Spatial and temporal variations in the commencement of seasonal activity in the Karoo paralysis tick, Ixodes rubicundis.

Successful prophylaxis of paralysis, induced in small stock by feeding female Ixodes rubicundus, is dependent on the accurate determination of the commencement of seasonal activity by the tick. The commencement of this activity was recorded for 11 consecutive years on a farm in the south-western Free State, South Africa, and for shorter periods on other farms, some of these in regions with markedly colder climates. The colder the mean minimum atmospheric temperatures during the 2 months preceding the start to tick activity, the earlier it commenced. This could differ by 4 weeks from year to year on the same farm. In a region with a low effective temperature activity commenced between 3-8 weeks earlier than in a region with a higher effective temperature.