Interactions of the parasite Pediobius foveolatus (Hymenoptera: Eulophidae) with two Nosema spp. (Microsporida: Nosematidae) of the Mexican bean beetle (Coleoptera: Coccinellidae)

The hymenopterous parasite Pediobius foveolatus (Crawford) was highly susceptible to Nosema epilachnae Brooks, Hazard and Becnel and N. varivestis Brooks, Hazard and Becnel, two naturally occurring microsporidia of the Mexican bean beetle, Epilachna varivestis Mulsant. 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 with N. epilachnae were capable of ovipositing in host larvae, and only one female transmitted the pathogen transovarially to some of her progeny. Female parasites, infected with N. varivestis , successfully transmitted the microsporidian transovarially to F6 individuals at rates varying from 5.8 to 70.0%. Both microsporidia were also transmitted mechanically from diseased to healthy hosts during parasite oviposition.