VIII SIMPOSIO INTERNAZIONALE ICPBR

HAZARDS OF PESTICIDES TO BEES

Bologna, 4-6 Settembre 2002

Controllo dei parassiti delle api

Varroa destructor resistance to pyrethroid treatments in the UK

H. M. Thompson, R. F. Ball, M.A. Brown and M.H. Bew

National Bee Unit, Central Science Laboratory, Sand Hutton, York, YO41 1LZ, UK. E-mail: h.thompson@csl.gov.uk

Varroa destructor was first detected in the UK in 1992 and since then there has been widespread use of the only two authorised pyrethroid treatments. A routine national screening programme for resistance to pyrethroids was established in 2000 and in August 2001 resistance was detected in southwest England [1]. The resistance outbreak was limited to 25 apiaries and was associated with misuse of the product. The toxicity of several varroacides was compared in the laboratory using mites from two sources, apparently susceptible colonies at CSL, York and the colonies identified as resistant in the south west of England. When comparing the mites tested with fluvalinate under the same conditions the 11-fold resistance factor in LC50 shown by the mites from the Devon apiary was far lower than the 440-fold resistance reported in Italy. The 200 ppm discriminatory dose for detecting resistant mites was the same as that identified by Trouiller.

The toxicity of flumethrin was similar to that reported in Italy for susceptible mites but slightly lower than for resistant mites. The data clearly demonstrated the cross-resistance to fluvalinate and flumethrin. The toxicity of coumaphos was similar to that reported for susceptible mites in Italy and well below the LC50 reported for resistant mites. This confirmed that there was no cross-resistance or multi-resistance to coumaphos in the mites from the fluvalinate resistant colonies. The toxicity of amitraz as Apivar strips was determined as a LT50 due to the instability of amitraz and showed similar results with mites from the CSL, York and from the Devon colonies showing that there was no cross-resistance or multi-resistance between fluvalinate and amitraz. The toxicity of cymiazole to mites from the CSL, York and Devon was also similar to that recorded for susceptible mite populations.

As the resistance was detected in the early stages this is the first time that truely comparable data have been generated for five different varroacides in mites from the same colonies. These laboratory data have allowed cymiazole, amitraz and coumaphos to be identified as control measures for the fluvalinate resistant mite. The use of the field kits as a strategy to detect resistance at an early stage has allowed the situation to be managed before it became widespread or resulted in colony collapse. We are currently undertaking research into mechanisms of varroa resistance to put in place a resistance management strategy.

Reference:

[1] Thompson H.M., Brown M.A., Ball R.F. and Bew M.H. (in press) First report of Varroa destructor resistance to pyrethroids