none In the course of a 4-year study of the epizootiology of Nosema pyrausta in the European corn borer, Ostrinia nubilalis , the braconid Macrocentrus grandii was recovered from the corn borer. Some of the braconids were also infected with N. pyrausta , and the level of N. pyrausta in the corn borer corresponded to the level of infection in the parasitoid. N. pyrausta infection reduced both the number of braconids exiting the corn borer host as well as adult emergence of M. grandii . Infected M. grandii females were able to transmit N. pyrausta to their progeny as well as serve as vectors for the pathogen in the laboratory.