Date of Award
The parasitic varroa mite, Varroa destructor (Anderson and Trueman), is a global threat to honey bee health and the leading cause of honey bee (Apis mellifera L.) colony mortality. In the constant battle against varroa, many apiarists turn to chemicals, such as formic acid, oxalic acid, or synthetic compounds, to control mite populations and save their colonies. However, each chemical treatment option exhibits certain shortcomings and the development of new varroa mite controls is key to combating varroa resistance and increasing safety to beekeepers and bees. The objective of this study was to assess the effectiveness of two organic methods of varroa mite control: powdered sugar and heat, in comparison to currently used chemical controls. In experiments using bees on single brood frames, powdered sugar and oxalic acid were similarly effective in controlling phoretic varroa (measured as mite drop after treatment). There was also no statistically significant difference in effectiveness between powdered sugar application methods (sifting or reverse vacuum). At the colony level, both the heat and formic acid treatments had significantly lower mite counts following the treatment period, while both powdered sugar treatments and the negative control (no treatment) colonies exhibited no significant differences in mite infestations following the treatment period. Heat and formic acid caused significantly greater adult bee mortality (554.6 + 162.5 and 115.1 + 31.8 respectively) than observed in the powdered sugar (low rate: 13.9 + 1.8; high rate: 13.5 + 2.7) and negative control (9.0 + 0.8) colonies. Heat caused significantly more larval and pupal bee mortality than all other treatment methods. Treatments at the colony level show that heat demonstrates the potential for effective varroa control but does kill a larger number of bees during the treatment period compared to formic acid. While powdered sugar does not show the ability to control varroa at the colony level in this study, it could be incorporated into an IPM strategy and used when the colony is broodless. Furthermore, sifting powdered sugar over a brood box provides researchers with a technique to collect hundreds of varroa to use in other control assays.
Johnson, Casey L., "CONTROL OF VARROA DESTRUCTOR USING POWDERED SUGAR AND HEAT" (2022). Open Access Master's Theses. Paper 2243.
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