Functional traits: Body Size (L = Large; M = Medium; S = Small; VS = Very Small), Nesting biology (AG: Above ground, BG: Below ground), Sociality (Sol: Solitary, Soc: Social, ?: unknown; *Par: Parasite); Onion peak bloom: + = bee species trapped when 80% and 100% of flowers of each inflorescence were open in both years (mid-November) samplings. Abundance () = number of specimens collected during the onion peak bloom. ● new record for San Juan province, Argentina.

In terms of abundance, traps collected a total of 1,765 individuals, with the families Apidae and Halictidae being the most frequently captured (Table I). Apis mellifera (Apidae) was the most abundant species during both years, representing 45.1 % of all bees collected. On the other hand, wild bees represented the majority of the specimens sampled, and about 63 % of them were identified as Lasioglossum (Dialictus) sp. 3 or L. (Dialictus) sp. 5 (Table I). The three bee species mentioned above comprised 76.7 % of the total individuals collected and were also particularly abundant at peak bloom (Table I). The abundance observed for the family Halictidae could be associated with their social habits, nesting aggregation behavior and the phenology peak of some species that coincided with the sampling period (Michener, 2007; Dalmazzo et al., 2014; Nelson et al., 2023).

Among functional traits, body sizes varied from VS to L among families (Table I; Fig. 1d), and traps captured a great richness of S and VS, reaching 76 % of all identified bee species (S= 20, and VS= 22, respectively). Regarding nesting biology and sociality, we observed that 87.3 % of bees nest below ground and 78 % were solitary (Table I). The results obtained are in agreement with previous local and global research which reported that the majority of bee species are solitary, being soil excavation their main nesting strategy (Danforth et al., 2019; Michelette & Camargo, 2000). In addition, species of the genus Lasioglossum Curtis were observed entering the onion flowers to obtain either pollen or nectar, or both; this behavior triggers the staminal column, causing the release of pollen (Korichi et al., 2021). In particular, we observed a great diversity of subgenus L. (Dialictus),which comprised 63 % of the wild bee individuals collected and their activity period match with flowering peak of onion (Table I). The observed dominance of Lasioglossum suggests that environmental conditions of this area provide adequate nesting and foraging resources. Due to the fact that some species of this genus display social behavior, which generally implies many individuals per nest (Michener, 2007; Danforth et al., 2019) and given the importance of them as a flower visitor across a wide range of crops (Nelson et al., 2023), future studies are needed to assess the species of Lasioglossum as pollinator of onion crop.

Since several species of bees were reported visiting onion flowers and improving pollination of the crop (Parker, 1982; Saeed et al., 2008; Devi et al., 2015; Korichi et al., 2021), the high diversity of species surveyed in this research is relevant for further pollination studies. Previous reports in the study area have identified about 60 species of wild bees visiting flowers of both wild and cultivated plant species, including at least seven species observed in onion crops (Michelette & Camargo, 2000; Allasino et al., 2023). Therefore, the new records found for the San Juan province emphasize the wide range of wild bees in arid areas of Argentina and highlight the lack of bee diversity studies conducted in such environments. Furthermore, the bee diversity documented in the present study increases the knowledge about the melittofauna in the surveyed area and provides a baseline for further ecological, conservation, and agricultural studies.