Microplitis croceipes(Cresson) andCotesia(=Apantales) marginiventris(Cresson) produced inHeliothis zea(Boddie) larvae infected withVairimorphasp. were compared with parasitoids produced in uninfected larvae. The criteria used for comparison were: percentage of hosts producing parasitoids, developmental time, longevity, and infection by the microsporidium. There was no significant difference in productivity of parasitoids in infected and control larvae. There was a small, though statistically significant, increase in the developmental time ofM. croceipesreared in infected larvae. The number of parasitoids infected byVairimorphawhen produced in infected larvae was not significant. Transmission ofVairimorphaby parasitoids produced in infected larvae was not significant; however,M. croceipesfemales which were exposed to infected larvae for oviposition transmitted the pathogen to a significant number of subsequent larvae.