This paper investigates the bionomics of the cleptoparasitic bee Mesoplia sapphirina Melo and Rocha-Filho, sp. nov. (described in the appendix), and of its ground-nesting host Centris flavofasciata Friese found along the Pacific coast of Guanacaste Province, Costa Rica. We explore the host-nest searching behavior, egg deposition, and hospicidal behavior of M. sapphirina. Anatomical accounts of its egg, first, second, and fifth larval instars are presented and compared with published descriptions of other ericrocidine taxa. Nests of the host bee as well as its egg and method of eclosion are also described.