The parasitoid wasps Spalangia cameroni Perkins and Muscidifurax raptor Girault & Sanders commonly co-occur in nature and are sometimes released together in efforts to control pest fly populations. Laboratory experiments were conducted to determine how the effectiveness of these wasps in killing house flies, Musca domestica L., and producing wasp progeny is affected by the wasp specie(s) used, host burial, and host age. For effectiveness in killing flies, there was a significant 3-way interaction. S. cameroni alone was consistently more effective than M. raptor alone or than the 2 species combined, regardless of host age and burial. However, the greater effectiveness of S. cameroni was most pronounced for buried hosts and among unburied hosts for young hosts. S. cameroni produced offspring regardless of host burial and host age. Host burial significantly decreased production of S. cameroni offspring only when S. cameroni was present and hosts were young. Host burial significantly reduced production of M. raptor offspring in all situations. M. raptor produced fewer offspring from young hosts than from old hosts under all conditions, producing no offspring from young buried hosts. Combining S. cameroni and M. raptor did not increase their effectiveness at killing hosts. Being with the other species versus a conspecific had no significant effect on production of M. raptor offspring and increased production of S. cameroni offspring only from young buried hosts.