, Megachilidae) that nest in snail shells, Journal of Hymenoptera Research 85, pp. 11-28 : 11

Rhodanthidium sticticum (Fabricius)

Material examined.

95 nests from various locations in Catalonia, north-eastern Spain (Suppl. material 2: Table S2).

Nest structure.

The nests of this species have a vestibular cell and one (rarely two) brood cells. The closing plug was made of resin mixed with sand particles and sometimes fragments of snail shells (Fig. 2C ). In most cases (62 nests), the closing plug was close to the aperture, but sometimes it was built a few mm inside the shell (33 shells). The vestibular cell was not delimited by a basal partition (Fig. 2D ) and was loosely filled with mineral fragments, soil particles and plant debris (Fig. 2D, E ). Most nests (90) had only one brood cell. Five nests contained two brood cells, and one nest contained three brood cells. Overall, we obtained 76 adult bees, 44 males and 33 females (M/F sex ratio: 1.3).

Shell choice.

Most nests (67) were built in shells of E. vermiculata (65). Other nests were built in shells of S. candidissima (9), C. aspersum (8, two of which juveniles), Otala lactea (O. F. Müller) (5), Iberellus sp. (4), and Theba pisana (O. F. Müller) (2) (Fig. 3 ). Multicell nests were found in E. vermiculata (two cells) and O. lactea (3 cells).

Shell manipulation.

Most nests were found in shells hidden within stone walls or under stones. However, despite many hours of observation, we never observed any females dragging or hiding shells.

Life cycle.

Eleven larvae from 21 nests collected in 2018 were transferred with their pollen nectar provisions into microtubes 4-10 days after collection. The feeding larval period lasted 3-6 weeks, and the pupal stage lasted 2-4 weeks. Adult eclosion occurred in July and August. Some larvae did not pupate and died during the autumn/winter.

Nest associates.

We recorded parasitism by the ruby wasp Chrysura refulgens (Spinola) in two nests from Cap Ras (Girona) and by Chaetodactylus cf. anthidii mites in one nest from Sta. Margarida de Montbui (Barcelona). Overall, the parasitism rate in the nests examined was 3.03%. In addition, the three nests from Lleida (Lleida) and two nests from Òdena (Barcelona) contained low numbers of C. cf. anthidii , which did not cause the death of the bee.

Pollens collected.

We analysed pollen samples in eight nests from Spain. We recorded 30 pollen types from 19 plant families. Of these, eight pollen types from six plant families were found in proportions greater than 10%. Most pollen grains identified (52%) were of the family Fabaceae (mostly Cytisus but also Trifolium repens ), followed by Brassicaceae (19%) and Asteraceae (10%). Individual nests tended to be provisioned with a dominant (>50%) pollen type: Cytisus pollen was dominant in five nests, Brassicaceae pollen in two nests, and Trifolium repens pollen in one nest (Fig. 4 and Suppl. material 3: Table S3). These results indicate that R. sticticum is a polylectic species with a preference for collecting Fabaceae pollen and that females show a certain level of specialization, probably conditioned by the dominant pollen types in each locality.

Figures

Figure 2. Photos and schematic drawings of nests of four species of Rhodanthidium. Rhodanthidium septemdentatum A shell of Caucasotachea vindobonensis with closing plug made of resin B schematic drawing of the inner nest structure in the shell. Rhodanthidium sticticum C shell of Eobania vermiculata with closing plug made of resin and soil particles D schematic drawing of the inner nest structure in the shell E photo of the shell with larva, pollen and filling of stones and plant partitions. Rhodanthidium siculum F shell of Eobania vermiculata with closing plug made of resin, sand and shell particles G schematic drawing of the inner nest structure in the shell. Rhodanthidium infuscatum H schematic drawing of the inner nest structure in the shell.

Figure 3. Proportions (in %) of shells used by Rhodanthidium sticticum (black columns) and Rhodanthidium septemdentatum (grey columns).

Figure 4. Proportions (in %) of pollen grains of plant families in studied nests of three species of Rhodanthidium.