Corynura ampliata (Alfken)

González-Vaquero, Rocío Ana, 2022, Solitary and semisocial behaviour in the Corynura group: new findings in a clade sister to all other Augochlorini bees (Hymenoptera: Halictidae), Journal of Natural History 56 (45 - 48), pp. 1841-1868 : 1850-1851

Corynura ampliata

( Figures 1c , 3 , 8e ; Tables S4–S 5)

Nest site

Two nesting areas were studied. One, 0.5 m wide × 0.5 m long, was in a gentle slope facing south, on the northern shore of Lake Huechulaufquen. The other one, 4 m wide × 10 m long, was in a flat area near Lake Lácar ( Figure 3a ). In the first site the earth was wet and loose, with a few stones; the days before had had intense rains, which explained the humidity of this usually arid area ( Devoto et al. 2009). In the second site the earth was dry, and it had a thick (1–2 cm) layer of volcanic ash, which was thicker in some parts of the area. Both sites had cushion plants ( Azorella prolifera (Cav.) Plunkett and Nicolas ), the exotic Scotch broom ( Cytisus scoparius (L.) Link), and some small shrubs. The nests were scattered in both areas, approximately 13 nests/m2. A few nests of H. reticulatus and Lasioglossum (Dialictus) sp. ( Halictidae : Halictini), and several anthills of Dorymyrmex sp. ( Formicidae : Dolichoderinae) were found at the second site.

Nest structure

Nest entrances had a radial tumulus of dried soil, diameter 30–40 mm ( Figure 3b ). Most entrances were totally covered by the soil of the tumulus, but in some nests the entrance was partially exposed and its position could be inferred ( Figure 3b , nest at the bottom). When the tumulus was removed, a bee showed her head immediately, and 20–30 seconds later reappeared backwards, moving her metasoma out of the tunnel while carrying some soil with her legs and depositing it at the surface ( Figure 1c ). This was done twice or thrice until the entrance was fully covered, resulting in a tumulus smaller than the previous one; no further movements were observed after the entrance was occluded. The entrances had a diameter of 4.0 mm (SD = 0.5, n = 10), and immediately below it the tunnel widened slightly (x = 5.2 mm SD = 0.8, n = 10). In only one nest, one cluster was found in a chamber 9.2 cm from the entrance; it was held in place by pillars of soil and contained six horizontally orientated closed cells ( Table S4 : nest 3). This cluster, which was in a chamber 33 mm high and 17 mm wide, was kept closed and is housed in the collection of MACN; no specimens emerged from it. In two nests ( Table S4 : nests 9, 10) four and five ovoid cells were found, most of them open, one filled with soil. Notably, no clusters were found in the other nests. Since the nests were dug on windy days, the soil fell permanently over the area that was being excavated, and some old cells (open or filled with soil) may have gone unnoticed – which would not have been the case for cells with pollen and/or immature stages, which are easily seen when a cell is accidentally broken in the process. The nests ended at 17.5 cm (SD = 4.3, n = 10).

Nesting behaviour

Five females were found in two nests, four females in two more, and the remaining six nests had only one female (Table S5). None of the females had well-developed ovaries. Most of the females had mandibles and wings unworn or with very little wear (Table S5), indicating they had recently emerged, but in two of the multi-female nests (Table S5: nests 8, 10) there was one female with fully worn mandibles and wings. Probably these females had been the founders of the nests, and the other bees were their daughters, which remained in the natal nest. The presence of females of two generations may indicate eusocial behaviour, although division of reproductive labour could not be confirmed. I believe these newly emerged daughters would not have helped their mother to produce a second generation, because the nests were studied at the end of the warm season in Patagonia (beginning of February) when few flowers remain in the field. Considering also that no larvae or pupae were found in the nests and that the first males appear in the field approximately by mid-December (in Los Lagos, Chile, Table S14), I infer that these bees were going to spend the winter as inseminated females, in their natal nests. The following spring these females might either found their own nest or re-use their natal nest. Unfortunately, data are insufficient to conclude whether this species is solitary or social, but it is univoltine in the area studied.

Figures

Figure 1. Some of the species studied. (a) Ca. aureoviridis; (b) Co. bruchiana; (c) Co. ampliata removing soil from the nest to the exterior.

Figure 3. Nesting site of Co. ampliata and H. reticulatus near Lake Lácar. (a) Habitat; (b) nest entrances with the characteristic tumulus of soil (in this case, Co. ampliata).

Figure 8. Profile of a typical nest of the studied species. (a) Co. bruchiana; (b) Co. nahuelita; (c) H. reticulatus (Table S12: nest 3); (d) Ca. aureoviridis; (e) Co. ampliata; (f) H. amplilobus (Table S10: nest 3). Scale bars = 1 cm.