Date: 04 September 2001 19:16

Varroa Resistance to Pyrethroids confirmed in the UK.
CSL Press Release

The National Bee Unit has just confirmed the presence of pyrethroid resistant varroa in the UK. Resistance to fluvalinate, the active ingredient of Apistan has been confirmed by laboratory testing in mites from an apiary in Devon, and field tests give strong reason to suspect resistance in other apiaries in the same area. It is almost certain that these mites will also be resistant to other pyrethroids including flumethrin, the active ingredient of Bayvarol.

Full details are available from the CSL website:

I will be providing further information and advice as the situation develops. In the meanwhile, if you have any questions or concerns, please get in touch.

James Morton

South-Eastern Regional Bee Inspector
Central Science Laboratory
National Bee Unit
Tel/fax: 020 8571 6450
Mobile: 07719 924 418
Address: 'Geertje', Canal Lock 92, Windmill Lane, Southall, Middx, UB2 4NH



Honeybee apiaries in the South West have been threatened by the first case of resistant varroa mites. Laboratory tests conducted during the week beginning 27 August 2001 at the Central Science Laboratory (CSL) confirmed that at least one apiary in Devon has mite populations resistant to pyrethroid.

The resistance found in Devon appears to be localised. Recent spot checks elsewhere in the country have revealed the continued high efficacy expected of Apistan and Bayvarol, the only two pyrethroid-based treatments authorised for use in the UK.

Medwin Bew, Head of Environmental Biology Group, CSL, said: "Beekeepers are requested most strongly to follow the label instructions on varroacide products carefully. Misuse (e.g., prolonged application of the product or abuse of the active ingredient, or use of cheap, untested analogues) has been the cause of every original focus of resistance in Europe.

"DEFRA is considering arrangements for dealing with this resistance case and any others which may be discovered. Updates will be posted on the CSL website ( as they occur.

"The beekeeper's colonies were first tested using a simple field kit developed by Vita (Europe) Ltd and CSL. This was part of a routine screening programme introduced some while ago by CSL with the aim of following up reported cases of suspect resistance or to check colonies of beekeepers believed to be misusing pyrethroid.

"So far five apiaries belonging to the beekeeper have been screened by field tests. The effectiveness of the test Apistan strips against varroa was found to be as low as 2%. This resistance is worrying and will almost certainly be of a similar order for both Apistan and Bayvarol. Apistan treatments are normally 95-100% effective. All the beekeeper's apiaries are under standstill notices."

Past studies have shown a close level of agreement between the results of field tests and confirmatory laboratory tests so we have no reason to suppose that the remaining unconfirmed field tests are other than sound.

Currently CSL is organising a resistance monitoring programme of neighbouring apiaries in the areas around these Devon colonies. This will be limited by the approach of autumn and its success will depend upon local beekeepers' co-operation. CSL has also stepped up its surveillance in other areas.

In the meantime, beekeepers wishing to undertake resistance testing on their own colonies should contact their Regional Bee Inspector for details about how to conduct the test and submit the results to the surveillance team at CSL.

Notes for Editors

1. Varroa is a serious Asian mite infestation of honeybees, first introduced into the UK in 1992. Colonies die if the infestation is left untreated. Varroa cannot be eliminated from infested hives but can be controlled to harmless levels through good husbandry and hygiene and by prompt treatment. Currently, two varroacides are authorised in the UK for treatment of varroa - Apistan and Bayvarol.

2. Varroa caused devastating losses of honey bees in the early years following its introduction. Although most beekeepers have now learned to live with the parasite, the majority of feral colonies have since collapsed. Since bees are important pollinators of many commercial crops and of wild flora it is essential that a healthy population is maintained. Without effective treatments available healthy managed colonies are now at risk unless resistant mite populations can be controlled and contained.

3. Apistan and Bayvarol treatments usually have an efficacy of 95-100% against varroa mites. A tenfold reduction of this efficacy means that treatment will not reduce mite populations below the threshold necessary to both preserve the colony and prevent further spread of damaging levels of mites to surrounding colonies and apiaries.

4. There is estimated to be about 1,900 beekeepers in Devon, managing approximately 12,000 colonies of bees. Devon is also a popular location for migratory beekeepers from other counties wishing to take advantage of moorland blossom. Many hundreds of beekeepers move colonies into Devon for about a month each August to crop honey from heather.

5. Advice on finding and dealing with varroa, and reducing the risks of resistance, is contained in the leaflet "Managing Varroa" which is available free of charge from the CSL National Bee Unit, Sand Hutton, York, YO41 1LZ or from its Regional Bee Inspectors. Details are also available on the CSL website at