Corynura nahuelita, Gonzalez-Vaquero and Roig-Alsina

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 : 1854-1855

Corynura nahuelita

( Figures 5 , 8b ; Tables S8–S9)

Nest site

The nesting area was in a south-facing slope, 6 m wide × 2 m long, on the northern shore of Lake Traful, on the side of Provincial Route 65 ( Figure 5a ). The ground was totally exposed to the sun, with almost no vegetation, and the earth was dry with some stones. The nests of Co. nahuelita were scattered, and only occasionally was a female observed entering a nest. A few centimetres away from one of the entrances there was an anthill of Dorymyrmex sp. ( Formicidae : Dolichoderinae).

Nest structure

The entrances of the nests were very small (x = 2.2 mm SD = 0.4, n = 5), but immediately below the burrow widened ( Figure 5d ) leading to a chamber, located 2.0– 8.8 cm (x = 4.2 cm SD = 2.1, n = 8) from the entrance. Each comb-like cluster had from 2 to 18 (x = 9.2 SD = 4.7, n = 13) cells, which were mostly vertically orientated ( Figure 5c,e ) with their openings facing the roof of the chamber, and in some cases the cluster followed the outline of some stone on which it was supported. The base and the ends of the clusters were somewhat attached to the substrate, and some of the peripheral cells were broken when extracted. For this reason it is difficult to define the size of the clusters, although the largest ( Figure 5c ) was 30.2 mm wide, 37.4 mm long and 19.8 mm high, and the upper side, which housed the openings of the cells, was slightly concave. Once the cluster was removed, due to the dry soil and the stones it was not possible to define whether the nest ended there, but in some nests a lower blind burrow that extended 2–3 cm beyond the chamber was observed ( Figure 8b ). One of the nests (Table S8: nest 2) had two clusters very close to each other, the first one inactive, probably from the previous year. Some clusters were opened 7 days later in the laboratory, and their measurements and contents were recorded (Table S8). The remaining clusters were left untouched, awaiting the emergence of adults. The cells, ovoid in shape ( Figure 5b ), had the following measurements: 2.0–3.0 mm width at neck; 2.6–4.5 mm maximum width; 7.1–9.5 mm length (n = 12). Some of the cells of active nests had fungi, and some were open and had faeces, while others had been filled with loose soil – clear indicators of a reused nest. Only one nest (Table S8: nest 5) was inactive, with no bees or active cells in it.

Nesting behaviour

One female was found in each of six nests; all of them had worn mandibles and wings, and well developed ovaries (Table S9). No bees were found in five nests; one of these nests was inactive but the others contained from one to four active cells. These data suggest solitary behaviour, but the study was carried out on sunny days, and some specimens were observed later flying around the area that had been dug. Moreover, one nest had 11 active cells (Table S8: nest 4), which might be too many cells to provision for a single bee. These data suggest that the species probably had solitary and social nests in the area studied.

One of the nests had unusual contents: four females with no mandible or wing wear, one of which had no ovary development while the other three had well-developed eggs in their ovaries (Table S9: nest 1). These females were found near the cluster, which had six open cells, but despite the intact wings and mandibles I do not believe these females had recently emerged. The pupae found in all nests studied were unsclerotised, and adults from the clusters that were taken to the laboratory did not emerge until 2 weeks later (after 4 January). It is plausible that the workers of that nest were foraging when the nest was dug, so I infer that this nest was semisocial, with three reproductive females in it. I discard communal behaviour because these females had no visible signs of wear in wings and mandibles, perhaps because foraging and construction were performed entirely by the workers.

Bees of both sexes emerged in the laboratory at the beginning of January. This agrees with data taken from collections, suggesting that males appear in the field from that moment on (Table S14). The proportion of pupae (4 f, 5 m) was similar to that of adults emerged from the nests (5 f, 5 m). Although I found several open cells in the nests, many with faeces, they could have been active the previous year, and left untouched by the bees, while others were filled with soil. The data suggest that the species is univoltine in the area studied.

Figures

Figure 5. Corynura nahuelita, nesting area in Puerto Arrayán, Neuquén. (a) Slope; (b) cell with faeces and a male pupa; (c) cluster with some open cells, and some broken cells; (d) entrance to a nest, gradually widened; (e) comb-like cluster. Scale bars: b, d, e = 5 mm; c = 1 cm.

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.