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It was not until the end of the 80s that a satisfactory
control of the mite Varroa destructor Anderson was
obtained with pyrethroid based acaricides like Apistan® which
have a high efficacy against varroa mite and a low
toxicity for bees. However since the middle of the
90’s, resistance of varroa mite to pyrethroids
has been claimed in different parts of the world; including
Western Europe and USA. Detection of strains of Varroa
destructor resistant to coumaphos, an OP (Perazin and
Checkmite), have been reported in Italy and North America
as a result of laboratory tests and field trials.
However, because of possible mite reinfestation at the
end of the treatment or the misuse of the products, field
efficacy tests cannot demonstrate with certainty the
presence or absence of resistance
Consequently, in 1994, a project of monitoring varroa
resistance to pyrethroids was initiated by VITA (EUROPE)
Limited.
| Techniques
Of Detection Of Resistance |
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The existence of varroa cross resistance to pyrethroids
(acrinathrin, flumethrin, and tau-fluvalinate : Bayvarol,
Klartan and Apistan)
has been first demonstrated at Udine University (Italy) using
a laboratory assay. We choose to use Udine’s methodology
applied to tau-fluvalinate because of its accuracy and easy
handling. To monitor varroa resistance to tau-fluvalinate,
we validated and standardised the methodology according to
possible geographical variations in mite susceptibility to
tau-fluvalinate.
Figure 1: Standard profile of the susceptibility to fluvalinate
of sensitive and resistant strains of varroa determined
in a lab assays. The LC50 of sensitive mites is 25 mg/kg
for resistant strain it is about 9000 mg/kg.
Figure 2: The relationship between field treatment efficacy
and the data obtained in a laboratory assay showed that
the test was able to detect resistance before lack of efficacy
can be observed in field. According to the regression curve,
an efficacy of 60% in laboratory is corresponding to 85%
efficacy in the field.
A laboratory assay and a field test kit were perfected
for the early detection of varroa resistance to pyrethroids.
The evolution of resistance has been followed in several
European countries. To reduce the side effects of long
transportation times on mite samples and multiply the
sites of operation, the methodology was transferred to
several European laboratories: Udine University (Italy),
THI (Freiburg. Germany), AFSSA (Sophia-Antipolis. France),
CAR (Guadalajara. Spain), CARI (Louvain-la-Neuve. Belgium)
and CSL (York. UK).
Successive campaigns of detection, corresponding to
hundreds of analyses, allowed the early detection of
varroa resistance in several regions of Western Europe.
When resistance was detected, alternative treatments
were used and allowed to avoid colony losses.
Figure 3: Results of monitoring campaigns
in 1995-97.
At least for the pyrethroid resistant strain present
in Western Europe, resistant varroa mite populations
tend to develop more slowly than susceptible mite populations.
Gradually, in the absence of pyrethroid based treatments,
the proportion of pyrethroid resistance naturally decreases.
Experiments conducted at the University of Udine showed
that resistance decreases from year to year by a two-fold
factor. The experiments were conducted both in an isolated
apiary and in production apiaries (Friuli. Italy), both
experiments gave similar results.
Figure 4: Decrease of the rate of resistance of varroa
population in isolated colony in absence of pyrethroid
based varroa treatment. At the start of the experiment,
resistance was 50%, two years after, it was 8% corresponding
to a field efficacy of 96%.
The chemical family of the active ingredient used
for varroa treatment must be changed regularly in order
for these substances to remain effective.
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Bruneau E., Jacobs F., and Trouiller
J.,
Résultats de
la campagne dedétection de la résistance de varroa
aux pyréthrinoïdes en Belgique 1997. Abeilles
et Compagnie 60 (1997) 5-6.
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Massimo Spreafico, Francesca Romana Eördegh,
Iris Bernardinelli, Mario Colombo, First detection of strains
of Varroa destructor
resistant to coumaphos : results of laboratory tests and
field trials. Apidologie 32 (2001) 49-55.
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Higes M., Llorente J., Sanz A., Meana A. and Calonge R., Varroa
: sensibilidad al fluvalinato, Vida Apicola 89 (1998) 41-45.
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Hillesheim E., Ritter W., and Bassand D., First data on resistance
mechanisms of Varroa jacobsoni (Oud.) against tau-fluvalinate,
Exp. Appl. Acarol. 20 (1996) 283-296.
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Trouiller J., and Faucon J.-P., Résistance de varroa
au fluvalinate — Résultats 1997 des analyses de
laboratoire, Santé de l’Abeille 1-2 (1997) 35-36.
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