An evaluation of two cypermethrin-based pour-on formulations on sheep infested with the biting louse,Bovicola ovis

Response of Triatoma infestans to pour-on cypermethrin applied to chickens under laboratory conditions

This article reports the effects of a pour-on formulation of cypermethrin (6% active ingredient) applied to chickens exposed to Triatoma infestans, the main vector of Chagas disease in rural houses of the Gran Chaco Region of South America. This study was designed as a completely random experiment with three experimental groups and five replicates. Third instar nymphs were fed on chickens treated with 0, 1 and 2 cc of the formulation. Nymphs were allowed to feed on the chickens at different time intervals after the insecticide application. Third-instar nymphs fed on treated chickens showed a higher mortality, took less blood during feeding and had a lower moulting rate. The mortality rate was highest seven days after the insecticide solution application and blood intake was affected until 30 days after the application of the solution.

Kinetic disposition of an aqueous formulation of alphacypermethrin applied to the dorsal mid-line of sheep with long wool and its effect on lice

A group of 5 adult Merino sheep with fleeces about 70 mm long (7-months growth of wool) was treated with a topical formulation of the synthetic pyrethroid insecticide, alphacypermethrin, applied to the dorsal mid-line. Insecticide concentrations at the tip, middle and base of wool staples collected from meridians along the back, upper and lower flanks were measured at intervals from 1 to 98 days after treatment. Some movement of the alphacypermethrin from the back to the lower body occurred within 24h after treatment, but despite careful application of the insecticide there was wide variation in the concentration between and within meridians. The majority of the alphacypermethrin remained close to the dorsal mid-line and near the tip of the staple. There were significant differences in the concentration between the tip, middle and base segments of the staples in the back and lower flank meridians (P < 0.05). Despite exposure of the sheep to normal weathering, there was 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 for 20 h differed significantly between samples collected at different times after treatment, lice survived for 20 h in wool taken from parts of the fleece that contained high (P < 0.05). The numbers of lice surviving in samples 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, concentrations of alphacypermethrin.

Evaluation of non-conventional treatments for control of the biting louse (Bovicola ovis) on sheep

A variety of non-conventional treatments was applied to biting louse (Bovicola ovis) infested sheep in order to evaluate ways in which farmers could control the louse infestations and still maintain Organic Production Standards. In one trial, louse scores of sheep shorn but kept dry or wetted by water alone or with water plus detergent were compared with unshorn sheep treated similarly. Shearing alone accounted for a 35.7-66.3% reduction in mean louse scores. Wetting alone either with water or with water and added detergent accounted for a 26.9-35.3% reduction in mean louse scores. The combined effects on mean louse scores of shearing and wetting, as opposed to shearing alone, were statistically significant on two of the three farms at 32-35 days post-treatment. The effects persisted for the duration of the trial (between 48 and 52 days), at which point shearing and wetting with detergent provided 95.3-99.6% control of lice. In a second trial, a range of insecticidal substances considered acceptable by Organic Production Standards, azadirachtin (neem), pyrethrum, soap, was applied to louse-infested sheep and their efficacy compared with that of a commercial formulation of cypermethrin. The sheep treated with azadirachtin and pyrethrum had significantly fewer lice than either the control or soap treated sheep over the 48 days of the trial. Neither azadirachtin nor pyrethrum were significantly less effective than cypermethrin. Control (reduction in louse score) of 85.0-100% was achieved over the period of the trial. It is concluded that most of the non-conventional treatments evaluated had a useful and cost-effective role to play in reducing louse numbers on sheep for at least 40-50 days. The lack of persistence compared with that obtained with conventional insecticides was the only apparent drawback.