Spatial heterogeneity of microscopically detected Nosema spp. infection in honeybees: Climate-associated patterns in the Eastern Black Sea Region of Türkiye

Nosemosis has emerged as the predominant microsporidian infection of honeybees (Apis mellifera L.) in many regions, including Türkiye, yet the climatic drivers of its epidemiology remain insufficiently quantified. This study assessed the effects of temperature and relative humidity on nosemosis prevalence across seven provinces in the climatically diverse Eastern Black Sea region. A dataset of 2688 colony-level observations was analyzed using generalized linear models, mixed-effects models, beta regression, generalized additive models, and spatial autocorrelation. Both temperature and humidity were consistently significant predictors (p < .001). Quadratic temperature terms and nonlinear GAM smooths were consistent with a thermal performance pattern, with infection peaking at intermediate ranges. Humidity exerted threshold-like effects, with disproportionately higher prevalence at upper quantiles. Province-level random effects accounted for ∼18% of variance, underscoring spatial heterogeneity, while elevation was not significant once climatic variables were included. Exploratory spatial analysis (Global Moran's I = −0.476, p = 0.043) tentatively suggested dispersion rather than clustering; however, given the very small number of spatial units (n = 7), this result should be regarded as hypothesis-generating only. The beta mixed-effects model achieved moderate predictive accuracy under cross-validation (RMSE ≈ 0.109). Collectively, these findings indicate that nosemosis prevalence in the region is strongly associated with climatic variability, exhibits nonlinear and threshold-like responses, and shows pronounced spatial heterogeneity. We emphasize that these are statistical associations and that unmeasured factors (e.g., colony strength, nutrition, pesticide exposure, management practices, and co-infections) likely contribute to the unexplained variance. By integrating hierarchical, nonlinear, and spatial approaches, this study establishes a climate-associated epidemiological assessment of nosemosis risk in A. mellifera and highlights the importance of localized climatic suitability under ongoing climate change.