Pathogens of the European corn borer, Ostrinia nubilalis, with special regard to the microsporidium Nosema pyrausta

The European corn borer, Ostrinia nubilalis, is the most important pest insect of corn (Zea maize) in Germany, other European countries and historically in North America. However, in Europe only a few reports on naturally occurring biotic mortality factors are available. In the present review, an overview on pathogens including nematodes attacking O. nubilalis is compiled. The primary data were originally derived from long-term diagnostic studies on pathogens of arthropods carried out by the Institute for Biological Control, Darmstadt, Germany. These are updated with findings from the literature and supplemented with data from other pest insects of the same lepidopterous Crambidae family. The most important and most frequently found pathogens are the microsporidium Nosema pyrausta, the fungi Beauveria bassiana and to some extent also Fusarium spp., and the bacteria Bacillus thuringiensis and Serratia marcescens. Thus far, viruses have not been detected. Data on practical use of B. thuringiensis, B. bassiana and other fungi, N. pyrausta, and some nematodes for biological control of O. nubilalis are presented. Because of the importance of N. pyrausta as a population regulator of O. nubilalis, causing a chronic disease in larvae and adults, the current knowledge on the occurrence, biology, transmission, effects on the host insect, interactions with beneficial insects and field experiments is presented. These data are complemented with former, unpublished studies on the occurrence and incidence of N. pyrausta in some German and French O. nubilalis populations (Hessen, Baden-Württemberg, Alsace). The review clearly indicates that pathogens may play an important role as naturally occurring mortality factors of O. nubilalis which may also be used as biocontrol agents or within conservation biological control strategies.