John Caldeira in Dallas wrote: (23 April 1996)
---------------Original Message---------------
I'm no expert in pesticide resistance, but David M. Noetzel, Extension
Entomologist Emeritus from University of Minnesota, suggests in American
Bee
Journal (December 1995, page 791) that HIGH doses of fluvalinate would
lead
to faster resistance than lower doses.
 
The thinking behind this is that killing 99% of the mites provides more
selection for resistance than, say, a mite treatment that only kills off
80%.
 
Sure wish we could kill 100% & be done with them!
 
Cheers,
John in Dallas
 
 
Thanks for your response John.  I have not read the ABJ aricle by David
Noetzel.  I'm searching for a UK copy.  Meanwhile can anyone summarise
further his evidence/reasoning?  It does alarm me because the widely
accepted principle is that weak, underdosing of medicaments leads to
pesticide resistance.  If we now have a contrary principle then there
could be very severe problems developing.  For instance, I believe if many
beekeepers underdose their fluvalinate treatment for fear of giving too
high a dose then there will be rapid development of resistant strains of
V.mite.
 
The appearance of the fluvalinate (and flumethrin) resistant strains in
Italy was a result of UNDERDOSING.  To save expense, strips were even cut
in half; often only one strip per hive was used. Home made strips were
(and still are!) made from diluted fluvalinate sheep dip solutions used by
sheep farmers to combat sheep scab! To be fair it is not unknown in UK.
 
The reason that Apistan and Bayvarol strips, only have a 98-99% knock down
is not just that the odd 1-2% are immune.  These pesticides are CONTACT
poisons.  There is always a random chance that some mites will not get
sufficient "contact" with the chemical to kill them.  All we can do so far
 is control the mite population so that it does not interfere unduly with
the bee colony development. (Secondary virus infections excepted).
 
Some of the surviving mites may be immune of course, but that can be dealt
with by changing the treatment every two years or so.  This is also why
most responsible national Agriculture Departments only licence one or two
treatments.  These can be changed later and so keep developing resistance
under control.
 
Happy beekeeping,
 
Glyn Davies
Ashburton, Devon. UK