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.
LABORATORY STUDIES ON RESISTANCE TO CYPERMETHRIN IN DAMALINIA OVIS (SCHRANK) (PHTHIRAPTERA: TRICHODECTIDAE)
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 LC95 and LC95. 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.
Structure of the epidermis in Ayrshire bullocks.
: The living epidermis and stratum corneum of cattle, when measured on cryostat sections, were both found to be approximately 30 micrometer thick. However, the corneum contained about 30 cell layers, whereas the living epidermis was composed of only four. Histological processing involving fixation, dehydration and paraffin embedding, resulted in the loss of half of the stratum corneum and proved to be unsuitable for study of this layer. Lipid derived mainly from the sebaceous gland was present between the squames in the outer two thirds of the corneum probably in the form of an emulsion with sweat.