§ Dr. Strang
To ask the Minister of Agriculture, Fisheries and Food to what insecticides sheep lice have developed resistance in other countries;; what resistance in sheep lice to insecticides has been suspected or detected in the United Kingdom; what percentage of sheep flocks in the United Kingdom are currently affected by sheep lice infestations; and what assessment he has made of the rate of spread of sheep lice infestation.
§ Mr. Waldegrave
In Australia, the chewing louse of sheep—Bovicola Damalinia ovis—has been shown to be resistant to the synthetic pyrethroid cypermethrin, both by laboratory bioassay and under field conditions.
Monitoring for insecticide resistance within United Kingdom populations of sheep ectoparasites—including the sheep chewing louse—has been undertaken for the past three years, under a Government-funded research project. There is no evidence to suggest that chewing lice are resistant to any licensed synthetic pyrethroid or ornaophosphorus formulation applied to sheep in the 284W United Kingdom. Suspected resistance to organochlorine insecticides, which are no longer used, was reported in sheep lice in Cumbria in 1965.
In the United Kingdom, the compulsory national dipping of sheep in organochlorine, organophosphate or synthetic pyrethroid plunge dip formulations between 1974 and 1992 for scab control, dramatically reduced the prevalence of B. ovis. During this period, a total of 24 incidences of infestation were recorded. These were located on Bodmin moor, Dartmoor, the North Yorkshire moors, the Peak district, the Lake district, the Pennine regions of Cumbria and County Durham, Mid Glamorgan and the Scottish islands. No assessment has been made of the incidence of sheep lice infestation since 1992.