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

Abstract

Lasioglossum (Dialictus) sablense Gibbs, 2010 (Hymenoptera: Halictidae) is endemic to Sable Island, an isolated sandbar located about 160 km east of Nova Scotia, Canada. Lasioglossum sablense is currently listed as Threatened due to its restricted geographic distribution, and promoting its conservation requires detailed information about nesting phenology, behaviour, and other life history details. We combined measurements of body size, wear, and ovarian status from adult females collected from flowers in 2016 and 2017 with measurements and behavioural observations of foragers collected at the Sable Island Station in 2019 and 2022, to compile a preliminary description of flight phenology and social behaviour. Like many members of its genus, L. sablense exhibited a diphasic life history. Phase 1 began when large, fertilized adult females emerged from hibernation, began nest and brood cell construction, and foraged to provision Brood 1, which comprised both daughters and sons. Most nests initiated during Phase 1 reactivated during Phase 2, with adult Brood 1 daughters foraging to provision Brood 2. Observations of bees at nest entrances demonstrated that some reactivated nests contained multiple adult females. Phase 1 foragers were larger, less worn, and had marginally higher levels of ovarian development than Phase 2 foragers. Five large females collected during Phase 2 had high levels of wear, suggesting they were long-lived Phase 1 foundresses that resumed foraging during Phase 2. Taken together, these observations suggest a mix of univoltine (single generation) and bivoltine (two generation) life histories, as well as a mix of solitary and social behaviour in L. sablense.