Horizontal Transmission of Nosema pyrausta (Microsporida: Nosematidae) in the European Corn Borer, Ostrinia nubilalis (Lepidoptera: Pyralidae)

Abstract

It was demonstrated in laboratory transmission tests that corn stalks inhabited by European corn borer (ECB), Ostrinia nubilalis (Hubner), larvae that are infected with Nosema pyrausta (Paillot), become readily contaminated, via spores in larval excrement and that contaminated feeding cavities provide a major source of infection for the healthy inhabitants of the stalk. Exposure of uninfected ECB larvae to damaged plant cavities that harbored actively feeding infected ECB larvae leads to higher frequencies of transmission than cavities that have been abandoned or are inhabited by uninfected individuals. Results also indicate that in each generation, there is a time lag following ECB oviposition before effective transmission takes place in the field, and in the second generation, ECB larvae continue to contaminate plant tissues with infectious spores until they enter diapause. This mechanism of transmission, along with larval feeding behavior and intraplant movement, contribute significantly to the horizontal spread and annual build-up of N. pyrausta within the ECB population.