We found many large female Lasioglossum sweat bees foraging on the flowers of an escaped Oenothera in a pastureland. The bees entered unopened buds to feed on the pollen, sometimes in groups of three or more. No male bees were present.

These look like they are Lasioglossum Oenothera?

The individual bee shown here is big -- 8mm. It bee has long mandibles with red coloration on the apical third of its mandibles. There are sharp angled edges on the front of scutum and sharp edges on the propodeum. The bee has indistinct bands on its abdomen, not visible to the naked eye. There are long hairs on the bee’s back legs, but the hairs on the bee’s femurs are sparse, simple and mostly located on one side.