none The impact of each of three microsporidia on the braconid parasitoid Macrocentrus grandii Goidanich within infected European corn borer, Ostrinia nubilalis (Hubner), hosts was studied. Nosema pyrausta (Paillot) and Nosema sp. infected M. grandii larval tissue. All three microsporidia decreased adult parasitoid eclosion. Female M. grandii eclosing after development in hosts infected with Vairimorpha necatrix (Kramer) or N. pyrausta lived for 10 to 14 days. Females infected with these two species did not transmit the pathogens transovarially to their offspring. Only male M. grandii adults eclosed from hosts infected with Nosema sp.