Oestrus ovis was endemic on all the farms included in a survey conducted in the southern Cape, but each farm had its own unique seasonal pattern of infestation. Flock sheep were infested 10-12 months and tracers 5-9 months of the year. Sporadic infestations occurred in winter and spring, while peaks were reached in summer and autumn. Development of O. ovis larvae deposited in autumn was retarded for up to 5½ months. Pupae of O. ovis formed from 27 April-9 August, with the exception of a single pupae formed on 29 June, failed to produce flies. Pupal periods ranged from 30 days in January to 80 days in June. Strategic anthelmintic treatments in May, August and November and a tactical treatment in March are recommended.
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