Dusting bees with powdered sugar has been examined as a remedial control for Varroa destructor Anderson and Trueman (varroa). Two modes of action have been proposed: one being that fine dust
impedes the locomotion of phoretic mites and induces them to fall off bees (Ramirez, 1994), and another being that dust induces a grooming response in bees that similarly dislodges mites (Macedo et al., 2002). When measured as a percentage of phoretic mites dislodged,
powdered sugar dusting has achieved experimental knock-down rates ranging from 77% (Aliano and Ellis, 2005) to more than 90% (Fakhimzadeh, 2001; Macedo et al., 2002), but a persistent problem has been translating these kinds of results into practical field applications.
The most comprehensive examination of powdered sugar as a
field-level varroa control was the work of Ellis et al. (2009) in Florida. These authors dusted the top bars of brood combs with powdered sugar every two weeks from April until the following February (11 months), compared numerous parameters of colony strength and varroa populations against a control group, and found no treatment effects on any parameter of interest. In spite of these negative, yet convincing results, we wanted to do a field study that: 1. exploited a brood-free period of the season when all mites are phoretic on adults and vulnerable to dust treatment (bee colonies in sub-tropical Florida are rarely brood-free); 2. compared more than one dust delivery method, and; 3. compared more than one treatment timing interval. We felt that these outstanding questions should be resolved before we abandon powdered sugar as a bee-safe (Fakhimzadeh, 2001) and chemical-free varroa control option.
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