KINETIC DISPOSITION OF AN AQUEOUS FORMULATION OF ALPHACYPERMETHRIN APPLIED TO THE DORSAL MIDLINE OF SHEEP WITH LONG WOOL AND ITS EFFECT ON LICE

A group of 5 adult Merino sheep with fleeces about 70 mm long (7-month s growth of wool) was treated with a topical formulation of the synthe tic pyrethroid insecticide, alphacypermethrin, applied to the dorsal m id-line. Insecticide concentrations at the tip, middle and base of woo l staples collected from meridians along the back, upper and lower han ks were measured at intervals from 1 to 98 days after treatment. Some movement of the alphacypermethrin from the back to the lower body occu rred within 24 h after treatment, but despite careful application of t he insecticide there was wide variation in the concentration between a nd within meridians. The majority of the alphacypermethrin remained cl ose to the dorsal mid-line and near the tip of the staple. There were significant differences in the concentration between the tip, middle a nd base segments of the staples in the back and lower flank meridians (P<0.05). Despite exposure of the sheep to normal weathering, there wa s no significant difference in the concentration of alphacypermethrin between samples collected at day 1 or day 98 after treatment (P>0.05). Numbers of pyrethroid-susceptible lice surviving exposure in vitro fo r 20 h differed significantly between samples collected at different t imes after treatment (P<0.05). The numbers of Lice surviving in sample s collected within 28 days after treatment tended to be lower than in those collected from 28 to 98 days but, in some samples, regardless of time after treatment, lice survived for 20 h in wool taken from parts of the fleece that contained high concentrations of alphacypermethrin . Copyright (C) 1996 Australian Society for Parasitology. Published by Elsevier Science Ltd.