I'm glad to see the interest in this thread.  Yes, Gould's paper is a great
read, as cited in my recent article at
http://scientificbeekeeping.com/pesticide-situation-part-4/

"For pests in which genes for resistance are recessive, the "refuge"
strategy may be used, as with Bt crops:
  The most widely used strategy for delaying evolution of pest resistance
to Bt crops is to grow ‘refuges’ of host plants that do not make Bt toxins
and thereby boost survival of susceptible pests. The hope is that rare
resistant pests that survive on Bt plants will mate with the relatively
abundant susceptible pests that thrive in refuges. If inheritance of
resistance is recessive, the resulting heterozygous offspring will die on
Bt crops, greatly delaying the evolution of resistance. This is sometimes
called the ‘high-dose refuge strategy’ because it works best if the dose of
toxin ingested is high enough to kill all, or almost all, of the
heterozygous insects that feed on Bt plants."
B. E. Tabashnik, Y. Carrière, Surge in insect resistance to transgenic
crops and prospects for sustainability. Nat. Biotechnol. 35, 926–935
(2017). 10.1038/nbt.3974pmid:2902000

The same would have applied to varroa resistance to fluvalinate, in which
resistant mites appeared to exhibit a fitness cost (reproducing less
effectively).

But that doesn't mean that resistance needs to come with a cost, or that
the resistance genes need to be recessive.  And with varroa, refuges don't
work the same way, since female mites mate with their brothers, with each
varroa bloodline being inbred until the mite population builds up in a
colony to the extent that some cells get invaded by two foundresses.

We should consider any and all varroacides to be stopgap measures, to be
used judiciously.  The long-term solution to varroa is to breed for
mite-resistance bees, which is why I'm focusing upon it.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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