Increased control of the sheep biting louse Bovicola (Damalinia) ovis withdeltamethrin formulated in a fractionated wool grease carrier

The synthetic pyrethroid deltamethrin (DM) containing a trace of [C-14]-DM was formulated with non-oxidised sterol and wax ester fractions (F1) of woo l grease and as the commercial preparation 'Clout-S'. These were applied as a 'backline' strip to sheep immediately after shearing and the concentrati on of [C-14]-DM at meridians adjacent to the application strip and at 1/4 a nd 3/4 of the dorsal-ventral distance was determined. The Fl formulation re sulted in significantly greater lateral spread of DM with less remaining at the application site (66 +/- 8% of dose) 98 days after treatment compared to 'Clout-S' (94 +/- 3% dose). Autoradiographic examination of treated wool demonstrated that there was more DM in the lower half of the wool staple w hen formulated in Fl compared to 'Clout-S'. Greater mortality occurred when sheep biting lice Bovicola (Damalinia) ovis were exposed in vitro to wool containing DM from Fl compared to 'Clout-S' treated sheep. In field trials there was increased efficacy against synthetic pyrethroid resistant B. ovis with Fl formulation than with 'CIout-S'. The study has demonstrated that s ynthetic pyrethroid availability, and therefore efficacy, can be significan tly increased when the insecticide is formulated in a 'carrier' with the ph ysicochemical characteristics of wool grease. (C) 2000 Elsevier Science B.V . All rights reserved.