Behavioral Resistance in Varroa destructor: First Evidence in Response to Acaricide?

The ectoparasite Varroa destructor (Mesostigmata: Varroidae) poses a major threat to honey bee colonies due to its role as a viral vector and its capacity to develop resistance to treatments. While physiological resistance and target-site mutations are well documented, behavioral mechanisms remain largely unexplored. This study investigated the potential existence of behavioral resistance in V. destructor, defined as a modification of behavior in response to an acaricidal molecule. Using Y-maze olfactometric assays, we evaluated mite responses to three acaricides-amitraz, tau-fluvalinate, and oxalic acid-across five French populations with distinct treatment histories. Forty groups of five mites were exposed to "acaricide/solvent" pairs, and choices were recorded after 18 h. Results revealed marked heterogeneity among populations. Two population exhibited significant avoidance of tau-fluvalinate, providing the first case of avoidance behavior in V. destructor, but no coinciding phenotypic resistance. No avoidance was detected for amitraz and oxalic acid. These findings suggest that behavioral resistance may exists in France but is not systematic. Identifying this phenomenon opens new perspectives on the parasite's adaptation to treatments and underscores the need to integrate behavioral aspects into control strategies.