The hymenopterous parasitePediobius foveolatus(Crawford) was highly susceptible toNosema epilachnaeBrooks, Hazard and Becnel andN. varivestisBrooks, Hazard and Becnel, two naturally occurring microsporidia of the Mexican bean beetle,Epilachna varivestisMulsant. After female parasites oviposited in late-instar larvae exposed previously to spores of each microsporidium as either early instar larvae or as late-instar larvae 24 h before parasite oviposition, progeny of the parasites were infected directly by the microsporidia and infection appeared to be systemic in nature. In heavily infected hosts, incidence of infection by both microsporidia in the parasites' progeny approached 100% and percentage mortality was also high. Mortality occurred primarily in the pupal stage and incidences of infection and mortality were directly related to degree of host infection or microsporidian virulence. Most infected adults were normal in appearance but some had malformed wings, greatly swollen abdomens, or both. Infection did not adversely affect the development period of emerging adults but adult longevity was significantly reduced. Adults were also susceptible to both microsporidia per os. Relatively few female parasites of the P generation that were infected withN. epilachnaewere capable of ovipositing in host larvae, and only one female transmitted the pathogen transovarially to some of her progeny. Female parasites, infected withN. varivestis, successfully transmitted the microsporidian transovarially to F6individuals at rates varying from 5.8 to 70.0%. Both microsporidia were also transmitted mechanically from diseased to healthy hosts during parasite oviposition.