Wille, A. and Orozco, E. 1969. The life cycle and behavior of the social bee <i>Lasioglossum (Dialictus) umbripenne</i> (Hymenoptera: Halictidae). Revista de Biología Tropical. 17, 2 (Dec. 1969), 199–245. DOI:https://doi.org/10.15517/rev.biol.trop. v17i2.28103.