LAUSR

The removal of Varroa destructor was assessed in Russian honey bee (RHB) colonies with known levels of Varroa Sensitive Hygienic (VSH) and brood removal activities. The expression of grooming behaviour using individual bees was also measured using three groups of RHB displaying different VSH levels: low hygiene (RHB-LH, < 35% VSH), medium hygiene (RHB-MH, 35–70%) and high hygiene (RHB-HH, > 70%). Italian colonies (5.43–71.62% VSH) served as control. Our results demonstrated, for the first time, significant relationships between two hygienic responses (VSH activity measured as percent change in infestation and the actual brood removal of Varroa-infested donor comb) and two measurements of mite fall (trapped old mites/trapped mites or O/T and trapped young mites/trapped mites or Y/T). However, these relationships were only observed in RHB colonies. In addition, the RHB colonies that displayed the highest levels of hygiene (RHB-HH) also groomed longer in response to the presence of a V. destructor mite based on individual bee assays. The positive regressions between the two hygienic measurements and O/T and their negative regressions with Y/T suggest that the removal of infested brood prevented successful mite reproduction, ultimately suppressing V. destructor infestations in the RHB colonies. In addition, it is demonstrated that RHB resistance to V. destructor rests on both an increased hygienic response and the removal of phoretic mites, released by hygienic behaviour, through grooming. Both resistance traits are reflected in the O/T and Y/T ratios found in trapped mites from RHB colonies. None of the measurements involving mite injuries were associated with any measurements of hygiene and colony infestations.