Univoltine but with an extended flight period. In central Europe the females are on the wing from the beginning of June to the end of July, and the males from the end of July to early September.
In southern Europe, the females fly from the end of March to the end of September and the males from mid-May to the beginning of November. (Ebmer,1988)
Mavromoustakis (1952) (treating Halictus smaragdulus in the broadest sense) reports adult activity from March to October