Rhodanthidium septemdentatum (Latreille)

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 septemdentatum (Latreille)

Material examined.

23 nests from five localities in the Czech Republic, Slovakia and Spain (Suppl. material 2: Table S2).

Nest structure.

All nests had a subterminal closing plug, a vestibular cell and one or two brood cells (Fig. 2 ). The vestibular cell was delimited by the closing plug and an inner partition, both made of resin and loosely filled with mineral fragments, soil and plant matter. In nests with two brood cells, there was no partition between the two (Fig. 2B ). Nests with two cells appeared to be more frequent in central Europe (Czech Republic and Slovakia) (11 of 17 nests examined) than in Spain (0 of 6 nests examined). Overall, we obtained 26 adult bees, 15 males and 11 females (M/F sex ratio: 1.4).

Shell choice.

All nests from the Czech Republic and Slovakia were built in shells of C. vindobonensis , whereas nests from Spain were found in Eobania vermiculata (O. F. Müller) (3), Sphincterochila candidissima (Draparnaud) (1), Cernuella virgata (Da Costa) (1), and Cornu aspersum (O. F. Müller) (1) shells (Fig. 3 ).

Shell manipulation.

Females of R. septemdentatum do not move shells. All marked shells from our experiment in Prokopské údolí remained in place with no nesting on the ground surface, and only one shell placed near the centre of the nesting site (group A) was found under the stone with a nest of R. septemdentatum . However, we found five unmarked shells with nests under the stones on the same nesting site and suspected that the shell probably fell under the stone because of the climatic conditions before the nesting season of R. septemdentatum ; alternatively, the space between the stones was utilized as a shelter by snails.

Life cycle.

We dissected five nests in September 2017. All of them contained adult bees inside their cocoons. We also found adults in two nests collected during the winter of 2017/2018. In the spring of 2018, 16 young larvae from nine nests were transferred with their pollen and nectar provisions to microtubes. The feeding larval stage lasted 5-8 weeks. Pupation occurred during July and August, and adults eclosed 2-4 weeks after pupation. Five larvae did not pupate and died during the winter. We conclude that R. septemdentatum overwinters in the adult stage in both study regions.

Nest associates.

There were no nest associates with any of the R. septemdentatum nests.

Pollens collected.

We analysed pollen samples from five nests from the Czech Republic. We recorded 41 pollen types from 22 plant families. Of these, 13 pollen types representing nine families were recorded in proportions higher than 10%. The most abundant pollen types were of the families Boraginaceae (20%, mostly Echium vulgare ), Rosaceae (14%, mostly Rubus and Filipendula ), Fagaceae (13%, mostly Fagus sylvatica ), Fabaceae (11%, mostly Cytisus ) and Plantaginaceae (7%) (Fig. 4 and Suppl. material 3: Table S3). Individual nests usually contained a mixture of pollen types from unrelated families. Only one nest contained a dominant pollen type (71% Echium vulgare pollen). The other nests contained 4-18 pollen types, of which only 2-5 represented more than 10% of the grains identified. These results indicate that R. septemdentatum is widely polylectic, and individual females do not specialize on any particular pollen source.

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.