Varroa destructor Infestation Intensity, Viral Burden, and Mite Acaricide-Resistance Markers in South Korean Honey Bee Colonies

Varroa destructor is a major parasitic threat to apiculture and an important vector of deformed wing virus (DWV). Previous national surveillance in South Korea has described the occurrence of the mite and associated viruses, but did not examine whether viral burden correlates with infestation intensity. In this secondary analysis of the 2025 national surveillance programme, colony-level mite counts were paired with DWV and Israeli acute paralysis virus (IAPV) measurements and resistance-marker genotyping. Virus detection differed little among infestation categories. Among virus-positive colonies, however, lower Ct values, indicating greater relative target abundance within each assay rather than absolute viral load, were associated with increasing infestation intensity across the observed range for DWV; for IAPV, the association was weaker and most evident in the most heavily infested colonies. Both associations persisted after adjustment for surveillance round and clustering within apiaries. Resistance-associated markers for fluvalinate and amitraz were detected in every successfully genotyped apiary based on one pooled sample of up to five mites per apiary. These apiary-level results cannot be equated with marker prevalence among individual mites. Because genotyping was not paired with bioassays or treatment-efficacy measurements, the findings do not demonstrate phenotypic resistance or field treatment failure.