LABORATORY STUDIES ON RESISTANCE TO CYPERMETHRIN IN <i>DAMALINIA OVIS</i> (SCHRANK) (PHTHIRAPTERA: TRICHODECTIDAE)

Abstract

Abstract A treated surface technique to measure the response of the sheep body louse, Damalinia ovis to contact insecticides is described. The responses of 30 populations of D. ovis to the synthetic pyrethroid cypermethrin showed wide variation at LC 95 and LC 95 . Half the populations sampled were considered as pyrethroid susceptible, based on 100% mortality at 5 ppm (or less) to cypermethrin. This suggests that factors other than pyrethroid resistance were responsible for inefficient lice control on the properties from which these populations were obtained. Lice surviving 5 ppm or greater were considered provisionally as resistant. When these individuals predominate, the proportion of the lice population killed by pour‐on treatments is insufficient to prevent detectable infestations being present soon after treatment.