Physical control of varroa mites ( Varroa destructor): the effects of various dust materials on varroa mite fall from adult honey bees (Apis mellifera) in vitro

In this study, we investigated the impact of ten different materials on the fall of varroa ( Varroa destructor) mites from adult honey bees (Apis mellifera) in vitro. To do this, we confined similar to 250 adult bees each to 144, 0.47 I glass jars, feeding them bee candy (honey / powdered sugar) ad lib. Seventy-two hours later, the bees were treated with 5 g of one of the ten materials and placed in one of two locations (in an incubator = 35 degrees C, 70% RH, or in a dark room = 22 degrees C, 50% RH; replicate schedule = 10 dusts and 2 controls x 6 jars / rep x 2 locations). Immediately after and 24 h after treatment application, we counted the number of mites that fell from the jar through the mesh lid when the jar was rolled for 30 s, inverted, and shaken for 30 s. Four days later, we estimated the number of bees alive in each jar and washed the bees to remove any remaining mites. With these data, we determined the mite drop efficacy of the materials and their acute impact on adult bee survivorship. In general, powdered sugar from Slovenia (82.7 +/- 4.1: mean +/- s.e. % mite fall), vacuum collected sugar (83.2 +/- 2.8), baby powder (83.8 +/- 5), and ground table sugar (69.6 +/- 5.5) induced higher levels of mite fall than the other materials. Fewer bees survived four days post treatment, however, with Slovenian powdered sugar and baby powder (9.6 +/- 5.6% and 3.2 +/- 1.2% survival, respectively) than bees treated with any other material (survival range from 67.1 - 95.5%). We also include a discussion of the particle size of each material and how it may affect material efficacy.