Effect of insecticidal ear tags on populations of lice (Damalinia ovis) infesting sheep. 
Polymer matrix ear tags containing 13.7% w/w tetrachlorvinphos or 8.5% w/w cypermethrin were applied to Merino wethers infested with lice and carrying two months wool.  The cypermethrin tags reduced louse numbers by a maximum of 89% in comparison to controls at 16 weeks after treatment and by 85% at the conclusion of the experiment 38 weeks after application.  Lice were not eradicated from any sheep.  The number of lice counted on sheep treated with tetrachlorvinphos-impregnated tags was not significantly different from controls.