Halictillus amplilobus Gonzalez-Vaquero. All

Halictillus amplilobus

(Figures 6, 8f; Tables S10–S11)

In Paititi Natural Reserve, in Sierra de los Difuntos (Figure 6a), I found a slope of wet compact soil facing south (Figure 6c), 3 m wide × 1 m long, which had nests of H. amplilobus and Pseudagapostemon pampeanus (Holmberg) (Halictidae: Caenohalictini). Nests were found on top of the hill, 160 m a.s.l., an area dominated by bushes of Colletia paradoxa (Spreng.) Escal. (Rhamnaceae), Baccharis spp. and Achyrocline satureioides (Lam.) DC. (Asteraceae).

The three nests that were dug had an entrance diameter slightly narrower (x = 2.3 mm SD = 0.4, n = 2) than that of the main tunnel (x = 3.2 mm SD = 0.6, n = 2) (Table S10). At 9.8 cm (SD = 2.8, n = 4) from the entrance there was a chamber of approximately 12 mm width by 26 mm height which contained a cluster of 4–9 (x = 6.8 SD = 2.2, n = 4) ovoid cells, horizontally orientated, with their openings facing the tunnel (Figure 6b,e). One of the nests had two clusters; the deeper one had only open, empty cells. Apparently the cluster was held only by the walls of the chamber, and in only one case by a pillar of soil. One of the nests had a blind tunnel facing backwards, which extended 2 cm beyond the chamber; the other nests ended at the chamber. The nests ended 16 cm from the surface (SD = 3.8, n = 2).

Two nests had one cluster of cells and one female bee, whose ovaries were developed and whose mandibles and wings showed some wear (Table S11: nests 1, 2). The other nest had two clusters and a dead female at the end of the tunnel, which had fungi on wings and metasoma but unworn mandibles, so I conclude it had died soon after emerging. Considering that the nests were dug on cold, rainy days, it can be inferred that all occupants were in the nest; therefore, this population of H. amplilobus would be solitary. Many open cells, two male pupae and a small larva were found in the nests. The first record of males flying nearby (Tandil, Table S14) is from spring, probably from a first brood. Considering that the nests were dug in summer and they had recently open cells (they were in good condition) and pupae, it is probable that the species is bivoltine in the area studied.