Ostrinia nubilalis populations from Slovakia, Romania, Austria, Serbia and Germany were collected in the autumn when the insects were in the larval stage. These insects were then established as laboratory populations. The number of pupae and adults that developed was always higher in the Nosema pyrausta non-inoculated (uninfected) populations than in the populations treated by the pathogen N. pyrausta (infected). Significant differences were also found among the populations from different countries. Infected females laid significantly fewer eggs compared to uninfected females. The average time for pupal eclosion or adult emergence was not signifi cantly different between the uninfected and infected populations of O. nubilalis. However, it was found that the infected females laid their eggs significantly sooner as compared to the uninfected females (37.383 days compared to 40.089 days). Under the same conditions, populations from colder regions developed faster than those from warmer regions. The place of origin of the population did not significantly influence larval weight, larval length or pupal weight. However, larvae infected with N. pyrausta spores had signifi cantly lower weight (average 0.0797 g) than uninfected larvae (0.0901 g). With regard to pupal weight, the difference between the infected and uninfected individuals was not signifi cant. It was confi rmed that N. pyrausta from one European country can infect and infl uence host larvae originating in other countries. Although there have been several statistically significant interactions with regard to the country of origin and N. pyrausta infection, it was not believed that N. pyrausta from one country would have specific effects on the mortality, developmental rate and larval or pupal weight of O. nubilalis populations from different countries.