Efficacy against sheep lice (Bovicola ovis) and fleece wetting of six shower dip preparations.
The relative efficacy of 6 shower dip chemicals most frequently used for the treatment of sheep lice (Bovicola ovis) in Western Australia was examined. Groups of 20 sheep infested with lice were treated with products containing either alphamethrin, cyhalothrin, diazinon or diazinon plus piperonyl butoxide and rotenone, formulated as emulsifiable concentrates, and with products containing either coumaphos or magnesium fluorosilicate, formulated as wettable powders. All treatments were applied through a shower dip (Sunbeam model SSD). Inspections for lice were conducted until 9 months after dipping. No lice were found on sheep treated with the 4 emulsifiable concentrate products. In contrast, treatment with the wettable powders, which contained either coumaphos or magnesium fluorosilicate as the active ingredient, did not eradicate the lice infestations. The degree to which the fleece was wetted was assessed 20 minutes after dipping and showed that the wettable powder dips penetrated the fleece less than the emulsifiable concentrate dips. Less fluid was retained by wool staples in an in-vitro test when dip wash was made with the wettable powders. It was concluded that the degree of wetting attained at dipping was an important factor in achieving eradication of sheep lice.
Improved Design and Use of Shower and Plunge Dipping Equipment for the Eradication of Sheep Body Lice (Bovicola ovis)
Considerable evidence was available indicating that wet dipping practices were failing to eradicate lice on sheep and that ineffective wetting was believed to be a major contributory factor. To examine wetting of sheep in plunge and shower dips, a series of experiments were undertaken to investigate both the mechanical and management opportunities which might improve the efficiency and efficacy of wet dipping of sheep for the eradication of the sheep body louse Bovicola ovis. Results indicated that significant improvements could be made to both shower and plunge dipping equipment and practices which would enhance the likelihood of eradication of sheep body lice. On shower dips there was no significant difference between modified nozzle arrangements and the existing Buzacott® single slot arrangement provided the pump pressure was maintained at >390 kPa at a flow rate >18 l/s (nozzle pressure >230 kPa). Pipe diameter had a substantial effect on pressure losses. Wetting of sheep was significantly affected by their position. Wetting of the sheep in a plunge dip was significantly improved by fully immersing the sheep twice during the course of their swim. Swim length was also significant. The work has also identified a number of issues associated with pesticide residues in raw wool, concerns over pesticide concentrations in the dip wash and a number of occupational health and safety issues. Email: roger.lund@agric.nsw.gov.au
Is the Benussi Effect a Kinetic Depth Effect?
Rapid, successive presentations of an eccentric circle pattern and its mirror-image elicited apparent depth and, as has been previously demonstrated for the Benussi effect, there was an increase in apparent depth with an increase in circle eccentricity. Taken together, these data were interpreted as contravening Wallach, Adams, and Weisz's account of the Benussi effect as an instance of the kinetic depth effect.