Evaluation of three synthetic pyrethroids in the control of sheep headfly disease.

Deltamethrin (0.01 per cent) applied to the heads of lambs and gimmers at 30 day intervals on two separate farms failed to control damage caused by the sheep headfly , Hydrotaea irritans. Permethrin (0.1 per cent) applied to gimmers at monthly intervals achieved a slight reduction in severity of damage but protection did not extend beyond 14 days. Polyvinyl chloride tags containing 8.5 per cent cypermethrin reduced damage in gimmers to a very low level with protection lasting throughout the summer. Weight gains of lambs suffering headfly damage were significantly less than unaffected lambs.