In a message dated 16/03/02 05:01:35 GMT Standard Time,
[log in to unmask] writes:

<< The down side of this is you may select for resistance to both at the same
time
 and wake up to a surprise that both treatments no longer work. Cross
resistance
 may also be obtained quicker. >>

It depends how similar the treatments are.  For example, although Apistan and
Bayvarol are different formulations of artificial pyrethroid, they are so
close that if the mites are resistant to one they will be resistant to the
other.  Although the mechanics of resistance can take many paths the one, in
Europe at least, that the mites use is to detoxify themselves.  Putting in in
human terms, the treatment selects for the mites with the most efficient
kidneys.  Mites with this form of resistance will therefore have a head start
in coming to terms with the next chemical treatment to come along.

Alternating between chemical and bio-technical (physical) treatments would
seem to be a likely way of postponing resistance.

Chris