Impact of intensive agriculture and pathogens on honeybee (Apis mellifera) colony strength in northwestern Italy

Honeybee colony survival has significantly decreased in many countries over recent decades, which has been associated with multiple factors including pathogens, parasites, resource availability, and environmental stressors, with agricultural intensification playing a key role. This study assessed the effects of Varroa destructor mite infestation, viral prevalence and load, and agrochemical concentrations in the hive matrix on colony strength in two apiaries located in different agricultural contexts (intensive vs traditional) in Northwestern Italy from March to September 2021. The results revealed that colonies in the intensively managed area exhibited lower colony strength and higher mortality rates. Varroa destructor was found to interact with viruses, potentially increasing their effective virulence. Pesticide concentrations in hive matrices correlated with reduced colony strength, exacerbated by elevated pathogen loads. These findings highlighted the effects of agricultural chemicals together with pathogens on worsening bee health, raising urgent concerns for environmental management and regulatory policy.