Abstract Nosema spp. are obligate intracellular parasites belonging to phylum Microsporidia. Two species of this genus including N. apis and N. ceranae are the causative agents of nosemosis in the European honeybee (Apis mellifera) and the Asian honeybee (Apis cerana). Nosemosis can cause queen supersedure, reduction of honey yield and dwindling the population of honeybees. A total number of 54 apiaries were randomly sampled from April to July 2011 and April to July 2012 in North Khorasan province, Iran. Collected samples were examined for infection with Nosema spp. In the collected bees from 30 apiaries in spring 2011, no infection was observed. Whereas, out of 24 sampled apiaries in spring 2012, 12 apiaries were infected. The reason of higher infection rate in spring 2012 was 53% increase in rainfall in this period compared to the same period of last year. In total, the prevalence rate of Nosema spp. infection in the study area 22.22% was calculated. Furthermore, the results showed that increase in rainfall will increase the rate of infection with Nosema spp.

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