Assessing the antiparasitic potential of Bifidobacterium sp. Ersapi20 isolated from the cuticle of honeybees against Varroa destructor Oudemans, 1904 (Acari: Varroidae)

The mite Varroa destructor Oudemans, 1904 (Acari: Varroidae) is a major contributor to honeybee colony losses worldwide. Actinobacteria are known for their wide distribution and production of biologically active compounds effective against various pathogens, including bacteria and parasites. This study aims to investigate the bioactive compounds produced by actinobacterial symbionts associated with Apis mellifera L., 1758 (Hymenoptera: Apidae) and evaluate their acaricidal potential against V. destructor. In 2022, a strain of Bifidobacterium sp. ERSapi20 was isolated from worker bees in Antalya, Türkiye, using a culture-based method. The antiparasitic activity of the extracellular solution and intracellular extract of the strain was assessed through direct spraying on V. destructor at varying concentrations of insect Ringer solution (0%, 25%, 50%, 75%, and 100%). The extracellular solution achieved 90% mite mortality within 16 hours, while the intracellular extract resulted in 100% mite mortality within 18 hours. This is the first report demonstrating acaricidal activity against V. destructor using intracellular extracts of actinobacterial strains. These findings support the hypothesis that honeybee-associated actinobacteria produce compounds effective against varroa mites, highlighting the potential of natural products for controlling V. destructor in honeybee colonies.