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The decline in pollinator insect abundance and diversity is increasing on a global scale. Major threats are the byproducts of numerous negative environmental pressures acting individually or in combination. They vary throughout different geographical areas, affecting the solitary bees differently. One of the most important negative pressures are the many parasites, predators and pests representing a threat to the successful reproduction of solitary bees in artificial nests. Especially vulnerable are the managed Osmia spp. bee populations reared for commercialization and trade. The primary goals of our monitoring study were: (i) to examine the presence and the prevalence of brood parasites in the various types of bees' nesting material and in semi-field rearing conditions using the nest section analyses; (ii) to determine the presence of Nosema spp. in samples of feces and homogenized bee abdomens using a multiplex PCR method; (iii) the evaluation of the survival success level and emergence mass of healthy bees at each of the four studied bee rearing locations separately, depending on different environments and on the implementation of different managing practices. We determined the presence and prevalence of nest destructor parasites and accompanying fauna. Their presence was positively correlated with bee rearing failures. The results of this study may be used as a baseline for further solitary bee nest parasites monitoring schemes. [ABSTRACT FROM AUTHOR]