Varroa mite removal from whole honey bee colonies by powdered sugar dusting is enhanced by crowding and mechanical agitation of treated workers

The honey bee parasite, Varroa destructor, is susceptible to removal by dusting agents that physically interfere with its ability to cling to its phoretic hosts. Here we describe modifications to established powdered sugar dusting techniques that modestly increased mite separation from hosts and allowed for greater reductions in whole colony mite infestation rates. These modifications increased body-to-body contact through crowding and mechanical agitation to supplement dusting effects on mite removal. Adult workers were isolated in a screened sugar shake box outside the colony, dusted with powdered sugar, then carefully shaken and bounced in crowded piles for one minute to separate mites from their hosts. Whole colony powdered sugar shake treatments resulted on average in a 92% reduction in post-treatment mite infestation rates over three successive mite treatments. Our modifications provided effective mite control comparable to the miticide Apiguard (thymol) without discernable negative effects on colonies. Four months after treatment, powdered sugar shake treated colonies had relatively similar-sized adult worker and brood populations as Apiguard treated colonies and larger adult populations than controls. Colonies also maintained queens and reared relatively few queen cells across treatments. Further comparisons of method components revealed that mechanical agitation of crowded workers enhanced mite separation from hosts due to powdered sugar dusting. Mechanical agitation alone only modestly increased mite separation compared to controls; however, high levels of mite separation associated with sugar dusting increased with agitation. These modified methods provide a rapid if laborious technique for reducing mite populations without chemical residues from restricted miticides.