Rapid spread of Amitraz resistance linked to a unique T115N mutation in the octopamine receptor of Varroa mites in Korea.

The Varroa mite, Varroa destructor, is an ectoparasitic pest of Western honey bees and poses a significant threat to apiculture. In Korea, widespread fluvalinate resistance has increased reliance on amitraz as an alternative acaricide. This study identified a novel mutation, T115N, in the β2-adrenergic-like octopamine receptor gene (OctβR) and confirmed its role in amitraz resistance. Genotyping of individual mites, based on time-dependent intoxication responses to a diagnostic dose of amitraz, revealed a strong correlation between genotype and resistance phenotype: mites with early intoxication responses were homozygous for the T115 allele, whereas those with delayed responses predominantly carried the homozygous N115 allele. Mites with homozygous N115 genotype exhibited a median lethal time approximately 2.8-fold longer than their T115 counterparts, confirming the resistance conferred by the T115N mutation. Quantitative sequencing was established to track the spread dynamics of T115N mutation in Korean Varroa mite populations over five years (2020-2024). While the mutation was rare from 2020 to 2022, its frequency increased sharply in 2023 and became widespread across Korea by 2024, coinciding with increased amitraz usage. These findings suggest region-specific selection for the T115N mutation driven by amitraz exposure.