| Summary: | Two species of microsporidia, <i>Nosema apis</i> and <i>Nosema ceranae</i>, are obligate intracellular parasites that are widespread in the world and cause the infectious disease (Nosemosis) of the Western honey bee <i>Apis mellifera</i>. Information on the prevalence and distribution of <i>Nosema</i> species in North Asia conditions is scarce. The main aim of the present study is to determine the prevalence of <i>Nosema</i> spp. (Nosemosis) in honey bees inhabiting some inland regions of North Asia (Western and Eastern Siberia, Altai Territory, Russia, and northeastern part of Kazakhstan). The objective of the paper is also to assess the influence of climatic factors on the spread of <i>N. ceranae</i>. Eighty apiaries in four ecological regions of North Asia (southern taiga, sub-taiga zone, forest steppe, and mountain taiga forests) were investigated with regard to distribution, prevalence, and diversity of <i>Nosema</i> infection in honey bees using duplex-PCR. <i>Nosema</i> infected bees were found in 65% apiaries of ecoregions studied, and coinfection was predominant (36.3% of <i>Nosema-</i>positive apiaries). Both <i>N. apis</i> and <i>N. ceranae</i> occur across subarctic and warm summer continental climates, but while <i>N. apis</i> predominates in the former, <i>N. ceranae</i> is more predominant in the latter. No statistically significant differences in <i>Nosema</i> distribution were identified in various climatic zones. In the sub-taiga zone (subarctic climate), low presence of colonies with pure <i>N. ceranae</i> and a significantly higher proportion of coinfection apiaries were revealed. Long-term epidemiological study of <i>Nosema</i> spp. prevalence in the sub-taiga zone showed a surprising percentage increase of <i>Nosema</i>-positive apiaries from 46.2% to 74.1% during 2012–2017. From 2012 to 2015, <i>N. apis</i> became a predominant species, but in 2016–2017, the coinfection was mainly detected. In conclusion, the results of this investigation showed that <i>N. ceranae</i> is widespread in all study ecoregions of North Asia where it exists in combination with the <i>N. apis</i>, but there is no replacement of <i>N. apis</i> by <i>N. ceranae</i> in the studied bee populations.
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