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From: "Max Watkins" <[log in to unmask]>
To: "'Informed Discussion of Beekeeping Issues and Bee Biology'"
<[log in to unmask]>
Date: Tue, 16 Mar 2010 12:25:59 -0000
Subject: Mite resistance costs

Just to add to this discussion, research performed by my late friend and
colleague, Professor Norberto Milani at the University of Udine in Italy
showed that the reproductive fitness of pyrethroid-resistant varroa mites
was lower than susceptible strains. The cost may not be obvious but it is
real. Resistant mites still go great guns and reproduce of course, but their
success was lower than for susceptible mites.

We monitored the pattern of emerging varroa resistance throughout Europe
back in the '90s and in truly isolated apiaries in northern Italy, we were
able to study the decline of resistance within mite populations once the
selection pressure of pyrethroids (flumethrin, tau-fluvalinate and
acrinathrin) was removed. The genes for pesticide resistance in varroa
become suppressed after around 3 years and the fact that such mite
infestations can be successfully controlled with these same pyrethroids
again demonstrates that the susceptible condition must have some advantage
to the mite under "natural" conditions.

Where pyrethroids (as agro treatments as well as proper bee treatments) have
been removed for around 3 years it has been possible to use these treatments
again but for one or two seasons only, otherwise the selection pressure
favours the resistant type once more and resistant mite levels grow.


Max


Dr Max Watkins
Director
Vita (Europe) Limited
21/23 Wote Street
Basingstoke
Hampshire RG21 7NE
UK

Tel.:   +44 (0)1256 473 177     Fax:   +44 (0)1256 473 179
Mobile: +44 (0) 7767 815 370

e-mail:  [log in to unmask]
web: http://www.vita-europe.com

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