This information is from 2008, ABJ:

The problem with fluvalinate

We have always considered fluvalinate a relatively "safe" material for honey bees; however its history is unclear with potentially significant implications for honey bee health. The original formulation of fluvalinate (racemic or having multiple forms) had an established lethal dose that killed 50% of the tested population (LD50) at 65.85 μg/bee for honey bees, which is considered relatively non-toxic (Atkins et al. 1981). However in the early 1990’s racemic fluvalinate was replaced with tau-fluvalinate (having a single form) resulting in a 2-fold increase in toxicity of this material to honey bees. The amended LD50 was then 8.78 μg/bee, a level considered moderately toxic to honey bees. In addition, US registration of this material changed hands several times over the past 20 years with potential changes being made in the formulation of fluvalinate.

Based on its prevalence in wax, wide-spread resistance in varroa and its toxicity to honey bees, fluvalinate appears to have outlived is usefulness.  

Fluvalinate should only be used as a material of last resort [!]

What Have Pesticides Got to Do with It?
Maryann Frazier, Chris Mullin, Jim Frazier and Sara Ashcraft

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