Callistochlora aureoviridis
Creators: name: González-Vaquero, Rocío Ana
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Halictidae
Callistochlora
Callistochlora aureoviridis

description: Callistochlora aureoviridis
(Figures 1a, 2, 8d; Tables S1–S 3)
Nest site
The aggregation of nests occupied an area of approximately 6 × 9 m, including both flat and gently north-west sloping portions. The site had some bushes and planted pines (Figure 2a), and the soil was humid and aerated. The entrances of most nests were hidden by vegetation cover. The aggregation of nests had from 202 to 272 entrances/m2 (Figure 2b), but this density dropped to 44 entrances/m 2 in the areas with little or no vegetation cover.
Nest structure
Most nests had a single entrance, and consisted of a straight tunnel which led to a central chamber containing a cluster of cells. The entrance of the chamber was 4.5 to 13.0 cm (x = 7.8 cm Standard Deviation SD = 1.7; n = 63) below the surface, and the chamber was followed by a blind burrow that ended at 8 to 25 cm (x = 14.9 cm SD = 3.6; n = 63) from the entrance of the nest. The tunnels of different nests were very close to each other, and in three nests the main tunnel had a short, blind bifurcation. Five nests had two entrances, and one even had three, all the tunnels converging in a single cluster. Most nests had a single comb-like cluster of cells (with their axes in parallel, Figure 2c,d), which was held in place by pillars of soil. Two clusters separated by only a few millimetres were found in two nests (Table S1: nests 53, 59). Each cluster had from 1 to 14 (x = 5.2 SD = 3.5; n = 65) ovoid cells, which were horizontally orientated. Some cells had fungi exteriorly (Table S1: nests 53, 54). Parasitoid pupae of Ripiphoridae (Coleoptera) were found in two cells (Table S1: nests 44, 49). Open cells with faeces or filled with soil were not found.
Nesting behaviour
Two bees were found in two nests, one bee was found in 22 nests, and no bees were found in the remaining 37 nests. All the specimens had some mandible and wing wear, and since only larvae (no pupae or open cells) were found in the nests dug at the end of spring, it is likely that all the bees belonged to the same generation. In the nests with two bees, both specimens had similar wear but one of them had no ovary development. In Nest 5, both occupants had mated (Table S2). Since the first males were detected in the summer (Gravel 2010), it is inferred that the bees had spent the winter as inseminated females. The nests containing two bees had a similar number of cells (x = 6 SD = 0, n = 2) to those with only one bee (x = 5.23 SD = 3.56, n = 22). The data suggest that these nests of Ca. aureoviridis would be semisocial. In the nests where only one bee was found, their ovaries were developed, with the exception of one female in each of three nests. Nests 25 and 61 (dug in January) each had a single female, and since no earlier stages but pupae were found in the cells I believe that the reduction in the ovaries observed was not due to a lack of development but an indication of the end of the breeding season for these bees. On the other hand, nest 2 (dug in December) had several larval instars in the cells, but its single female had not mated. One possible explanation is that the queen of the nest had recently died, and this worker remained in the nest; another is that this unmated female was the mother of the larvae which would all have become males.
It is worth considering that the area was being sampled for bees on flowers throughout the study (Gravel 2010), and thus some specimens that belonged to the nests may have been collected before/during the study. In addition, the nests were dug on sunny days, and later in the afternoon many bees were observed flying over the area that had been excavated. These bees could be the sole occupants of the active nests where no bees were found (solitary nests), or the workers of the nests where only one bee was found inside (semisocial nests). I have found evidence of two semisocial nests, but given that all other nests had one or no occupants inside, I infer that the species has solitary nests as well; hence, the species may be socially polymorphic.
The nests dug at the end of December had larvae of several instars (Figure 2e), and only one male pupa was found (Table S1: nest 7). At the beginning of January I found a higher proportion of pupae (Figure 2f), which were ready to emerge approximately 15 days later, when fully sclerotised pupae were found in the cells (nests dug 14–16 January). Since I found no evidence of open, used cells in the nests dug in December, and only advanced larvae and pupae in January (but no eggs or small larvae), I infer that the species is univoltine in the area studied.
The pupae showed a strong bias to males (1.9:1; n = 220) (Table S3). Considering the material collected by Gravel (2010), males appear in the field in January, in high numbers. In the nests studied by mid-January, the male pupae had more advanced sclerotisation of the cuticle than the female pupae did; hence, I infer that males emerge earlier than females. Protandry may occur because male eggs were laid earlier, or because the development time of males is shorter than that of females (Yanega 1997).
description: Published as part of 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), pp. 1841-1868 in Journal of Natural History 56 (45 - 48) on pages 1848-1850, DOI: 10.1080/00222933.2022.2134833, http://zenodo.org/record/7389012