Phenology and social status of the endemic Sable Island Sweat Bee,Lasioglossum sablense

The Sable Island Sweat Bee ( Lasioglossum (Dialictus) sablense Gibbs, 2010) is endemic to Sable Island, an isolated sandbar located about 160 km east of Nova Scotia. L. sablense is classified as Threatened due to its restricted geographic distribution, so promoting its conservation requires detailed information about nesting phenology and behaviour. We combined measurements and dissections of adult females collected in 2016 and 2017 with behavioural observations of nests and foragers on the grounds of the Sable Island Station in 2019 and 2022, to compile the first description of flight phenology and social status. Like many members of its subgenus, L. sablense exhibits a diphasic life history. Phase 1 begins when large adult females emerge from hibernation, begin burrow and brood cell construction, and forage to provision Brood 1, which comprises both daughters and sons. Most, but not all, nests initiated during Phase 1, reactivate during Phase 2, as adult Brood 1 daughters emerge from their nests and initiate foraging to provision Brood 2. This suggests a mix of univoltine (single generation) and bivoltine (two generation) reproductive strategies. Behavioural observations at nest entrances demonstrated that during Phase 2, reactivated nests sometimes contained multiple adult females, suggesting the potential for colonies to become social. Comparisons of body size and ovarian status of Phase 1 and 2 females collected from flowers, showed Phase 2 foragers were significantly smaller than Phase 1 foragers and had somewhat lower levels of ovarian development, as expected if Phase 2 females were workers from eusocial nests. However, five large females collected during Phase 2, which had high levels of wear, likely were Phase 1 foundresses that resumed foraging during Phase 2. Taken together, these observations suggest a mix of phenological and social strategies, including both univoltine and bivoltine life histories, and a mix of solitary and social behaviour among reactivated colonies in Phase 2.