Persistence of Nosema pyrausta and Vairimorpha necatrix Measured by Microsporidiosis in the European Corn Borer1

Abstract

Aqueous suspension of spores of Nosema pyrausta (Paillot) were applied to com foliage with and without Shade during the whorl and pollen-shedding stages of plant development. Larvae of Ostrinia nubilalis (Hubner) were placed on the plants at certain times after application of the microsporidium. Shade did not affect the persistence of N. pyrausta as detennined by the prevalence of a microsporidiosis in the European com borer. Evidently, the structure of the corn plant protects N. pyrausta spores from the detrimental effects of ultraviolet radiation. Aqueous suspensions of spores of N. pyrausta and Vairimorpha necatrix (Kramer) were applied separately to corn foliage in both the whorl and pollen-shedding stages of plant development. European com borer larvae exposed to N. pyrausta had an equal or greater prevalence of microsporidiosis than those exposed to V. necatrix during both stages of plant development. During the whorl stage of plant development, insects exposed to V. necatrix had a greater intensily of microsporidiosis, measured as spores per mg of infecled tissue. During the pollen-shedding stage of plant development, there were no differences in intensity between microsporidia. Both microsporidia caused an infection in corn borer larvae 12 days after applicalion.