Evaluations of the Removal of <italic>Varroa destructor</italic> in Russian Honey Bee Colonies that Display Different Levels of <italic>Varroa</italic> Sensitive Hygienic Activities.

The removal of <italic>Varroa destructor</italic> was assessed in Russian honey bee (RHB) colonies with known levels of <italic>Varroa</italic> 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 <italic>Varroa</italic>-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 <italic>V. destructor</italic> 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 <italic>V. destructor</italic> infestations in the RHB colonies. In addition, it is demonstrated that RHB resistance to <italic>V. destructor</italic> 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. [ABSTRACT FROM AUTHOR]