>I do not understand why OA would damage mites but not bees.  Can anyone explain?

OA does damage the bees. However, the actual explanation is "the dose makes the poison." Toxins act differently on different organisms, in different doses, and different methods of delivery. 

> Although the acute toxic effect of OA on varroa is beneficial to the colony, studies have also shown long-term (Moosbeckhofer, 2001) and temporary negative effects on adult bees (Martin-Hernandez et al., 2007) often resulting in increased bee mortality and poor overwintering especially when OA is administered using the trickling method

> In both trials during week 1 post-treatment, bee mortality was significantly higher than in the control groups. Similarly, when brace comb was removed (Group 4), this allowed the more even distribution of the product directly on the bees, bee mortality was further increased.

> Finally, although other more persistent sub-lethal effects such as a decrease in worker activity, nursing ability, and longevity have been documented (Schneider, Eisenhardt, & Rademacher, 2012), the test colonies in the present study appeared to develop normally in the spring.

Mary F Coffey & John Breen (2016) The efficacy and tolerability of Api-Bioxal® as a winter varroacide in a cool temperate climate, Journal of Apicultural Research, 55:1, 65-73, DOI: 10.1080/00218839.2016.1200866

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