David W. Inouye seeks: "reference that might document the appearance of
resistance by Varroa mites to chemicals used by beekeepers..."
Best bet I know of is Tom Sanford's APIS newsletter.  Surf to:
http://www.ifas.ufl.edu/~mts/apishtm/apis.htm
 
You will find plenty of references and cross references.  Tom's site is
about the best going IMHO.
 
Aaron Morris - I think, therefore I bee!