Collective versus individual amitraz treatments shape Varroa destructor infestation and viral load dynamics in...

Varroa remains a major constraint on sustainable apiculture due to its role in amplifying and transmitting honeybee viruses that contribute to colony decline. Although chemical control is widely applied, the virological outcomes of coordinated, apiary-level Varroa management under field conditions remain poorly defined. This study assessed the relationship between Varroa infestation intensity and viral genome loads by comparing collective, synchronised amitraz applications with individually applied treatments across 14 apiaries in Central Anatolia, Türkiye. Genome loads of ABPV, BQCV, DWV-A, DWV-B, and SBV were quantified in age-synchronised young worker bees using real-time qPCR, alongside histopathological evaluation of asymptomatic infections. Collective Varroa control achieved significantly greater and more uniform reductions in mite infestation and was associated with marked decreases in DWV-B genome loads at the colony level. Reductions in DWV-A and ABPV were also observed, though with greater inter-colony variability. Histopathology revealed mild, localised midgut epithelial alterations consistent with subclinical viral infection. The results suggest that coordinated amitraz-based Varroa management is associated with reduced virus amplification under field conditions and may contribute to limiting virus-associated colony losses.