Winter Bottom Beehive Cadavers as a Tool for Assessing Nosema ceranae Infestation Intensity in Honeybee Colonies in...

Honeybee (Apis mellifera) colony density is frequently assumed to influence the level of Nosema ceranae infestation in managed colonies. In Slovakia, winter bottom beehive debris (dead worker bees) is routinely collected between January and February, providing a unique and uniform material for evaluating the degree of Nosema infestation prior to the breeding season. This study assesses the suitability of winter hive debris for estimating the infestation intensity of Nosema species and examines whether regional differences in beekeeping density are associated with variation in Nosema ceranae infestation levels. A total of 6221 samples from 43 Slovak districts collected between 2022 and 2024 were examined using microscopy confirmed by duplex PCR. Nosema ceranae was detected in 74.3% of samples, while Nosema apis was not detected. Although higher colony densities tended to be associated with increased proportions of moderately and strongly infested colonies, statistical modelling confirmed a statistically significant but modest positive association between colony density and infestation intensity. These results indicate that winter bottom beehive debris is a valuable material for assessing Nosema infestation pressure at the colony and regional levels, while also highlighting the contribution of additional environmental and management factors.