More research on powdered sugar for varroa control:

>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

> We set up 64 equalized, queen-right colonies (single-body Langstroth hives with screen floors) and divided them equally between two apiary sites in Oconee County, Georgia, USA (33º 50' N; 84º 34' E). Once in their respective apiaries, each colony was randomly assigned one of 8 treatment combinations: 1. initiation of powdered sugar treatment (a) in January (broodless period) or (b) in March (brood area rapidly expanding); 2. treatment applied at an interval of (a) every other month for a duration of 9 days (4 treatments 3 days apart) or (b) treatment applied one day at an interval of every 2 weeks, and; 3. powdered sugar applied as (a) a dusting of 120 g (250 ml) powdered sugar with a sifter over the top bars of brood combs then brushing the sugar down between frames using a bee brush or (b) powdered sugar (same quantity) blown into the hive entrance with forced air from a shop vacuum cleaner custom-fitted with a chamber made of polyvinyl chloride (PVC) plumbing components holding the powdered sugar. There were 8 colonies (replicates) per treatment combination. The treatment interval ran from January to October, inclusive.

> The method was ineffective at reducing varroa in 75% of our analyses. Moreover, 10-month colony survival between treated and non-treated colonies was virtually identical, and poor, at 38-39%. Powdered sugar is thus, at best, another “weak” IPM component that may contribute toward varroa management when used in conjunction with other components.

Jennifer A Berry, et al
Journal of Apicultural Research 51(4): 367-368 (2012)

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