First report of deltamethrin tolerance in the cattle chewing louse Bovicola bovis in the UK

THE chewing louse Bovicola bovis is the most common and clinically important species of louse found in cattle in the UK (Craufurd-Benson 1941) and causes significant economic losses. Clinical signs of infection include pruritus and excoriation which may lead to alopecia, skin trauma and infection (Matthysse 1946), and hide damage such as spot and fleck lesions that cause losses of up to £20 million per annum in the UK (Coles and others 2003). Treatment is usually by the use of topical insecticides such as synthetic pyrethroid and macrocyclic lactone formulations. Recently, there have been concerns over the development of pyrethroid resistance in chewing lice (Ellse and others 2012, Levot 2012). Inadequate coverage of the body resulting from pour-on and spot-on formulations exposes lice distal to the zones of drug penetration to sublethal doses of insecticide, which potentially exacerbates selection for resistance (Johnson and others 1995, Ellse and others 2012). Facultative parthenogenesis may also allow populations of lice with alleles conferring resistance to increase rapidly in size and predominate within the overall louse population (Ellse and others 2012). To date, there has been no clear evidence of insecticide tolerance or resistance in the UK B. bovis populations. The present study was undertaken in response to reported treatment failures with pyrethroid insecticides. B. bovis were collected from …