Nosema pyrausta: Its biology, history, and potential role in a landscape of transgenic insecticidal crops

Nosema pyrausta, an entomopathogenic microsporidium, is an important population regulator of the European corn borer, Ostrinia nubilalis. This manuscript is a review of research on the relationships between N. pyrausta and O. nubilalis. N. pyrausta was described from O. nubilalis in Hungary in 1927 and from O. nubilalis in IA in 1950. It affects the basic biology of O. nubilalis by slowing larval development, reducing percentage pupation, and decreasing adult longevity, oviposition and fecundity. Infections are maintained in a population by vertical and horizontal transmission. Success of vertical transmission depends on intensity of infection. Horizontal transmission is dependent on stage of larval development at time of infection, quantity of inoculum, and host density. Abiotic and biotic factors coupled with N. pyrausta usually have an additive effect in decreasing the fitness of O. nubilalis. i.e., cold temperatures reduce fecundity and increase larval mortality, host plant resistance reduces the number of larvae per plant. Also, microbial and chemical insecticides are more effective in reducing plant feeding if the insect is infected with N. pyrausta. Predators in general feed on N. pyrausta-infected O. nubilalis with no decrease in fitness. Parasitoids do coexist with N. pyrausta, however, parasitoid fecundity is usually reduced when developing in a N. pyrausta-infected host. Previously unreported data are presented on the prevalence of N. pyrausta in O. nubilalis populations from many parts of the US. These data demonstrate that N. pyrausta continues to be present and fluctuate in populations of O. nubilalis as it has since its discovery in the US. Also, the dynamics of its presence remain similar through changes in corn production including crop rotations, reduced tillage and transgenic insect-resistant varieties. (C) 2008 Elsevier Inc. All rights reserved.